Phosphatidylinositol-3,4,5-trisphosphate is required for insulin-like growth factor 1-mediated survival of 3T3-L1 preadipocytes

Adipocyte number, a determinant of adipose tissue mass, reflects the balanc e between the rates of proliferation/differentiation us. apoptosis of pread ipocytes. The percentage of 3T3-L1 preadipocytes undergoing cell death foll owing serum deprivation was reduced by 10 nM insulin-like growth factor (IG F)-1 (from 50.0 +/- 0.74 for control starved cells to 27.5 +/- 3.18). TUNEL staining confirmed the apoptotic nature of the cell death. The protective effect of IGF-1 was blocked by phosphoinositide 3-kinase (PI3K) inhibitors, wortmannin, and LY294002, but was unaffected by rapamycin, PD98059, or SB2 03580, which inhibit mammalian target of rapamycin (mTOR), ERK kinase (MEK1 ), and p38 MAPK respectively. Exogenous PI(3,4,5)P3 (10 muM), the principal product of IGF-1-stimulated PI3K in 3T3-L1 preadipocytes, had a modest sur vival effect on its own, reducing cell death from 47.9 +/- 3.4% to 35.6 +/- 3.58. When added to the combination of IGF-1 and LY294002, PI(3,4,5)P3 rev ersed most of the inhibitory effect of LY294002 on IGF-1-dependent cell sur vival, protein kinase B/Akt phosphorylation, and caspase-3 activity. Taken together, these results implicate PI(3,4,5)P3 as a necessary signal for the anti-apoptotic action of IGF-1 on 3T3-L1 preadipocytes.