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Role of Protein Targeting to Glycogen (PTG) in the Regulation of Protein Phosphatase-1 Activity

1997; Elsevier BV; Volume: 272; Issue: 32 Linguagem: Inglês

10.1074/jbc.272.32.20198

1083-351X

Matthew Brady, John A. Printen, Cynthia Corley Mastick, Alan R. Saltiel,

Muscle Physiology and Disorders

We have recently cloned from 3T3-L1 adipocytes a novel glycogen-targeting subunit of protein phosphatase-1, termed PTG (Printen, J. A., Brady, M. J., and Saltiel, A. R. (1997) Science 275, 1475–1478). Differentiation of 3T3-L1 fibroblasts into highly insulin-responsive adipocytes resulted in a marked increase in PTG expression. Immobilized glutathione S -transferase (GST)-PTG fusion protein specifically bound either PP1 or phosphorylase a . Addition of soluble GST-PTG to 3T3-L1 lysates increased PP1 activity against 32 P-labeled phosphorylase a by decreasing the K m of PP1 for phosphorylase 5-fold, while having no effect on the V max of the dephosphorylation reaction. Alternatively, PTG did not affect PP1 activity against hormone-sensitive lipase. PTG was not a direct target of intracellular signaling, as insulin or forskolin treatment of cells did not activate a kinase capable of phosphorylating PTG in vivo or in vitro . Finally, PTG decreased the ability of DARPP-32 to inhibit PP1 activity from 3T3-L1 adipocyte lysates. These data cumulatively suggest that PTG increases PP1 activity against specific proteins by several distinct mechanisms.