Oncogenic src, raf, and ras stimulate a hypertrophic pattern of gene expression and increase cell size in neonatal rat ventricular myocytes

Abstract

In response to hormones and growth factors, cultured neonatal ventricular myocytes increase in profile, exhibit myofibrillogenesis, and re- express genes whose expression is normally restricted to the fetal stage of ventricular development. These include atrial natriuretic factor (ANF), β- myosin heavy chain (β-MHC), and skeletal muscle (SkM)-α-actin. By using luciferase reporter plasmids, we examined whether oncogenes that activate the extracellular signal-regulated kinase cascade (src(F527), Ha-ras(V12), and v- raf) increased expression of 'fetal' genes. Transfection of myocytes with src(F527) stimulated expression of ANF, SkM-α-actin, and β-MHC by 62-, 6.7- , and 50-fold, respectively, but did not induce DNA synthesis. Stimulation of ANF expression by src(F527) was greater than by Ha-ras(V12), which in turn was greater than by v-raf. General gene expression was also increased but to a lesser extent. The response to src(F527) was inhibited by dominant- negative Ha-ras(N17). Myocyte area was increased by src(F527), Ha-ras(V12), and v-raf, and although it altered myocyte morphology by causing a pseudopodial appearance, src(F527) did not detectably increase myofibrillogenesis either alone or in combination with Har-ras(V12). A kinase-dead src mutant increased myocyte size to a much lesser extent than src(F527) and also did not inhibit ANF-luciferase expression in response to phenylephrine. We conclude that members of the Src family of tyrosine kinases may be important in mediating the transcriptional changes occurring during cardiac myocyte hypertrophy and that Ras and Raf may be downstream effectors.