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PKC Mediates CCL18-Stimulated Collagen Production in Pulmonary Fibroblasts

Department of Medicine, University of Maryland School of Medicine; and Research Service, Baltimore VA Medical Center, Baltimore, Maryland

Correspondence and requests for reprints should be addressed to Dr. Sergei P. Atamas, M.D., Ph.D., University of Maryland School of Medicine, Division of Rheumatology and Clinical Immunology, 10 South Pine Street, MSTF 8-34, Baltimore, MD 21201. E-mail: satamas{at}umaryland.edu

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 (PKC, PKC, and PKC), two isoforms (PKC and PKC) have been implicated in profibrotic intracellular signaling. The role of PKC-mediated signaling in the regulation of collagen production remains unclear. In this study, PKC was found mostly in the cytoplasm, whereas PKC and PKC were found mostly in the nucleus of cultured primary pulmonary fibroblasts. In response to stimulation with CCL18, PKC but not PKC or PKC underwent rapid (within 5–10 min) transient phosphorylation and nuclear translocation. Inhibition with dominant-negative mutants of PKC and ERK2, but not PKC or PKC, 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 PKC Gö6976. Stimulation of fibroblasts with CCL18 caused an increase in intracellular calcium concentration. Consistent with the known calcium dependence of PKC signaling, blocking of the calcium signaling with the intracellular calcium-chelating agent BAPTA led to abrogation of PKC nuclear translocation, ERK2 phosphorylation, and collagen production. These observations suggest that in primary pulmonary fibroblasts, PKC but not PKC or PKC mediate the profibrotic effect of CCL18. PKC may therefore become a viable target for future antifibrotic therapies.

Key Words: chemokines • fibroblast • fibrosis • lung • signal transduction

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