We have previously shown that deletion of
protein kinase C epsilon (PKCε) in mice results in protection against
glucose intolerance caused by a high fat diet. This was in part due to reduced
insulin uptake by hepatocytes and
insulin clearance, which enhanced
insulin availability. Here we employed mouse embryonic fibroblasts (MEFs) derived from wildtype (WT) and PKCε-deficient (PKCε(-/-)) mice to examine this mechanistically. PKCε(-/-) MEFs exhibited reduced
insulin uptake which was associated with decreased
insulin receptor phosphorylation, while downstream signalling through IRS-1 and Akt was unaffected. Cellular fractionation demonstrated that PKCε deletion changed the localization of the
insulin receptor, a greater proportion of which co-fractionated with
flotillin-1, a marker of membrane microdomains.
Insulin stimulation resulted in redistribution of the receptor in WT cells, while this was markedly reduced in PKCε(-/-) cells. These alterations in
insulin receptor trafficking were associated with reduced expression of
CEACAM1, a receptor substrate previously shown to modulate
insulin clearance. Virally-mediated reconstitution of PKCε in MEFs increased
CEACAM1 expression and partly restored the sensitivity of the receptor to
insulin-stimulated redistribution. These data indicate that PKCε can affect
insulin uptake in MEFs through promotion of receptor-mediated endocytosis, and that this may be mediated by regulation of
CEACAM1 expression.