Overexpression of delta Np63 in a human nasopharyngeal carcinoma cell line downregulates CKIs and enhances cell proliferation.

p63 belongs to a member of the tumor suppressor protein p53 family. Due to alternative promoter usage, two types of p63 proteins are produced. The DeltaNp63 isoform lacks the N-terminal transactivation domain and is thought to antagonize TAp63 and p53 in target gene regulation. DeltaNp63 has been found to be overexpressed in numerous human squamous cell carcinomas, including nasopharyngeal carcinoma (NPC). However, the role of DeltaNp63 overexpression in NPC pathogenesis has not been clear. In this study, we use a DeltaNp63 overexpressing human NPC cell line (NPC-076) to explore the possible roles of DeltaNp63 in cell proliferation and cell-cycle regulation. We found that the proliferation of NPC-076 cell is greatly suppressed when the overexpressed DeltaNp63 is silenced by specific DeltaNp63 siRNA. Further studies show that DeltaNp63 silencing results in the upregulation of CKIs, including p27(kip1) and p57(kip2) in both mRNA and protein levels. Cell-cycle analysis shows that DeltaNp63 silencing also results in an increased G1 phase cell and apoptotic cell population. Our findings indicate that DeltaNp63 plays important roles in the regulation of NPC-076 cell-cycle progression, and may play a role in the maintenance of NPC-076 tumor cell phenotype. (c) 2008 Wiley-Liss, Inc.