CHARACTERIZATION OF PROMOTER ELEMENTS OF THE RABBIT CARDIAC SARCOPLASMIC-RETICULUM CA(2-ATPASE GENE REQUIRED FOR EXPRESSION IN CARDIAC-MUSCLE-CELLS())

The sarcoplasmic reticulum Ca2+-ATPase (SERCA2) plays a critical role in the contractile performance of cardiac and slow-twitch skeletal mus cle by restoring cytosolic calcium to low resting levels during the co ntractile cycle. We have previously shown that SERCA2 expression in th e heart is altered by a number of pathophysiological stimuli. In an ef fort to define molecular mechanisms regulating expression of the SERCA 2 gene in cardiac muscle cells, deletions of a 1460-bp promoter fragme nt were generated and inserted into a luciferase reporter plasmid. Pro moter constructs were transiently transfected into embryonic cardiocyt es and skeletal muscle cell lines Sol 8 and C2C-12 in vitro and inject ed into adult myocardium in vivo. Results demonstrate that sequences f rom the transcription start site to -284 are both necessary and suffic ient for high-level transcription of the reporter gene in differentiat ing muscle cells and in fetal cardiocytes in culture. We further demon strate that this promoter fragment is highly active in vivo when injec ted into rat hearts, suggesting that the same regulatory elements are functional in vivo as well as in vitro. The region of the gene from -2 84 to -658 exerts a modest positive effect in cardiocytes and Sol 8 my otubes but exerts a negative effect in C2C-12 fast skeletal muscle cel ls. This initial analysis of transcriptional regulation of the SERCA2 gene will serve as a foundation for the study of alterations of expres sion of the gene in pathological conditions.