Identification and characterisation of transcription factors that respond to nutrients in pancreatic β cells
The objective of this project was to explore the role of nutrients, mainly glucose and fatty acids, in the regulation of insulin gene expression via the complex interaction factors and positive or negative cis-acting DNA elements located throughout the promoter region, which is positioned up to 300bp. Insulin is a vital endocrine hormone, for the regulation of growth and metabolism. Synthesis of insulin occurs in pancreatic cells. The regulation of tissue- and temporal-specific insulin gene expression and its activation in response to extracellular inducers are two fundamental processes that attract many molecular biologists. Therefore to achieve the objective three major approaches were undertaken in this project. 1. Characterizing and identifying the transcription factors that bound to the negative regulatory element (NRE) within the region -258 to -280 of the human insulin promoter. This was done by applying a promising and unique method including a proteomic approach. The major findings propose NRE bind multiple positive and negative factors. 2. Studying in detail the effect of glucose on the factors that bound to the - 230 to -280 region which included NRE binding factors and PDX-1 which binds A-boxes, in various pancreatic rodent cell lines and isolated human islet of Langerhans. This study shows that the glucose stimulating response of the NRE in b cell lines and human islets does not require synergy between adjacent sequence elements such as E2 binding USF and A5 binding the PDX-1. Therefore, the NRE binding factors are able to demonstrate convincingly the existence of short-term transcriptional control of the insulin gene regulated by glucose. 3. Studying the expression of the lipogenic transcription factor SREBPs in the islets of Langerhans and their role in controlling the expression of several genes. The present study provided the first demonstration of the role of SREBPs in mediating the effect of nutrient signals, particularly glucose, on the insulin promoter and its mRNA.