Mutations in exons 5-8 of the p53 gene, independent of their type and location, are associated with increased apoptosis and mitosis in invasive breast carcinoma

Impact of TP53 mutations in breast cancer: Clinicopathological features and prognosisImpact of TP53 mutations in breast CA

Background

TP53 is a crucial tumor suppressor gene. However, the mutation pattern of TP53 in Chinese patients with breast cancer has not yet been determined.

Methods

A total of 411 untreated patients with invasive breast cancer diagnosed at Guangdong Provincial People's Hospital (GDPH) between June 2017 to September 2018 were recruited into the study. Mutational alterations in TP53 were detected and correlations between TP53 mutations and clinicopathological features analyzed. Comparative analysis of the data in the GDPH cohort with those in the METABRIC cohort were carried out.

Results

A significantly higher rate of TP53 mutations was detected in the GDPH cohort (51.3%) compared with the METABRIC cohort (34.4%) (P < 0.01). In the GDPH cohort, 77.8% of the mutations were located in the conserved areas across exons 5–8 of TP53; among these, 112 were identified as missense mutations and mainly clustered in the DNA‐binding region. R273C/H (n = 11) and R248Q/W (n = 10) were two of the most common mutation sites of TP53 detected in the cohort of GDPH patients. Logistic regression multivariate analysis showed that histological grade III, ki‐67 > = 25%, HR‐ and Her2+ in breast cancer had higher mutation probability of TP53 (P < 0.001 in the GDPH cohort). Furthermore, receiver operating characteristic (ROC) model combining molecular typing and Ki‐67 was established to predict the mutation of TP53, and the AUC was 0.846.

Conclusions

A significantly higher rate of TP53 mutation was detected in the Chinese cohort compared with the METABRIC. Correlation analysis revealed a significant association of TP53 mutation with HR‐ and HER2+, higher Ki‐67 and histological grade in breast cancer patients.

Key points of basic theories and clinical practice in rAd-p53 ( Gendicine ™) gene therapy for solid malignant tumors

INTRODUCTION

Wild-type p53 gene is an essential cancer suppressor gene which plays an important role in carcinogenesis and malignant progressions. The p53 gene family participates in almost all the key procedures of cancer biology, such as programmed cell death, angiogenesis, metabolism and epithelial-mesenchymal transition. The mutation or functional defects of the p53 gene family are detected in most of the solid malignant tumors, and the restoration of the p53 gene by adenovirus-mediated gene therapy becomes a promising treatment for cancer patients now.

AREAS COVERED

In the present review, the potential therapeutic effects of recombinant adenovirus p53 rAd-p53 ( Gendicine ™) were reviewed to explore the biological mechanism underlying the adenovirus-mediated p53 gene therapy. Then, the key points of the drug administration were discussed, including the routes of administration, dosage calculation and treatment cycles, based on findings of the preclinical and clinical trials in order to establish a standard treatment for the p53 gene therapy.

EXPERT OPINION

As an important part of the combined therapy for the cancer patients, the adenovirus-mediated p53 gene therapy was blossomed to be a promising treatment strategy. A new evaluation criteria and guideline for the gene therapy is urgently needed for the further clinical practice.

More targets, more pathways and more clues for mutant p53

Mutations in the transcription factor p53 are among the most common genetic alterations in human cancer, and missense p53 mutations in cancer cells can lead to aggressive phenotypes. So far, only few studies investigated transcriptional reprogramming under mutant p53 expression as a means to identify deregulated targets and pathways. A review of the literature was carried out focusing on mutant p53-dependent transcriptome changes with the aims of (i) verifying whether different p53 mutations can be equivalent for their effects, or whether there is a mutation-specific transcriptional reprogramming of target genes, (ii) understanding what is the main mechanism at the basis of upregulation or downregulation of gene expression under the p53 mutant background, (iii) identifying novel candidate target genes of WT and/or mutant p53 and (iv) defining cellular pathways affected by the mutant p53-dependent gene expression reprogramming. Nearly 600 genes were consistently found upregulated or downregulated upon ectopic expression of mutant p53, regardless of the specific p53 mutation studied. Promoter analysis and the use of ChIP-seq data indicate that, for most genes, the expression changes could be ascribed to a loss both of WT p53 transcriptional activation and repressor functions. Pathway analysis indicated changes in the metabolism/catabolism of amino acids such as aspartate, glutamate, arginine and proline. Novel p53 candidate target genes were also identified, including ARID3B, ARNT2, CLMN, FADS1, FTH1, KPNA2, LPHN2, PARD6B, PDE4C, PIAS2, PRPF40A, PYGL and RHOBTB2, involved in the metabolism, xenobiotic responses and cell differentiation.

The substitutions G245C and G245D in the Zn(2+)-binding pocket of the p53 protein result in differences of conformational flexibility of the DNA-binding domain

Transcription activation of the proapoptotic target genes is a means by which the p53 protein implements its function of tumor suppression. Zn(2+) is a known regulator of p53 binding to the target genes. We have previously obtained an evidence that amino acid substitutions in the p53 Zn(2+)-binding pocket can presumably exert an influence on Zn(2+) position in the Zn(2+)-p53 complex and thereby affect p53 binding to DNA. With these background considerations, our aim was to estimate the effect of the putative changes in the Zn(2+) position in its binding pocket due to the G245C and G245D substitutions on the conformation of the p53 DNA-binding motif. Statistical analysis of the molecular dynamics (MD) trajectories of the mutant p53-Zn(2+) complexes was used to detect significant deviations in conformation of the mutant p53 forms. MD simulations demonstrated that (1) the two substitutions in the Zn(2+)-binding pocket caused changes in the conformation of the p53 DNA-binding motif, as compared with the wild-type (WT) p53; (2) binding of Zn(2+) to the p53 mutant forms reduced the effect of the substitutions on conformational change; and (3) Zn(2+) binding in the normal position compensated the effect of the mutations on the conformation in comparison to the altered Zn(2+) position.

[Expression and clinical significance of bromodomain-containing protein 7 in non-small cell lung cancer]

背景与目的

溴区包含蛋白7（bromodomain-containing protein 7, BRD7）基因属于bromodomain家族成员，该家族的大多数成员与上皮类肿瘤的发生密切相关。本研究旨在探讨BRD7在非小细胞肺癌（non-small cell lung cancer, NSCLC）中的表达及其临床意义。

方法

采用免疫组化法检测101例NSCLC癌组织及其33例正常肺组织中BRD7的表达情况。

结果

BRD7在NSCLC组织中的阳性表达率明显高于正常肺组织；BRD7在淋巴结转移组阳性表达率高于无淋巴结转移组；BRD7的阳性表达率随着TNM分期的升高而升高。BRD7的阳性表达与患者年龄、性别、吸烟情况、病理类型、分化程度无关（P>0.05）。

结论

BRD7在NSCLC中有较高的表达率，除了与淋巴结转移有关外，还与TNM分期有关，提示BRD7可能与肺癌的发生、发展和转移有关。

The missing zinc: p53 misfolding and cancer

The p53 tumor suppressor is a transcription factor that contains a single zinc ion near its DNA binding interface. Zn(2+) is required for site-specific DNA binding and proper transcriptional activation. In addition to its functional significance, zinc plays a dominant role in determining whether p53 folds productively or misfolds. Insufficient zinc and excess zinc cause p53 to misfold by distinct mechanisms which both result in functional loss. The zinc-binding status of p53 in the cell is impacted significantly by the presence of tumorigenic mutations and by metal ion homeostasis. This review discusses mechanisms by which zinc modulates folding and misfolding of p53, how improper metal binding and release leads to loss of function and cancer, and how misfolding can be rescued by metallochaperones.

Proteasome inhibitors potentiate etoposide-induced cell death in human astrocytoma cells bearing a mutated p53 isoform

Resistance to anticancer agents is often due to defects of intracellular pathways of cell death. Thus, the identification of the apoptotic pathways that can still be recruited by chemotherapeutic agents in cancerous cells can disclose new opportunities to treat malignancies. Here we show that human astrocytoma ADF cells (which are resistant to "mitochondriotropic" agents as well as to the antineoplastic drug etoposide and to proteasome inhibitors when used alone) undergo dramatic apoptotic death when exposed to a combination protocol based on the use of etoposide in the presence of proteasome inhibitors. Sensitization to cell death involved an autoamplifying loop of caspase activation, where the "executioner" phase of apoptosis was sustained by cooperation of caspase-2, -9, -8, and -3. We also show that sensitization of cells to the combination protocol involved the nuclear relocalization of p53, despite the presence of a polymorphism in its DNA-binding domain, suggesting the likely induction of p53-dependent proapoptotic genes. Conversely, p53 phosphorylation on Ser-15 did not play any role in apoptosis. In conclusion, use of etoposide in combination with proteasome inhibitors may represent an effective strategy to restore sensitivity to apoptosis in human astrocytoma cells bearing multiple defects of intracellular apoptotic pathways.

Relationship of p53, Bcl-2, Ki-67 index and E-cadherin expression in early invasive breast cancers with comedonecrosis as an accelerated apoptosis

AIMS

To study the relationship between comedonecrosis formation and morphology, apoptosis, and p53, Bcl-2, Ki-67 index and E-cadherin expression in early invasive breast cancer.

EXPERIMENTAL DESIGN

Early invasive breast cancers were first divided into two groups according to the presence (CN+ tumours) or absence (CN- tumours) of comedonecrosis. The histological grade, apoptosis, and expression of E-cadherin, Ki-67, p53 and Bcl-2 in the cancer-affected area, and in normal ducts from the specimen, were then examined.

RESULTS

Less tubule and gland formation was seen in CN+ tumours than in CN- tumours, although the histological grade between the groups was not different. During early comedonecrosis, cells undergo apoptosis and subsequent necrosis. p53 was higher in CN+ tumours than in CN- tumours and normal ducts, whereas Bcl-2 was lower in CN+ tumours than in CN- tumours and normal ducts. Both tumours had higher Ki-67 than in normal ducts, but no difference was evident between the tumours. CN+ tumours had slightly higher E-cadherin than that in CN- tumours, but lower than that in normal ducts. The level of comedonecrosis was positively correlated with p53, but inversely correlated with Bcl-2 in all tumours, and p53 and Bcl-2 were inversely correlated with each other. Furthermore, comedonecrosis and p53 were correlated with Ki-67 in CN+ tumours, and Bcl-2 was correlated with Ki-67 in CN- tumours.

CONCLUSION

Comedonecrosis may be actively regulated through an apoptotic procedure in massive cancers for their survival and progression, and the above proteins may be associated cooperatively in this process. CN+ and CN- tumours may have opposite proliferative systems under the p53-Bcl-2 pathway.

Tumor-derived p53 mutants induce NF-kappaB2 gene expression

Overexpression of mutant p53 is a common theme in tumors, suggesting a selective pressure for p53 mutation in cancer development and progression. To determine how mutant p53 expression may lead to survival advantage in human cancer cells, we generated stable cell lines expressing p53 mutants p53-R175H, -R273H, and -D281G by use of p53-null human H1299 (lung carcinoma) cells. Compared to vector-transfected cells, H1299 cells expressing mutant p53 showed a survival advantage when treated with etoposide, a common chemotherapeutic agent; however, cells expressing the transactivation-deficient triple mutant p53-D281G (L22Q/W23S) had significantly lower resistance to etoposide. Gene expression profiling of cells expressing transcriptionally active mutant p53 proteins revealed the striking pattern that all three p53 mutants induced expression of approximately 100 genes involved in cell growth, survival, and adhesion. The gene NF-kappaB2 is a prominent member of this group, whose overexpression in H1299 cells also leads to chemoresistance. Treatment of H1299 cells expressing p53-R175H with small interfering RNA specific for NF-kappaB2 made these cells more sensitive to etoposide. We have also observed activation of the NF-kappaB2 pathway in mutant p53-expressing cells. Thus, one possible pathway through which mutants of p53 may induce loss of drug sensitivity is via the NF-kappaB2 pathway.

X-tile: a new bio-informatics tool for biomarker assessment and outcome-based cut-point optimization

The ability to parse tumors into subsets based on biomarker expression has many clinical applications; however, there is no global way to visualize the best cut-points for creating such divisions. We have developed a graphical method, the X-tile plot that illustrates the presence of substantial tumor subpopulations and shows the robustness of the relationship between a biomarker and outcome by construction of a two dimensional projection of every possible subpopulation. We validate X-tile plots by examining the expression of several established prognostic markers (human epidermal growth factor receptor-2, estrogen receptor, p53 expression, patient age, tumor size, and node number) in cohorts of breast cancer patients and show how X-tile plots of each marker predict population subsets rooted in the known biology of their expression.

Modulation of gene expression by tumor-derived p53 mutants

p53 mutants with a single amino acid substitution are overexpressed in a majority of human cancers containing a p53 mutation. Overexpression of the mutant protein suggests that there is a selection pressure on the cell indicative of an active functional role for mutant p53. Indeed, H1299 cells expressing mutant p53-R175H, p53-R273H or p53-D281G grow at a faster rate compared with a control cell line. Using p53-specific small interfering RNA, we show that the growth rate of mutant p53-expressing cells decreases as mutant p53 level decreases, demonstrating that the increased cellular growth is dependent on p53 expression. Increased growth rate is not observed for H1299 cell clones expressing mutant p53-D281G (L22Q/W23S), which has been shown to be defective in transactivation in transient transcriptional assays. This shows that the increased growth rate imparted by mutant p53 in H1299 cells requires the transactivation function of mutant p53. By performing microarray hybridization analyses, we show that constitutive expression of three common p53 mutants (p53-R175H, p53-R273H, and p53-D281G) in H1299 human lung carcinoma cells evokes regulation of a common set of genes, a significant number of which are involved in cell growth regulation. Predictably, H1299 cells expressing p53-D281G (L22Q/W23S) are defective in up-regulating a number of these genes. The differences in expression profiles induced by individual p53 mutants in the cells may be representative of the p53 mutants and how they can affect gene expression resulting in the observed "gain of function" phenotypes (i.e., increased growth rate, decreased sensitivity to chemotherapeutic agents, and so forth).

Mutation of p53 in head and neck squamous cell carcinoma correlates with Bcl-2 expression and increased susceptibility to cisplatin-induced apoptosis

BACKGROUND

The p53 protein, a well-known tumor suppressor that functions primarily as a transcription factor, initiates cell cycle arrest and apoptosis after genotoxic stress. The antiapoptotic regulator Bcl-2 is a downstream modulator of p53-induced apoptosis. Loss of function of the p53 tumor suppressor through mutation is an important event that contributes to cellular transformation. Mutation of p53 is one of the most common genetic alterations in squamous cell carcinomas of the head and neck (SCCHN). We hypothesized that p53 mutation is associated with Bcl-2 expression and susceptibility to apoptosis in SCCHN.

METHODS

Exons 5 to 8 of the p53 gene were sequenced in 22 SCCHN tumor samples and correlated with the Bcl-2 expression and apoptosis rates in these tumors. In addition, a Bcl-2-expressing SCCHN cell line, UMSCC74B, was stably transfected with a temperature-sensitive mutant p53 construct, and Bcl-2 expression levels were examined at the mutant and the wild-type temperatures.

RESULTS

Bcl-2 expression was inversely correlated with wild-type p53 status in SCCHN tumors (p = .05). Furthermore, there was a modest increase (1.7-fold) in apoptosis in the wild-type p53 tumors compared with mutant p53 SCCHN. Immunoblotting of UMSCC74B cells stably transfected with the temperature-sensitive mutant p53 construct demonstrated that shifting these cells to the mutant p53 temperature (39.5 degrees C) resulted in decreased expression of Bcl-2 compared with levels in cells grown at the wild-type p53 temperature (32.5 degrees C). Further investigation showed that SCCHN cells expressing predominantly mutant p53 and decreased Bcl-2 were more susceptible to cisplatin-induced apoptosis than vector-transfected controls (p < .0001).

CONCLUSIONS

These results suggest that p53 mutation directly modulates Bcl-2 expression and therefore susceptibility to chemotherapy-induced apoptosis in SCCHN cells in vitro.

A novel case of a CAT to AAT transversion in codon 179 of the p53 gene in a supratentorial primitive neuroectodermal tumor harbored by a young girl. Case report and review of the literature

BACKGROUND

The most common cytogenetic abnormality encountered in primitive neuroectodermal tumors (PNET)/medulloblastoma is loss of heterozygosity in the region of the short arm of chromosome 17. There is some evidence that supratentorial PNET has different cytogenetic markers than infratentorial PNET/medulloblastoma. Particularly, loss of 17p is more frequent in the latter than in the former. We describe a young girl diagnosed with supratentorial PNET (SPNET). Analysis of the tumor suppressor gene p53 in the tumorous tissue revealed a rare transversion mutational event of CAT to AAT in position 179 of exon 5. To the best of our knowledge, this is the first case of such a transversion at codon 179 in the p53 gene in SPNET.

CASE REPORT

A 12-year-old girl was admitted with nausea, headache and vision disturbances. MRI of the brain showed a large space- occupying lesion in the right frontal lobe. Histological examination of the macroscopic resection of the tumor revealed PNET of the brain. Polymerase chain reaction-single strand conformation polymorphism analysis of all p53 exons was performed, and a unique variant of a transversion at codon 179 of exon 5 was revealed. Therapy was started according to the Children's Cancer group protocol (CCG-99702) designated for treatment of high-risk central nervous system embryonal tumors. She received an initial course of chemotherapy, consisting of cyclophosphamide and vincristine for mobilizing and harvesting peripheral blood stem cells (PBSCs). Then she was given craniospinal irradiation (3,600 cGy) with a boost to the tumor bed (1,980 cGy) and three consecutive courses of high-dose chemotherapy with carboplatin, vincristine and thiotepa/cyclophosphamide, with PBSCs support after each course.

RESULTS

The patient is in complete remission 17 months after diagnosis, based on the results of physical examination and imaging studies.

DISCUSSION

The mutation results in an alteration of the amino acid HIS to ASN. The amino acids surrounding position 175 play an important role in stabilizing the p53/DNA complex. There are only 12 known mutations of the reported type, and the finding of such a rare mutational event in a low-incidence p53 mutation tumor, such as SPNET, might add additional insight into the p53-SPNET relationship in tumorigenesis. Although not widely accepted, it is possible that different mutations of the p53 gene in patients with brain tumors may imply a different ultimate prognosis. In our case, we cannot exclude the fact that transversion of CAT to AAT in position 179 of exon 5 may explain prolonged survival of a patient with good response to therapy.

Flow cytometry and quantitative immunohistochemical study of cell cycle regulation proteins in invasive breast carcinoma: prognostic significance

BACKGROUND

Between January 11, 1991 and January 8, 1992, 104 patients with previously untreated, invasive, primitive breast carcinoma were admitted to the authors' hospital.

METHODS

For each patient, flow cytometry DNA analyses on frozen samples and on immunohistochemical staining were performed, including Ki-67, cyclin A, p53, and p21(waf1) (p21), with assessment of the percentages of positive nuclei were assessed. Correlations with classic clinicopathologic data and survival (overall, metastasis free, or recurrence free) and a multivariate analysis were performed.

RESULTS

After a multivariate analysis according to a Cox model that was stratified by age, tumor size, tumor grade, lymph node status, and receptor status, among the factors studied, the presence of p21 was the unique remaining prognostic factor for patients with invasive breast carcinoma. Because of the lack of a correlation between p21 and proliferative factors (Ki-67, S-phase, and cyclin A), the authors combined p21 with those markers and found that, for the different combinations, after statistical analysis, only p21 combined with S-phase or with cyclin A and lymph node status were salient survival prognostic factors.

CONCLUSIONS

Immunohistochemical study of proteins involved in the cell cycle and assessment of proliferative activity using flow cytometric DNA analysis aided the authors in singling out correlations of cyclin A and S-phase, along with p21, with metastasis free survival and overall survival in patients with invasive breast carcinoma. These promising results will require confirmation in a larger series of patients.

Predictive value of tumour cell proliferation in locally advanced breast cancer treated with neoadjuvant chemotherapy

We previously reported that defects in apoptotic pathways (mutations in the TP53 gene) predicted resistance to doxorubicin monotherapy. The aim of this study was to evaluate whether cell proliferation, as assessed by mitotic frequency and Ki-67 levels, may provide additional predictive information in the same tumours and to assess any potential correlations between these markers and mutations in the TP53 gene and erbB-2 overexpression. Surgical specimens were obtained from ninety locally advanced breast cancers before commencing primary chemotherapy consisting of weekly doxorubicin (14 mg/m2) for 16 weeks. 38% of the patients had a partial response (PR) to therapy, 52% had stable disease (SD) while 10% had progressive disease (PD). Univariate analysis showed a significant association between a high cell proliferation rate (expressed as a high mitotic frequency) and resistance to doxorubicin (P = 0.001). Further analyses revealed this association to be limited to the subgroup of tumour expressing wild-type TP53 (P = 0.016), and TP53 mutation status was the only factor predicting drug resistance in the multivariate analyses. The finding that a high mitotic frequency, as well as a high Ki-67 staining, correlated to TP53 mutations (P = 0.001 for both), suggests TP53 mutations are the key predictor of drug resistance, although cell proliferation may play an additional role in tumours harbouring wild-type TP53. Regarding overall (OS) and relapse-free survival (RFS), multivariate analyses (Cox' proportional hazards regression) revealed a high histological grade and negative oestrogen receptor (ER) status to be the variables that were most strongly related to breast cancer death (P = 0.001 and P = 0.001, respectively). A key reason for this difference with respect to the factors predicting chemotherapy resistance could be due to the adjuvant use of tamoxifen in all patients harbouring ER-positive tumours.

Correlations of Breast Carcinoma Biomarkers and p53 Tested by FASAY and Immunohistochemistry

p53 status is an important predictive factor in breast cancer, but the results of many studies are ambiguous. We tested p53 by functional analysis of separated alleles in yeast (FASAY) as well as by immunohistochemistry (IHC) and evaluated correlations with main prognostic factors, proliferation, and Bcl-2. Thirty-two tumors were tested with antibodies BP53-12, DO1, DO11, DO12, and by FASAY. Spearman rank correlations were tested separately with age, tumor type, pT, grade, pN, NPI, Ki-67, S-phase, proliferation index, Bcl-2, and steroid receptor status determined by ER, PR, and pS2. FASAY showed significant correlations with ductal type, grade and proliferation, and an inverse correlation with functional estrogen receptor and Bcl-2. FASAY provided better correlations compared to p53 IHC. We conclude that FASAY shows significant correlations with main prognostic/predictive factors and provides more reliable biological information compared to p53 IHC. Apoptosis is positively linked to proliferation and is not under the control of p53, which is frequently mutated in highly proliferating carcinomas. FASAY seems to be very important in assessing the predictive significance of p53 for a specific therapy of breast cancer.

Dominant negative knockout of p53 abolishes ErbB2-dependent apoptosis and permits growth acceleration in human breast cancer cells

We previously reported that the ErbB2 oncoprotein prolongs and amplifies growth factor signalling by impairing ligand-dependent downregulation of hetero-oligomerised epidermal growth factor receptors. Here we show that treatment of A431 cells with different epidermal growth factor receptor ligands can cause growth inhibition to an extent paralleling ErbB2 tyrosine phosphorylation. To determine whether such growth inhibition signifies an interaction between the cell cycle machinery and ErbB2-dependent alterations of cell signalling kinetics, we used MCF7 breast cancer cells (which express wild-type p53) to create transient and stable ErbB2 transfectants (MCF7-B2). Compared with parental cells, MCF7-B2 cells are characterised by upregulation of p53, p21(WAF) and Myc, downregulation of Bcl2, and apoptosis. In contrast, MCF7-B2 cells co-transfected with dominant negative p53 (MCF7-B2/Delta p53) exhibit reduced apoptosis and enhanced growth relative to both parental MCF7-B2 and control cells. These data imply that wild-type p53 limits survival of ErbB2-overexpressing breast cancer cells, and suggest that signals of varying length and/or intensity may evoke different cell outcomes depending upon the integrity of cell cycle control genes. We submit that acquisition of cell cycle control defects may play a permissive role in ErbB2 upregulation, and that the ErbB2 overexpression phenotype may in turn select for the survival of cells with p53 mutations or other tumour suppressor gene defects.