Glucose-stimulated insulin biosynthesis depends on insulin-stimulated insulin gene transcription.

Glucose stimulation of pancreatic beta-cells leads to insulin secretion as well as up-regulation of insulin biosynthesis. The acute elevation in pro-insulin levels is thought to be exclusively because of the activation of translation of pre-existing prepro-insulin mRNA. Glucose-stimulated insulin gene transcription is believed to be a long term effect and should therefore not contribute to the acute elevation in pro-insulin levels. We have recently shown that glucose activates insulin gene transcription within minutes and that secreted insulin is one of the key factors triggering this process in an autocrine manner. We now provide evidence that 50% of the glucose-stimulated, acute pro-insulin biosynthesis within 30 min results from up-regulated insulin gene transcription. Our data led us to propose that glucose elevates pro-insulin levels by stimulating both transcriptional and post-transcriptional/post-translational events to an equal extent. Whereas the stimulatory effect on transcription is mediated by insulin secreted in response to glucose, glucose directly stimulates the post-transcriptional/post-translational processes.