Fig. 1.
Menin suppresses GLP1R transcript levels by binding to the GLP1R promoter and recruiting PRMT5. At 4 wk of age, Menl/l and littermates Menl/l-Ubc9-CreER mice were treated with tamoxifen (200 mg·kg body wt−1·day−1 ip) for 2 days followed by 1 day off and finally another 2 days to achieve menin excision. Sixteen weeks after tamoxifen treatment, mice were euthanized, and organs were harvested at 20 wk of age. Menin excision upon tamoxifen treatment (A) in Menf/f-Ubc9-CreER mice leads to increased GLP1R transcript in pancreatic islets (n = 4) (B) and liver (n = 3 for Menl/l and n = 6 for MenΔ/Δ) (C). D: menin-null pancreatic islet-derived menin excisable (PIME-MenΔ/Δ) cells express higher GLP1R transcript levels compared with menin expressing PIME-Menf/f cells (n = 5). Menin complemented MEF cells (MEF-Men1Δ/Δ+Menin; E) when compared with vector complemented menin-null (MEF-Men1Δ/Δ) MEF cells (triplicates), which expressed lower levels of GLP1R mRNA (F). G and H: two different amplicons were used to amplify DNA obtained by chromatin-immunoprecipitation (ChIP) using MIN6 cells. Alignment showing GLP1R promoter sequence homology (black) vs. nonhomologous region (white) between different eutherian species, including humans and primates, with Mouse-Ch17:30901346-30901495 (target region for amplicon pair 1) (G) and Mouse-Ch17:30901523-30901674 (target region for amplicon pair 2) (H) upstream from the GLP1R transcription start site (TSS, Mouse-Ch17:30901877). Chromatin-immunoprecipitation (ChIP) using MIN6 cells and quantitative RT-PCR shows greater enrichment for anti-menin (I), and anti-PRMT5 (J) antibodies compared with IgG controls (representative plots of two similar experiments). PRMT5 knockdown in MEFs (K) increases GLP1R transcript levels (L) compared with vector controls (plots of three similar experiments). Data sets are expressed as means ± SE and were analyzed using unpaired t-test. #P < 0.0001. $P = 0.0546. *P < 0.002. & P < 0.001. ¶P < 0.01.