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1 Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States
2 Biochemistry, United States
3 Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States; Geriatric Research, Education, and Clinical Center, South Texas Veterans Health Care System-Audie L Murphy Division, San Antonio, Texas, United States
* To whom correspondence should be addressed. E-mail: binxz{at}yahoo.com.
Store-operated Ca2+ influx (SOC) plays critical roles in the activation of endothelial nitric oxide (NO) synthase (eNOS) and generation of NO. Recent studies indicate stromal interaction molecule 1 (STIM1) is the molecule responsible for SOC activation following Ca2+ depletion in the ER. Retinoic acids (RA) have beneficial effects in the treatment of renal diseases. The mechanism of the RA action is still largely unknown. In the current study we have used primary cultured rat mesangial cells to examine the effect of RA on SOC and STIM1. In these cells BK caused concentration-dependent [Ca2+]i mobilization. Treatment of the cells with RA, while had no effect on the initial peak, reduced the plateau phase of BK-mediated [Ca2+]i response, indicating the inhibition of SOC by RA. The level of STIM1 protein but not mRNA in RA treated cells was significantly reduced. RA treatment did not affect TGF-
-mediated gradual Ca2+ influx which occurred by a superoxide anion mediated mechanism, indicating RA specifically inhibited SOC. Expression of eNOS were detected in cells grown in media containing 11 and 30, but not 5.5mM glucose. Downregulation of STIM1 protein and SOC by RA or STIM1 dsRNA were associated with abolished NO production. The 26S proteasome inhibitor lactacystin blocked the RA-mediated downregulation of SOC, suggesting the involvement of ubiquitin-proteasome pathway in RA-mediated STIM1 protein downregulation. Our data suggest that glucose-induced eNOS expression and NO production in mesangial cells may contribute to hyperfiltration in diabetes and RA may prevent eNOS activation by downregulation of STIM1 and SOC.
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