The N terminus-truncated splicing variant of TAp63 is known as ⌬Np63. ⌬Np63 lacks transactivation function and is thought to antagonize the transcriptional regulation of the p53 and TAp63 target genes. Overexpression of ⌬Np63 has been observed in a number of human cancers, suggesting a role in carcinogenesis. In the present study we present data showing that the ⌬Np63 gene promoter activity is positively regulated by ⌬Np63␣, and such positive autoregulation is mediated via activation of STAT3 activity. We show that expression of ⌬Np63␣ in Hep3B cells induces Stat3 phosphorylation on Tyr-705 and Ser-727. A putative STAT3-responsive element (STAT3-RE) is identified in the ⌬Np63 promoter region. Electrophoretic mobility shift and avidin biotin-Conjugated DNA assays show direct binding of STAT3 to STAT3-RE of the ⌬Np63 promoter, and such binding is stimulated by ⌬Np63␣. Binding of the endogenous STAT3 to the ⌬Np63 promoter in Hep3B cells was demonstrated by a chromatin immunoprecipitation assay. The stimulation of the ⌬Np63 transcriptional activity by ⌬Np63␣ is abolished by Janus kinase 2 (JAK2)/STAT3 inhibitor AG490, dominant-negative STAT3, STAT3 small interfering RNA, and deletion of the STAT3-RE sequence from ⌬Np63 promoter. Taken together these observations clearly indicated that autoregulation of ⌬Np63 gene transcription is mediated through activation of STAT3 and its subsequent binding to the STAT3-RE. Because the activation of STAT3 by interleukin-6 also leads to ⌬Np63 up-regulation and the blockade of ⌬Np63 or STAT3 expression by siRNA leads to repression of the cell growth, the identified regulatory pathway is presumably of cell physiological significance.The discovery of the transcription factor p63 was soon followed by back-to-back reports showing that p63 is essential for the development of a number of epithelial structures, including skin, breast, prostate, urothelia, and others (1). High levels of p63 expression were found in the basal cells of many stratified epithelial tissues in which a majority of human neoplasm develops (1). A number of studies contended that p63 identifies keratinocyte stem cells (2); however, subsequent work by others soon found that p63 expression is not limited to stem cells of the epithelial tissues that express this gene (3).p63 is a transcription factor that transactivates p53 target genes. Splicing variants lacking N-terminal transactivation domain, known as ⌬Np63, are thought to antagonize p53 and p63 (4). ⌬Np63 is predominantly expressed in the basal cells of various stratified epithelia and is overexpressed in some human cancers including bladder carcinoma, non-small cell lung cancers, nasopharyngeal carcinoma, and liver cancers. These observations suggest that overexpression of ⌬Np63 may have important implications in carcinogenesis (5-8). Recently, Harmes et al. (9) reported the presence of a p53 binding site located at Ϫ495 to Ϫ473 relative to the transcriptional start site of exon-3Ј in the ⌬Np63 promoter region, suggesting that p53 may regulate the promoter activ...

Nanog is a transcription factor that is essential for the maintenance of pluripotency of the embryonic stem cells. Nanog has been shown to be expressed in various kinds of human tumors, suggesting a role in tumorigenesis. In this study, we found that Nanog expression was upregulated by inhibition of protein kinase C (PKC) activity in six human cancer cell lines examined. In a Nanog non-expressing human nasopharyngeal carcinoma cell line, NPC-076, Nanog mRNA level and protein level were both induced and dose-dependently promoted by exposure to PKC inhibitors. Knockdown experiments showed that PKCα and PKCδ were two subtypes exerted most of the effect. The reporter assay showed that Nanog promoter activity was promoted by exposure of the cells to PKC inhibitors and the effect was dependent on the presence of the Octamer-Sox composite element. The involvement of Octamer-Sox composite element was further supported by the observation that silencing of Oct4 and Sox2 in NPC-076 cells attenuated the effects of PKC inhibitors. In Nanog-expressing human embryonal carcinoma cell lines, NT2/D1 and NCCIT, Nanog expression was suppressed by exposure to PKC activator Phorbol-12-myristate-13-acetate (PMA). Further study showed that overexpression of PKCα elicited a repressive effect on Nanog expression in NT2/D1 cells. Consistently, mutation of the Octamer-Sox composite element abolished the suppressive effect by PKC activator. Nanog expression was of cellular significance in that ectopic expression in NPC-076 stimulated cell proliferation and knockdown of the endogenous Nanog expression in NT2/D1-suppressed cell proliferation.

Overexpression of DeltaNp63 has been observed in a number of human cancers, suggesting a role for DeltaNp63 in carcinogenesis. In the present study, we show that inhibition of glycogen synthase kinase-3beta (GSK-3beta) by lithium chloride (LiCl) elicited a stimulatory effect on DeltaNp63 promoter activity in HEK 293T cells. Exposure to LiCl induced DeltaNp63 promoter activation as well as DeltaNp63 protein expression in the cells. The effect of GSK-3beta on DeltaNp63 expression was further confirmed by the use of two highly specific GSK-3beta inhibitors, SB216763 and SB415286. Further study showed the presence of a putative beta-catenin responsive element (beta-catenin-RE) in the DeltaNp63 promoter region, and the stimulation of DeltaNp63 promoter activity by GSK-3beta inhibitor is markedly abolished by mutation or deletion of the putative beta-catenin-RE. Data are also presented to show that beta-catenin acts together with Lef-1 to influence DeltaNp63 promoter activity and protein expression.