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Zheng Wang, Hua Yang, Jose E. Capo-Aponte, Nili Parekh, Peter S. Reinach; Tak1 Interactions With TRPV1 and CB1 Control IL-6 and IL-8 Release in Human Corneal Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):416.
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Corneal epithelial injury-induced transient receptor potential vanilloid 1 (TRPV1) channel activation provokes inflammation through increases in IL-6 and IL-8 release whereas costimulation of the cannabinoid receptor subtype 1 (CB1) blunts this response. We determined in SV40-immortalized human corneal epithelial cells (HCEC) if the opposing effects elicited by TRPV1 and CB1 activation on IL-6 and IL-8 release are elicited through differential modulation of JNK1/2 and NF-ΚB activation through changes in transforming growth factor-β-activated kinase 1 (TAK1) phosphorylation.
HCEC lysates were coimmunoprecipated with either anti TRPV1, TAK1, CB1 or TAB1 antibodies followed by Western blotting with an appropriate antibody to probe for protein-protein interactions. Changes in I-ΚB phosphorylation status provided readout of NF-ΚB activation. ELISA determined the individual effects of TRPV1 and CB1 activation as well as TAK1 inhibition on IL-6 and IL-8 release.
Ten µM capsaicin or 5 µM WIN55,212-2 induced transient activation through interactions between TRPV1 and CB1. These receptors also had the same effects on TAK1 as well as its associated partner, TAB1. TRPV1 and CB1-induced TAK1 phosphorylation (i.e. activation) was larger and invariant during exposure to 1 µM okadaic acid. Capsaicin induced larger increases in TAK1 phosphorylation than those caused by 10 µM WIN55,212-2. These effects were eliminated by either 5 µM capsazepine or AM251, respectively. Receptor-induced TAK1, JNK1/2, I-ΚB phosphorylation and increases in IL-6 and IL-8 release were fully blocked by a selective TAK1 inhibitor, 10 nM (5Z)-7-oxozeaenol.
Capsaicin-induced TAK1-TAB1 complexation mediates IL-6 and IL-8 increases through JNK1/2 and NF-ΚB phosphorylation. Differences in the magnitude of TAK1 activation induced by either TRPV1 or CB1 stimulation may help explain why only capsaicin induced rises in IL-6 and IL-8 release. TAK1 may be a drug target to reduce injury-induced corneal inflammation without compromising TRPV1-induced increases in corneal wound healing.
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