The adaptor molecule Lnk negatively regulates tumor necrosis factor-alpha-dependent VCAM-1 expression in endothelial cells through inhibition of the ERK1 and -2 pathways.
Lnk, with APS and SH2-B (Src homology 2-B), belongs to a family of SH2-containing proteins with potential adaptor functions. Lnk regulates growth factor and cytokine receptor-mediated pathways implicated in lymphoid, myeloid, and platelet homeostasis. We have previously shown that Lnk is expressed and up-regulated in vascular endothelial cells (ECs) in response to tumor necrosis factor-alpha (TNFalpha). In this study, we have shown that, in ECs, Lnk down-regulates the expression, at both mRNA and protein levels, of the proinflammatory molecules VCAM-1 and E-selectin induced by TNFalpha. Mechanistically, our data indicated that, in response to TNFalpha, NFkappaB/p65 phosphorylation and translocation as well as IkappaBalpha phosphorylation and degradation were unchanged, suggesting that Lnk does not modulate NFkappaB activity. However, Lnk activates phosphatidylinositol 3-kinase (PI3K) as reflected by Akt phosphorylation. Our results identify endothelial nitric-oxide synthase as a downstream target of Lnk-mediated activation of the PI3K/Akt pathway and HO-1 as a new substrate of Akt. We found that sustained Lnk-mediated activation of PI3K in TNFalpha-activated ECs correlated with the inhibition of ERK1/2 phosphorylation, whereas phosphorylation of p38 and c-Jun NH(2)-terminal kinase (JNK) mitogen-activated protein kinases (MAPKs) was unchanged. ERK1/2 inhibition decreases VCAM-1 expression in TNFalpha-treated ECs. Collectively, our results identify the adaptor Lnk as a negative regulator in the TNFalpha-signaling pathway mediating ERK inhibition and suggest a role for Lnk in the interplay between PI3K and ERK triggered by TNFalpha in ECs.
Fitau
Juliette
J
INSERM, U643, Nantes, France.
Boulday
Gwénola
G
Coulon
Flora
F
Quillard
Thibaut
T
Charreau
Béatrice
B
D048868:Adaptor Proteins, Signal Transducing; D001483:Base Sequence; D002478:Cells, Cultured; D017931:DNA Primers; D004730:Endothelium, Vascular / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011506:Proteins / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D019010:Vascular Cell Adhesion Molecule-1 / Q000235:genetics* / Q000276:immunology
D048868:Adaptor Proteins, Signal Transducing; D017931:DNA Primers; D047908:Intracellular Signaling Peptides and Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D011506:Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D019010:Vascular Cell Adhesion Molecule-1; C490778:SH2B3 protein, human