Shisheva A, Shechter Y
Department of Hormone Research, Weizmann Institute of Science, Rehovot, Israel.
Biochem Pharmacol. 1994 Apr 29;47(9):1537-44. doi: 10.1016/0006-2952(94)90529-0.
In previous studies, we demonstrated that while okadaic acid stimulates glucose metabolism, it suppresses the bioresponses of insulin itself in rat adipocytes (Shisheva and Shechter, Endocrinology 129: 2279-2288, 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 acid restored insulin-stimulated actions on glucose metabolism. The effect 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 inhibited by high concentrations of okadaic acid, or when added to the cells after okadaic acid. Cell resensitization was unique to staurosporine and could not be produced by various agents that reduce cellular protein kinase A- or protein kinase C-dependent phosphorylation, such as phenylisopropyl 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 okadaic acid-induced lipolysis to the same extent as staurosporine, was not capable of restoring insulin responses. Further studies aimed at elucidating this reversing effect revealed that staurosporine did not reactivate okadaic acid-inhibited protein phosphatases 1 and 2A in both cellular and cell-free systems. In summary, we report here a unique dynamic system in which insulin and pervanadate bioeffects can be fully suppressed and again re-expressed without reactivation of protein phosphatase 1 or 2A. The precise site for both effects, although still obscure, appears to be downstream from autophosphorylated insulin receptor.
在先前的研究中，我们证明，虽然冈田酸能刺激葡萄糖代谢，但它会抑制大鼠脂肪细胞中胰岛素自身的生物反应（希舍娃和谢克特，《内分泌学》129: 2279 - 2288，1991）。刺激和抑制作用均归因于冈田酸对蛋白磷酸酶1和2A的依赖性抑制。我们在此报告，在冈田酸处理之前，将脂肪细胞暴露于星形孢菌素可恢复胰岛素对葡萄糖代谢的刺激作用。在低至70 nM的星形孢菌素浓度下，该效应达到半数最大效应，在400 - 500 nM时完全表现出来（为对照的80 - 87%）。同样，过氧钒酸盐的胰岛素样效应，也被冈田酸抑制，经星形孢菌素预处理后完全恢复。星形孢菌素在恢复被高浓度冈田酸抑制的细胞反应方面效果较差，或者在冈田酸加入细胞后再添加时效果也不佳。细胞再敏化是星形孢菌素所特有的，各种能降低细胞蛋白激酶A或蛋白激酶C依赖性磷酸化的试剂，如苯异丙基腺苷（PIA）、K - 252a和GF 109203X，都不能产生这种效果。星形孢菌素（400 nM）部分逆转了冈田酸诱导的脂解作用，但不能逆转β - 肾上腺素能刺激诱导的脂解作用。PIA虽然在拮抗冈田酸诱导的脂解作用方面与星形孢菌素程度相同，但不能恢复胰岛素反应。旨在阐明这种逆转效应的进一步研究表明，在细胞和无细胞系统中，星形孢菌素都不会重新激活被冈田酸抑制的蛋白磷酸酶1和2A。总之，我们在此报告了一个独特的动态系统，其中胰岛素和过氧钒酸盐的生物效应可以被完全抑制，然后在蛋白磷酸酶1或2A未重新激活的情况下再次表达。虽然这两种效应的确切位点仍然不清楚，但似乎位于自磷酸化胰岛素受体的下游。
