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  • Title: c-Myb-dependent inositol 1,4,5-trisphosphate receptor type-1 expression in vascular smooth muscle cells.
    Author: Afroze T, Sadi AM, Momen MA, Gu S, Heximer S, Husain M.
    Journal: Arterioscler Thromb Vasc Biol; 2007 Jun; 27(6):1305-11. PubMed ID: 17363689.
    Abstract:
    OBJECTIVE: The IP3 receptor-1 (IP3R1) mediates Ca2+ signals critical to vascular smooth muscle cell (VSMC) proliferation. The cell cycle-associated transcription factor c-Myb increases Ca2+ at the G1/S transition. Here we show the mechanism through which c-Myb regulates expression of IP3R1. METHODS & RESULTS: Ribonuclease protection confirmed transcriptional start (TS), and qRT-PCR revealed a 6-fold increase in IP3R1 mRNA as immortalized VSMC progress from G0 to G1/S. A c-Myb neutralizing antibody decreased IP3R1 mRNA expression 3-fold, and abolished the 3.4-fold increase in IP3R1 protein observed at G1/S. Primary aortic VSMCs in culture and proliferating carotid VSMCs in vivo showed similar regulation of IP3R1 mRNA and protein. Sequence analysis of a 3.1-Kb mouse IP3R1 promoter revealed 17 putative c-Myb binding sites. Reporter assays demonstrated a 2-fold increase in promoter activity in G1/S- versus G0-synchronized VSMCs, which was abolished by functional c-Myb knockdown or deletion of promoter sequences upstream and downstream of TS. Point mutations in Myb sites-13 or -15 significantly blunted G1/S-specific promoter induction in both immortalized and primary VSMCs. Gel shift and ChIP confirmed binding of c-Myb to sites-13 and -15 in G1/S stage VSMCs. CONCLUSION: c-Myb regulates cell cycle-associated IP3R1 transcription in VSMCs via specific highly conserved Myb-binding sites in the IP3R1 promoter.
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