PHORBOL-MYRISTATE ACETATE TRANSACTIVATES THE AVIAN BETA(3) INTEGRIN GENE AND INDUCES ALPHA(V)BETA(3) INTEGRIN EXPRESSION

1,25-Dihydroxyvitamin D-3 (1,25(OH)(2)D-3) transactivates the avian be ta(3) integrin gene whose promoter contains at least two vitamin D res ponse elements, one of which is in close proximity to a candidate AP1 site (TGACTCA). Since fos/jun and steroid hormones interact to regulat e gene expression, we asked whether phorbol-12-myristate-13-acetate (P MA), which stimulates binding of fos/jun to AP1 sites, transactivates the avian beta(3) integrin gene and, if so, does the phorbol ester mod ulate 1,25(OH)(2)D-3 induction of the gene. We find the candidate AP1 sequence comigrates with the consensus AP1 sequence on electromobility shift assay when incubated with recombinant c-jun protein. Furthermor e, PMA prompts expression of beta(3) integrin mRNA in the avian monocy tic line, HD11. The increase in message reflects transactivation of th e beta(3) gene and is mirrored by plasma membrane appearance of the in tegrin heterodimer alpha(v) beta(3). Moreover, attesting to the functi onal significance of PMA-enhanced alpha(v) beta(3) expression, cells t reated with concentrations of the phorbol ester that induce the beta(3 ) gene, spread extensively on plastic, an event blocked by an anti-alp ha(v) antibody and a peptide mimetic known to inhibit alpha(v) beta(3) -mediated cell attachment. Interestingly, co-addition of 1,25(OH)(2)D- 3 and PMA prompts greater expression of alpha(v) beta(3) than when the cells are exposed to either agent alone and PMA enhances 1,25(OH)(2)D -3-induced beta(3) integrin mRNA expression. Thus, PMA and 1,25(OH)(2) D-3 impact on the avian beta(3) integrin gene independently and in com bination. (C) 1996 Wiley-Liss, Inc.