Transcriptional activity of the ΔNp63 promoter is regulated by STAT3

The N terminus-truncated splicing variant of TAp63 is known as Delta Np63.Delta Np63 lacks transactivation function and is thought to antagonize the transcriptional regulation of the p53 and TAp63 target genes. Overexpression of Delta 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 Delta Np63 gene promoter activity is positively regulated by Delta Np63 alpha, and such positive autoregulation is mediated via activation of STAT3 activity. We show that expression of Delta Np63 alpha in Hep3B cells induces Stat3 phosphorylation on Tyr-705 and Ser-727. A putative STAT3-responsive element ( STAT3-RE) is identified in the Delta Np63 promoter region. Electrophoretic mobility shift and avidin biotin-Conjugated DNA assays show direct binding of STAT3 to STAT3-RE of the Delta Np63 promoter, and such binding is stimulated by Delta Np63 alpha. Binding of the endogenous STAT3 to the Delta Np63 promoter in Hep3B cells was demonstrated by a chromatin immunoprecipitation assay. The stimulation of the Delta Np63 transcriptional activity by Delta Np63 alpha 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 Delta Np63 promoter. Taken together these observations clearly indicated that autoregulation of Delta 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 Delta Np63 up-regulation and the blockade of Delta Np63 or STAT3 expression by siRNA leads to repression of the cell growth, the identified regulatory pathway is presumably of cell physiological significance.