Mitogenic Effects Of Insulin Research Articles

Effets à long terme de l'insuline sur la conversion adipocytaire des cellules de la lignée Ob17

The Ob17 cell line was established from the epididymal fat pad of ob/ob mice. Chronic exposure to physiological concentrations of insulin led to a net increase in lipogenic enzyme activities (EC50 = 1 to 3 nM). Proinsulin exerted the same effects at higher concentrations (EC50 = 10 to 30 nM). The mitogenic effects of both hormones appeared only at supraphysiological concentrations (EC50 = 300 nM). We conclude this was a net dissociation between the lipogenic and mitogenic effects of insulin during differentiation of the Ob17 cells.

Reversal by insulin of concanavalin A inhibition of myotube formation and evidence for common binding sites.

Concanavalin A (Con A) inhibits fusion of trypsin-treated myoblasts. This inhibition is reversed by the addition of supraphysiological concentrations (4 micrograms/ml) of insulin either during continuous presence in culture or by pulse additions at 36 and 48 h of culture, just before the time that cultures not treated with Con A undergo myoblast fusion. This reversal is not due to the mitogenic effects of insulin. Under reversal conditions, no specific displacement of bound [125I]iodo-Con A was detected nor did insulin stimulate metabolite uptake. Cell surface replicas of hemocyanin-tagged Con A showed that insulin reversal of the inhibition of myotube formation correlated with the alteration of Con A-binding sites from a clustered configuration present in the inhibited cells to a dispersed state correlated with normal myotube formation. Although a causal relationship has yet to be shown, the data suggest that insulin-mediated reversal of Con A inhibition of myoblast fusion may be related to the ability of insulin at supraphysiological levels to alter the translational mobility of cell surface components containing glucose and/or mannose residues capable of binding Con A. Evidence is presented which suggests that insulin and Con A share common binding sites, since in the physiological range of insulin concentrations (1 ng/ml), Con A pretreatments results in an inhibition of specific [125I]iodo-insulin binding, and antagonistic interactions of insulin and Con A on metabolite uptake and cell proliferation occur. Thus, it appears that the insulin receptors of developing skeletal muscle are glycoproteins containing glycopyranosides.