Integrin dependence of brain natriuretic peptide gene promoter activation by mechanical strain

Expression of the brain natriuretic peptide (BNP) gene in cultured neonatal rat ventricular myocytes is activated by mechanical strain in vitro. We ex plored the role of cell-matrix contacts in initiating the strain-dependent increment in human BNP (hBNP) promoter activity. Coating the culture surfac e with fibronectin effected a dose-dependent increase in basal hBNP lucifer ase activity and amplification of the response to strain. Preincubation of myocytes with an RGD peptide (GRGDSP) or with soluble fibronectin, each of which would be predicted to compete for cell-matrix interactions, resulted in a dose dependent reduction in strain-dependent hBNP promoter activity. A functionally inert RGE peptide (GRGESP) was without effect. Using fluoresc ence-activated cell sorting, we demonstrated the presence of beta(1), beta( 3), and alpha(V)beta(5) integrins in myocytes as well as non-myocytes and a lpha 1 only in non-myocytes in our cultures. Inclusion of antibodies direct ed against beta(1), beta(3), or alpha(V)beta(5) but not alpha(1), alpha(2), or cadherin, was effective in blocking the BNP promoter response to mechan ical strain. These same antibodies (anti-beta(3), -beta(1), and -alpha(V)be ta(5)) had a similar inhibitory effect on strain-stimulated ERK, p38 MAPK, and, to a lesser extent, JNK activities in these cells. Cotransfection with chimeric integrin receptors capable of acting as dominant-negative inhibit ors of integrin function demonstrated suppression of strain-dependent BNP p romoter activity when vectors encoding beta(1) or beta(3), but not beta(5), alpha(5), or a carboxyl-terminal deletion mutant of beta(3) (beta(3)B), we re employed. These studies underscore the importance of cell-matrix interac tions in controlling cardiac gene expression and suggest a potentially impo rtant role for these interactions in signaling responses to mechanical stim uli within the myocardium.