AMP-ACTIVATED PROTEIN-KINASE IS ACTIVATED BY LOW GLUCOSE IN CELL-LINES DERIVED FROM PANCREATIC BETA-CELLS, AND MAY REGULATE INSULIN RELEASE

The role of the AMP-activated protein kinase (AMPK) cascade in the glu cose-sensitive pancreatic beta cell lines HIT-T15 and INS-1 was addres sed. In both cell types, removal of glucose leads to a > 5-fold activa tion of AMPK activity. Activation of AMPK was due to phosphorylation, since the effect was reversed by protein phosphatase treatment of the extracts, and was restored by re-addition of MgATP and the purified up stream kinase. When the effects of different concentrations of medium glucose were examined, insulin secretion and AMPK activity were invers ely related, and varied over the same concentration range. The activat ion in response to glucose removal appeared to be due to changes in th e concentration of the known regulators of the cascade, i.e. AMP and A TP, since AMPK activation was associated with a large increase in the cellular AMP/ATP ratio, and the two parameters varied over the same ra nge of glucose concentrations. In late-passage HIT-T15 cells that had lost the glucose-dependent insulin secretion response, both AMPK activ ity and the AMP/ATP ratio also became insensitive to the extracellular glucose concentration. Treatment of INS-I cells, but not HIT-T15 cell s, with AICA riboside (5-aminoimidazole-4-carboxamide riboside) result s in accumulation of the ribotide, ZMP (AICA riboside monophosphate), and activation of AMPK. AICA riboside treatment of INS-1 cells, and of isolated rat islets, had both inhibitory and stimulatory effects on i nsulin secretion. These results show that in beta cell lines the AMP-a ctivated protein kinase, like its yeast homologue the SNF1 complex, ca n respond to the level of glucose in the medium, and may be involved i n regulating insulin release.