Role of protein targeting to glycogen (PTG) in the regulation of protein phosphatase-1 activity.
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 32P-labeled phosphorylase a by decreasing the Km of PP1 for phosphorylase 5-fold, while having no effect on the Vmax 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.
Brady
M J
MJ
Department of Cell Biology, Parke-Davis Pharmaceutical Research Division, Warner-Lambert Company, Ann Arbor, Michigan 48105, USA.
Printen
J A
JA
Mastick
C C
CC
Saltiel
A R
AR
D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D051379:Mice; D009419:Nerve Tissue Proteins / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010750:Phosphoproteins / Q000494:pharmacology; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D015398:Signal Transduction
D002352:Carrier Proteins; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D004791:Enzyme Inhibitors; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; C104748:Ppp1r3c protein, mouse; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1