FULLY-DIFFERENTIATED mouse 3T3-L1 fibroblasts accumulate large amounts of lipid at 7-10 days after induction by insulin or by dexamethasone and a methyl xanthine1-3. G proteins mediate transmembrane signalling from a diverse group of cell-surface receptors to effector units that include phospholipase C, adenylyl cyclase and ion channels4-6. They are also targets or regulation themselves7-10. 3T3-L1 fibroblasts display marked changes in levels of G protein when induced to differentiate to adipocytes11-15. Here we show that cholera toxin, which ADP-ribosylates and activates the G protein subunit G(s-alpha), blocks the induction of differentiation, whereas increasing intracellular cyclic AMP directly with the dibutyryl analogue or indirectly with pertussis toxin or forskolin does not affect differentiation. Oligodeoxynucleotides antisense to the sequence encoding G(s-alpha) accelerate differentiation markedly. The time course of adipogenesis declined from 7-10 days in controls to roughly 3 days in cultures treated with antisense-G(s-alpha) oligodeoxynucleotides, whereas oligodeoxynucleotides, antisense to G(i-alpha-1), G(i-alpha-3), and sense and missense to G(s-alpha), had no such effect. Antisense-G(s-alpha) alone induced differentiation by day 7, indicating that G(s-alpha) activity modulates differentiation in 3T3-L1 cells, acting in a new role which is independent of increased intracellular cAMP.
