Long-term effects of rapamycin treatment on insulin mediated phosphorylation of Akt/PKB and glycogen synthase activity

S Varma, A Shrivastav, S Changela… - Experimental cell …, 2008 - Elsevier
S Varma, A Shrivastav, S Changela, RL Khandelwal
Experimental cell research, 2008Elsevier
Protein kinase B (Akt/PKB) is a Ser/Thr kinase that is involved in the regulation of cell
proliferation/survival through mammalian target of rapamycin (mTOR) and the regulation of
glycogen metabolism through glycogen synthase kinase 3β (GSK-3β) and glycogen
synthase (GS). Rapamycin is an inhibitor of mTOR. The objective of this study was to
investigate the effects of rapamycin pretreatment on the insulin mediated phosphorylation of
Akt/PKB phosphorylation and GS activity in parental HepG2 and HepG2 cells with …
Protein kinase B (Akt/PKB) is a Ser/Thr kinase that is involved in the regulation of cell proliferation/survival through mammalian target of rapamycin (mTOR) and the regulation of glycogen metabolism through glycogen synthase kinase 3β (GSK-3β) and glycogen synthase (GS). Rapamycin is an inhibitor of mTOR. The objective of this study was to investigate the effects of rapamycin pretreatment on the insulin mediated phosphorylation of Akt/PKB phosphorylation and GS activity in parental HepG2 and HepG2 cells with overexpression of constitutively active Akt1/PKB-α (HepG2-CA-Akt/PKB). Rapamycin pretreatment resulted in a decrease (20–30%) in the insulin mediated phosphorylation of Akt1 (Ser 473) in parental HepG2 cells but showed an upregulation of phosphorylation in HepG2-CA-Akt/PKB cells. Rictor levels were decreased (20–50%) in parental HepG2 cells but were not significantly altered in the HepG2-CA-Akt/PKB cells. Furthermore, rictor knockdown decreased the phosphorylation of Akt (Ser 473) by 40–60% upon rapamycin pretreatment. GS activity followed similar trends as that of phosphorylated Akt and so with rictor levels in these cells pretreated with rapamycin; parental HepG2 cells showed a decrease in GS activity, whereas as HepG2-CA-Akt/PKB cells showed an increase in GS activity. The changes in the levels of phosphorylated Akt/PKB (Ser 473) correlated with GS and protein phoshatase-1 activity.
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