ΔNp63α Repression of the Notch1 Gene Supports the Proliferative Capacity of Normal Human Keratinocytes and Cervical Cancer Cells

Abstract

The p53 family member p63 is a master regulator of epithelial development. One of its isoforms, ΔNp63α, is predominantly expressed in the basal cells of stratified epithelia and plays a fundamental role in control of regenerative potential and epithelial integrity. In contrast to p53, p63 is rarely mutated in human cancers, but it is frequently overexpressed in squamous cell carcinomas (SCC). However, its functional relevance to tumorigenesis remains largely unclear. We previously identified the Notch1 gene as a novel transcriptional target of p53. Here, we show that ΔNp63α functions as a transcriptional repressor of the Notch1 gene through the p53-responsive element. Knockdown of p63 caused upregulation of Notch1 expression and marked reduction in proliferation and clonogenicity of both normal human keratinocytes and cervical cancer cell lines overexpressing ΔNp63α. Concomitant silencing of Notch1 significantly rescued this phenotype, indicating the growth defect induced by p63 deficiency to be, at least in part, attributable to Notch1 function. Conversely, overexpression of ΔNp63α decreased basal levels of Notch1, increased proliferative potential of normal human keratinocytes, and inhibited both p53-dependent and p53-independent induction of Notch1 and differentiation markers upon genotoxic stress and serum exposure, respectively. These results suggest that ΔNp63α maintains the self-renewing capacity of normal human keratinocytes and cervical cancer cells partly through transcriptional repression of the Notch1 gene and imply a novel pathogenetical significance of frequently observed overexpression of ΔNp63α together with p53 inactivation in SCCs. Cancer Res; 70(10); 4034-44. ©2010 AACR.

Reduction of NOTCH1 expression pertains to maturation abnormalities of keratinocytes in squamous neoplasms

“…The role of Notch in regulation of squamous epithelium differentiation has also been suggested by studies using cultured cervical 28 and esophageal keratinocytes. 35 Collectively, these results indicate that Notch1 in squamous neoplasms K Sakamoto et al reduced NOTCH1 expression affects the terminal differentiation, thus highlighting the essential role of NOTCH1 in maintaining normal epithelial integrity.…”

“…Another possible mechanism of the asymmetric activation is the suppression of Notch signaling by protein degradation mediated by Numb, which is distributed differentially in the daughter cells and governs asymmetric cell division. 47,48 The transcription of NOTCH1 gene is suppressed by TP63(DN) in cervical keratinocytes, 28 and TP63(DN) inhibits differentiation in the oropharyngeal SCC cell line. 49 Our findings using Ca9-22 cells are consistent with these results, suggesting that the interplay between NOTCH1 and TP63(DN) in differentiation is common in non-cornified epithelia of various sites.…”

“…In uterine cervical cells, TP63(DN) acts as a transcriptional repressor of NOTCH1, which results in maintenance of self-renewing capacity. 28 In Ca9-22 cells, transfection of TP63(DN) only slightly decreased NOTCH1 expression and TP63(TA) did not have a significant effect on NOTCH1. Both TP63(TA) and TP63(DN) decreased K13 expression (Figure 3f).…”

The role of P63 in cancer, stem cells and cancer stem cells

“…In turn, elevated p63 expression counteracts the ability of Notch to restrict growth and promote differentiation. Additionally, knockdown of TP63 upregulates Notch expression and causes a reduction in the proliferation and clonogenicity of keratinocytes [132]. Conversely, overexpression of ΔNp63α leads to decreased level of Notch and increased proliferative potential of keratinocytes.…”

Ctip2 is a dynamic regulator of epidermal proliferation and differentiation by integrating EGFR and Notch signaling

“…Previous reports have shown that p53 positively regulates Notch1 transcription in response to genotoxic stress and in tumors (Yugawa et al, 2007), whereas another p53 family transcription factor, p63, transcriptionally represses Notch1 expression in proliferating keratinocytes (Yugawa et al, 2010). EGFR signaling regulates Notch1 gene expression negatively and indirectly by transcriptional suppression of p53, and downregulation of EGFR expression in differentiating keratinocytes may contribute to derepression of Notch1 gene expression (Kolev et al, 2008).…”