MECHANICAL STRAIN INCREASES EXPRESSION OF THE BRAIN NATRIURETIC PEPTIDE GENE IN RAT CARDIAC MYOCYTES

Using a device that applies cyclical strain (1 Hz) to ventricular card iocytes cultured on collagen-coated silicone elastomer surfaces, we ha ve demonstrated strain-dependent increases in brain natriuretic peptid e (BNP) secretion, BNP mRNA levels, and expression of a transiently tr ansfected -1595 human BNP-luciferase reporter. When actinomycin D (10 mu M) was introduced concomitantly with the strain stimulus, the strai n-induced increase in BNP mRNA was eliminated, and the decay of transc ripts was identical in the control and strained cells, indicating the lack of independent effects on transcript stability. Strain-dependent -1595 human BNP-luciferase activity was completely inhibited by cheler ythrine, a-aminopurine, genistein, and W-7 and only partially or not a t all by KN-62, wortmannin, and H-89. The effects of these individual agents paralleled their effects on mitogen-activated protein kinase (M APK) activity, but not c-Jun N-terminal kinase (JNK) activity, in the cells. Overexpression of wild-type MAPK and, to a lesser extent, JNK i ncreased strain-dependent BNP promoter activity, whereas dominant-nega tive mutants of MAPK kinase, JNK kinase, or Ras completely blocked str ain-dependent reporter activity. These findings provide the first demo nstration that mechanical strain can increase myocardial gene expressi on through a transcriptional mechanism and suggest important roles for MAPK and JNK in mediating this effect.