miR-375 Targets 3′-Phosphoinositide–Dependent Protein Kinase-1 and Regulates Glucose-Induced Biological Responses in Pancreatic β-Cells

  1. Abdelfattah El Ouaamari12,
  2. Nadine Baroukh12,
  3. Geert A. Martens3,
  4. Patricia Lebrun12,
  5. Daniel Pipeleers3 and
  6. Emmanuel van Obberghen12
  1. 1Institut National de la Santé et de la Recherche Médicale, U907, Nice, France
  2. 2Université de Nice-Sophia Antipolis, Faculté de Médecine, Institut de Génétique et Signalisation Moléculaire, IFR 50, Nice, France
  3. 3Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium
  1. Corresponding author: Emmanuel Van Obberghen, emmanuel.van-obberghen{at}unice.fr

Abstract

OBJECTIVE—MicroRNAs are short, noncoding RNAs that regulate gene expression. We hypothesized that the phosphatidylinositol 3-kinase (PI 3-kinase) cascade known to be important in β-cell physiology could be regulated by microRNAs. Here, we focused on the pancreas-specific miR-375 as a potential regulator of its predicted target 3′-phosphoinositide–dependent protein kinase-1 (PDK1), and we analyzed its implication in the response of insulin-producing cells to elevation of glucose levels.

RESEARCH DESIGN AND METHODS—We used insulinoma-1E cells to analyze the effects of miR-375 on PDK1 protein level and downstream signaling using Western blotting, glucose-induced insulin gene expression using quantitative RT-PCR, and DNA synthesis by measuring thymidine incorporation. Moreover, we analyzed the effect of glucose on miR-375 expression in both INS-1E cells and primary rat islets. Finally, miR-375 expression in isolated islets was analyzed in diabetic Goto-Kakizaki (GK) rats.

RESULTS—We found that miR-375 directly targets PDK1 and reduces its protein level, resulting in decreased glucose-stimulatory action on insulin gene expression and DNA synthesis. Furthermore, glucose leads to a decrease in miR-375 precursor level and a concomitant increase in PDK1 protein. Importantly, regulation of miR-375 expression by glucose occurs in primary rat islets as well. Finally, miR-375 expression was found to be decreased in fed diabetic GK rat islets.

CONCLUSIONS—Our findings provide evidence for a role of a pancreatic-specific microRNA, miR-375, in the regulation of PDK1, a key molecule in PI 3-kinase signaling in pancreatic β-cells. The effects of glucose on miR-375 are compatible with the idea that miR-375 is involved in glucose regulation of insulin gene expression and β-cell growth.

Footnotes

  • Published ahead of print at http://diabetes.diabetesjournals.org on 30 June 2008.

    Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/ for details.

    The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

    See accompanying commentary, p. 2567.

    • Accepted June 20, 2008.
    • Received November 15, 2007.
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  1. Diabetes vol. 57 no. 10 2708-2717
  1. All Versions of this Article:
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