Transcriptional regulation plays an important role in determining tissue specificity and every tissue is characterized by a set of specific transcription factors. In the pancreas, the major transcription factor that restricts insulin gene expression to the pancreatic beta cells is the homeodomain protein Pdx-1. Insulin production is essential for maintaining glucose homeostasis and defects in glucose-regulated insulin gene transcription result in diabetes. We have recently discovered that glucose regulates insulin gene expression in beta cells by hyperacetylation of histone H4. Interestingly, in liver cells where the insulin gene is transcriptionally silent, no significant histone acetylation is associated with the insulin gene promoter. However, introduction of Pdx-1 into liver cells caused increased histone H4 acetylation at the normally silent insulin gene promoter in a glucose-dependent manner and stimulated insulin production. Based on these data, we hypothesize that introduction of Pdx-1 into liver cells activates the normally silent insulin gene in response to high levels of glucose by increasing histone H4 acetylation. The major goal of this proposal is to understand how introduction of Pdx-1 into the liver cells stimulates the transcription of the normally silent insulin gene, by addressing the following questions: 1. Does introduction of Pdx-1 into liver cells cause glucose-regulated changes in histone modification, at the normally silent insulin gene locus? 2. Does Pdx-1 change histone H4 acetylation levels in liver cells by recruiting co-activators or co-repressors to the insulin gene promoter in a glucose-dependent manner? 3. Does the introduction of the beta-cell specific transcription factor Ribe3b1 into the liver cells cause changes in histone modification as observed with Pdx-1? Understanding of how Pdx-1 stimulates the transcription of the normally silent insulin gene in liver cells, will facilitate the development of liver cell lines that can produce insulin in a glucose-dependent manner. The development of such non-beta cell lines will be important for the treatment of type I and as well as type II diabetes.
