A concerted effort is being made to understand the molecular programs underlying ? cell formation and function in order to provide therapeutic insight into new diabetes treatment strategies. From these studies, the MafA transcription factor has been demonstrated to be both an essential regulator of mature ? cell function, and inactivated in mouse models of type 2 diabetes mellitus. MafA and the only other closely related large Maf protein expressed in islet cells, MafB, were originally characterized in our laboratory and elsewhere due to their respective significance in stimulating islet ? (i.e. MafA, insulin) and a cell (MafB, glucagon) hormone gene transcription. Significantly, MafA synthesis has been shown to be critical to the production of functional ? cells, with the presence of MafB in insulin+ cells associated with immature and relatively dysfunctional cells. Our analyses of MafA and MafB protein chimeras have shown that the C-terminal leucine- zipper (dimerization) region regulates the distinct endogenous insulin gene activation ability of MafA in cell-based assays, as well as in phosphorylation-dependent DNA binding in vitro. We hypothesize that these sequences also provide distinguishing activating properties to MafA in vivo. This hypothesis will be tested by analyzing the functional characteristics of transgenes expressing either a MafB/A chimera or MafB on islet ? cell function in MafA(panc mice, which lack MafA expression throughout the pancreas due to the actions of a transgenic Cre recombinase in MafAfl/fl mice. Strikingly, human islets were found to be unlike rodents by expressing MafA and MafB in ? cells. Since no other differences were observed in islet-enriched transcription factor distribution between species, our analysis of MafB transgenic mice will also provide insight into whether this factor contributes to observed changes in glucose sensing and insulin secretion characteristics between human and rodent islets. We hypothesize that the MafA C-terminal sequences create unique binding surfaces for transcriptional coregulatory proteins. Surprisingly, there is a paucity of information regarding the role these proteins play in islet ? cell development or function. We have implemented an 'in cell'chemical cross-linking strategy to isolate and characterize such molecules from mouse ? cells. Exciting preliminary data illustrate the ability of MafA to bind MLL2, Rbbp5, Ash2, Dpy30, and Wdr5, components of the euchromatin mixed lineage leukemia 2 (MLL2) histone 3 lysine 4 trimethylation complex. Experiments are proposed to determine how MLL2 influences MafA-mediated gene activation and islet ? cell function. The data generated here will provide valuable insight into the transcriptional regulatory mechanisms that will likely be impactful in the production of cellular therapeutics for diabetes treatment.
A compelling body of evidence indicates that the MafA transcription factor represents a barometer of islet ? cell functionality. Our proposed studies will focus on determining how MafA together with its transcriptional coregulators impact islet ? cell biology. We believe that our findings will be essential to the ongoing efforts to generate ? cells from ES, iPS and/or adult cell sources for T1DM treatment.
|Matsuoka, Taka-Aki; Kawashima, Satoshi; Miyatsuka, Takeshi et al. (2017) Mafa Enables Pdx1 to Effectively Convert Pancreatic Islet Progenitors and Committed Islet ?-Cells Into ?-Cells In Vivo. Diabetes 66:1293-1300|
|Hunter, Chad S; Stein, Roland W (2017) Evidence for Loss in Identity, De-Differentiation, and Trans-Differentiation of Islet ?-Cells in Type 2 Diabetes. Front Genet 8:35|
|Paul, Leena; Walker, Emily M; Drosos, Yiannis et al. (2016) Lack of Prox1 Downregulation Disrupts the Expansion and Maturation of Postnatal Murine ?-Cells. Diabetes 65:687-98|
|Dai, Chunhua; Kayton, Nora S; Shostak, Alena et al. (2016) Stress-impaired transcription factor expression and insulin secretion in transplanted human islets. J Clin Invest 126:1857-70|
|Conrad, Elizabeth; Dai, Chunhua; Spaeth, Jason et al. (2016) The MAFB transcription factor impacts islet ?-cell function in rodents and represents a unique signature of primate islet ?-cells. Am J Physiol Endocrinol Metab 310:E91-E102|
|Banerjee, Ronadip R; Cyphert, Holly A; Walker, Emily M et al. (2016) Gestational Diabetes Mellitus From Inactivation of Prolactin Receptor and MafB in Islet ?-Cells. Diabetes 65:2331-41|
|Scoville, David W; Cyphert, Holly A; Liao, Lan et al. (2015) MLL3 and MLL4 Methyltransferases Bind to the MAFA and MAFB Transcription Factors to Regulate Islet ?-Cell Function. Diabetes 64:3772-83|
|Zhu, Xiaodong; Hu, Ruiying; Brissova, Marcela et al. (2015) Microtubules Negatively Regulate Insulin Secretion in Pancreatic ? Cells. Dev Cell 34:656-68|
|Matsuoka, Taka-aki; Kaneto, Hideaki; Kawashima, Satoshi et al. (2015) Preserving Mafa expression in diabetic islet ?-cells improves glycemic control in vivo. J Biol Chem 290:7647-57|
|Conrad, Elizabeth; Stein, Roland; Hunter, Chad S (2014) Revealing transcription factors during human pancreatic ? cell development. Trends Endocrinol Metab 25:407-14|
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