TLR4-NOX4-AP-1 signaling mediates lipopolysaccharide-induced CXCR6 expression in human aortic smooth muscle cells.
CXCL16 is a transmembrane non-ELR CXC chemokine that signals via CXCR6 to induce aortic smooth muscle cell (ASMC) proliferation. While bacterial lipopolysaccharide (LPS) has been shown to stimulate CXCL16 expression in SMC, its effects on CXCR6 are not known. Here, we demonstrate that LPS upregulates CXCR6 mRNA, protein, and surface expression in human ASMC. Inhibition of TLR4 with neutralizing antibodies or specific siRNA interference blocked LPS-mediated CXCR6 expression. LPS stimulated both AP-1 (c-Fos, c-Jun) and NF-kappaB (p50 and p65) activation, but only inhibition of AP-1 attenuated LPS-induced CXCR6 expression. Using dominant negative expression vectors and siRNA interference, we demonstrate that LPS induces AP-1 activation via MyD88, TRAF6, ERK1/2, and JNK signaling pathways. Furthermore, the flavoprotein inhibitor diphenyleniodonium chloride significantly attenuated LPS-mediated AP-1-dependent CXCR6 expression, as did inhibition of NOX4 NADPH oxidase by siRNA. Finally, CXCR6 knockdown inhibited CXCL16-induced ASMC proliferation. These results demonstrate that LPS-TLR4-NOX4-AP-1 signaling can induce CXCR6 expression in ASMC, and suggest that the CXCL16-CXCR6 axis may be an important proinflammatory pathway in the pathogenesis of atherosclerosis.
Patel
Devang N
DN
Department of Veterans Affairs South Texas Veterans Health Care System, San Antonio, TX, USA.
Bailey
Steven R
SR
Gresham
John K
JK
Schuchman
David B
DB
Shelhamer
James H
JH
Goldstein
Barry J
BJ
Foxwell
Brian M
BM
Stemerman
Michael B
MB
Maranchie
Jodi K
JK
Valente
Anthony J
AJ
Mummidi
Srinivas
S
Chandrasekar
Bysani
B
D002478:Cells, Cultured; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000502:physiology*; D011112:Polymyxin B / Q000494:pharmacology; D034622:RNA Interference; D000075744:Receptors, CXCR6; D019707:Receptors, Chemokine / Q000096:biosynthesis*; D011991:Receptors, Virus / Q000096:biosynthesis*; D015398:Signal Transduction / Q000502:physiology*; D051197:Toll-Like Receptor 4 / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000502:physiology*; D015854:Up-Regulation
C106330:CXCR6 protein, human; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D000075744:Receptors, CXCR6; D019707:Receptors, Chemokine; D011991:Receptors, Virus; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D018808:Transcription Factor AP-1; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C498910:NOX4 protein, human; D011112:Polymyxin B