Sterol Regulatory Element Binding Protein 1c (SREBP 1c) is strongly expressed in MIN6 β cells

Abstract

Protein Kinase B (PKB, also known as Akt) is an important signalling molecule which has been shown to become activated in response to many stimuli, including insulin, growth factors and a variety of survival promoting agents. The signalling pathway by which insulin activates PKB has been well characterised. Insulin receptor ligation results in Phosphatidylinositol3' kinase activation, which leads to phosphorylation of PKB on its activatory sites (Thr 308 and Ser 473) following its translocation to the membrane. PKB is also activated by p adrenergic agonists (such as isoproterenol) in fat cells by an as yet unidentified mechanism. This is particularly interesting since these agonists usually produce opposing physiological effects to insulin. In order to elucidate the mechanism by which p adrenergic agonists activate PKB, we stimulated primary rat adipocytes with isoproterenol and other agents such as CPT-CAMP and forskolin. We then measured the activity of PKB and one of its downstream effectors, Glycogen Synthase Kinase 3 (GSK-3), in the presence and absence of inhibitors such as wortmannin and the PKA inhibitor H-89. We present evidence for the involvement of several different pathways in the regulation of PKB and GSK-3 by isoproterenol.Agonists in Rat Epididymal Fat Cells.