Pigment epithelium-derived factor (PEDF) ameliorates advanced glycation end product (AGE)-induced hepatic insulin resistance in vitro by suppressing Rac-1 activation.
Advanced glycation end products (AGEs) could be implicated in insulin resistance. However, the molecular mechanisms underlying this are not fully understood. Since pigment epithelium-derived factor (PEDF) blocks the AGE-signaling pathways, we examined here whether and how PEDF improves insulin resistance in AGE-exposed hepatoma cells, Hep3B cells. Proteins were extracted from Hep3B cells, immunoprecipitated with or without insulin receptor substrate-1 (IRS-1) antibodies, and subjected to Western blot analysis. Glycogen synthesis was measured using [ (14)C]-d-glucose. AGE induced Rac-1 activation and increased phosphorylation of IRS-1 at serine-307 residues, JNK, c-JUN, and IkappaB kinase in association with decreased IkappaB levels in Hep3B cells. PEDF or overexpression of dominant negative Rac-1 blocked these effects of AGE on Hep3B cells. Further, AGEs decreased tyrosine phosphorylation of IRS-1, and subsequently reduced the association of p85 subunit of phosphatidylinositol 3-kinase with IRS-1 and glycogen synthesis in insulin-exposed Hep3B cells, all of which were inhibited by PEDF. Our present study suggests that PEDF could improve the AGE-elicited insulin resistance in Hep3B cells by inhibiting JNK- and IkappaB kinase-dependent serine phosphorylation of IRS-1 via suppression of Rac-1 activation. PEDF may play a protective role against hepatic insulin resistance in diabetes.
Yoshida
T
T
Department of Medicine, Kurume University School of Medicine, Kurume, Japan.
Yamagishi
S
S
Nakamura
K
K
Matsui
T
T
Imaizumi
T
T
Takeuchi
M
M
Koga
H
H
Ueno
T
T
Sata
M
M
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D005136:Eye Proteins / Q000494:pharmacology*; D005799:Genes, Dominant; D017127:Glycation End Products, Advanced / Q000494:pharmacology*; D006003:Glycogen / Q000096:biosynthesis; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism; D020672:I-kappa B Proteins / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D000072000:NF-KappaB Inhibitor alpha; D009414:Nerve Growth Factors / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D015843:Serpins / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*; D000099174:Pigment Epithelium-Derived Factor
D048868:Adaptor Proteins, Signal Transducing; D005136:Eye Proteins; D017127:Glycation End Products, Advanced; D006003:Glycogen; D051550:I-kappa B Kinase; D020672:I-kappa B Proteins; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D000072000:NF-KappaB Inhibitor alpha; D009414:Nerve Growth Factors; D010750:Phosphoproteins; D019000:Phosphotyrosine; D015843:Serpins; D020830:rac1 GTP-Binding Protein; D000099174:Pigment Epithelium-Derived Factor; C526292:IRS1 protein, human; C000606204:NFKBIA protein, human