INCREASED EXPRESSION OF G(I-ALPHA-2) IN MOUSE EMBRYO STEM-CELLS PROMOTES TERMINAL DIFFERENTIATION TO ADIPOCYTES

The level of G(salpha) activity has been shown to modulate the rate of adipogenesis i(salpha) mouse embryo fibroblast 3T3-L1 cells (H.-Y. Wa ng, D. C. Watkins, and C. C. Malbon. Nature Lond. 358: 334-337, 1992). For the current work the role of G(ialpha2), a G protein mediator of inhibitory control of adenylyl cyclase, in regulating terminal differe ntiation of these cells was explored by stable transfection of fibrobl asts expressing wild-type and a constitutively active mutant of G(ialp ha2) (Q205L). Under the influence of the cytomegalovirus promoter, the expression vector yielded a 1.7-fold (Q205L mutant G(ialpha2)) and 2. 2-fold (wild-type G(ialpha2)) increase in steady-state levels of these G protein alpha-subunits. Elevation of G(ialpha2) expression or expre ssion of constitutively active G(ialpha2) (Q205L) promoted lipid accum ulation in these clones, the hallmark of terminal differentiation of 3 T3-LI fibroblasts to adipocytes. Increasing G(ialpha2) activity promot es adipogenic conversion, as was previously observed by decreasing G(s alpha) either by inducers of differentiation or by oligodeoxynucleotid es antisense to G(salpha). Thus G(salpha) and G(ialpha2) are shown to be counterregulatory with respect to promoting differentiation of 3T3- L1 mouse embryo fibroblasts to adipocytes in the absence of exogenousl y added inducers of differentiation. This is the first report demonstr ating the induction of terminal differentiation of cells by the overex pression of a G protein a-subunit, further implicating G proteins as r egulators of complex biological responses such as adipogenesis.