Targeting of PKCzeta and PKB to caveolin-enriched microdomains represents a crucial step underpinning the disruption in PKB-directed signalling by ceramide.
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.
Hajduch
Eric
E
Centre de Recherche des Cordeliers, Paris F-75006, France.
Turban
Sophie
S
Le Liepvre
Xavier
X
Le Lay
Soazig
S
Lipina
Christopher
C
Dimopoulos
Nikolaos
N
Dugail
Isabelle
I
Hundal
Harinder S
HS
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
D051242:Caveolin 1; D002518:Ceramides; D002784:Cholesterol; D007328:Insulin; D011493:Protein Kinase C; D051057:Proto-Oncogene Proteins c-akt; D000099221:Protein Kinase C zeta