TRANSCRIPTIONAL REGULATION OF PHOSPHOLAMBAN GENE AND TRANSLATIONAL REGULATION OF SERCA2 GENE PRODUCES COORDINATE EXPRESSION OF THESE 2 SARCOPLASMIC-RETICULUM PROTEINS DURING SKELETAL-MUSCLE PHENOTYPE SWITCHING

Chronic 1 Hz stimulation of the canine latissimus dorsi muscle produced a time-dependent switch from the fast-twitch to the slow-twitch phenotype, This included changes in the proteins of the sarcoplasmic reticulum, After 3 days of muscle stimulation, there was down-regulation of fast-twitch Ca-ATPase (SERCA1a) mRNA and induction of slow-twitch Ca-ATPase (SERCA2a) mRNA; most changes in both mRNAs were nearly complete after 14 days of stimulation, Although the induction of phospholamban mRNA began after 3 days of muscle stimulation, its up-regulation was not completed until the muscle had been stimulated for 42 days, The time course of expression of SERCA2a protein was very different from that of SERCA2a mRNA, suggesting that SERCA2 gene expression is regulated at the translational as well as the transcriptional level, The time course of expression of phospholamban protein closely followed that of phospholamban mRNA, suggesting that this gene is under transcriptional control, Thus coordinated expression of SERCA2a and phospholamban proteins is achieved via translational control of the SERCA2 gene and transcriptional control of the phospholamban gene.