GAP JUNCTION CX26 GENE MODULATION BY PHORBOL ESTERS IN BENIGN AND MALIGNANT HUMAN MAMMARY CELLS

Connexin (Cx) 26, a major gap junction protein expressed in mammary ep ithelial cells, has been considered to be a tumor suppressor gene cand idate. This study investigated the molecular mechanism of transcriptio nal up-regulation of Cx26 by phorbol ester (TPA) in human immortalized MCF-10 mammary epithelial cells and MDA-MB-231 mammary cancer cells. Such up-regulation was mediated through the protein kinase C pathway a nd could be blocked by the PKC inhibitor, calphostin C. Based on the r esults of the nuclear run-on assay, there was a TPA-induced increase i n the rate of transcriptional initiation. We identified a TPA-induced DNase I hypersensitivity (DH) region approximately 1 kb 5' upstream of the ATG translation starting site. Sequence analysis revealed that th is DH region was located in intron 1 and contained two TRE-like TGAT/A TCA elements, two 5'TTCA3' motifs and a 5'AGGAAG3' PEA3 motii. Both TR E-like elements were capable of binding AP1. TPA inducibility of this DH region was seen by the CAT reporter assay and appeared to be direct ion-dependent suggesting a functional cooperation between PEA3/TTCA an d TRE. (C) 1998 Elsevier Science B.V.