Inhibitory effect of ceramide on insulin-induced protein kinase Czeta translocation in rat adipocytes.
Ceramide has been confirmed to be a signal mediator of apoptosis that is induced by tumor necrosis factor-alpha (TNF-alpha). It has also been reported that ceramide may induce insulin resistance as well as TNF-alpha. We investigated the effect of ceramide on insulin signaling pathways, such as insulin receptor (IR) beta-subunit, insulin receptor substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and protein kinase Czeta (PKCzeta) in rat adipocytes. We examined insulin-stimulated [(3)H]2-deoxyglucose (2-DOG) uptake in rat adipocytes pretreated with N-hexanoylsphingosine (C(6)-ceramide, 10 to 30 micromol/L). Insulin-induced 2-DOG uptake was significantly reduced by C(6)-ceramide pretreatment. We also examined the effect of various concentrations of C(6)-ceramide pretreatment on insulin-induced autophosphorylation of the IR beta-subunit, tyrosine phosphorylation of IRS-1, enzyme activity of PI3K, and membrane-associated PKCzeta immunoreactivity. Pretreatment with C(6)-ceramide significantly reduced autophosphorylation of the IR beta-subunit, tyrosine phosphorylation of IRS-1, and enzyme activity of PI3K. Moreover, membrane-associated PKCzeta immunoreactivity and immunoprecipitable PKCzeta enzyme activity, downstream of PI3K, were significantly suppressed by C(6)-ceramide pretreatment. These results suggest that ceramide may induce insulin resistance via the suppression of IRS-1-PI3K signaling, and subsequent activation of PKCzeta.
Miura
Atsushi
A
Third Department of Internal Medicine, Gifu University School of Medicine, Gifu, Japan.
Kajita
Kazuo
K
Ishizawa
Masayoshi
M
Kanoh
Yoshinori
Y
Kawai
Yasunori
Y
Natsume
Yoshiyuki
Y
Sakuma
Hiroya
H
Yamamoto
Yoritsuna
Y
Yasuda
Keigo
K
Ishizuka
Tatsuo
T
D017667:Adipocytes / Q000187:drug effects / Q000201:enzymology*; D000818:Animals; D015153:Blotting, Western; D002518:Ceramides / Q000494:pharmacology*; D003847:Deoxyglucose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000201:enzymology; D010766:Phosphorylation / Q000187:drug effects; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014443:Tyrosine / Q000378:metabolism; D000099221:Protein Kinase C zeta
D002518:Ceramides; D003847:Deoxyglucose; D005947:Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D011493:Protein Kinase C; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D014443:Tyrosine; D000099221:Protein Kinase C zeta