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

Abstract

Expression of the brain natriuretic peptide (BNP) gene in cultured neonatal rat ventricular myocytes is activated by mechanical strain in vitro. We explored the role of cell-matrix contacts in initiating the strain- dependent increment in human BNP (hBNP) promoter activity. Coating the culture surface with fibronectin effected a dose-dependent increase in basal hBNP luciferase 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 fluorescence-activated cell sorting, we demonstrated the presence of β1,β3, and α(v)β5 integrins in myocytes as well as non- myocytes and α1 only in non-myocytes in our cultures. Inclusion of antibodies directed against β1,β3, or α(v)β5, but not α1, α2, or cadherin, was effective in blocking the BNP promoter response to mechanical strain. These same antibodies (anti-β3, -β1, and -α(v)β5) 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 inhibitors of integrin function demonstrated suppression of strain-dependent BNP promoter activity when vectors encoding β1 or β3, but not β5, α5, or a carboxyl-terminal deletion mutant of β3 (β3B), were employed. These studies underscore the importance of cell-matrix interactions in controlling cardiac gene expression and suggest a potentially important role for these interactions in signaling responses to mechanical stimuli within the myocardium.