Increased expression of G(iα2) in mouse embryo stem cells promotes terminal differentiation to adipocytes

The level of G(sα2) activity has been shown to modulate the rate of adipogenesis in mouse embryo fibroblast 3T3-L1 cells (H.-Y. Wang, D. C. Watkins, and C. C. Malbon. Nature Lond. 358: 334-337, 1992). For the current work the role of G(iα2), a G protein mediator of inhibitory control of adenylyl cyclase, in regulating terminal differentiation of these cells was explored by stable transfection of fibroblasts expressing wild-type and a constitutively active mutant of G(iα2) (Q205L). Under the influence of the cytomegalovirus promoter, the expression vector yielded a 1.7-fold (Q205L mutant G(iα2)) and 2.2-fold (wild-type G(iα2)) increase in steady-state levels of these G protein α-subunits. Elevation of G(iα2) expression or expression of constitutively active G(iα2) (Q205L) promoted lipid accumulation in these clones, the hallmark of terminal differentiation of 3T3-L1 fibroblasts to adipocytes. Increasing G(iα2) activity promotes adipogenic conversion, as was previously observed by decreasing G(sα) either by inducers of differentiation or by oligodeoxynucleotides antisense to G(sα). Thus G(sα) and G(iα2) are shown to be counterregulatory with respect to promoting differentiation of 3T3-L1 mouse embryo fibroblasts to adipocytes in the absence of exogenously added inducers of differentiation. This is the first report demonstrating the induction of terminal differentiation of cells by the overexpression of a G protein α-subunit, further implicating G proteins as regulators of complex biological responses such as adipogenesis.