Overexpression of the glycogen targeting (G(M)) subunit of protein phosphatase-1.
The G(M) glycogen-targeting subunit of protein phosphatase-1 (PP1) is believed to be involved in dephosphorylation of the enzymes of glycogen metabolism. To assess the roles of G(M) on glycogen metabolism, we created site-directed G(M) mutants and overexpressed them in Chinese hamster ovary (CHO) cells expressing human insulin receptor. Overexpressed G(M) recruited glycogen synthase as well as PP1 to the glycogen pellet, and upregulated basal glycogen synthase activity. Overexpressed G(M)-67A (Ser-67 replaced with alanine) exhibited decreased sensitivity to suppression of glycogen synthase activity by forskolin, while overexpression of G(M)-48A (Ser-48 replaced with alanine) preserved glycogen synthase activation in response to insulin. These observations indicate that in CHO cells overexpressing G(M); (1) G(M) translocates glycogen synthase to the glycogen pellet and affected basal glycogen synthase, (2) Ser-67 might be involved in the suppression of glycogen synthase activity by glycogenolytic agents, and (3) Ser-48 might not commit to activation of glycogen synthase by insulin.
Yamamoto-Honda
R
R
Institute for Diabetes Care and Research, Asahi Life Foundation, 1-6-6 Marunouchi, Chiyoda-ku, Tokyo, 100-0005, Japan.
Honda
Z
Z
Kaburagi
Y
Y
Ueki
K
K
Kimura
S
S
Akanuma
Y
Y
Kadowaki
T
T
D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology; D016466:CHO Cells; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D004789:Enzyme Activation / Q000187:drug effects; D015870:Gene Expression; D006003:Glycogen / Q000378:metabolism*; D006006:Glycogen Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D010749:Phosphoprotein Phosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D011714:Pyrans; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013141:Spiro Compounds; D014162:Transfection
D000935:Antifungal Agents; D007328:Insulin; D011714:Pyrans; D011993:Recombinant Fusion Proteins; D013141:Spiro Compounds; C053079:tautomycin; D005576:Colforsin; D006003:Glycogen; D006006:Glycogen Synthase; D011972:Receptor, Insulin; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1