Identification of a thermolabile component of
the human neutrophil NADPH oxidase. A model
for chronic granulomatous disease caused by
deficiency of the p67-phox cytosolic
R W Erickson, … , T L Leto, J T Curnutte
J Clin Invest. 1992;89(5):1587-1595. https://doi.org/10.1172/JCI115753.
Mild heating of human neutrophils inactivates the respiratory burst oxidase, producing a defect in superoxide production and bacterial killing comparable to that seen in patients afflicted with chronic granulomatous disease (CGD). We have now investigated the
mechanism and specificity of this inactivation by examining the effect of mild heating on the known oxidase components: the membrane-bound subunits of the cytochrome b558 (gp91-phox and p22-(gp91-phox) and the two cytosolic oxidase factors (p47-(gp91-phox and p67-(gp91-phox).
Heating (46 degrees C for 7.5 min) caused intact neutrophils to lose greater than 85% of their capacity to produce superoxide, a defect which was localized to the cytosolic, but not the membrane, fraction. Complementation studies with CGD cytosols deficient in either p47-phox or p67-p47-phox suggested that the defective component of heat-inactivated cytosol was p67-phox. This was confirmed by experiments showing that recombinant p67-phox, but not p47-phox, exhibited lability at 46 degrees C and completely reconstituted oxidase activity of heat-treated cytosol. These studies indicate that mild heating of either intact neutrophils or normal neutrophil cytosol results in a selective inactivation of p67-phox, providing a model oxidase system for the extremely rare p67-phox-deficient form of CGD.
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AModel for Chronic Granulomatous Disease Caused by Deficiencyof thep67-phox Cytosolic Component
Richard W. Erickson,* StephenE.Malawista,t MichaelC.
Garrett,'Gretchen VanBlaricom,$ Thomas L.
Leto,*and John T. Cumutte*
*Department of Molecular and Experimental Medicine, The ScrippsResearchInstitute, LaJolla, California 92037;tDepartment of Internal Medicine, Yale University School ofMedicine, New Haven, Connecticut 06510;and§Laboratory ofHostDefenses,
National Institute ofAllergy and Infectious Diseases, National Institutes ofHealth, Bethesda, Maryland 20892
Mildheating of humanneutrophilsinactivates therespiratory
burstoxidase,producingadefect insuperoxide productionand bacterial killingcomparable to thatseenin patientsafflicted withchronic granulomatous disease(CGD). We havenow in-vestigated the mechanism andspecificityof thisinactivation by examining the effect of mildheatingonthe known oxidase com-ponents: the membrane-boundsubunits ofthecytochrome
(gp9l-phox andp22-phox) and the twocytosolicoxidase fac-tors (p47-phox and p67-phox). Heating (460C for 7.5 min)
caused intact neutrophilsto lose >85% of their
produce superoxide, a defect which was localizedtothe
Complementationstudies with CGD cytosolsdeficient ineither p47-phoxor p67-phox
suggested that the defective component of heat-inactivated cy-tosol wasp67-phox.Thiswasconfirmedby experiments show-ing thatrecombinant p67-phox, but notp47-phox, exhibited lability at460Candcompletelyreconstituted oxidaseactivity
of heat-treated cytosol. These studies indicate that mildheating
of either intactneutrophilsornormalneutrophil cytosolresults ina selective inactivation ofp67-phox,providingamodel oxi-dase system for theextremelyrarep67-phox-deficientform of CGD.(J.Clin. Invest.1992.89:1587-1595.) Keywords: cyto-kineplast *heating*phagocyte*
neutrophilsonsurfacesproduces anucleate, granule-poor cytoplasmic fragments termed cyto-kineplasts
(CKP),'which retain the chemotactic and
phago-Thiswork has beenpublishedin part in abstract form(1990.Clin. Res. 38:435a).
Addressreprintrequests to Dr.Curnutte, Departmentof Molecular andExperimental Medicine,SBR 12, TheScrippsResearchInstitute,
10666 North Torrey Pines Road, La Jolla, CA 92037.
Receivedfor publication 31May 1991andinrevisedform20 No-vember1991.
1.Abbreviationsused in this paper: CGD, chronicgranulomatous dis-ease; CKP, cytokineplast; GTPyS, guanosine
5'-043-thiotriphos-phate);phox, phagocyteoxidase (usedtodesignate proteincomponents of the phagocyte respiratory burst oxidase); PIPES,
cytic function of the parent cells, but lack the capability of undergoing a respiratory burst (1-6). Subsequent studies (7)
have shown that the loss of respiratory burst activity in
cyto-plastsis directly linked to the length oftime neutrophils in suspensionarepreexposedtoelevatedtemperatures(45°C). In theneutrophil,the NADPH oxidase is responsible for the oxi-dativeburst, directing thetransportof electrons from NADPH
NADPH+ 202-- NADP++ 20- + H+
This respiratory oxidase isamulticomponentenzymecomplex that is associated with the plasma membrane after activation of the cellbyavariety of stimuli (8-10). The absence ofa
respira-toryburst in CKP preparations functionally resembles
neutro-philsof patients suffering from the inherited disorderchronic
granulomatousdisease (CGD), in which afflicted individuals
areincapable of initiatingorsustaining the neutrophil
respira-toryburst (1 1). The study of this disease has helped identifyat
least four oxidase components, two of which are membrane-bound andtwoof whicharecytosolicintheresting neutrophil. InX-linked inheritance, themostcommonform of CGD (55% of CGDcases), genetic alterations ingenelocusXp21.1 of
theX-chromosome resultinthe complete lack of the 91-kD
trans-membrane glycoprotein subunit (gp9l-phox[for
phago-cyteoxidase]) of the heterodimeric cytochrome b558 (13, 14). This mode ofinheritance is also marked by a concomitant loss of the cytochrome 22-kD subunit, p22-phox (15-17), although thegeneencoding this protein has been localizedto
chromo-some 16(gene locus 16q24 ). Similarly, mutations involv-ing the p22-phox gene (18), involvinvolv-ing- 5%of CGD patients
( 12), also leadtothe absence ofboth cytochrome subunits(17).
Incertainrarevariantforms of CGD, mutationsin the genefor
eithergp9l-phox orp22-phox lead to a cytochrome complex, which is quantitatively and spectrally normal but is nonfunc-tional(19-22). Of the remaining 40% of CGDcasesinwhich cytochrome b558 is functionally normal, a complete absence of
oneofthe two known cytosolic components of the oxidase is
seen: p47-phox (35% of CGD cases), encoded on gene locus 7ql1.23, and p67-phox (5% of CGD cases), encoded on gene locus1q25 (12, 23-31). Given the apparent similarity of respi-ratory burst oxidase dysfunction in CKP and CGD
neutro-phils,weexplored the possibilitythatheatedneutrophils might
suffer from anacquired defect in one or more oxidase
In this reportwe show that mild heating inactivates the neutrophil respiratory burst oxidase through a mechanism
in-volving the specific thermolability of the p67-phox cytosolic component. The rarity ofp67-phox-deficient CGD patients
has madeit difficult to study the functional role of p67-phox
©TheAmerican Society for Clinical Investigation, Inc. 0021-9738/92/05/1587/09 $2.00
andto preparep67-deficientcytosolforusein cell-free
comple-mentation studiestoidentifythemoleculardefect inCGD
pa-tients. Wenowdescribeamethod which both enables the
pro-duction ofa model p67-phox-deficient cytosol system and demonstrates the mechanism by which the respiratory burst oxidase is disabled by mild heattreatment.
Allreagents used wereofthe bestgradecommercially available, and wereobtained fromsources previouslydescribed (32).
Preparation of neutrophils. Blood was obtainedinmost cases by venipuncture from normal donorsand CGD patients with their in-formedconsent.Neutrophilswerepreparedusing acid-citrate-dextrose asthe anticoagulant, dextran to sediment erythrocytes, and Ficoll-Paque(PharmaciaLKB,Uppsala,Sweden)density-gradient centrifuga-tiontoseparate mononuclear cellsfromneutrophilsaspreviously de-scribed(33). Forexperiments requiring purified cytosolicand mem-branefractions, neutrophilswereobtained byleukapheresis ofdonors andpatients (after acquiring their informed consent)andpurifiedas reportedbefore(34). Normal donors wereadministered dexametha-sone(4 mgorally12and 2 hbefore procedure)toincrease neutrophil yields. Neutrophilsweremaintainedat4VCatall stagesofpurification afterdextransedimentation.
Intact neutrophil functional studies. Purified neutrophils were heated at460C for7.5 minand assayedfor O° productionasdetailed below, whilecontrolneutrophilswerekeptonice.Degranulationwas
assessedbyquantitatingthe extracellular releaseof vitamin
B12-bind-ing protein fromphorbol12-myristate 13-acetate(PMA)-treated neu-trophilsusingapreviously describedmethodfor measuringthebinding of[57Co]vitamin B12tothisprotein(35, 36). Neutrophil bactericidal activitywasmeasuredinvitrousingStaphylococcusaureusstrain502A asoutlined earlier (36, 37).
Neutrophilfractionation. Unstimulated neutrophilsweredisrupted bynitrogen cavitation andpurifiedmembrane andcytosolfractions were prepared as previously described (32-34, 38) and stored at -70°C.Membranefractionswerebroughtto 1.25X 109cell
equiva-lents/ml (- 5 mgprotein/ml) in5 mM1,4-piperazinediethanesulfonic
acid (PIPES),50 mMKC1, 1.75 mMMgCl2, 1.5 mMNaCl,0.5 mM ATP, 0.63mM EGTA, 0.34Msucrose,pH7.3;cytosolic materialwas preparedat9X I07cellequivalents/ml (- 2 mgprotein/ml)in 10 mM PIPES, 100 mM KCI, 3.5 mMMgCl2, 3 mM NaCl, pH 7.3 (also termed "relaxbuffer") supplementedwith 1 mM ATP and 1.25 mM EGTA.Sodiumdeoxycholate-solubilizedmembraneswereprepared accordingto apublishedmethod(32)forusein thecell-free assay of superoxide production.
Heat treatment of neutrophils and cellfractions. Purified neutro-philsweresuspendedat 108cells/mlin25°Cphosphate-bufferedsaline (PBS)containing 138 mMNaCl,2.7 mMKCI,8.1 mM Na2HPO4, 1.47mM KH2PO4,pH 7.3. One volumeof this suspensionwasthen addedto3 volofPBSpreequilibrated to46°Cinasiliconized glass vessel equipped with amagnetic stirrer. Aliquots were removed at
various times and stored on icefor 15 min before assay forsuperoxide production.
Purified neutrophilcytosol was removed from storage at -70°C and allowed to come to room temperature before heating. Cytosols weretransferred to siliconized glass tubes and heated in a 46°C water bathwith constantagitation forup to 20 min.Aliquotswereremoved attimedintervals,transferred to ice for 5 min, and then allowedto
equilibrateat roomtemperature beforeanalysisin thecell-free oxidase activation system.
Purified membrane vesicles were allowedtothaw at room tempera-ture, and then transferred to asiliconizedglass tube for heat treatment. Single-volume aliquotswereremoved atvarious times,anddiluted with 5 vol relaxbufferat4°C.Samples were then incubated on ice for 10 minbefore analyzing oxidaseactivityin the presence of normal cytosol.
Whole-cellsuperoxide production.Therateofgeneration of super-oxidebyintactneutrophilswasdeterminedat370C inaThermoMax kineticmicroplatereaderequippedwitha550±1nmfilter (Molecular DevicesCorp.,MenloPark, CA)aspreviously described (39).Inthis assay(totalvolume 0.25ml), cytochromecreduction inapair of reac-tions(oneof which contained 15Mgofsuperoxidedismutase [SOD])
wascontinuouslymeasuredat550nmafter stimulation ofthe neutro-phil suspension byPMAat afinalconcentration of 200ng/ml.
Maxi-mumreaction velocitiesweredeterminedusingSoftMaxkinetic analy-sis software(version 2.01,Molecular DevicesCorp.).The SOD-inhibit-ablerateofsuperoxide productionwascalculated by subtractingthe
velocityoftheSOD-containingreaction from that measured in its
companion reaction without SOD. Absorbance changes were con-verted to nanomoles °2 as described previously for this 550-nm filter(39).
Cell-freeassayofoxidaseactivation.The kinetics of activation of NADPHoxidasewerestudiedin acell-freesystemusingmembranes and cytosol from unstimulated neutrophils as previously described
(40).Inthis assay system, theoxidase is activatedat250C bythe addi-tion of SDS in the presence of NADPH(0.16mM)andcytochromec
(0.1 mM).Reaction mixturesof 0.15mltotal volume wereincubated in 96-well Linbro microtitration plates (Flow Laboratories, Inc.,
McLean, VA)andcontained cytosol (0-2X 106cellequivalents)and eithermembranevesicles(4X 105cellequivalents)or deoxycholate-solubilizedmembranes(1.25X 106cellequivalents). The optimal con-centration of SDS foractivation of the oxidasewas40MM for
experi-ments using deoxycholate-solubilized membranes and 90 MM for assaysusingmembranevesicles.Again,measurements ofSOD-inhibit-ablecytochrome creduction were obtainedon aThermomaxplate
reader,withsubsequentdetermination of maximal velocitiesby Soft-Maxsoftwareandconversiontonanomoles °2 asdescribedabove.
Complementationof CGDpatientandheat-treatedcytosol frac-tionswasaccomplished by adding equalvolumesoftestcytosols (2
X 106cellequivalents)tothecomplete cell-freeassayusing deoxycho-late-solubilizednormal membranes.This volumeofnormalcytosol (2
X 106cellequivalents)wassufficienttogenerate NADPHoxidase
activ-ity>40 nmolOj/minper107cellequivalentsmembranes. All other parametersofthecell-freeassay systemremainedasdescribedabove.
Thedeterminations of CGDpatientandheat-treatedcytosolrate ordercharacteristicsweremade in thecell-free oxidasesystem, as
previ-ously reported (34, 41).Eitherrelaxbufferor an excess(3.6 X 106cell
equivalents)oftestcytosolwasaddedtoreaction mixtures (0.15 ml)
containingnormalcytosolinvaryingamounts(3.6x I05to1.6 x106
production using deoxycholate-solubilizednormal membranes(1.25
X 106cellequivalentsperreaction). Forkineticstudies ofheated or
p67-phox-deficient cytosol reconstituted with recombinant oxidase factors(seebelow),asimilarcell-freeassaywasemployed. Again,
vary-ingamounts(3.6XI0 to1.6X 106cellequivalents)ofeitherheated or
Mgof recombinantproteinper 106 cellequivalents
cytosol.Assayswerecarriedoutusingdeoxycholate-solubilizednormal membranes(1.25 X 106 cellequivalents perreaction) as described above.
Preparation, heat treatment, and cell-freeassay ofpreactivated NADPHoxidase. Purifiedneutrophilsweresuspendedat5X I07cells/
mlin PBS(supplementedwith 0.5 mMMgCl2,0.9 mM CaCI2,and 7.5 mMglucose)andstimulated with 200ng/mlPMAfor 10 minat37°C. Theseactivatedneutrophilswerewashedtwice with PBS and resus-pendedat108cells/mlin 0.34 Msucrosebufferedwith 10 mMHepes, pH7.3.This suspensionwassonicated for three consecutive bursts of 10seach,usingaSonifier celldisruptormodel W185(Heat
Systems-Ultrasonics,Inc.,Plainview,NY)at aconstantpower of 50 W.A
low-speedcentrifugation (500g, 10min, 4°C)wasperformedtosediment
remainingintact cells anddebris, and theresultingsupernatantwas
removedto wetice for immediateuse.Thispreactivatedoxidasewas
was added to a5.0-ml polypropylene test tube prewarmed at either 37 or460C.Heated incubationswerecarriedoutwithconstantagitation ofthe suspension, removing0.07-mlaliquots directly to iced microcen-trifuge tubesat1 min intervals. NADPH oxidaseactivitywasmeasured asdescribedabovefor the cell-free activation assay with thefollowing modifications: no SDSwasused, the total assay volume wasincreased to0.75 ml, and reactionswere runinsemi-microcuvettesutilizinga
Uvikon model 810 dual-beam spectrophotometer (Kontron Electron-ics,Inc., RedwoodCity, CA). Reactions containing3X 106cell equiva-lentsactivated oxidase(0.03ml) were initiated by the additionof0.16 mM NADPH.TheSOD-inhibitable reduction ofcytochrome c was
measuredcontinuouslyat550nmwith theSOD-containing reactionin the reference beam. Maximum reaction velocitiesweredeterminedby visualestimation. Incertain experiments, recombinantp47- and p67-phox (5 ggof either [or both]) wereaddedto reactionscontaining preactivated oxidase (3 X 106cell equivalents)thatwas heat-inacti-vated(460C,7.5 min) todetermine whetheroxidase activitycould be restored. The completereactionmixture was then allowedtoincubate
at250C for3 minbeforeinitiationof superoxideproduction bythe additionofNADPH.
Recombinant protein studies. Both recombinant p47-phox and p67-phoxwerederived from baculovirusconstructs(BV/p47and BV/ p67)asdescribedelsewhere(42).Eachoftheseeukaryotic expression vectorscontains the complete coding sequencesofone ofthese two cytosolic oxidasecomponents,enabling productionof complete native proteinslacking anyadditional fusionprotein sequences. The recombi-nantproteins werepurified from baculovirus-infected insectcell (Sf9) lysates 3-4 d postinfection, using ion-exchange chromatography. Theseproteins exhibitedthesamemolecularweightsasthenative
neu-trophil proteinsandwereestimatedtobe>90% purebySDS-PAGE. The pure proteinsweredilutedto0.2 mg/mlwith relaxbuffer and heated for various time periodsat46°C, asdescribed above. These solutions contained 0.1 mMdithiothreitoltoinhibit oxidative damage of proteins.Thecell-freeassay system usedto testtheactivityof these recombinantfactorswasessentiallythesame asthatdescribedabove, with modifications(42).Briefly,these reactions(0.1 mlfinal volume) contained variableamountsofpurerecombinant p47-phoxor p67-phox, I05cellequivalentsofneutrophil cytosol,and 5XI05cell equiva-lentsofdeoxycholate-solubilized membranes. Theoxidase reactions wereactivated by addition of 40MMarachidonic acid instead of SDS. Inexperimentsinvolvingtherestoration ofheat-treatedcytosol with therecombinantfactors, thecytosolwasheatedfor7.5 minat46°C before use inareaction containing 106cellequivalents ofthe heat-treated cytosol, 5 X I05cell equivalents ofdeoxycholate-solubilized membranes, andvariableamounts(0-1,000 ng)of therecombinant cytosolic factors.
cytosol, heated normalcytosol, andrecombinant cytosolic proteins weresubjectedtodiscontinuousSDS-PAGEprior to electrophoretic transfertoZeta-Probe(BioRad Laboratories, Richmond, CA)or nitro-celluloseblottingmembranes,accordingto ageneral method(43,44).
Ananti-peptide antibodyraised inarabbitagainstamino acidresidues 447-460(DEP K ES E K AD AN NQ)of thep67-phoxcomponent of theneutrophilNADPHoxidasewasusedastheprimary antibody for the cytosolimmunoblots.Therecombinant proteins were probed with goatantibodiesraised against these purified factors as described elsewhere(42).Inboth cases, the boundprimary antibodieswere de-tected with appropriate species-specific secondary antibody-alkaline phosphatase conjugates (BioRad Laboratories) using 5-bromo-4-chloro-3-indolyl phosphateandp-nitrobluetetrazoliumassubstrates. Dataanalysisand curvefitting. Allvariances shown are standard deviations, unlessotherwise noted. Theexponential relationship
be-tweencytosolconcentration and maximalratevelocityin thecell-free assay systemwasdetermined bytwomethods: (a) nonlinearregression analysis power curve fitting using Enzfitter(Elsevier-Biosoft; Cam-bridge, UK)dataanalysis software;and(b) least-squareslinear regres-sionsoflog-logtransformplotsofmaximum reactionvelocityvs.
nor-malcytosolconcentration(34). Enzfitter powercurveanalyseswere
basedon theequation:V=K(C'),where V=maximalrate velocity, K =constant,C=cytosol concentration,and P = rate order.
Thecontrolledheating of intact neutrophils at temperatures
ranging from 39to470C has been shown to decrease the
capa-bilityofthese cells toproduce superoxide (7, 45).For the
exper-iments described in thisreport,460Cwaschosenastheoptimal
temperatureforinactivating the respiratoryburstonthe basis
of extensiveempirical trials. Neutrophils preincubatedat460C forvarying lengths of timeweresubsequently assayed for their ability to produce superoxide in response to stimulation by
PMAat370C (Fig. 1). Superoxide production remained largely unaffected after 2 min at460C, and then abruptly declined
overthenext3 min. By 8 minanalmostcomplete abolishment ofsuperoxide production wasobserved. Controlexperiments showed that preincubationat460C forup to 10min didnot
induce neutrophils to produce superoxide in the absence of PMA, nordid it affect their viability as measured bytrypan
bluedye exclusion (> 95% viable cells).This patternof
heat-in-duced inactivation ofrespiratory burst activity is comparable
tothatpreviously described (7).
To obtain abroader understanding of the effect of mild heating on neutrophils,wealsostudiedtwootherfacets of
neu-trophil function: bacterial killing and degranulation. Table I
summarizes these results andcompares the functional
capabili-ties of heatedneutrophilstothose obtained from CGDpatients with either the standard or variant form ofthe disease. A strong resemblence is seen betweenthese heated neutrophils and their
heated andCGD neutrophils to kill S. aureus.
One of themanypossible mechanismstoexplainthe46°C inactivation ofthe respiratory burst was that theNADPH oxi-daseitself,or oneof itssubunits,wasdamaged by theheating.
To test thispossibility, purified membrane and cytosol
frac-tions from46°C-treated neutrophils disrupted by nitrogen
o a 0
0 2 4 6 8 10
Time at 46 degrees (minutes)
Figure1. Inhibition of intact neutrophil superoxide production by preincubationat460C.Neutrophilswereheatedat2.5X I07cells/ml in PBS andaliquotsremovedat30-sintervals.Superoxide production afterstimulation with 200ng/mlPMA wasassayedasdescribed in Methodsusingakineticmicroplatereader and computer software that calculated the maximalratesof absorbancechangeat550nm.
TableI. Selected Functional Properties ofHeated Neutrophils
assay Heated CGD VariantCGD
production 5.8±4.2 (n=4) 0.4±0.8(n=12) 5.8 (n =2)
1 h 44.6±15.6 (n=3) 50.9±35.9 (n=12) 48.8(n=2)
2 h 60.9±34.5 (n=3) 68.5±32.1(n=12) 45.7(n =2) Degranulation 45.3±21.0 (n=3) Notdetermined 57.6 (n = 2)
Purifiedneutrophilswereincubatedat4VC(control)or460C for 7.5min.
Functionalassays wereperformedasoutlined in Methods, and the resultsare
presentedaspercentageof (unheated) control activity. 14CGDpatients (none ofwhom weretakinginterferon-yatthetime)were also studied. 12 of these
patients hadacompleteabsenceofrespiratoryburstactivity (duetomutations ingp9 I -phox, p22-phox,p47-phox,andp67-phox) while2hada variantform of X-linked CGDinwhich therewas aresidual level(-5%ofnormal)of
°2-production owingto a95%deficiency of cytochromeb. The control level of
°2-productionwas 149.2±33.8nmol/minper IO' cells (n=14). Normalbacterial killing (expressedas thepercentcolony-forming units killed by incubation with
controlneutrophils)was46.7±18.8%(n=7)after 1 h ofincubation,and
66.4±19.0% (n=7)after 2 h of incubation. Controlneutrophilsreleased
42.0±22.7%(n =7) of theirtotalvitaminB,2-binding protein intothe extracel-lularmedium(degranulation)after30 minofexposure to PMA.
tationwereanalyzedinacell-free oxidase activationsystem. As
shown in Table II, membranesfromboth unheated (control) and heat-treated (46°) neutrophils showed normal activity
when activated with SDS inthepresenceofcontrol cytosol. In contrast,cytosolic fractions fromheatedneutrophilsshoweda
dramatic reduction in activitywhen comparedtothat observed with untreated cytosol. In control experiments, membrane
fractions fromheat-treatedneutrophilsshowed normalactivity in thecell-freesystemwhen tested atconcentrationsranging above and below that shown in TableII(datanotshown).In
parallel experiments performedwithCKP,therewas asimilar lossofcytosol oxidase activitywhen assayed in the cell-free oxidase activationsystem(datanotshown).
Giventherelatively selective inactivation ofthecytosolic fraction,we nextinvestigatedwhether the effect could be
dupli-catedby 46°Ctreatmentofcytosol and membranefractions
obtained from unheatedneutrophils. Asshown inFig. 2, the heated membrane fraction showed only mildly compromised
oxidase activitywhen assayedwith controlcytosol, while the heat-treatedcytosolic fractiondemonstratedatime-dependent
repro-ducibly generate cytosols inhibited by >95% by heating at
46°C for20 min.Addition of10,uMguanosine
5'-0-(3-thiotri-phosphate) (GTPyS) failed to restore any activity in these heated cytosolpreparations,anindicationthat lossofoxidase
activityin46°C-treatedcytosol isnotduetothermaldamage of this essential nucleotide cofactor (data not shown). A func-tionaldefect wasthus shown tobe inducible in (previously)
normalcytosol,indicatingtheinactivation by heating ofa
Determination of the heat-labile cytosolic oxidase compo-nent wasaccomplished by cytosol complementation studiesin
the cell-freeassay system (Table III). Cytosolsprepared from CGDpatientswith identical modes of inheritanceare
incapa-ble ofassociatingwith each otherin the presence of normal
membranes to form activatable oxidase, whereas cytosol frac-tions prepared from patients with different cytosolic oxidase component deficiencies are capable of complementation in the cell-free oxidase activation system (26, 40). Normal cytosol that was heat-treated at 460C for 20 min was assayed for com-plementation with four different cytosol proparations from CGD patients lacking either p47-phox (patients CGD1 and CGD2) or p67-phox (patients CGD3 and CGD4). No oxidase activity was detectable in reactions combining heated cytosol withp67-phox-deficientcytosol,suggesting that the p67-phox component ofheatedcytosol is functionally inactive. In con-trast, heated cytosol was capable of complementing p47-phox-deficient cytosols, demonstrating a retention of p47-phox func-tion in the heat-treated cytosol.
Kineticstudies were undertaken to determine further func-tional similarities between heated normal and p67-phox-defi-cient CGD cytosols. We have previously reported (34, 38, 41) that the order of the oxidase-activating reaction with respect to normal cytosol concentration is 2.52±0.09 SE (n=7), afinding which implies that at least three kinetically independent solu-ble components (or component complexes) are required for the formation ofactiveoxidase. In these same studies, when oxi-dase was activated at varying concentrations of normal cytosol inthe presence of an excess of p47-phox (or
p67-phox)-defi-cient cytosol, the yield of active oxidase no longer varied as the 2.5 power of normal cytosol concentration. Instead, oxidase activity increased in direct proportion to the concentration of normal cytosol, indicating that the defective cytosols were con-tributing all but one of the required kinetic components. The results of similar experiments performed with cytosol from
460C-heatedneutrophils or heat-treated cytosol are shown in Fig. 3, where log-log plots of normal (unheated) cytosol con-centration vs. maximum reaction velocity are shown. The slope of each line defines the order of the oxidase-activating reaction with respect to normal cytosol concentration. In the absence of heat-inactivated cytosols, normal control cytosol showed the
expected slopeof - 2.5. The presence ofexcess heat-treated cytosol altered the dependence of oxidase yield on
TableI. Cell-free Activation of NADPH Oxidase Using
Membranes and CytosolDerivedfrom Control and 46°C-treated IntactNeutrophils
Cytosol Membrane Superoxideproduced
nmolOjminper10' cell equivalentsmembranes
Control Control 38.5
Control 460C 28.7
460C Control 4.5*
460C 460C 2.9
Experiments were carried out as described in Methods. Neutrophils were incubated at460Cor4°C(control) for 7.5minbeforedisruption and preparation of cytosol and membrane fractions. Each reaction
(0.15ml) contained 4X IO'cellequivalents of membrane vesicles (fromeither control or460C-treatedneutrophils) and 2 X 106 cell
o3 < L.
0 2 4 6 8 10 12 14
Timeat 46 degrees
Figure 2.Effect of460C heatingonoxidase function in membranes andcytosol.Cytosolicand membranefractions fromuntreated nor-malneutrophilswereobtained bynitrogen cavitationasdescribedin Methods. Thesefractionsweresubjectedto46°Cheat treatment, and aliquotswereremoved atthe timesindicated foranalysisof superox-ideproductionin thecell-free oxidase activationsystem. In the upper panel,heat-treated membranes(3.2x 105cellequivalents)were as-sayed for oxidaseactivity withnormaluntreatedcytosol (1.8X 106 cellequivalents).Inthe lowerpanel,heatedcytosol(2.5 X 106cell equivalents)wasassayed foractivity usingnormaluntreated deoxy-cholate-solubilizedmembranes(6.3X I05cellequivalents).Control cytosolicandmembranefractionswerekeptat room temperaturefor thedurationof the time coursepriortodetermination of oxidase activity.Controlactivitywasdefinedasthat observed when cytosol (lowerpanel) or membranes (upper panel) incubated at 25°C for 14 min weresubstituted for the 46°C-treatedfractionin thecell-free as-say. Controlactivitieswere63.3±12.3 and 73.8±18.2 nmol0/min per107cellequivalentsmembranesforthe upper and lowerpanels, respectively. The results shown are the means±SDofthree experi-ments, eachperformed with cytosoland membranesfromadifferent donor.
untreated cytosol concentration from 2.5 order to approxi-mately first order. Thesefindingsindicate that heated cytosols appeartosuffer from a defect in one kinetic component, much like cytosols obtained from CGD patients lacking either
p47-phoxorp67-phox.Coupled with the data presentedin Tables II and III, these results strongly suggest that heat treatment of neutrophils selectively inactivates the p67-phox cytosolic oxi-dase component.
Thespecificthermolabilityofp67-phoxwasdirectly demon-stratedbythe 46°C heat treatment of the purified recombinant cytosolic oxidase factorsrp47-phoxandrp67-phox (Fig. 4). The effects of heat treatment on the two recombinant factors were
assessed under conditions in which the reconstituted oxidase activitywasthemostsensitivetothe addition of these exoge-nousfactors. Previous work has shown that thetwo
recombi-nantfactors (whencombined with plasma membranes) donot supportoxidase activation without the addition of whole
cyto-sol,indicatingtherequirementof other solublecomponent(s) (42). The oxidase activity of reactions (0.1 ml) containing 5
X 105 cell equivalents of membranes and a suboptimum
by>20-foldby the addition of1
ggof each ofthe recombinant cytosolic factors (under these conditions,>95%ofcytochrome
creductionwasinhibitableby superoxide dismutase).
Pretreat-mentof these recombinant cytosolic factorsat460C revealed that thep67-phoxcomponent wasmarkedly sensitivetoheat. While rp47-phox showed onlyaslight decrease in its abilityto supportoxidase activity after preincubationat460C foraslong
min,heattreatmentof rp67-phox resulted ina
progres-sive lossof its activity with time (Fig. 4). By 6
min,>90% of rp67-phoxactivitywaslost. These inactivation kinetics closely resemble those observed with cytosol treated in thesame man-ner(Fig. 2), suggesting that there isadirect thermal effecton
p67-phox that doesnotinvolve the participation of other
fac-tors inwhole cytosol.Westernblottingof heatedcytosolorthe
pure recombinant proteins confirmed that the heat-treated p67-phox hadretainedthesameapparent molecularweightas
intactp67-phox (data not shown). It is therefore unlikelythat
the heat inactivationprocessinvolved proteolysis.
Thestrongestevidenceindicating that p67-phox istheonly oxidase component substantially affected by this mild heat
treatment wasobtained from experiments in which the
recom-binantcytosolic factorswereusedtoreconstitute the activity of heat-treated normal cytosol (Table IV). Normal cytosol was
heated at 46°C for 7.5 min, yielding activities that were
re-Table III. Complementationamong Various TypesofCGD
Cytosols DeficientinOxidase Components and460C-treated
Cytosol1 Normal 46°C CGD, CGD2 CGD3 CGD4
nmolOIminper 107 cellequivalents membranes
Buffer 44.1 0.4 0.2 0.8 0.1 0.1
460C 0.4 13.3 21.1 0.6 0.1
CGD, 1.4 2.1 18.3 25.0
CGD2 5.1 39.0 33.2
CGD3 0.1 1.0
NADPHoxidase was activated in a cell-free system asdescribedin Table IIexcept that each 0.15-mlreaction contained amixture of 22
ul(2 X 106cell equivalents)ofcytosol 1 (orrelaxbuffer, where indicated)and22ul (2 x 106cellequivalents)of cytosol 2. The heat-treatedcytosolwasprepared byheatingnormalcytosolfor 20 min
at46°C.Patients1and 2(CGD,andCGD2)weredeficient in
p47-phox, patients3 and4(CGD3andCGD4)were deficientinp67-phox.
The results shown arerepresentativeof sixexperiments,each per-formedusingheatedcytosolfromadifferent normal donor.Atotal of sevendifferentp47-phox-deficient patientsand two different
tosol from Heated Cells Heated Cytosol couldexplainthe well-established heat lability of NADPH
oxi-dase in its activated state (46). Intheseexperiments,
neutro-m=0.84 1.6 m=0.82 phils stimulated withPMAand thensonicatedwereusedas a
source of activated oxidase. As shownin Fig. 6, this type of
1.2 0 oxidase
460Cthan either intact
preactivatedoxidasewas 4Control y Control reduced from 22.0±3.2 to 1.4±0.6 nmolO/minper 107 cell
m=2.47 m=2.51 equivalents(n= 3),after heatingat460Cfor7.5min.
Recombi-0.4 nantp47- and p67-phox failedto augment the activity of this heatedpreactivated oxidase: additionof5,000ng rp47-phox or 6.4 6.6 6.8 7.0 6.4 6.6 6.8 7.0 rp67-phox resulted in
107cellequivalents, respectively(n=3). The addition of 5,000 log (Unheated
cy'tosolconcentration) ng of both recombinant oxidase factors also failed to reconsti-Effect of460C-treatedcytosols on the order of the oxidase- tuteactivity(1.21±0.28nmolO-/minper
I07cell equivalents reaction with respect to normal unheated cytosol concen- [n = 3]).Unlike the situationobserved withcytosol and mem-he cell-free oxidase assays were carried out as described in branes from unstimulated neutrophils, 460C heating of preac-using normal membranes at 1.25 X 106 cell equivalents per tivated NADPH oxidase produces a defect that cannot be re-action andvarying concentrations of normal (unheated) paired by the addition of rp47- and rp67-phox.
presence (-) of an excess amountofheat-treated cytosol (3.6X 10'
cellequivalentsper 0.1 5-mlreaction).The heat-treatedcytosol used in theexperimentdepicted in the left panel wasderivedfrom heated neutrophils,whereasthat used in therightpanel was prepared by heating normal cytosol at460Cfor 20 min. The slopes of the lines (m)reflectthe order of the activationreactionwith respecttonormal (unheated) cytosol concentration.Theresults in theleft panelare
representative oftwoseparateexperiments;those in therightpanel
areselectedfrom 10differentexperiments.Forthese 10 determina-tions,theslopesin the absence and presence of heatedcytosolwere
Wehave demonstrated that heat treatment of either normal neutrophils or their cytosol selectively inactivates a single
NADPHoxidasecomponent, giving risetoacytosolbearinga
closefunctionalresemblancetothatderived froma rareclass of
CGDpatients suffering fromaninherited loss of p67-phox. In
thisregard, heat inactivation of neutrophil cytosolcanprovide
ducedby>92%whenassayedwithnormal deoxycholate-solu-bilized membranesinthe cell-free system. Theaddition of in-creasing amounts ofrp47-phox failed to restore the oxidase activity ofheatedcytosol,while almostcompleterecovery(to activity levels closetothose observed withunheatedcytosol)
was seenwith theaddition of phox. The quantity of
rp67-phox neededtoattainnearlyfull restoration ofactivity (200-400 ng) wasclose to that required for full reconstitution of
p67-phox-deficientCGDcytosol(42)and consistent with the level ofp67-phox estimatedto bepresentinnormalneutrophil cytosol (- 100 ng/106 cell equivalents) (42). Recombinant p67-phoxalsoreconstitutedthe kineticactivityofheated cyto-solasmeasuredby therate order constantrelating cytosol
con-centrationtooxidaseactivity.As showninFig. 5,heated cyto-solsupplementedwithrp67-phoxshoweda meanrate orderof 2.12±0.32,avaluesimilarto those observed with normal cyto-sol (2.44±0.08) and with p67-phox-deficient cytosol supple-mentedwithrp67-phox (2.42±0.07).The levelofactivityin the reconstituted reaction mixtureswasless than thatseenin
ex-periments 1and 2 inTable IV wherenearnormalactivitywas obtained. Thisapparently isdue tovariations in the specific activitiesofdifferentpreparationsofrp67-phox. The reconsti-tutionofboth oxidaseactivityandnormal kinetic behavior in heatedcytosolby rp67-phox providesstrongevidence that the defectinoxidaseactivityproduced bymildheatingofnormal neutrophils is duetothespecific thermolability ofone of the oxidasecomponents,p67-phox.
The susceptibility of p67-phoxto mild heating led us to
investigate whether the loss of function of this component
0 40 _ rp47phox
0 2 4 6 8 10
Time at 46 degrees (minutes)
Figure4.Effect of460Cheatingonrecombinant cytosol oxidase fac-tors.Purerecombinantp47-phox (e)orp67-phox (v)washeatedat
460Cat30-s intervals for indicatedtimes, asdescribed in Methods. Theactivities of theseproteinsweretestedinthecell-freeoxidase
activationsystemusing1 ggeach ofrp47-phoxandrp67-phox (either heatedorunheated), 105cellequivalents ofwholenormalcytosol,
and 5X I05cellequivalentsofdeoxycholate-solubilizedmembranes.
The datapointsareaveragesofduplicate reaction mixtures (assayed
simultaneously) obtained inarepresentative experiment.Inthetwo
suchexperiments performed,theaverageactivities of reactions
sup-plemented with unheatedrp47-phoxorrp67-phoxwere20.2 and 15.9
nmol O2/minperI07cellequivalent membranes, respectively.The
averageactivityof reactions thatlacked recombinant factorswas0.8
nmolO/minper 107cellequivalentsmembranes. The kinetics of therp67-phoxinactivationwerenearlyidentical in thetwo
experi-ments:at 2min,54.6% and62.6% ofcontrolactivity;at4min,22.5% and 19.1%;at6min7.3%and7.9%;andat8min,8.3% and 6.1%.
c 1.2 0
x %- 0.4
Figure 3. 1 activatingi
TableIV. Reconstitution of460C-treatedCytosolActivity by Recombinantp67-phox
constituents Quantity Expt.I Expt.2 Expt.3
ng percentcontrol activity
Heatedcytosol 5.1 7.3 0.7
Heated cytosol 200 10.4 9.2 0.7
plusrp47phox 1 400 15.8 6.9 0.6
pur4ox1000 21.9 8.2 0.4
Heated cytosol 200 78.1 96.6 42.9 400 87.9 116.9 44.1 plusrp67-phox}
1000 95.6 121.5 70.3
NADPHoxidase was activated in thecell-freesystemasdescribed in Methodsusing reaction mixtures (0.1 mlin totalvolume) which contained deoxycholate-solubilizedmembranes(5x I05cell
equiva-lents), normalcytosol heatedat460Cfor 7.5 min(106cell equiva-lents), and recombinantcytosolfactors(rp47-phoxorrp67-phox)in theamountsindicated in the table. Resultsfromthree separate
ex-perimentsareshown,eachperformedwithadifferentpreparationof cytosol.Superoxide productionisexpressedasthe percentage of controlactivity,which is definedasthat measuredin the presenceof
106cellequivalents ofunheatedcytosol. * Themeancontrolactivity
forthe threeexperimentswas29.2±4.3 nmol0/min/0I cell
amodel system for the oxidase defectinthis type of CGDin a
manner analogous to the 560C inactivation ofthe complement systemin serum.
Thebehavior ofheatedneutrophilsin cellfunction studies isconsistent with the selective inactivation ofanoxidase
com-ponent. The lossofrespiratoryburstfunction in heatedcells
parallels the observed defect in thekillingof S. aureus,a
corre-lation to be expectedgiventhe central roleof the respiratory
heated neutrophils also demonstrated a reduced capacity to
degranulate. Although this effect may beindependent ofthe
findingof a similar 50% reduction in degranulation in two patients
with variantX-linkedCGD suggests there may bealinkage of
someneutrophil functionstotherespiratoryburstoxidase(or its components). Although the heat treatment of neutrophils (orneutrophil cytosol)representsa useful model for the oxi-dasedefect in thep67-phox-deficientform ofCGD,it should notbe construed as astrictparadigm forthisdisease.
Thefindingthatp67-phox functionis lost by mildheating
in vitro raises the question ofwhether this critical oxidase com-ponentmightbesimilarly affected during periods of high fever
invivo. Even though the present studies do not directly address thisissue,wehave observed thatnormalcytosolcan beheated
at 41°C for upto 30 min with no demonstrable decrease in
activityin the cell-free oxidase activation system. Based on this
findingit does not appear that the thermolability of p67-phox
seen inourpreparations at 46°C has physiological relevance. What effect extended incubations of several hours and longer under fever conditions might have upon neutrophil oxidase function remainsto beinvestigated.
Elucidation ofthe mechanism bywhichp67-phoxis dis-abledbyheattreatmentand how this alteration then interferes withoxidaseactivation willrequire furtherstudies.
lightof thefindingthat heat-inactivated p67-phox(inboth
re-combinant and nativeforms)is stillrecognizable by
immuno-blottingand hasan unalteredapparent molecular weight. In thisrespect, heatedcytosol differsmarkedlyfrom
p67-phox-deficient CGDcytosol,which demonstratesacompletelack of
recom-binantp67-phox byitself results in defective oxidasefunction,
a heat-induced conformational change in p67-phox may be involved.
The baculovirus-derived recombinant NADPH oxidase
components,rp47-phoxand rp67-phox, have provideda
power-fulmeans toinvestigatedirectly defects in the respiratory burst NADPH oxidase. We have shown that the inactivation of NADPHoxidase by controlled heating doesnotappear tobe duetothe action ofheat shock proteins,ashad beenpreviously
suggested (45). Instead, loss of oxidase activity canbe attrib-utedtothethermolabilityofp67-phox alone,since
recombi-nantp67-phox demonstrated thesamesensitivitytoheatthat
was observed with whole neutrophil cytosol. These
experi-mentshave providedadirect and independentmeansoftesting
the kinetically derived model proposing thermal damagetoa
single soluble oxidasecomponent.In that heating results in the selective inactivation ofp67-phox, and in that the oxidase activ-ity of heated cytosolcanbecompletely reconstituted by
recom-binant p67-phox, this system should be useful in exploring functional relationships involving genetically engineered
E E 0.8
6.4 6.6 6.8
log (Cytosol Concentration)
0 1 2 3 4 5 6 7 8 9 10
Time at Incubation Temperature
Figure 6. Effect of heatingonactivated oxidase obtained from stimu-latedneutrophils. Preactivated NADPH oxidasewaspreparedas
noted underMethods, and subjectedtoheattreatment at37(v) and 460C(v). Asacontrol,aportion of the oxidase preparationwaskept
onice(v). Aliquotswereremovedto wetice after theindicated times ofheating and promptly assayed for activity. Reactionswereinitiated
with the addition of 0.16 mM NADPH, and the superoxide dismu-tase-inhibitable reduction ofcytochromec wasmeasuredusinga
dual-beamspectrophotometer. Themeancontrolactivityforthe threeexperiments performedwas22.0±3.2 nmol0/minperI07 cell equivalents.
tural variants ofp67-phox. Furthermore,thefindingthat rp67-phoxrestores normalkinetic behaviortobothheatedcytosol
andp67-phox-deficientCGDcytosolindicates that thistypeof
reconstitution system maybe useful forstudying the intricate
kinetic details ofthe mechanismbywhichtheNADPHoxidase
sensi-tivityto mildheating,both at370C(Fig. 6 and reference46) and (especially)at460C. The mechanismresponsiblefor this
inactivation, however,isnotclear. The failure ofrp67-phoxto restoreactivity doesnotruleoutthepossibilitythatp67-phox thermolabilityis stillacausalorcontributoryfactor. For
exam-ple, rp67-phoxmaynotbe abletoexchangewithheat-damaged p67-phox inthe activated oxidase. Alternatively,the
quater-nary structureof this form of the oxidasemaybedisruptedat
46°Cand contributetothe loss ofenzymeactivityinaddition to any specific effects on p67-phox. Additional experiments
aimed atdeducingthe mechanismbywhichthepreactivated
oxidase isdamaged by 46°C heatingcouldprovide insightsinto the functional roles of the various oxidase componentsinthe activeenzyme.Inabroadersense,the heat inactivation ofboth
normalcytosolandpreactivatedoxidaseprovidesapotentially valuable model system for studying the role that p67-phox playsboth inactivatingNADPHoxidase in normalphagocytes
and in causingthe respiratory burst defect in CGDpatients lackingthisprotein.
The authorsacknowledgeJames 0.Tolleyforhis skill inperforming Westernblotsdescribedinthismanuscript,Dr.IyadAlosachie for
pro-vidingtherabbit antiserumcontainingthep67-phox anti-peptide
anti-body, and Tercia L. Ku-Balai for herexpertise in carryingoutthe neutrophilfunctionalstudies.
This workwassupportedin partbygrantsfrom the National
Insti-tutesof Health(AI-24838, RR-00833, AR-10493,andAR-07107) and
from the ArthritisFoundation(Dr. Malawista).Dr.Curnuttewas an
EstablishedInvestigatorof theAmerican HeartAssociationatthe time
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