The Regulation of cAMP-Dependent Protein Kinases in Normal and Transformed L6 Myoblasts
L6 myoblasts are a permanent cell line which differentiates in culture to form multinucleate myotubes containing large numbers of the proteins characteristic of mature muscle (Yaffe, 1968). There is some evidence which suggests a role for the cAMP-dependent protein kinases in the regulation of this process (Ball and Sanwal, 1980; Curtis and Zalin, 1981). In this report we have compared the cAMP-dependent protein kinases of L6 myoblasts and a spontaneously-transformed L6 cell line which is unable to differentiate in culture. In particular we have studied the type I cAMP- dependent protein kinase as we have found previously (Rogers et al., 1984) that this isozyme is regulated during differentiation, suggesting that it is somehow involved in the control of this process. We show that the regulatory subunit of this isozyme (RI)* is degraded rapidly in L6 myoblasts in the presence of cAMP, and that this behaviour is altered in the spontaneously-transformed cell line. We also present some data which suggest a physiological role for changes in RI levels during the process of withdrawal from the cell cycle.
KeywordsRegulatory Subunit Dependent Protein Kinase Myogenic Cell cAMP Analogue Myogenic Cell Line
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