C-reactive protein inhibits insulin activation of endothelial nitric oxide synthase via the immunoreceptor tyrosine-based inhibition motif of FcgammaRIIB and SHIP-1.
Insulin promotes the cardiovascular protective functions of the endothelium including NO production by endothelial NO synthase (eNOS), which it stimulates via Akt kinase which phosphorylates eNOS Ser1179. C-reactive protein (CRP) is an acute-phase reactant that is positively correlated with cardiovascular disease risk in patients with type 2 diabetes. We previously showed that CRP inhibits eNOS activation by insulin by blunting Ser1179 phosphorylation. We now elucidate the underlying molecular mechanisms. We first show in mice that CRP inhibits insulin-induced eNOS phosphorylation, indicating that these processes are operative in vivo. In endothelial cells we find that CRP attenuates insulin-induced Akt phosphorylation, and CRP antagonism of eNOS is negated by expression of constitutively active Akt; the inhibitory effect of CRP on Akt is also observed in vivo. A requirement for the IgG receptor FcgammaRIIB was demonstrated in vitro using blocking antibody, and reconstitution experiments with wild-type and mutant FcgammaRIIB in NIH3T3IR cells revealed that these processes require the ITIM (immunoreceptor tyrosine-based inhibition motif) of the receptor. Furthermore, we find that endothelium express SHIP-1 (Src homology 2 domain-containing inositol 5'-phosphatase 1), that CRP induces SHIP-1 stimulatory phosphorylation in endothelium in culture and in vivo, and that SHIP-1 knockdown by small interfering RNA prevents CRP antagonism of insulin-induced eNOS activation. Thus, CRP inhibits eNOS stimulation by insulin via FcgammaRIIB and its ITIM, SHIP-1 activation, and resulting blunted activation of Akt. These findings provide mechanistic linkage among CRP, impaired insulin signaling in endothelium, and greater cardiovascular disease risk in type 2 diabetes.
Division of Pulmonary and Vascular Biology, Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Keiji
K
Tanigaki
Chieko
C
Mineo
Ivan S
IS
Yuhanna
Ken L
KL
Chambliss
Michael J
MJ
Quon
Ezio
E
Bonvini
Philip W
PW
Shaul
D016475:3T3 Cells; D000818:Animals; D001011:Aorta; D002097:C-Reactive Protein / Q000276:immunology*; D002417:Cattle; D004730:Endothelium, Vascular / Q000502:physiology*; D004789:Enzyme Activation; D006801:Humans; D000072181:Inositol Polyphosphate 5-Phosphatases; D007329:Insulin Antagonists / Q000494:pharmacology*; D051379:Mice; D052250:Nitric Oxide Synthase Type III / Q000276:immunology / Q000378:metabolism*; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000276:immunology / Q000502:physiology*; D010766:Phosphorylation; D017452:Receptors, IgG / Q000276:immunology / Q000502:physiology*; D015398:Signal Transduction
C499173:FCGR2B protein, human; D007329:Insulin Antagonists; D017452:Receptors, IgG; D002097:C-Reactive Protein; D052250:Nitric Oxide Synthase Type III; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases; C000606430:INPP5D protein, human; C000606433:Inpp5d protein, mouse; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases