EXPRESSION OF A CONSTITUTIVELY ACTIVATED FORM OF PROTEIN-KINASE-B (C-AKT) IN 3T3-L1 PREADIPOSE CELLS CAUSES SPONTANEOUS DIFFERENTIATION

Insulin/IGF-1 is required for differentiation of 3T3-L1 adipose cells. Downstream targets of insulin/IGF-1 that lead to adipocyte differenti ation appear to include Ras, phosphatidylinositol LPI) 3-kinase, Raf, and mitogen-activated protein kinase. We have tested whether protein k inase B (PKB), a serine/threonine kinase activated by PT 3-kinase, is sufficient for 3T3-L1 preadipose cell differentiation. A plasmid vecto r encoding a version of Pf(B that is constitutively activated (Gag-PKB ) was expressed in 3T3-L1 preadipose cells (Gag-PKB cells). Spontaneou s morphological Changes indicative of adipocyte differentiation were o bserved in Gag-PKB cells, The cells assumed a spherical shape and they acquired characteristic Lipid droplets that stained positively for Oi l Red O. Northern blot analysis detected upregulation of LPL and aP2 m RNA, specific indicators of adipocyte differentiation, Our data demons trate that constitutive activation ol PKB is sufficient to trigger adi pocyte differentiation.