Regulation of protein phosphatase 1 and 2A activities by insulin during myogenesis in rat skeletal muscle cells in culture.

作者：Malathi Srinivasan, Najma Begum · 发表于：Journal of Biological Chemistry · 年份：1994 · DOI：10.1016/s0021-9258(18)99905-9 · 被引用次数：90 · 研究领域：Muscle Physiology and Disorders、Glycogen Storage Diseases and Myoclonus、Mitochondrial Function and Pathology

In this study, we examined protein phosphatase 1 (PP-1) and protein phosphatase 2A (PP-2A) activities during various stages of myogenesis and their regulation by insulin in rat skeletal muscle cells. Protein phosphatase activities were measured using 32P-labeled phosphorylase a, glycogen synthase, and phosphorylase kinase as substrates. Spontaneous PP-1 activity increased progressively in cultures from 2 to 5 days, PP-2A activities remained constant in days 2-4 cultures and increased sharply on day 5. Most of the times in culture, a significant proportion (approximately 65%) of PP-1 was in a form that could be activated by trypsin. Insulin stimulated PP-1 activity (40-80% increase over basal) in a time (t1/2 approximately 5 min)- and dose (EC50 approximately 0.1 nM)-dependent manner. Insulin activation of PP-1 was accompanied by a corresponding inhibition in PP-2A activity. The effects of insulin on PP-1 and PP-2A were differentiation dependent and were observed only in cells at fusion (day 5) and post-fusion. The insulin's effect on PP-1 correlated with the gradual appearance of PP-1 G subunit in cells at fusion. Immunoprecipitation of PP-1 from 32P-labeled cells with an antibody directed against the site 1 sequence of rabbit skeletal muscle PP-1G detected a 160-kDa protein, phosphorylation of which was significantly increased by insulin. This correlated well with the increase observed in immunoprecipitated PP-1G activity. Treatment of cells with a cAMP agonist (SpcAMP) comp...