mutant p53

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Mutant p53 accumulates in cycling and proliferating cells in the normal tissues of p53 R172H mutant mice

Mutant p53 accumulates in cycling and proliferating cells in the normal tissues of p53 R172H mutant mice

Many different types of cancer show a high incidence of p53 mutations, leading to the expression of mutant p53 proteins. Although we are unable to validate whether the properties and induction of the mutp53 protein in these morphologically normal tissues are the same as that of the mutp53 protein in tumours, we did find that increased mutp53 protein accumulation is more relevant to cell and tissue types with high proliferative rate such as small intestine, thymus, spleen and anagen hair follicles. The accumulation of mutp53 protein is not spontaneous or uncontrolled, it occurs in a cell- and tissue-specific manner (Figure 1). The high accumulation of the mutp53 protein within the crypts is remarkable. We stained large numbers of sections from small intestine of different p53 R172H mice, we generally only detected elevated mutp53 protein in cycling CBC and rapidly proliferating TA cells within the small intestinal crypts (Figures 3). Our study is the first to describe elevated mutp53 protein levels in CBC and TA cells of intestinal crypts. Although we do not understand whether and how elevated mutant p53 proteins might perturb intestinal stem cells and affect tumorigenesis, this p53 R172H mouse model will provide a valuable tool for understanding the role of mutant p53 protein in the cancer initiation. In human specimens clusters of intensely stained p53 positive nuclei have been seen in clones present in skin [37] and fallopian tube (p53 signatures)
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New therapeutic strategies to treat human cancers expressing mutant p53 proteins

New therapeutic strategies to treat human cancers expressing mutant p53 proteins

inactive state by WEE1 through phosphorylation of CDK1 at tyrosine 15 [124, 146]. WEE1 is highly expressed in several cancer types, including hepatocellu- lar carcinoma [147], cervical cancers [148], lung cancers [149], squamous cell carcinoma [148, 150], colorectal cancers [151], gastric cancers [152], leukemia [153, 154], melanoma [155], and ovarian cancers [156]. High ex- pression of WEE1 has been reported in some cancers in response to elevated replication stress, and has been as- sociated with tumor progression and poor outcome [148, 155, 156] (Fig. 2B). Loss of WEE1 activity sensitizes p53 inactive cells to DNA damaging agents and radio- sensitization [157–160]. Recently Moser and colleagues performed RNAi kinome viability screens in HNSCC to identify novel therapeutic drug targeting mutant p53 pro- tein [150]. Kinase targets were selected on the basis of impaired viability and increased apoptosis following kin- ase knocking-down. Putative survival kinases included signaling proteins within the focal adhesion and integrin (CAMK2B, FYN, ILK, EPHA3, EIF2AK4, TRIB2), PI3K signaling (PIK4CB, PIK3CB, PIP5K1B, TRIB2, FGFR3, ALK), SRC signaling (FYN, TXK, CAM2KB), and G2/M cell cycle regulation (WEE1, NEK4, TTK, AURKA, CHK1). WEE1 was implicated as a critical survival kinase for TP53 mutant HNSCC cells. Treatment with WEE1 inhibitor MK-1775 caused unscheduled mitotic entry and apoptotic death selectively in mutp53 versus wild-type p53 cell lines. It also in- creased cisplatin-induced killing in a mutp53 orthoto- pic xenograft model [150]. In patients with HNSCC undergoing curative-intent surgery and heterogeneous adjuvant therapy, TP53 mutations were associated with reduced survival, independent of pathologic nodal stage or primary tumor site [161]. TP53 muta- tions were validated as a prognostic biomarker in a cohort of patients treated homogeneously with pri- mary surgery and postoperative radiotherapy [162]. Further our group analyzed TP53 status by direct se- quencing of exons 2 through 11 of a prospective series of 121 HNSCC samples and assessed its associ- ation with outcome in 109 followed-up patients [125]. A TP53 mutation was present in 58% of the tumors and TP53 mutations were significantly associated with a shorter recurrence-free survival [125]. In an ortho- topic murine model evaluating 48 validated HNSCC cell lines, TP53 mutations correlated with higher growth rate, cervical nodal metastases, and decreased survival, suggesting a biologic basis for inferior prog- nosis [163]. Cells carrying wtp53 protein arrest at the G1 checkpoint of the cell cycle to repair damaged DNA, before DNA replication (Fig. 3B). Cells with defective p53 pathway as for those carrying mutant p53 proteins rely mainly on DNA repair at the G2 checkpoint [164]. Indeed several inhibitors of the G2
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Dysregulation of microRNA biogenesis in cancer: the impact of mutant p53 on Drosha complex activity

Dysregulation of microRNA biogenesis in cancer: the impact of mutant p53 on Drosha complex activity

indicating, for the first time, that mutp53 may be responsible at least in part for the miRNAs downregula- tion observed in cancer. Moreover, we found that another missense mutp53-R175H, inhibits the expression of several of these miRNAs in breast cancer cells (SKBR3). This strongly points out a general mechanism that involves different p53 proteins with missense muta- tions and suggests that the signature of miRNAs downregulated by mutp53 proteins in different solid tumors has, at least in part, common members. From a mechanistic point of view, through pri- pre- and mature form analysis, we found that mutp53 downre- gulates miRNAs not only at transcriptional but also at post-transcriptional level. In agreement, we dem- onstrated that endogenous mutp53 proteins (R273H and R175H) directly bind p72/82 through its N- terminal domain, hindering the association of this DEAD-box with the Microprocessor complex and pri- miRNAs, and leading to the inhibition of the biogen- esis of a subset of miRNAs positively regulated by p72. Of note we found that the endogenous wtp53 has an opposite effect on the expression of mutp53 repressed miRNAs on colon cancer cell lines con- firming the contribution of mutant p53 GOF on miRNA repression.
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Clinical outcome and expression of mutant P53, P16, and Smad4 in lung adenocarcinoma: a prospective study

Clinical outcome and expression of mutant P53, P16, and Smad4 in lung adenocarcinoma: a prospective study

Methods: We investigated associations among P53 mutant (P53 Mut ) expression, and P16 and Smad4 loss-of-expression, with clinical outcome in 120 LAC patients who underwent curative resection, using immunohistochemical (IHC) methods. Results: Of the 120 patients, 76 (63.3%) expressed P53 Mut protein, whereas 54 (45.0%) loss of P16 expressed and 75 (62.5%) loss of Smad4 expressed. P53 Mut expression was associated with tumor size ( P = 0.041) and pathological stage ( P = 0.025). Loss of P16 expression was associated with lymph node metastasis ( P = 0.001) and pathological stage ( P < 0.001). Loss of Smad4 expression was associated with tumor size ( P = 0.033), lymph node metastasis ( P = 0.014), pathological stage ( P = 0.017), and tumor differentiation ( P = 0.022). Kaplan-Meier survival analysis showed that tumor size ( P = 0.031), lymph node metastasis ( P < 0.001), pathological stage ( P < 0.001), P53 Mut protein expression ( P = 0.038), and loss of p16 or Smad4 expression ( P < 0.001) were significantly associated with shorter overall survival(OS), whereas multivariate analysis indicated that lymph node metastasis ( P = 0.014) and loss of p16 or Smad4 expression ( P < 0.001) were independent prognostic factors. Analysis of protein combinations showed patients with more alterations had poorer survival ( P < 0.001). Spearman correlation analysis showed that loss of Smad4 expression inversely correlated with expression of P53 Mut ( r = − 0.196, P = 0.032) and positively with lost P16 expression ( r =0.182, P = 0.047).
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Repression of endogenous p53 transactivation function in HeLa cervical carcinoma cells by human papillomavirus type 16 E6, human mdm-2, and mutant p53.

Repression of endogenous p53 transactivation function in HeLa cervical carcinoma cells by human papillomavirus type 16 E6, human mdm-2, and mutant p53.

6 Repression of Endogenous p53 Transactivation Function in HeLa Cervical Carcinoma Cells by Human Papillomavirus Type 16 E6, Human mdm-2, and Mutant p53 FELIX HOPPE-SEYLER* AND KARIN BUT[r]

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Original Article RITA has growth inhibitory activity on colon cancer HCT116 cells expressing wild-type p53, but not SW480 cells harboring mutant p53, via repressing wild-type p53 ubiquitination

Original Article RITA has growth inhibitory activity on colon cancer HCT116 cells expressing wild-type p53, but not SW480 cells harboring mutant p53, via repressing wild-type p53 ubiquitination

gical resection, chemotherapy and radiation therapy [5]. Loss of p53 function, either through mutation or post-translational modification, has been extensively reported in CRC, and closely associated with unchecked prolifera- tion, tumor progression, and therapeutic resis- tance [6]. Mutation of the p53 gene is one of the most frequent genetic alterations in CRC [6]. Mutant p53 (MT-p53) is incapable of recog- nizing WT-p53 DNA binding sites in the promot- er of p53 target genes, resulting the loss of p53 function against cancer, and even worse, some p53 mutations acquire new and distinct onco- genic properties and contribute to malignant process through the interaction with sequence- specific transcription factors, such as NF-Y, E2F1, NF-κB and Vitamin D receptor [7, 8]. Indeed, MT-p53 seem to be capable of activat- ing promoters of genes that are usually not acti- vated by the WT-p53 protein, such as c-myc and MDR1 [9]. Inducible knockdown of endog- enous MT-p53 in CRC cell line (SW480) and pancreatic cancer cell line (MIA-PaCa-2) trig- gers the proliferative defect [9]. Knockin mice that carry one null allele and one mutant allele of the p53 gene (R172H or R270H) developed novel tumors compared to p53-null mice [10, 11]. In other CRC cases, p53 retains its wild- type form, but the p53 is maintained at a low level or becomes functionally inactive by the effect of the over-expressed murine double minute 2 (MDM2) [12]. MDM2 is an E3 ubiqui- tin ligase, which mediates p53 ubiquitination and proteasomal degradation. Recent studies have unveiled numerous additional actions of MDM2 which are implicated in p53 inactiva- tion. MDM2 binds to the transactivation domain of p53, prevents p53 from interacting with the transcriptional machinery and inhibits p53- responsive gene expression [13]. Besides, MDM2 exports p53 from the nucleus abolish- ing its transcriptional activity [13]. Therefore, in the past few years, much effort has been made toward identification of small molecules capa- ble of restoring normal p53 functions in cells harboring MT-p53 and of preventing the inter- action of MDM2 with p53 to stabilize WT-p53 and maintain its function.
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Survival in males with glioma and gastric adenocarcinoma correlates with mutant p53 residual transcriptional activity

Survival in males with glioma and gastric adenocarcinoma correlates with mutant p53 residual transcriptional activity

Stratification of cancer patients with TP53 mutations based on transcriptional activity scores. In order to estab- lish a prognostic tool that would link mutant p53 activity to patient survival, an integrated functional genomics meta-analysis was carried out that included 2,314 cancer patients with sporadic TP53 missense mutations and 1,049 LFS patients with germline TP53 mutations (Figure 1). In total, 58 cancer studies (spanning at least 18 different cancer types; Supplemental Table 1) were compiled to generate a sporadic cancer patient dataset that included 403 unique p53 single amino acid substitutions (19, 20). Germline TP53 mutation carriers, including 188 unique p53 single amino acid substitutions, were collected from the International Agency for Research on Cancer (IARC) TP53 database (21). All patients with TP53 muta- tions were subsequently divided into subgroups along a gradient of residual transcriptional activity based on a comprehensive panel of p53 mutants originally generated by saturation mutagenesis throughout the p53 coding region that covers all clinically identified TP53 mutations (22). Specifically, we assigned a median transcriptional activity value to each clinically observed TP53 mutation relative to WT p53 (Sup- plemental Tables 2 and 3), as derived from monitoring 8 different p53 responsive promoter elements (p21, Mdm2, Bax, 14-3-3, p53AIP1, GADD45, Noxa, and p53R2) (22). Importantly, this analysis includes many low-abundance mutations that have been identified due to the increased use of next-generation sequencing for mutation testing in the clinic.
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Mutant p53 establishes targetable tumor dependency by promoting unscheduled replication

Mutant p53 establishes targetable tumor dependency by promoting unscheduled replication

ChIP analysis and sequencing. ChIP and ChIP-Seq were performed using standard methods (69). Briefly, exponentially growing H1299 cells expressing either empty vector or the p53 mutant p53R273H were fixed with formaldehyde, extracted, and immunoprecipitated with antibodies against p53 (DO1 and FL-393, Santa Cruz Biotechnology Inc.). DNA fragments were eluted from immunoprecipitates, reverse crosslinked, and purified. Purified DNA (150 ng) was sequenced at the Donnelly Sequencing Center at the University of Toronto. ChIP sam- ples were run on the Illumina HiSeq 2500 System, and individual fastq files were used for analysis. Sequences were aligned to the human genome (HG19) and analyzed using DNASTAR ArrayStar (version 12) software. Peaks were visualized using SeqMan Pro software (DNAS- TAR). ChIP-Seq experiments were normalized by reads assigned per million mapped reads (RPM). Genome sequences that showed bind- ing of p53 in p53-R273H–expressing cells but no binding in vector cells or where there was greater than 1.5-fold higher binding in the p53- R273H cells were chosen for further analysis. Gene lists for RNA-Seq and ChIP-Seq were compared to determine which genes were upregu- lated by mutant p53 and which also have p53 binding to the promoter. For ChIP analysis, DNA samples were suspended in water and the presence of cyclin A and CHK1 promoter fragments were analyzed by 3 contiguous sets of primers as listed in Supplemental Table 1.
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Mutant p53 induces a hypoxia transcriptional program in gastric and esophageal adenocarcinoma

Mutant p53 induces a hypoxia transcriptional program in gastric and esophageal adenocarcinoma

We show for the first time to our knowledge the ability of mutant p53 to induce hypoxia during pri- mary tumor growth using real-time in vivo luciferase reporter–based imaging. Importantly, we found that the greatest impact of mutant p53 on hypoxia occurred during the early stages of primary tumor growth, a phenomenon that attenuated as the tumors grew larger over time. These results could represent a techni- cal limitation of the in vivo reporter system or the strong propensity to activate hypoxia signaling during tumor growth, especially with the rapid growth kinetics of mouse xenografts. However, these results may also indicate the potential pathological importance of mutant p53–mediated hypoxia induction during the initiation/early formation of primary tumor growth or even in the preneoplastic phase, providing a growth advantage to the p53 mutant cell prior to oncogene activation. Once the tumor reaches a sufficient size, the effect of mutant p53 on hypoxia induction is difficult to discern. There is evidence to support the impor- tance of hypoxia-induced angiogenesis during these early stages of tumorigenesis: progression from hyper- plasia to neoplasia requires neovascularization, enabling the transition from dysplastic lesions to overt can- cer (54). It will be important for future studies to investigate the importance of hypoxia induction by mutant p53 using models of gastroesophageal premalignancy or early neoplasia.
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Mutant p53 protects ETS2 from non-canonical COP1/DET1 dependent degradation

Mutant p53 protects ETS2 from non-canonical COP1/DET1 dependent degradation

Mutations in the tumor suppressor gene TP53 contribute to the development of approximately half of all human cancers. One mechanism by which mutant p53 (mtp53) acts is through interaction with other transcription factors, which can either enhance or repress the transcription of their target genes. Mtp53 preferentially interacts with the erythroblastosis virus E26 oncogene homologue 2 (ETS2), an ETS transcription factor, and increases its protein stability. To study the mechanism underlying ETS2 degradation, we knocked down ubiquitin ligases known to interact with ETS2. We observed that knockdown of the constitutive photomorphogenesis protein 1 (COP1) and its binding partner De-etiolated 1 (DET1) significantly increased ETS2 stability, and conversely, their ectopic expression led to increased ETS2 ubiquitination and degradation. Surprisingly, we observed that DET1 binds to ETS2 independently of COP1, and we demonstrated that mutation of multiple sites required for ETS2 degradation abrogated the interaction between DET1 and ETS2. Furthermore, we demonstrate that mtp53 prevents the COP1/DET1 complex from ubiquitinating ETS2 and thereby marking it for destruction. Mechanistically, we show that mtp53 destabilizes DET1 and also disrupts the DET1/ETS2 complex thereby preventing ETS2 degradation. Our study reveals a hitherto unknown function in which DET1 mediates the interaction with the substrates of its cognate ubiquitin ligase complex and provides an explanation for the ability of mtp53 to protect ETS2.
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Mutant p53–associated myosin X upregulation promotes breast cancer invasion and metastasis

Mutant p53–associated myosin X upregulation promotes breast cancer invasion and metastasis

and was found to be significantly upregulated only in mutant p53– expressing pancreatic cancers as compared with the other types of pancreatic tumors investigated, which had either lost p53 function or had other mutations that drive PDAC formation in the mouse (Supplemental Figure 6C and refs. 41, 42). Myo10 was upregulated in PDACs when compared with primary pancreatic ductal epithe- lial cells (PDEC) from WT mice (5.46, 1.57, and 1.32-fold for the 3 probes tested). To confirm these observations, quantitative RT- PCR (qRT-PCR) was performed on a subset of these murine PDACs. Myo10 mRNA was higher in the tumors carrying mutant p53 (R175H) as compared with p53 loss-of-function and PTEN-deleted PDACs (Supplemental Figure 6D). Strong Myo10 immunostaining was also detected in PDAC tissue sections from mice expressing mutant p53 (p53R172H) compared with p53-deleted mice (Fig- ure 6C). Furthermore, increased Myo10 labeling correlated with p53 accumulation in late pancreatic intraepithelial neoplasia (late PanIN) and PDAC, whereas little Myo10 expression was detected in the p53-negative early PanIN tissue samples (Figure 6D). In line with these in vivo data, we observed a similar correlation between p53 gain-of-function mutations and Myo10 expression also in human PDAC cell lines (Figure 6E).
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Mutant p53 regulates ovarian cancer transformed phenotypes through autocrine matrix deposition

Mutant p53 regulates ovarian cancer transformed phenotypes through autocrine matrix deposition

m-p53 promotes survival of detached cells independently of cell-cell adhesion. In ovarian cancer patients, car- cinoma cells residing within peritoneal fluids adhere to each other and form multicellular suspended cell clusters (41, 42) (Figure 2A). Similarly in our model, we observed that within a 24-hour period, FNE-m-p53 cells, but not control cells, formed compacted cell clusters in suspension (Figure 2A and Supplemental Fig- ure 2A), raising the possibility that m-p53 expression promotes cell-cell adhesion. To determine if expression of m-p53 promotes cell-cell adhesion that contributes to the assembly of the compacted multicellular FNE Figure 1. Mutant p53 promotes survival of detached fallopian tube nonciliated epithelial (FNE) cells. (A) Montage of representative (n = 8–10/group) phase-contrast video clips from time-lapse recording of FNE cells transduced with empty vector or mutant p53 (m-p53) variants (R175H, R249S, or R273H) and maintained in suspension for the indicated time. Arrows point to dying cells. Clips are representative of 8–10 movies per condition with 100–150 cells per movie acquired during one recording session (Supplemental Video 1). (B) Schematic depiction of the ethidium bromide (EtBr) incorporation assay used to quantify cell death (red) within multicellular clusters (green) grown in suspension. (C and D) Representative (n = 3–4 experiments) phase-contrast and pseudocolored fluorescence images documenting the level of EtBr incorporation into GFP-labeled FNE vector control (pWZL in C, pLenti 6 in D) or FNE- m-p53 (R175H, R249S, and R273H) cellular clusters maintained in suspension for 96 hours. (E) Quantification of the EtBr incorporation distribution in cell clusters from 4 (R175H) and 3 (R249S and R273H) independent experiments. n = 50–60 cellular clusters in control and m-p53 R175H groups, and n = 61, 42,
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The mutant p53 ID4 complex controls VEGFA isoforms by recruiting lncRNA MALAT1

The mutant p53 ID4 complex controls VEGFA isoforms by recruiting lncRNA MALAT1

splicing factor SRSF1 bridges MALAT1 to mutant p53 and ID4 proteins in breast cancer cells... Mutant p53 and ID4 delocalize MALAT1 from nuclear speckles and favor its association with.[r]

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Mutant p53 confers chemoresistance in non-small cell lung cancer by upregulating Nrf2

Mutant p53 confers chemoresistance in non-small cell lung cancer by upregulating Nrf2

decreased Sp1 binding to the Nrf2 promoter, may confer cisplatin sensitivity, a favorable chemo-response, thereby leading to favorable outcomes in lung cancer patients. Moreover, a decrease in Nrf2 mRNA expression by wild- type p53 corresponded with its protein expression. These findings suggest that Nrf2 expression is predominately regulated by wild-type p53 at the transcription level. Conversely, Nrf2 mRNA and its protein expression levels in H1299 cells were markedly elevated by different mutant p53 expression vector transfections when compared with VC cells (Figure 1C). A previous report has indicated that Nrf2 expression is driven by the NF-κB signaling pathway in acute myeloid leukemia [23]. Mutation of p53 gene prolongs NF-κB activation and promotes chronic inflammation and inflammation-associated colorectal cancer [36]. Therefore, mutant p53 not only confers drug resistance via upregulation of Nrf2 expression but it also may activate the NF-κB signaling pathway for additional enhancement of Nrf2 expression (Figure 1C).
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Suppression of gain-of-function mutant p53 with metabolic inhibitors reduces tumor growth in vivo

Suppression of gain-of-function mutant p53 with metabolic inhibitors reduces tumor growth in vivo

HL2). We at first transfected H27 and H83 cells with siRNA against p53. p53 siRNA efficiently downregulated mRNA (36-hour transfection) and protein (48-hour transfection) expression in H27 cells (Figure 1A), while scrambled siRNA did not. The knockdown of mutant p53 protein induced apoptosis and cell cycle arrest in H27 cells, as evidenced by PARP cleavage and reduced cyclin D3 expression (Figure 1A). The levels of phosphor- ERK and ERK1/2 were simultaneously decreased, but phosphor-AMPK was not reduced upon downregulation of mutant p53 protein in H27 cells. Interestingly, when cell numbers were counted after gene knockdown, cell proliferation was found to be inhibited in H27 cells (Figure 1B and 1C). When cells were analyzed by FACS with Annexin V/PI staining, approximately 35% of p53- siRNA-treated H27 cells were in the course of apoptosis (Figure 1D and 1E). Surprisingly, parallel transfection of H83 cells with siRNA-p53 had no effect on apoptosis, cell cycle arrest, or cell proliferation (Figure 1). These results critically indicate that cells expressing the GOF mutant p53 protein (H27) are addicted to this protein and
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ERβ decreases the invasiveness of triple-negative breast cancer cells by regulating mutant p53 oncogenic function

ERβ decreases the invasiveness of triple-negative breast cancer cells by regulating mutant p53 oncogenic function

In the present study we searched for ERβ1- interacting proteins and target genes that may account for the decreased invasiveness of ERβ1-expressing TNBC cells [26, 27]. We focused on mutant p53 signaling since p53 is frequently mutated in TNBC and mutant p53 proteins promote tumor metastasis [10, 12, 17, 28]. We used as an indicator of mutant p53 gain-of-function the expression of genes that are regulated by mutant p53. We focused on those genes that inhibit metastasis in breast cancer including SHARP-1 and the ERα-regulated CCNG2 [3, 10, 29–31] and the pro-metastatic factor Follistatin [32]. As shown in Figure 1A (top), expression of ERβ1 in mutant p53 (p53280K)-expressing MDA-MB-231 cells upregulated SHARP-1, CCNG2 and the tumor suppressor ADAMTS9 [33] and downregulated Follistatin. The relevance of mutant p53 to the expression of these genes was further demonstrated by the upregulation of SHARP1, ADAMTS9 and GRP87 following knockdown of mutant p53 in MDA-MB-231 cells (Figure 1A, bottom). A similar gene expression signature was observed following upregulation of ERβ1 in another TNBC cell line. BT549 cells have mesenchymal-like morphology and express a different hot spot p53 mutant (p53249S). The changes in the expression of SHARP-1, CCNG2 and Follistatin mRNAs were also confirmed at the protein level (Figure 1B, top). In addition to altering the expression of metastasis-associated genes, ERβ1 induced epithelial transformation in these cells as it did in MDA-MB-231 cells (Figure 1B, bottom) [27]. In contrast to mutant p53- expressing TNBC cells, ERβ1 did not alter the epithelial- like morphology of the p53 null SUM159 TNBC cells (Figure 1C, top). In these cells, ERβ1 was found to regulate the expression of Follistatin, ADAMTS9 and
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Overcoming the Dominant Negative Effect of Mutant p53+/R172H Mice.

Overcoming the Dominant Negative Effect of Mutant p53+/R172H Mice.

Mutant p53 proteins accumulate in tumors, function as dominant negative inhibitors to block wild type p53 activity and some mutant p53 proteins display gain-of-function properties which enhance cancer progression [1-3, 5, 6]. Thus, there is significant interest in therapeutic strategies aimed at the mutant p53 protein. Potential strategies include converting the mutant p53 protein into a protein that has wild type p53 activity, decreasing the stability of the mutant p53 protein, blocking the dominant negative effect and inhibiting the interactions of the mutant p53 with other proteins it has hijacked to enhance cancer progression [4, 19, 20, 64]. Our functional in vivo studies demonstrate that the depletion of C/EBPβ restores and enhances wild type p53 pro-apoptotic function even in the presence of a mutant p53 with a “hot spot” mutation to overcome the dominant negative effect of mutant p53 in UVB-treated epidermis in vivo. These results could have potential therapeutic benefit in p53 +/mut cancers because; 1) overcoming the dominant negative
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Modulation of MDR/MRP by wild type and mutant p53

Modulation of MDR/MRP by wild type and mutant p53

Loss of wild-type p53 activity and acquisition of a multidrug resistance (MDR) phenotype, two apparently key factors in the resistance of human cancers to chemotherapy, may be interrelated. Wild-type p53 represses expression of both the MDR-1 gene (encoding the prototypical MDR protein P-glycoprotein [PGP]) and MRP-1 (encoding the MDR-associated protein) (1, 2). Using a temperature-sensitive p53 mutant, Sullivan et al. (3) recently claimed in the JCI that the introduction of a mutant p53 variant promoted MRP expression and

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Mutant p53 uses p63 as a molecular chaperone to alter gene expression and induce a pro-invasive secretome

Mutant p53 uses p63 as a molecular chaperone to alter gene expression and induce a pro-invasive secretome

Our findings thus far suggest that the global targets of mutant p53 are also direct targets of p63. Furthermore, we also observed constitutive regulation of these genes by p63. Based on these results, we speculated that mutant p53 may be directly recruited to the promoters of its target genes with p63. Data from ChIP analyses were consistent with this hypothesis, as induced mutant p53 was found to be associated with these p63-REs in the promoters of PLK2, DKK1, METTL7B, OCEL1, TMEM205 and TFPI2 in H1299 cells (Fig. 7A). These observations were not restricted to the inducible system, as in MDA-MB-468 cells the endogenous p53 R273H mutant was also bound to these p63-REs (Fig. 7B). Further confirmation of mutant p53 recruitment to these sites was demonstrated using another endogenous p53 mutant (R280K) expressed in MDA-MB-231 (Fig. 7C). Thus, these results provide firm evidence that mutant p53 and p63 are co-recruited to these p63-REs. Silencing of p63 in MDA-MB-231 cells resulted in complete dissociation of the endogenous p53 mutant from the promoter of TFPI2, suggesting that mutant p53 uses p63 as a molecular chaperone to tether to these promoter regions (Fig. 7D). Collectively, these data support a model where a small subset of wild-type p53 transactivated targets are also the targets that drive mutant p53 gain-of-function. Transactivation by mutant p53 is achieved by the recruitment of p63 as a molecular chaperone that enables mutant p53 to bind to the promoters of these target genes.
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Reactivation of mutant p53 by capsaicin, the major constituent of peppers

Reactivation of mutant p53 by capsaicin, the major constituent of peppers

Mutp53 proteins may drive tumor progression, metasta- sis and resistance to therapies [4], leading to poorer patient outcomes [28]. Therefore, reactivation of mutp53 proteins holds great promises in cancer therapy [29]. As a proof of principle, clearing of mutp53 has been shown to reduce tumor malignancy and to impair mutp53 gain-of-function (GOF), thus improving the apoptotic response to drugs [30, 31]. In addition, as mutp53 pro- teins exert a dominant negative effect on wtp53 [32], changing the balance between folded–misfolded p53 proteins may restore wild-type over mutant p53 func- tions, as also reported by our previous studies [17, 18, 33]. Restoration of wtp53 activity is extremely helpful for eradicating established tumors [34–36] and does not dam- age nontransformed cells [37]. Several small molecules have been tested for p53 reactivation in mutp53-carrying cells [10, 11, 38] while studies exploiting the effect of natural compounds are limited. Here, we show that CPS, the major constituent of peppers, induced mutp53 protein degradation, in part through autophagy, and that such abrogation restored wild-type p53 activities over mutant p53 functions.
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