title: Targeting of PKCzeta and PKB to caveolin-enriched microdomains represents a crucial step underpinning the disruption in PKB-directed signalling by ceramide.
abstract: Elevated ceramide concentrations in adipocytes and skeletal muscle impair PKB (protein kinase B; also known as Akt)-directed insulin signalling to key hormonal end points. An important feature of this inhibition involves the ceramide-induced activation of atypical PKCzeta (protein kinase C-zeta), which associates with and negatively regulates PKB. In the present study, we demonstrate that this inhibition is critically dependent on the targeting and subsequent retention of PKCzeta-PKB within CEM (caveolin-enriched microdomains), which is facilitated by kinase interactions with caveolin. Ceramide also recruits PTEN (phosphatase and tensin homologue detected on chromosome 10), 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 PKCzeta 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 CEM contribute significantly to ceramide-induced inhibition of PKB-directed signalling.
authors.affiliation: Centre de Recherche des Cordeliers, Paris F-75006, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Hajduch
authors.forename: Sophie
authors.initials: S
authors.lastname: Turban
authors.forename: Xavier
authors.initials: X
authors.lastname: Le Liepvre
authors.forename: Soazig
authors.initials: S
authors.lastname: Le Lay
authors.forename: Christopher
authors.initials: C
authors.lastname: Lipina
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Dimopoulos
authors.forename: Isabelle
authors.initials: I
authors.lastname: Dugail
authors.forename: Harinder S
authors.initials: HS
authors.lastname: Hundal
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000201:enzymology; D000818:Animals; D051242:Caveolin 1 / Q000172:deficiency; D002518:Ceramides / Q000494:pharmacology*; D002784:Cholesterol / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D007328:Insulin / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000201:enzymology; D011493:Protein Kinase C / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction; D000099221:Protein Kinase C zeta
chemical_list: D051242:Caveolin 1; D002518:Ceramides; D002784:Cholesterol; D007328:Insulin; D011493:Protein Kinase C; D051057:Proto-Oncogene Proteins c-akt; D000099221:Protein Kinase C zeta