Identification of HNF and HNF4 Mediated Regulators of Insulin Secretion in Beta-Cells

jThe 13-cells play a major role in glucose homeostasis, and there is a network of transcription factors that controls the proper development and normal function of 13-cells. Among the 13-cell enriched transcription factors that form a regulatory network, Hepatocyte Nuclear Factor lu (HNF1cz) and HNF4ct are the master: regulators of 13-cells, and the inherited mutations on the genes encoding these transcription factors cause monogenic dominant forms of diabetes known as maturity-onset diabetes of the young (MODY). MODY patients are mainly characterized by the defect in insulin secretion from 13-cells and we have been studying HNFIt and HNF4t-mediated regulators in insulin secretion from 13-cells. These gene-specific transcription factors initiate transcription by recognizing promoter regions of the target genes and mediating interactions with various proteins including transcriptional coregulators to recruit the remainder of the main transcriptional machinery; however, the detailed list of their functional binding partners leading to proper insulin secretion is not well known. Thus, we have conducted yeast two-hybrid screenings to identity putative binding partners of HNFIa and HNF4a in 13-cells, which need to be further characterized by follow-up studies. Therefore, we propose to (1) confirm the interactions by these putative binding partners in vivo and in vitro (Aim 1), and (2) examine the effects of these interactions on overall transcription and insulin secretion from 13-cells (Aim 2) within the funding period. These studies will help us to sort out the key interactions made by HNF1c and l-INF4a in 13-cells, and eventually lead to structural and physiological studies. Structural investigation by X-ray crystallography will help us to understand the atomic details of functional complex formation made by these 3-cell-specific master regulators and disruption by MODY mutations. In the long run, physiological studies will be designed to address the importance of these key interactions and the pathways involved in normal insulin secretion from 13-cells. These findings should be valuable in understanding the transcription regulatory mechanisms by HNF1x and HNF4a, and rational targeting of these transcription factors in order to modulate their activities, promote regeneration of 13-cells, enhance 13-cell function, and reverse the adverse effects by the mutations, thus potential treatments for various forms of diabetes.