Protein phosphatase 2A is the main phosphatase involved in the regulation of protein kinase B in rat adipocytes

In adipocytes, protein kinase B (PKB) has been suggested to be the enzyme that phosphorylates phosphodiesterase 3B (PDE3B), a key enzyme in insulin's antilipolytic signalling pathway. In order to screen for PKB phosphatases, adipocyte homogenates were fractionated using ion-exchange chromatography and analysed for PKB phosphatase activities. PKB phosphatase activity eluted as one main peak, which coeluted with serine/threonine phosphatases (PP)2A. In addition, adipocytes were incubated with inhibitors of PP. Incubation of adipocytes with 1 μM okadaic acid inhibited PP2A by 75% and PP1 activity by only 17%, while 1 μM tautomycin inhibited PP1 activity by 54% and PP2A by only 7%. Okadaic acid, but not tautomycin, induced the activation of both PKBα and PKBβ. Finally, PP2A subunits were found in several subcellular compartments, including plasma membranes (PM) where the phosphorylation of PKB is thought to occur. In summary, our results suggest that PP2A is the principal phosphatase that dephosphorylates PKB in adipocytes.