PKCα Mediates CCL18-Stimulated Collagen Production in Pulmonary Fibroblasts

A CC chemokine, CCL18, has been previously reported to stimulate collagen production in pulmonary fibroblasts. This study focused on the role of protein kinase C (PKC) in the profibrotic signaling activated by CCL18 in pulmonary fibroblasts. Of the three PKC isoforms that are predominantly expressed in fibroblasts (PKCα, PKCδ, and PKCε), two isoforms (PKCδ and PKCε) have been implicated in profibrotic intracellular signaling. The role of PKCα-mediated signaling in the regulation of collagen production remains unclear. In this study, PKCα was found mostly in the cytoplasm, whereas PKCδ and PKCε were found mostly in the nucleus of cultured primary pulmonary fibroblasts. In response to stimulation with CCL18, PKCα but not PKCδ or PKCε underwent rapid (within 5–10 min) transient phosphorylation and nuclear translocation. Inhibition with dominant-negative mutants of PKCα and ERK2, but not PKCδ or PKCε, abrogated CCL18-stimulated ERK2 phosphorylation and collagen production. The effect of CCL18 on collagen production and the activity of collagen promoter reporter constructs were also abrogated by a selective pharmacologic inhibitor of PKCα Gö6976. Stimulation of fibroblasts with CCL18 caused an increase in intracellular calcium concentration. Consistent with the known calcium dependence of PKCα signaling, blocking of the calcium signaling with the intracellular calcium-chelating agent BAPTA led to abrogation of PKCα nuclear translocation, ERK2 phosphorylation, and collagen production. These observations suggest that in primary pulmonary fibroblasts, PKCα but not PKCδ or PKCε mediate the profibrotic effect of CCL18. PKCα may therefore become a viable target for future antifibrotic therapies