Islet β-Cell-Specific MafA Transcription Requires the 5′-Flanking Conserved Region 3 Control Domain

Abstract

MafA is a key transcriptional activator of islet β cells, and its exclusive expression within β cells of the developing and adult pancreas is distinct among pancreatic regulators. Region 3 (base pairs −8118 to −7750 relative to the transcription start site), one of six conserved 5′ cis domains of the MafA promoter, is capable of directing β-cell-line-selective expression. Transgenic reporters of region 3 alone (R3), sequences spanning regions 1 to 6 (R1-6; base pairs −10428 to +230), and R1-6 lacking R3 (R1-6^ΔR3) were generated. Only the R1-6 transgene was active in MafA⁺ insulin⁺ cells during development and in adult cells. R1-6 also mediated glucose-induced MafA expression. Conversely, pancreatic expression was not observed with the R3 or R1-6^ΔR3 line, although much of the nonpancreatic expression pattern was shared between the R1-6 and R1-6^ΔR3 lines. Further support for the importance of R3 was also shown, as the islet regulators Nkx6.1 and Pax6, but not NeuroD1, activated MafA in gel shift, chromatin immunoprecipitation (ChIP), and transfection assays and in vivo mouse knockout models. Lastly, ChIP demonstrated that Pax6 and Pdx-1 also bound to R1 and R6, potentially functioning in pancreatic and nonpancreatic expression. These data highlight the nature of the cis- and trans-acting factors controlling the β-cell-specific expression of MafA.

EL250 cells were kindly provided by D. Mortlock at Vanderbilt University Medical Center.

This work was supported by grants from the National Institutes of Health (DK50203 to R.S., DK60581 to R.G.M., VUMC9183 to B.S.-P., DK072504 to L.S., and DK083160 to C.S.H.), the American Lebanese Syrian Associated Charities (ALSAC) (to B.S.-P.), and the Vanderbilt Molecular Endocrinology Training Program (5T32 DK07563 to J.C.R.). The transgenic mice were developed with Vanderbilt Transgenic/ES shared resource grants CA68485 and DK20593. Partial support was also provided to the Molecular Biology Core Laboratory by the Vanderbilt University Diabetes Research and Training Center (Public Health Service grant P60 DK20593).