Targeting of PKC{zeta} and PKB to caveolin-enriched microdomains represents a crucial step underpinning the disruption in PKB-directed signaling by ceramide

Elevated ceramide concentrations in adipocytes and skeletal muscle impair PKB/Akt-directed insulin signalling to key hormonal end-points. An important feature of this inhibition involves the ceramide-induced activation of atypical PKCζ, which associates with and negatively regulates PKB. Here we demonstrate that this inhibition is critically dependent upon the targeting and subsequent retention of PKCζ-PKB within caveolin-enriched microdomains, which is facilitated by kinase interactions with caveolin. Ceramide also recruits PTEN, a 3'-phosphoinositide phosphatase, thereby creating a repressive membrane microenvironment from which PKB cannot signal. Disrupting the structural integrity of caveolae by cholesterol depletion prevented caveolar targeting of PKCζ and PKB and suppressed kinase-caveolin association, but, importantly, also ameliorated ceramide-induced inhibition of PKB. Consistent with this, adipocytes from caveolin-1(-/-) mice, which lack functional caveolae exhibit greater resistance to ceramide compared with caveolin-1(+/+) adipocytes. We conclude that the recruitment and retention of PKB within caveolin-enriched microdomains contributes significantly to ceramide-induced inhibition of PKB-directed signalling.