The TP63 gene encodes two major protein variants; TAp63 contains a p53-like transcription domain and consequently has tumor suppressor activities whereas ΔNp63 lacks this domain and acts as an oncogene. The two variants show distinct expression patterns in normal tissues and tumors, with lymphocytes and lymphomas/leukemias expressing TAp63, and basal epithelial cells and some carcinomas expressing high levels of ΔNp63, most notably squamous cell carcinomas (SCC). Whilst the transcriptional functions of TAp63 and ΔNp63 isoforms are known, the mechanisms involved in their regulation are poorly understood. Using squamous epithelial cells that contain high levels of ΔNp63 and low/undetectable TAp63, the DNA demethylating agent decitabine (5-aza-2'-deoxycytidine, 5-dAza) caused a dose-dependent increase in TAp63, with a simultaneous reduction in ΔNp63, indicating DNA methylation-dependent regulation at the isoform-specific promoters. The basal cytokeratin KRT5, a direct ΔNp63 transcriptional target, was also reduced, confirming functional alteration of p63 activity after DNA demethylation. We also showed high level methylation of three CpG sites in the TAP63 promoter in these cells, which was reduced by decitabine. DNMT1 depletion using inducible shRNAs partially replicated these effects, including an increase in the ratio of TAP63:ΔNP63 mRNAs, a reduction in ΔNp63 protein and reduced KRT5 mRNA levels. Finally, high DNA methylation levels were found at the TAP63 promoter in clinical SCC samples and matched normal tissues. We conclude that DNA methylation at the TAP63 promoter normally silences transcription in squamous epithelial cells, indicating DNA methylation as a therapeutic approach to induce this tumor suppressor in cancer. That decitabine simultaneously reduced the oncogenic activity of ΔNp63 provides a "double whammy" for SCC and other p63-positive carcinomas. Whilst a variety of mechanisms may be involved in producing the opposite effects of DNA demethylation on TAp63 and ΔNp63, we propose an "either or" mechanism in which TAP63 transcription physically interferes with the ability to initiate transcription from the downstream ΔNP63 promoter on the same DNA strand. This mechanism can explain the observed inverse expression of p63 isoforms in normal cells and cancer.

• Keywords
• DNA methylation, TAp63, alternative promoter usage, decitabine, keratinocytes, squamous cell carcinoma, ΔNp63,
• Publication type
• Journal Article MeSH

BACKGROUND: ΔNp63 overexpression is a common event in squamous cell carcinoma (SCC) that contributes to tumorigenesis, making ΔNp63 a potential target for therapy. METHODS: We created inducible TP63-shRNA cells to study the effects of p63-depletion in SCC cell lines and non-malignant HaCaT keratinocytes. DNA damaging agents, growth factors, signaling pathway inhibitors, histone deacetylase inhibitors, and metabolism-modifying drugs were also investigated for their ability to influence ΔNp63 protein and mRNA levels. RESULTS: HaCaT keratinocytes, FaDu and SCC-25 cells express high levels of ΔNp63. HaCaT and FaDu inducible TP63-shRNA cells showed reduced proliferation after p63 depletion, with greater effects on FaDu than HaCaT cells, compatible with oncogene addiction in SCC. Genotoxic insults and histone deacetylase inhibitors variably reduced ΔNp63 levels in keratinocytes and SCC cells. Growth factors that regulate proliferation/survival of squamous cells (IGF-1, EGF, amphiregulin, KGF, and HGF) and PI3K, mTOR, MAPK/ERK or EGFR inhibitors showed lesser and inconsistent effects, with dual inhibition of PI3K and mTOR or EGFR inhibition selectively reducing ΔNp63 levels in HaCaT cells. In contrast, the antihyperlipidemic drug lovastatin selectively increased ΔNp63 in HaCaT cells. CONCLUSIONS: These data confirm that ΔNp63-positive SCC cells require p63 for continued growth and provide proof of concept that p63 reduction is a therapeutic option for these tumors. Investigations of ΔNp63 regulation identified agent-specific and cell-specific pathways. In particular, dual inhibition of the PI3K and mTOR pathways reduced ΔNp63 more effectively than single pathway inhibition, and broad-spectrum histone deacetylase inhibitors showed a time-dependent biphasic response, with high level downregulation at the transcriptional level within 24 h. In addition to furthering our understanding of ΔNp63 regulation in squamous cells, these data identify novel drug combinations that may be useful for p63-based therapy of SCC.

• Keywords
• DNA damage, Growth factor signaling, Histone deacetylase inhibitors, Oncogene addiction, Squamous cell carcinoma, ΔNp63,
• MeSH
• Histone Deacetylase Inhibitors MeSH
• Carcinogenesis MeSH
• Humans MeSH
• Cell Line, Tumor MeSH
• Tumor Suppressor Proteins metabolism   MeSH
• Tumor Suppressor Protein p53 * genetics   MeSH
• Family MeSH
• Carcinoma, Squamous Cell * drug therapy   genetics   metabolism   MeSH
• Transcription Factors metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Histone Deacetylase Inhibitors MeSH
• Tumor Suppressor Proteins MeSH
• Tumor Suppressor Protein p53 * MeSH
• TP63 protein, human MeSH Browser
• Transcription Factors MeSH

ΔNp63, also known as p40, regulates stemness of normal mammary gland epithelium and provides stem cell characteristics in basal and HER2-driven murine breast cancer models. Whilst ΔNp63/p40 is a characteristic feature of normal basal cells and basal-type triple-negative breast cancer, some receptor-positive breast cancers express ΔNp63/p40 and its overexpression imparts cancer stem cell-like properties in ER+ cell lines. However, the incidence of ER+ and HER2+ tumours that express ΔNp63/p40 is unclear and the phenotype of ΔNp63/p40+ cells in these tumours remains uncertain. Using immunohistochemistry with p63 isoform-specific antibodies, we identified a ΔNp63/p40+ tumour cell subpopulation in 100 of 173 (58%) non-triple negative breast cancers and the presence of this population associated with improved survival in patients with ER- /HER2+ tumours (p = 0.006). Furthermore, 41% of ER+ /PR+ and/or HER2+ locally metastatic breast cancers expressed ΔNp63/p40, and these cells commonly accounted for <1% of the metastatic tumour cell population that localised to the tumour/stroma interface, exhibited an undifferentiated phenotype and were CD44+ /ALDH- . In vitro studies revealed that MCF7 and T47D (ER+ ) and BT-474 (HER2+ ) breast cancer cell lines similarly contained a small subpopulation of ΔNp63/p40+ cells that increased in mammospheres. In vivo, MCF7 xenografts contained ΔNp63/p40+ cells with a similar phenotype to primary ER+ cancers. Consistent with tumour samples, these cells also showed a distinct location at the tumour/stroma interface, suggesting a role for paracrine factors in the induction or maintenance of ΔNp63/p40. Thus, ΔNp63/p40 is commonly present in a small population of tumour cells with a distinct phenotype and location in ER+ and/or HER2+ human breast cancers.

• Keywords
• CD44, HER2, aldehyde dehydrogenase, breast, cancer stem cells, oestrogen receptor, p40, p63, ΔNp63,
• MeSH
• Phenotype MeSH
• Heterografts MeSH
• Humans MeSH
• Mice MeSH
• Biomarkers, Tumor analysis   metabolism   MeSH
• Neoplastic Stem Cells metabolism   pathology   MeSH
• Tumor Suppressor Proteins metabolism   MeSH
• Breast Neoplasms genetics   metabolism   pathology   MeSH
• Receptor, ErbB-2 genetics   metabolism   MeSH
• Receptors, Estrogen genetics   metabolism   MeSH
• Transcription Factors metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• ERBB2 protein, human MeSH Browser
• Biomarkers, Tumor MeSH
• Tumor Suppressor Proteins MeSH
• Receptor, ErbB-2 MeSH
• Receptors, Estrogen MeSH
• TP63 protein, human MeSH Browser
• Transcription Factors MeSH

Signal Transducer and Activator of Transcription 3 (STAT3) is a transcription factor with many important functions in the biology of normal and transformed cells. Its regulation is highly complex as it is involved in signaling pathways in many different cell types and under a wide variety of conditions. Besides other functions, STAT3 is an important regulator of normal stem cells and cancer stem cells. p63 which is a member of the p53 protein family is also involved in these functions and is both physically and functionally connected with STAT3. This review summarizes STAT3 function and regulation, its role in stem cell and cancer stem cell properties and highlights recent reports about its relationship to p63.

• Keywords
• Cancer stem cells, STAT3, Stem cells, p63,
• MeSH
• Phosphorylation MeSH
• Humans MeSH
• Human Embryonic Stem Cells metabolism   MeSH
• Methylation MeSH
• MicroRNAs metabolism   MeSH
• Mouse Embryonic Stem Cells metabolism   MeSH
• Mice MeSH
• Neoplastic Stem Cells metabolism   MeSH
• Tumor Suppressor Proteins chemistry   metabolism   MeSH
• Neoplasms metabolism   MeSH
• Cellular Reprogramming MeSH
• STAT3 Transcription Factor chemistry   metabolism   MeSH
• Transcription Factors chemistry   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• MicroRNAs MeSH
• Tumor Suppressor Proteins MeSH
• TP63 protein, human MeSH Browser
• STAT3 Transcription Factor MeSH
• Transcription Factors MeSH

The TP63 gene encodes two major protein variants that differ in their N-terminal sequences and have opposing effects. In breast, ΔNp63 is expressed by immature stem/progenitor cells and mature myoepithelial/basal cells and is a characteristic feature of basal-like triple-negative breast cancers (TNBCs). The expression and potential role of TAp63 in the mammary gland and breast cancers is less clear, partly due to the lack of studies that employ p63 isoform-specific antibodies. We used immunohistochemistry with ΔNp63-specific or TAp63-specific monoclonal antibodies to investigate p63 isoforms in 236 TNBCs. TAp63, but not ΔNp63, was seen in tumour-associated lymphocytes and other stromal cells. Tumour cells showed nuclear staining for ΔNp63 in 17% of TNBCs compared to 7.3% that were positive for TAp63. Whilst most TAp63+ tumours also contained ΔNp63+ cells, the levels of the two isoforms were independent of each other. ΔNp63 associated with metaplastic and medullary cancers, and with a basal phenotype, whereas TAp63 associated with androgen receptor, BRCA1/2 wild-type status and PTEN positivity. Despite the proposed effects of p63 on proliferation, Ki67 did not correlate with either p63 isoform, nor did they associate with p53 mutation status. ΔNp63 showed no association with patient outcomes, whereas TAp63+ patients showed fewer recurrences and improved overall survival. These findings indicate that both major p63 protein isoforms are expressed in TNBCs with different tumour characteristics, indicating distinct functional activities of p63 variants in breast cancer. Analysis of individual p63 isoforms provides additional information into TNBC biology, with TAp63 expression indicating improved prognosis.

• Keywords
• Androgen receptor, BRCA1, BRCA2, PTEN, TAp63, Triple-negative breast cancer, ΔNp63,
• MeSH
• Phenotype MeSH
• PTEN Phosphohydrolase genetics   MeSH
• Humans MeSH
• Neoplasm Recurrence, Local genetics   MeSH
• Mutation genetics   MeSH
• Tumor Suppressor Proteins genetics   MeSH
• Protein Isoforms genetics   MeSH
• BRCA1 Protein genetics   MeSH
• BRCA2 Protein genetics   MeSH
• Gene Expression Regulation, Neoplastic genetics   MeSH
• Transcription Factors genetics   MeSH
• Triple Negative Breast Neoplasms genetics   metabolism   mortality   MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• BRCA1 protein, human MeSH Browser
• BRCA2 protein, human MeSH Browser
• PTEN Phosphohydrolase MeSH
• Tumor Suppressor Proteins MeSH
• Protein Isoforms MeSH
• BRCA1 Protein MeSH
• BRCA2 Protein MeSH
• PTEN protein, human MeSH Browser
• TP63 protein, human MeSH Browser
• Transcription Factors MeSH

BACKGROUND: p63, a member of the p53 protein family, plays key roles in epithelial development and carcinogenesis. In breast cancer, p63 expression has been found predominantly in basal-A (epithelial-type) triple-negative breast carcinomas (TNBC). To investigate the functional role of p63 in basal-A TNBC, we created MDA-MB-468 cell lines with inducible expression of the two major N-terminal p63 isoforms, TAp63α and ∆Np63α. RESULTS: TAp63α did not have significant effect on gene expression profile and cell phenotype, whilst the main effect of ΔNp63α was reduction of cell adhesion. Gene expression profiling revealed genes involved in cell adhesion and migration whose expression relies on overexpression of ΔNp63α. Reduced cell adhesion also led to decreased cell proliferation in vitro and in vivo. Similar data were obtained in another basal-A cell line, BT-20, but not in BT-549 basal-B (mesenchymal-like) TNBC cells. CONCLUSIONS: In basal-A TNBC cells, ∆Np63α has much stronger effects on gene expression than TAp63α. Although p63 is mentioned mostly in connection with breast cell differentiation and stem cell regulation, we showed that a major effect of p63 is regulation of cell adhesion, a process important in metastasis and invasion of tumour cells. That this effect is not seen in mesenchymal-type TNBC cells suggests lineage-dependent functions, mirroring the expression of ∆Np63α in primary human breast cancers.

• Keywords
• Adhesion, Triple-negative breast cancer, p63 isoforms,
• MeSH
• Cell Adhesion genetics   MeSH
• Cell Cycle genetics   MeSH
• Gene Expression * MeSH
• Heterografts MeSH
• Cells, Cultured MeSH
• Humans MeSH
• Disease Models, Animal MeSH
• Cell Line, Tumor MeSH
• Tumor Suppressor Proteins genetics   MeSH
• Cell Proliferation MeSH
• Protein Isoforms MeSH
• Gene Expression Profiling MeSH
• Transcription Factors genetics   MeSH
• Triple Negative Breast Neoplasms genetics   pathology   MeSH
• Cell Survival genetics   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Tumor Suppressor Proteins MeSH
• Protein Isoforms MeSH
• TP63 protein, human MeSH Browser
• Transcription Factors MeSH