INTERDEPENDENT TRANSCRIPTION CONTROL ELEMENTS REGULATE THE EXPRESSIONOF THE SPRR2A GENE DURING KERATINOCYTE TERMINAL DIFFERENTIATION

Expression of the SPRR2A gene, a member of the small proline-rich fami ly of cornified cell envelope precursor proteins, is strictly linked t o keratinocyte terminal differentiation both in vivo and in vitro. In this study, we explored the molecular mechanisms underlying this regul ation in transiently transfected primary keratinocytes induced to diff erentiate in vitro. Deletion mapping and site-directed mutagenesis of SPRR2A promoter-chloramphenicol acetyltransferase constructs indicate that four transcription control elements are essential and sufficient for promoter activity, These elements were further characterized by el ectrophoretic mobility shift and identified as (i) an inverted octamer doublet, bound by the POU domain factor Oct-ii (Skn-1a/i, Epoc-1), (i i) an interferon-stimulated response element recognized by interferon regulatory factors 1 and 2, (iii) an Ets binding site partially overla pping the interferon-stimulated response element, and (iv) a TG box re cognized by the Spl family of zinc finger transcription factors, Destr uction of a single terminal differentiation element is sufficient to c ompletely abolish transcription from the SPRR2A promoter, indicating t hat these transcription control elements function in concert in an int erdependent manner, Apparently, integration of signals transmitted by the above-mentioned transcription factors is necessary and sufficient to promote gene expression during keratinocyte terminal differentiatio n.