STAT3, stem cells, cancer stem cells and p63.

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.

TAp63 and ΔNp63 (p40) in prostate adenocarcinomas: ΔNp63 associates with a basal-like cancer stem cell population but not with metastasis.

Like other malignancies, prostate tumors are thought to contain cancer stem-like cells (CSCs) that are responsible for growth, metastasis, and therapy resistance. ΔNp63 (also called p40) is a regulator of normal prostate stem/progenitor cell activities and a marker of normal basal epithelial cells. The levels of ΔNp63 are reduced in prostate adenocarcinomas, although there is also evidence that ΔNp63 is involved in CSC regulation and drives metastasis to the bone. We studied metastatic deposits of prostate cancers with isoform-specific ΔNp63 and TAp63 antibodies. We identified p63-positive cells in only 3 of 42 metastatic prostate tumors (7%), including 2/38 (5.3%) "usual-type" adenocarcinomas. ΔNp63 and TAp63 isoforms were present in the nuclei of a small subpopulation (< 1%) of tumor cells in these metastases. ΔNp63-positive cells showed a basal-like cell phenotype (cytokeratin 8- and androgen receptor-negative, high molecular weight cytokeratin- and cytokeratin 19-positive), distinct from the tumor bulk. TAp63-positive cells were similar but were sometimes cytokeratin 8-positive. A subset of ΔNp63-positive tumor cells were CD44-positive, a marker of "basal" CSCs but were not positive for the "epithelial" CSC marker ALDH1. TAp63 was not associated with either of these CSC markers. None of the tumors containing p63-positive cells showed evidence of bone metastasis, compared with 28% of the p63-negative tumors. These data show that both ΔNp63 and TAp63 are present in only a small proportion of prostate adenocarcinomas and do not associate with metastasis. The data suggest heterogeneity of CSCs in prostate cancer, similar to other cancer types.

∆Np63/p40 correlates with the location and phenotype of basal/mesenchymal cancer stem-like cells in human ER+ and HER2+ breast cancers.

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.

Prima-1 and APR-246 in Cancer Therapy.

BACKGROUND: p53 is the most mutated protein in cancer and the reactivation of its inactive mutated form represents one possibility for antitumor therapy. Reactivation leads to the initiation of apoptosis followed by the suppression of the malignant phenotype. Prima-1 and its methylated form Prima-1Met (also called APR-246) are compounds capable of reactivating mutated p53. Both are low-molecular substances that have been tested in a number of tumor cell lines and tumors bearing mutated p53. AIM: This article summarizes what is currently known about both compounds, describes the possibilities of their use in anti-tumor therapy, and outlines the results of currently undergoing clinical trials of APR-246. CONCLUSION: The results show that the mechanism of action of both compounds is still not clear. The mechanism is only known clearly in the case of Prima-1, and APR-246 is only known to induce apoptosis. The specificity of both substances for mutated p53 differs considerably and depends mainly on the cell model employed and the type of mutation. In addition to p53 reactivation itself, these compounds likely influence other mechanisms that also affect cytotoxic activity. Key words: Prima-1Met - APR-246 - Prima-1 - reactivation of p53 - apoptosis NPU I - LO1413. This work was supported by the project MEYS - NPS I - LO1413. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Accepted: 16. 07. 2018.

Possible Usage of p63 in Bioptic Diagnostics.

BACKGROUND: The p63 transcription factor is a p53 homologue; however, its role in development and oncogenesis is more unambiguous than that of p53. TP63 encodes a variety of N-and C-terminal isoforms with different expression patterns and functions. The most frequently studied are N-terminal variants DNp63 (p40) and TAp63. p40 is a characteristic basal or myopithelial cell marker of stratified epithelium and it partakes in the regulation of proliferation and differentiation. The TAp63 isoform is more expressed in the suprabasal cell layer but is also expressed in primary oocytes, lymphocytes and stromal cells. It induces apoptosis and plays a role in the maintenance of genome integrity. The role of each isoform differs also in tumor progression. p40 is generally considered to behave as an oncoprotein in the regulation of cancer stem cells, while TAp63 expression is associated with a better prognosis. AIM: Nuclear expression of p63 is a widely used as a diagnostic marker in the clinical pathology of a spectrum of malignancies, mostly lung squamous cell carcinomas and urogenital tract carcinomas; however, it also used during examination of breast (BC) and prostate carcinoma bioptic samples. However, cytoplasmic or extracellular p63 expression is observed in neoplastic cells when the 4A4 antibody is used. This mini-review briefly summarizes the possibilities and pitfalls of p63 usage, particularly when it is used in bioptic diagnostics of BC and prostate carcinoma and highlights the potential applications of isoform specific p40 and TAp63 antibodies. It also describes other clinical usages of p63, for instance in the histogenetical classification of tumors. Key words: p63 - DNp63 (p40) - TAp63 - breast carcinoma - prostate carcinoma This work was supported by the project MEYS - NPS I - LO1413. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Accepted: 17. 8. 2018.