TRANSACTIVATION OF THE HUMAN KERATIN-4 AND EPSTEIN-BARR-VIRUS ED-L2 PROMOTERS BY GUT-ENRICHED KRUPPEL-LIKE FACTOR

The Kruppel-like family of transcription factors comprises genes that appear to have tissue-restricted functions, Expression of gut-enriched Kruppel-like factor (GKLF) may be important in the switch from prolif eration to differentiation in the squamous epithelium, We sought to de termine transcriptionally mediated effects of GKLF on two promoters ac tive in the esophageal squamous epithelium, namely the Epstein-Barr vi rus ED-LS and human keratin 4 promoters. Both promoters contain a CACC C-like motif previously shown to bind GKLF. To determine whether GI(LF regulates genes containing this element, we first demonstrated expres sion and then cloned the full-length human GI(LF hom an esophageal squ amous carcinoma cell line. In a transient transfection system, GKLF in creased the activity of both promoters >25-fold, localized to regions containing the CACCC-like element, Recombinant GKLF specifically binds the CACCC-like motif in both promoters. GKLF epitope-tagged protein l eads to the formation of two proteins of 65 and 34 kDa. The chromatogr aphically purified 65-kDa protein binds the CACCC-like element from bo th Epstein-Barr virus ED-L2 and keratin 4 promoters, which is not atte nuated by the 34-kDa protein. In summary, GKLF is expressed in esophag eal squamous epithelial cells and transcriptionally activates two esop hageal epithelial promoters important at the transition toward differe ntiation.