Involvement of Phosphoinositol-glycan in Induction of Differentiation, from Preadipocytes to Adipocytes, of 3T3-L1 Cells by Insulin-like Growth Factor I.

Abstract

Using a serum-free culture system, we examined the effects of insulin-like growth factor I (IGF-I) and insulin on the differentiation, from preadipocytes to adipocytes, of 3T3-L1 cells, and the signal transduction mechanism after the stimulation by IGF-I of adipocyte differentiation. IGF-I and insulin stimulated the adipose conversion of 3T3-L1 cells differently. IGF-I strongly stimulated adipose conversion on coupling with dexamethasone and l-methyl-3-isobutylxanthine, while insulin did not couple with them. The potency of the effect of induction by IGF-I of adipocyte differentiation of 3T3-L1 cells was considerably higher than that of the effect of insulin. Therefore, it was suggested that IGF-I is important in adipose conversion of 3T3-L1 cells. Inositol-monophosphate, a specific inhibitor of the phosphoinositol-glycan (Pl-glycan) action, suppressed IGF-I induced adipose conversion. Therefore, we think that Pl-glycan released from the plasma membrane may be involved in the IGF-I function in adipocyte differentiation of 3T3-L1 cells as a second messenger.