Activation of the cytochrome c gene by electrical stimulation in neonatal rat cardiac myocytes

Abstract

Activation of cytochrome c (cyt c) transcription in electrically stimulated neonatal rat cardiac myocytes is preceded by transient expression of the activating protein-1 family of transcription factors, c-Fos, c-Jun, and JunB, as well as nuclear respiratory factor-1 (NRF-1). Mutations in either the NRF-1 or in the two cyclic AMP response elements on the cyt c promoter significantly reduce cyt c promoter activation produced either by electrical stimulation (Xia, Y., Buja, L.M., Scarpulla, R.C., and McMillin, J.B. (1997) Proc. Natl. Acad. Sci. U.S.A. 94, 11399-11404) or by transfection of c-jun into nonpaced cardiac myocytes. Electrical stimulation of cardiac myocytes activates the c-Jun N-terminal kinase (McDonough, P.M., Hanford, D.S., Sprenkle, A.B., Mellon, N.R., and Glembotski, C.C. (1997) J. Biol. Chem. 272, 24046-24053) so that the fold-activation of the cyt c promoter is increased by pacing when either c-jun or c-fos/c-jun were cotransfected. Physical association of NRF-1 protein with the NRF-1 enhancer element and of c-Jun with the cyclic AMP response element binding sites on the cyt c promoter was demonstrated by gel shift competition assays and by antibody super shifts. This is the first demonstration that induction of NRF-1 and c- Jun by pacing of cardiac myocytes directly mediates cyt c gene expression and mitochondrial proliferation in response to hypertrophic stimuli in the heart.