DREAM Complex Maintenance of Human Beta Cell Quiescence

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Summary Types 1 and 2 diabetes result entirely or in part from a reduction in numbers of normally functioning pancreatic beta cells. Residual beta cells are present in most people with diabetes, suggesting that regenerative therapies may be uniquely helpful. Inducing human beta cells to regenerate has proven impossible until recently. This has changed with the discovery by several labs of drugs that inhibit the kinase, DYRK1A, and which induce human beta cells to replicate at “rates”, or more properly, “labeling indices”, of ~2%. Proliferation can be augmented by combining DYRK1A inhibitors with TGF-beta superfamily inhibitors or with GLP1 receptor agonists, generating labeling indices of 5-8%. Although these are exciting advances, they also demonstrate that >90% of human beta cells are recalcitrant to cell cycle entry. The cause of this remarkable refractoriness to proliferation is poorly understood. DYRK1A inhibition alters intracellular trafficking of the NFaT family of transcription factors. In the course of our studies on human insulinomas, we have uncovered a parallel pathway, the DREAM-MMB complex, that also restricts human beta cell proliferation. We show here that the extended family of ~200 canonical DREAM-MMB complex genes and proteins appear to be present in human beta cells, and that DREAM complex is switched from a repressive to a proliferative configuration by DYRK1A inhibition. In addition, we have also observed potential overlapping roles for Trithorax and Polycomb complexes with the DREAM complex in restraining human beta cell proliferation. Accordingly, in this application, we propose three Specific Aims: Aim 1. Complete The Characterization of the Functional DREAM-MMB Complex in the Human Beta Cell. Aim 2. Delineate Candidate DREAM-MMB Complex Target Genes in the Human Beta Cell. Aim 3. Aim 3. Define Genome-Wide Integration of Repressive and Proliferative DREAM-MMB Mediators with Trithorax and Polycomb Chromatin Regulators and DREAM Target Genes in Human Beta Cells. Our overarching goals are: 1) to clearly and comprehensively define the fundamental mechanisms that enforce quiescence in the adult human beta cell; 2) to more clearly elucidate the fundamental mechanisms through which DYRK1A inhibitors, TGFβ inhibitors and GLP1RA’s synergize to induce their remarkable rates of human beta cell proliferation; and 3) to reveal novel pathways and further expand therapeutic targets for human beta cell regeneration for diabetes.