Investigating the role of the Pdx1 C-terminal interaction domains during pancreatic endocrine differentiation and proliferation.

Vanderbilt University, Nashville TN

Investigators

Abstract

Project Summary/Abstract Diabetes is characterized by a reduction in functional insulin-producing β cells within the pancreatic islet, leading to the onset of hyperglycemia. Establishment of adult -cell mass occurs during gestation and is highly variable across the human population. Individuals that are born with less -cell mass may have increased risk of developing Type 2 Diabetes (T2D) later in life. Current studies aim to create therapies by generating new replacement  cells in vitro or expanding existing  cells in vivo, raising the relevance for understanding the molecular mechanisms controlling both differentiation and proliferation of β cells. Known transcriptional networks regulate pancreas organogenesis. One key member of this network is the homeobox transcription factor, pancreatic and duodenal homeobox 1 (Pdx1) which is essential for -cell differentiation and proliferation. Our published data revealed that  cells lacking Pdx1 or with ectopically high Pdx1 levels fail to progress through the cell cycle.  cells with elevated Pdx1 are also more likely to undergo apoptosis. Taken together, these data suggest that dynamic regulation of Pdx1 levels is required for β-cell proliferation and maintenance of functional β-cell mass. Many transcription factors, including Pdx1, contain domains that mediate physical interactions with other transcriptional regulators, that directly affect target gene selection, protein stability, or function. Our group identified a motif located within the Pdx1 C-terminus, between amino acids (aa) 210-238, through which Pdx1 interacts with either Oc1/Hnf6 (aa210-238) or the E3 ubiquitin ligase substrate adapter protein, SPOP (aa224- 238). Our collaborators have shown that these interactions overlap and are mutually exclusive. Interaction of Pdx1 with SPOP results in Pdx1 degradation, while interaction with Oc1 stabilizes Pdx1 and promotes endocrine cell differentiation. Here I propose that the balance between SPOP and Oc1 interactions with the Pdx1 C- terminus directly influences the choice between proliferation or differentiation. Ultimately, the proposed studies will examine the novel role of these Pdx1 C-terminal interacting domains in vivo and will provide insight into the mechanism by which these interacting partners influence endocrine differentiation and proliferation during development. Results of the proposed studies will inform efforts to optimize directed differentiation of β cells ex vivo for cell-based therapies and in vivo to expand β-cell mass in individuals with diabetes.