Regulation of human involucrin promoter activity by POU domain proteins

POU domain transcription factors are expressed in the epidermis and are thought to be important regulators of keratinocyte gene expression. In the present article we demonstrate that POU transcription factors suppress transcription of the human involucrin (hINV) promoter. Cotransfection of pINV-2473, a construct containing 2473 base pairs of hINV upstream sequence linked to luciferase, with POU homeodomain transcription factors Oct1, Oct2, Brn4, SCIP, Skn1a or Skn1i, results in a strong suppression of basal promoter activity. The hINV upstream region includes a consensus POU transcription factor binding site, 5'-ATGCAAAT-3', centered around nucleotide -1277. Although this site interacts with POU factors, assays of promoter activity for a series of progressive 5' end truncations demonstrate that this site is not required for POU factor-dependent transcriptional suppression. Suppression is observed with the shortest truncation construct tested, pINV-41, suggesting that this inhibition may be mediated by effects on TATA box proteins. SCIP mutants that lack transactivation or DNA binding domains were shown to suppress transcription, suggesting that the DNA binding and transactivation domains are not required for suppression. Moreover, cotransfection of the pINV-2473 with pKSM13(+)OCT, which contains a single consensus OCT binding site, results in an increase in basal promoter activity, suggesting that endogenous POU factors suppress hINV promoter activity. In addition to inhibiting basal transcription, POU transcription factors also suppress phorbol ester-stimulated hINV promoter activity. These studies suggest that suppression of hINV promoter activity does not require the amino-terminal segment of the POU factor or direct POU factor interaction with DNA and suggest that the suppression may be via indirect interaction with other proteins in the vicinity of the TATA box. Thus, involucrin joins the ranks of a small set of genes that are regulated by POU factors in an octamer binding site-independent manner.