Activation of the Cytochrome c Gene by Electrical Stimulation in Neonatal Rat Cardiac Myocytes: ROLE OF NRF-1 AND c-Jun

Yang Xia,L Maximilian Buja,Jeanie B Mcmillin

doi:10.1074/jbc.273.20.12593

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.

Highlights

Hypertrophic growth is a basic mechanism for increasing cell size in post-mitotic cardiac muscle
Since both nuclear respiratory factor-1 (NRF-1) and Fos/Jun mRNAs appear in time just prior to activation of cyt c gene expression, and since activating protein-1 (AP-1) factors play a central role in mitogenesis (17), we asked whether AP-1 is involved in cyt c gene expression, and whether this involvement is a direct interaction
Subsequent to the rise in NRF-1, a small (67%) but significant induction of cyt c mRNA in the transfected, unstimulated myocytes was observed at 12 and 24 h (Fig. 1). These results suggest that induction of c-jun early gene expression, either by transfection or by electrical stimulation (1), is important for subsequent expression of nrf-1

Summary

Introduction

Hypertrophic growth is a basic mechanism for increasing cell size in post-mitotic cardiac muscle. 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).

Results

Conclusion