Phorbol myristate acetate transactivates the avian beta 3 integrin gene and induces alpha v beta 3 integrin expression.

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3)transactivates the avian beta 3 integrin gene whose promoter contains at least two vitamin D response elements, one of which is in close proximity to a candidate AP1 site (TGACTCA). Since fos/jun and steroid hormones interact to regulate gene expression, we asked whether phorbol-12-myristate-13-acetate (PMA), which stimulates binding of fos/jun to AP1 sites, transactivates the avian beta 3 integrin gene and, if so, does the phorbol ester modulate 1,25(OH)2D3 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. Furthermore, PMA prompts expression of beta 3 integrin mRNA in the avian monocytic line, HD11. The increase in message reflects transactivation of the beta 3 gene and is mirrored by plasma membrane appearance of the integrin heterodimer alpha v beta 3. Moreover, attesting to the functional significance of PMA-enhanced alpha v beta 3 expression, cells treated with concentrations of the phorbol ester that induce the beta 3 gene, spread extensively on plastic, an event blocked by an anti-alpha v antibody and a peptide mimetic known to inhibit alpha v beta 3-mediated cell attachment. Interestingly, co-addition of 1,25(OH)2D3 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)2D3-induced beta 3 integrin mRNA expression. Thus, PMA and 1,25(OH)2D3 impact on the avian beta 3 integrin gene independently and in combination.