Inflammatory mediators modulate thrombin and cathepsin-G signaling in human bronchial fibroblasts by inducing expression of proteinase-activated receptor-4
American Journal of Physiology - Lung Cellular and Molecular Physiology
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Human lung fibroblasts express proteinase-activated receptor-1 (PAR 1), PAR2 and PAR3, but not PAR4. Because PAR2 has inflammatory effects on human primary bronchial fibroblasts (HPBF), we asked 1) whether the inflammatory mediators TNF-α and LPS could modify HPBF PAR expression and 2) whether modified PAR expression altered HPBF responsiveness to PAR agonists in terms of calcium signaling and cell growth. TNF-α and LPS induced PAR4 mRNA expression (RT-PCR) at 6 h and 24 h, respectively. TNF-α and LPS also upregulated PAR2 mRNA expression with similar kinetics but had negligible effect on PAR1 and PAR3. Flow cytometry for PAR1, PAR2, and PAR3 also demonstrated selective PAR2 upregulation in response to TNF-α and LPS. Intracellular calcium signaling to SLIGKV-NH2 (a selective PAR2-activating peptide; PAR2-AP) and AYPGQV-NH2 (PAR4-AP) revealed that TNF-α and LPS induced maximal responses to these PAR agonists at 24 h and 48 h, respectively. Upregulation of PAR2 by TNF-α heightened HPBF responses to trypsin, while PAR4 induction enabled cathepsin-G-mediated calcium signaling. Cathepsin-G also disarmed PAR 1 and PAR2 in HPBF, while tryptase disarmed PAR 2. Induction of PAR4 also enabled thrombin to elicit a calcium signal through both PAR1 and PAR4, as determined by a desensitization assay. In cell growth assays the PAR4 agonists cathepsin-G and AYPGQV-NH2 reduced HPBF cell number only in TNF-α-treated HPBF. Moreover, the mitogenic effect of thrombin (a PAR 1/PAR4 agonist) but not the PAR1-AP TFLLR-NH2, was ablated in TNF-α-treated HPBF. These findings point to an important mechanism, whereby cellular responses to thrombin and cathepsin-G can be modified during an inflammatory response. Copyright © 2007 the American Physiological Society.