Plasma Membrane Subdomain Compartmentalization Contributes to Distinct Mechanisms of Ceramide Action on Insulin Signaling

  1. Eric Hajduch1,2,3
  1. 1Centre de Recherche des Cordeliers, INSERM, UMR-S 872, Paris, France;
  2. 2Université Pierre et Marie Curie–Paris 6, UMR-S 872, Paris, France;
  3. 3Université Paris Descartes, UMR-S 872, Paris, France;
  4. 4Division of Endocrinology, University of Pittsburgh, Pittsburgh, Pennsylvania.
  1. Corresponding author: Eric Hajduch, eric.hajduch{at}crc.jussieu.fr.

Abstract

OBJECTIVE Ceramide is now recognized as a negative regulator of insulin signaling by impairing protein kinase B (PKB)/Akt activation. In different cells, two distinct mechanisms have been proposed to mediate ceramide inhibition of PKB/Akt: one involving atypical protein kinase C zeta (PKCζ) and the other the protein phosphatase-2 (PP2A). We hypothesized that ceramide action through PKCζ or PP2A might depend on plasma membrane (PM) structural organization and especially on caveolin-enriched domain (CEM) abundance.

RESEARCH DESIGN AND METHODS We have used different PKCζ mutant constructs or the PP2A inhibitor, okadaic acid (OKA), to selectively inhibit PKCζ- and PP2A-dependent pathways in cells expressing different caveolin-1 levels and evaluated the impact of insulin and ceramide on PKB/Akt activity in different PM subdomains.

RESULTS Although the PKCζ-mediated negative effect of ceramide on insulin-stimulated PKB/Akt was dominant in adipocytes, a ceramide action through PP2A outside CEMs, prevented by OKA, was also unraveled. To test the importance of CEM to direct ceramide action through the PKCζ pathway, we treated 3T3-L1 preadipocytes devoid of CEMs with ceramide and we saw a shift of the lipid-negative action on PKB/Akt to a PP2A-mediated mechanism. In fibroblasts with low CEM abundance, the ceramide-activated PP2A pathway dominated, but could be shifted to a ceramide-activated PKCζ pathway after caveolin-1 overexpression.

CONCLUSIONS Our results show that ceramide can switch from a PKCζ-dependent mechanism to a PP2A pathway, acting negatively on PKB/Akt, and hence revealing a critical role of CEMs of the PM in this process.

Footnotes

  • 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.

    • Received June 17, 2009.
    • Accepted November 23, 2009.
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  1. Diabetes vol. 59 no. 3 600-610
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