Visit our Expo - Redox and Inflammation signaling 2012

Session III : Protein kinase cascades as therapeutic targets Poster III, 60
Molecular mechanisms of the deleterious action of ceramide on insulin signalling:
involvement of caveolae
Sophie Turban1, Xavier Lelièpvre2, Soazig Le Lay3, Olivier Bourron2, Harinder S.
Hundal1 & Eric Hajduch2.
1Department of Molecular Physiology, Dundee, UK, e-mail: s.turban@dundee.ac.uk,
2Inserm U671, Paris, France, 3Max Planck Institute, Dresden, Germany
Several studies have revealed that in peripheral tissues, insulin resistance might be associated
with intracellular formation of ceramide, the main secondary messenger of the sphingomyelin
transmembrane signalling pathway. We have recently shown that ceramide inhibited insulininduced
activation of protein kinase B (PKB), a key protein in insulin signalling, by
promoting its association and phosphorylation by protein kinase Cz (PKCz).
Caveolae are small invaginations of the plasma membrane that are enriched in cholesterol and
sphingolipids like ceramide. Interestingly, many signalling proteins such as PKCz have been
found in those microdomains. The purpose of the study was to investigate the mechanisms
involved in the negative effect of ceramide on the insulin pathway and to determinate whether
caveolae would be the place where the lipid inhibits PKB via the activation of PKCz. We
show that ceramide induces the recruitment of PKCz in the caveolin rich domain. Moreover
the concomitant recruitment of PKB is observed in those compartments. We report that
cholesterol depletion and destruction of caveolae structures in 3T3-L1 adipocytes, L6 muscle
cells and isolated human adipocytes with methyl-beta-cyclodextrin prevents the deleterious
effect of ceramide on the insulin-induced translocation and activation of PKB in the plasma
membrane. In addition we demonstrate that in isolated adipocytes from caveolin-1 knock-out
mice, ceramide did not alter the insulin-induced phosphorylation of PKB. All together these
findings indicate that in insulin sensitive tissues, ceramide inhibit PKB via PKCz within
caveolae.
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