A DYNAMIC SYSTEM FOR SUPPRESSION AND REEXPRESSION OF INSULIN AND PERVANADATE BIORESPONSES IN RAT ADIPOCYTES - TREATMENT WITH OKADAIC ACID AND STAUROSPORINE

In previous studies, we demonstrated that while okadaic acid stimulate s glucose metabolism, it suppresses the bioresponses of insulin itself in rat adipocytes (Shisheva and Shechter, Endocrinology 129: 2279-228 8, 1991). Both stimulation and suppression were attributed to okadaic acid-dependent inhibition of protein phosphatases 1 and 2A. We report here that exposure of adipocytes to staurosporine prior to okadaic aci d restored insulin-stimulated actions on glucose metabolism. The effec t was half-maximal at staurosporine concentrations as low as 70 nM and was fully expressed (80-87% of the control) at 400-500 nM. Similarly, the insulin-like effect of pervanadate, which was also suppressed by okadaic acid, was restored completely with staurosporine pretreatment. Staurosporine was less effective in restoring cell responses inhibite d by high concentrations of okadaic acid, or when added to the cells a fter okadaic acid. Cell resensitization was unique to staurosporine an d could not be produced by various agents that reduce cellular protein kinase A- or protein kinase C-dependent phosphorylation, such as phen ylisopropyl adenosine (PIA), K-252a and GF 109203X. Staurosporine (400 nM) partially reversed lipolysis induced by okadaic acid but not that induced by beta-adrenergic stimulation. PIA, which antagonized okadai c acid-induced lipolysis to the same extent as staurosporine, was not capable of restoring insulin responses. Further studies aimed at eluci dating this reversing effect revealed that staurosporine did not react ivate okadaic acid-inhibited protein phosphatases 1 and 2A in both cel lular and cell-free systems. In summary, we report here a unique dynam ic system in which insulin and pervanadate bioeffects can be fully sup pressed and again re-expressed without reactivation of protein phospha tase 1 or 2A. The precise site for both effects, although still obscur e, appears to be downstream from autophosphorylated insulin receptor.