Oncogenic src, raf, and ras stimulate a hypertrophic pattern of gene expression and increase cell size in neonatal rat ventricular myocytes.
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), beta-myosin heavy chain (beta-MHC), and skeletal muscle (SkM)-alpha-actin. By using luciferase reporter plasmids, we examined whether oncogenes that activate the extracellular signal-regulated kinase cascade (srcF527, Ha-rasV12, and v-raf) increased expression of "fetal" genes. Transfection of myocytes with srcF527 stimulated expression of ANF, SkM-alpha-actin, and beta-MHC by 62-, 6.7-, and 50-fold, respectively, but did not induce DNA synthesis. Stimulation of ANF expression by srcF527 was greater than by Ha-rasV12, which in turn was greater than by v-raf. General gene expression was also increased but to a lesser extent. The response to srcF527 was inhibited by dominant-negative Ha-rasN17. Myocyte area was increased by srcF527, Ha-rasV12, and v-raf, and although it altered myocyte morphology by causing a pseudopodial appearance, srcF527 did not detectably increase myofibrillogenesis either alone or in combination with Ha-rasV12. A kinase-dead src mutant increased myocyte size to a much lesser extent than srcF527 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.
Fuller
S J
SJ
Section of Cardiac Medicine, National Heart and Lung Institute Division, Imperial College School of Medicine, London SW3 6LY, United Kingdom. stephen.fuller@ic.ac.uk
Gillespie-Brown
J
J
Sugden
P H
PH
D000199:Actins / Q000378:metabolism; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology; D048429:Cell Size; D002478:Cells, Cultured; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D017930:Genes, Reporter; D011905:Genes, ras; D016391:Genes, src; D019833:Genistein / Q000494:pharmacology; D006131:Growth Inhibitors / Q000494:pharmacology; D006321:Heart / Q000254:growth & development*; D008156:Luciferases / Q000235:genetics; D009206:Myocardium / Q000166:cytology*; D018995:Myosin Heavy Chains / Q000494:pharmacology; D027384:Oncogene Proteins v-raf; D011401:Promoter Regions, Genetic / Q000187:drug effects; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015682:Retroviridae Proteins, Oncogenic / Q000494:pharmacology; D014162:Transfection; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism
D000199:Actins; D006131:Growth Inhibitors; D015682:Retroviridae Proteins, Oncogenic; D009320:Atrial Natriuretic Factor; D019833:Genistein; D008156:Luciferases; D019061:src-Family Kinases; D027384:Oncogene Proteins v-raf; D019908:Proto-Oncogene Proteins c-raf; D018995:Myosin Heavy Chains