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Isolation and partial characterization of a monoclonal antibody to the Rous sarcoma virus transforming protein pp60src.


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Vol. 45, No. 3 JOURNALOFVIROLOGY,Mar. 1983, p. 1190-1194


CopyrightC1983,AmericanSociety forMicrobiology





of a




the Rous



Transforming Protein



Departmentof Microbiology, University of Virginia Medical School, Charlottesville, Virginia 22908 Received15October1982/Accepted 16 November 1982

Transformation of cells by Ro,ussarcomavirus is mediated by the product of the

viral src gene, pp6OSrc. A hybridoma cell line producing an immunoglobulin G3

antibodytopp6Osrc wasisolatedafter lymph node cells from immune mice were

fused with mouse myeloma cells (P3-NS1-1). Micewere immunized with p6Osrc

purified from Escherichia coli cells expressing the src gene product. The

monoclonal antibody immunoprecipitated pp60src from Rous sarcoma

virus-transformed cells and recognizedanantigenic determinant located in the

amino-terminal third of the pp6Osrc protein.

Cellulartransformation by Rous sarcoma

vi-rus (RSV)requiresthefunctionalexpression of

the RSV src gene (19, 40). Brugge and

co-workers first identified the RSVsrcgene

prod-uct, showing that sera from rabbits bearing RSV-inducedtumors(TBR sera)

immunoprecip-itated a 60,000-molecular-weight

phosphopro-tein (pp6Osrc) from RSV-transformed cells but

notfromnormal cellsorfrom cellsinfected with

transformation-defective RSV (1, 2, 31). The

RSVsrcgeneproductisaproteinkinase(7, 24).

pp60Src isolated as an immune complex with

TBR seraexhibits aunique phosphotransferase


tyro-sine in theimmunoglobulinheavychain(7-9, 11,

21, 25, 37, 38). This activity appears to be an


prep-arationsofitreadilyphosphorylate tyrosineina

variety ofsubstrates (11,25, 30). In

RSV-trans-formed cells, the cellular expression of


results in the phosphorylation of tyrosine in

severalspecificcellularproteins(10,12, 32, 36).

These unique phosphorylation events, coupled

with the intrinsic kinase activity of pp6Osrc,

suggestthatphosphorylationofdefined cellular

target proteins plays a critical role in cellular


The biochemical characterization of


has thus far been carriedoutwithTBRsera(1,

2, 8, 21, 24, 34, 35) or serafrom mice bearing


bothareheterogeneous,polyclonalantisera with

specifities for severalantigenic determinants of

src. However, adetailed analysis ofthe

struc-ture and function of


would be greatly


anti-bodies specific for defined antigenic

determi-nants of the src protein. Unfortunately, the

isolation of such monoclonal antibodies has

beenhindered by thelow levels ofpp60"rc

pres-ent in RSV-transformed cells and the difficulty

of obtaining adequate amounts of purified src

protein for immunization. Recently,

recombi-nant DNA techniques have been used to

con-struct bacterial plasmid vectors that direct the

synthesis ofhighlevels ofp6Osrc in Escherichia

coli (16, 26). The p6Osrc partially purified from

bacterialextractsexhibits protein kinase activity

(14, 26) and isimmunogenic inrabbits,yielding

antisera (rabbit anti-p60src) that react with

pp6Osrcfrom RSV-transformedcells(15).

In this paper we describe the isolation and

initial characterization ofamonoclonalantibody

topp6Osrc. WeusedPrague Astrain (PrA) RSV

p60srcpurified fromE. coli (14, 15) asanantigen

for both theimmunizationofBALB/cmice and

the screening of hybridoma culture fluids. The

monoclonalantibody that was isolated

immuno-precipitatedpp6Osrc from RSV-transformed cells

andrecognizedanantigenic determinant located

in the amino-terminal third of the



Toisolate hybridoma celllinesproducing

anti-body specific for


we first immunized

BALB/c miceby injection into thehindfootpads



emulsifiedin complete Freund

adju-vant.Each mousereceivedapproximately20,ug

ofp6OSrc purifiedfromextractsofE. coli

(bear-ing the plasmid pLac-src) by the method of

Gilmer and Erikson (15). Two weeks after this

immunization, popliteal lymph nodes were

re-moved, and the lymphocytes were fused with


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NOTES 1191

P3-NS1-1 mouse myeloma cells (27). Culture

fluids from the hybrid cellswereassayed for the

presence of antibody to srcprotein by a

solid-phase radioimmunoassay with bacterial p6Osrcas

antigenand125I-rabbit antimouse Fab (39).

For-ty-one hybrid cultures (ofa total of182) were

judged positive for the production of

cross-reactive antibody. These hybrids were sub-cloned by limiting dilution, and individual

cul-ture supernatants were tested for the ability to



from extracts of


or3P-labeled PrA

RSV-infect-ed chicken embryo (CE) cells. Three clones

produced antibodies directed against proteins

from RSV-infected CE cells; clone R2D2

im-munoprecipitated a 60,000Mr phosphoprotein,

identified as pp6(Yrc, clone G2K9






_'W SW _s0



pitated a120,000OMrphosphoprotein, and clone

C3PO immunoprecipitated a 56,000-Mr

phos-phoprotein. R2D2antibodywas of the

immuno-globulin G3 isotype, with kappa light chains.

G2K9 andC3PO antibodieswereof the

immuno-globulin M isotype with kappa light chains.

Preliminary data indicate that both G2K9 and

C3PO react with normal cell phosphoproteins

thatmaybe antigenically relatedtopp60Src.

Threecriteriaestablished R2D2as a

monoclo-nal antibody to pp6fyrc. First, R2D2 culture

fluid, ascites fluid,orculturefluid from a

repre-sentative subclone, R2D2-E4,

immunoprecipi-tateda60,000-Mr phosphoproteinfrom extracts

of either [35S]methionine- or 32P-labeled PrA

RSV-infected CE cells (Fig. 1A and B). The

60,000-Mr protein comigrated with pp60src















12 3



12 3

4 5




FIG. 1. Immunoprecipitationof RSVsrcproteinwithR2D2 monoclonalantibody. (A)Immunoprecipitation

of[35S]methionine-labeledextractsof PrARSV-infected CE cells. Cellswerelabeled for4 to5 hin Dulbecco

modified Eagle mediumlackingmethionine but supplemented with5% dialyzed fetal calf serum and 200,uCiof

[35S]methionine (Amersham Corp.)perml.Cellextractswereprepared and incubated with antiseraaspreviously

described (3,29). Immunecomplexesformed withmousemonoclonalantibodieswereincubated with rabbit anti-mouse Fab to ensure complete adsorption ofimmunoglobulin classes that do not bind protein A. Immune

complexes wereboiled in sample buffer and subjectedtoelectrophoresison 10.5%polyacrylamide gels (23).

Stainedgelswere equilibrated inEn3Hance(NewEngland Nuclear Corp.) to provide fluorographic enhance-ment. Immunoprecipitationwith (lane 1) culture fluid from clone R2D2, (lane 2) culture fluid from subclone R2D2-E4, (lane 3)culture fluid from mousemyelomacells(P3-NS1-1),(lane 4)rabbitanti-p60src,(lane 5) normal rabbit serum. Molecular weights were determined from the relative migration rates of a standard mix of peptides containing myosin (200,000), 3-galactosidase (116,000), phosphorylase A (92,500), bovine serum albumin (66,000), human gammaglobulin heavy chain (55,000), ovalbumin (42,000), carbonic anhydrase (31,000), soybean trypsin inhibitor (21,500), and cytochrome c (12,500). (B) Immunoprecipitation of


extracts of PrA RSV-infected CEcells.Cells were incubated for1.5 hwith 500pCiofcarrier-free32p,(ICN) per ml in phosphate-free medium 199 (Gibco Diagnostics) supplemented with 5% dialyzed fetal calf serum. Cell extracts were immunoprecipitated with antibody preparations as described for panel A. Immunoprecipitations were carried out withthefollowing culture fluids or antisera: lane 1, R2D2; lane 2, subclone R2D2-E4; lane 3, P3-NS1-1; lane 4, rabbitanti-p60Wrc; lane5, normal rabbitserum.(C) Immunoprecipitationof[35S]methionine-labeledextracts of tsCH119 RSV-infected CE cells. Cells were labeled and extracts were prepared and incubated with antibody as describedfor panelA.Lanes: 1, R2D2; 2, P3-NS1-1; 3, rabbitanti-p60src; 4, normalrabbit serum.

VOL. 45,1983

4io.qwfw +*& k


on November 10, 2019 by guest



1192 NOTES

munoprecipitated byrabbit antiserum to



(rabbit anti-p60sc) (Fig. 1A and B) or

TBR sera (data notshown). To confirm that the

60,000-Mr protein recognized by R2D2 was

structurally identical to


we subjected

the32P-labeled 60,000-Mrproteins immunopreci-pitated by TBR sera and R2D2 to partial Staphy-lococcus aureus V-8 protease digestion (4), and

the products were resolved by polyacrylamide

gel electrophoresis. Ineachcase, identical 32p_

labeled polypeptide products with molecular

weights of 34,000 (p34) and 26,000 (p26) were

observed (Fig. 2).

Second, clone R2D2 immunoprecipitated a

structurally altered form of the src protein

pres-entin CE cells infected with RSV tsCH119, an

RSV mutantcontaining a deletion within the src

gene (3). CEcells infected with tsCH119

synthe-size a 53,000-molecular-weight src protein

(p53src) containing a deletion of amino acid resi-dues 202 through 255 (3). Both R2D2 and rabbit anti-p60src immunoprecipitated a p53src from

ex-tracts of



tsCH119-in-fectedcells (Fig. 1C).

Third, clone R2D2 was used to

immunopre-cipitateahybrid protein ofp6ysrcand

,-galacto-A P


p34- *@ *


-43* WwVWWW ,i,

X2.3 .;4 to( 7 e 91Ot1 1213 14

FIG. 3. Immunoprecipitation of src-Pgal hybrid protein(p130)by monoclonal antibodyR2D2.Cultures of E. colicarrying plasmid pLSZ and expressing an src-,gal hybrid protein of 130,000 molecular weight were labeled for 2 to 3 h in sulfate-depleted growth mediumcontaining 100 ,uCiof[35 ]sulfateperml (16). The cells werewashed two times in1 mM EDTA-10

mM Tris-hydrochlonde (pH 8.0), and the extracts

wereprepared by the method of Gilmer andErikson

(15). As anegative control, cultures of E. coli contain-ing a plasmid with the src-3galcoding sequence but lacking the lactose operator-promoter (pSZ) were grownand labeledin thesamemanner.Odd-numbered lanes, immunoprecipitations of extracts of E. coli (pLSZ) cells; even-numbered lanes, immunoprecipita-tions of the pSZ cells. Immunoprecipitaimmunoprecipita-tions were carried out with(lanes1and2) monoclonalantibody

R2D2, (lanes 3 and 4) monoclonal antibody G2K9, (lanes 5 and 6) P3-NS1-1, (lanes7 and8) rabbit

anti-p60Src, (lanes 9 and 10) tumor-bearing mouse sera,

(lanes 11 and 12) normalrabbit serum, and(lanes 13 and 14) normal mouse serum. The molecularweight of p130 was determined as described in the legend to Fig. 1.

p26- 4

FIG. 2. Partial V-8 protease digestion patterns of

pp60Sc immunoprecipitated by monoclonal antibody R2D2 and TBR sera. Extracts of 32Pi-labeled PrA RSV-infected CE cellswereimmunoprecipitatedwith either R2D2 monoclonal antibodyor TBRsera, and the immunecomplexesweresubjected to electropho-resis on a 10.5% polyacrylamide gel. Radioactive

proteins migratingwithanapparentmolecularweight of60,000wereexcised from thegel, digestedwith S.

aureusV-8protease,andsubjectedtopolyacrylamide gel electrophoresis bythe methodof Cleveland et al.

(4). (A) Samples immunoprecipitated with R2D2. Lanes:1, undigested;2 and3,incubatedwith 10,ugof

V-8 protease. (B) Samples immunoprecipitated with TBRsera. Lanes: 1, undigested; 2 and3, incubated

with10,ug of V-8protease. Molecularweightsof the labeledpeptidesweredeterminedasdescribed in the


sidase (src-,gal) from extracts of E. coli. The

src-3gal hybrid protein contains the

amino-ter-minal 204 amino acids of p6Osrc fused with

1-galactosidase and is encoded by a plasmid

(pLSZ) in which the first612 basepairs of the

PrA RSVsrcgene(20)arejoined tothegene for

1-galactosidase (17).The fusedcoding sequence

is under the control of the lactose

operator-promoter (17, 33). The details of this

construc-tion willbepresentedelsewhere(J. T. Parsons,

A. Fenton, and V. Wilkerson, manuscript in

preparation). A protein of 130,000 molecular

weight(p130) wasimmunoprecipitated from

ex-tracts of [35S]sulfate-labeled E. coli containing

pLSZ bytumor-bearingmousesera, rabbit

anti-p6OSrC, and R2D2 monoclonalantibody (Fig. 3).

Incubation of the same extracts with normal

rabbit serumnormalmouseserum,culture fluid

from mouse myeloma cells,orG2K9 cells

(pro-ducing an antibody directed against a normal

cellular protein) did not immunoprecipitate

p130. Similarly, incubation of the antibodies


4$;W- --...%---.: IN*

on November 10, 2019 by guest


[image:3.489.253.445.77.225.2] [image:3.489.70.219.365.512.2]

NOTES 1193

with [35S]sulfate-labeled extracts from E. coli

containingafusedsrc-,gal codingsequencebut

lacking the lactose operator-promoter (E. coli

[pSZ]) didnotresult intheimmunoprecipitation

of p130(Fig. 3). These datanotonlyconfirm that

R2D2 recognizes a pp6Src determinant, but

lo-calize that determinant within the

amino-termi-nalthirdof the pp60frc sequence.

To investigate the reactivity ofR2D2

mono-clonal antibody with src proteins encoded by

otherASVs, we used R2D2 to

immunoprecipi-tate pp6Osrc from extracts of

[35S]methionine-labeled PrA RSV-, Schmidt-Ruppin (SR) strain

RSV-, or B77 ASV-infected CE cells. R2D2

antibody immunoprecipitated B77 ASV pp60frc

(Fig.4A) andto alesserextentSR RSVpp6&src

(Fig. 4B). In each case, rabbit anti-p60src

im-munoprecipitated a comparable amount of

pp6OSrc. Weobservednoimmunoprecipitation of

normal cellpp6AYrc (5,28)orof the transforming

proteins of Fujinami ASV (p140) (13) or Y-73

ASV (p90) (18, 22)by R2D2 (datanotshown).

Herewe have reported the isolation and

par-tial characterization ofamonoclonalantibodyto

the src gene product, pp6Osrc, of PrA RSV.

Several facets of the isolation and

characteriza-tion of this monoclonalantibody relyon

bacteri-alplasmids thatexpressallor partof thep6(Yrc

protein. First, the plasmid pLac-src expresses

highlevelsofthesrcprotein (16), thereby

facili-tating the isolation of purified



bacterial src protein, we readily

hyperimmun-izedmice, whereas repeated attempts to

hyper-immunize mice with pp60Yrc prepared from CE

or vole cells (6) have been unsuccessful. The

isolation of the monoclonal antibodyR2D2

dem-onstrates theutilityof this approach. Secondly,

bacterial plasmids containing apart ofthe src

coding sequence fused, in frame, to E. coli

I-galactosidase provideusefulreagentsfor

charac-A B C

_-w S:


1 2 3 4 1 2 3 4 1 2 3 4

FIG. 4. Reactivity of R2D2 monoclonal antibody with the src proteins ofB,, ASV, SR RSV, and PrA RSV. CE cells infected withB-n ASV (A), SRRSV (B), or PrARSV (C) were labeled with

[355]methio-nine, and extracts were prepared and immunoprecipi-tatedas described in the legend to Fig. 1. Lanes: 1, R2D2; 2, P3-NS1-1; 3, rabbit anti-p6Osrc; 4, normal rabbitantiserum.

terizingthe determinantsrecognized by

individ-ual monoclonal antibodies. Construction of

similarplasmidsbearing discrete regions of the

src gene sequence should provide a bank of

plasmids that specify hybrid proteins useful for

the identification and mapping of unique


The isolationof the cloneR2D2represents an

initial step in the establishment of a panel of

monoclonal antibodies with multiple specifities

forpp6O(sc. Suchantibodies will facilitate

analy-sis of the structure and function of pp60src as

well asothertransforming proteins encoded by

related sarcoma viruses.

Wethank BettyCreasy for excellent technical assistance. We especiallythank Tona Gilmer and Ray Erikson for provid-ing rabbitanti-p6&Y'antibody and for the many discussions duringthe courseof this work.

J.T.P.isarecipientof a Faculty Research Award from the AmericanCancer Society. This work was supported by Public HealthServicegrantsCA29243 andCA27578 from the Nation-al Cancer Institute and grant MV-29D from the American Cancer Society.


Usingmethods similar tothose describedabove,we have isolated an additional 15 stable hybridoma cell linesproducing monoclonal antibodies specific for PrA RSVpp6Yrc. The characterizationof these monoclo-nalantibodies is in progress.


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FIG. 3.protein Immunoprecipitation (p130) by monoclonal antibody
FIG. 4.rabbittatedR2D2;(B),withRSV.nine, Reactivity of R2D2 monoclonal antibody the src proteins of B,, ASV, SR RSV, and PrA CE cells infected with B-n ASV (A), SR RSV or PrA RSV (C) were labeled with [355]methio- and extracts were prepared and immunopreci


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