CALL FOR PAPERS Cellular Mechanisms of Tissue Fibrosis Requirement for active glycogen synthase kinase-3 in TGF- 1 upregulation of connective tissue growth factor (CCN2/CTGF) levels in human gingival fibroblasts

Bahammam M, Black SA, Jr, Sume SS, Assaggaf MA, Faibish M, Trackman PC. Requirement for active glycogen synthase kinase-3 in TGF1 upregulation of connective tissue growth factor (CCN2/CTGF) levels in human gingival fibroblasts. Am J Physiol Cell Physiol 305: C581–C590, 2013. First published July 3, 2013; doi:10.1152/ajpcell.00032.2013.—Connective tissue growth factor (CCN2/CTGF) mediates transforming growth factor(TGF)-induced fibrosis. Drug-induced gingival overgrowth is tissue specific. Here the role of the phosphoinositol 3-kinase (PI3K) pathway in mediating TGF1-stimulated CCN2/CTGF expression in primary human adult gingival fibroblasts and human adult lung fibroblasts was compared. Data indicate that PI3K inhibitors attenuate upregulation of TGF1-induced CCN2/CTGF expression in human gingival fibroblasts independent of reducing JNK MAP kinase activation. Pharmacologic inhibitors and small interfering (si)RNA-mediated knockdown studies indicate that calcium-dependent isoforms and an atypical isoform of protein kinase C (PKC) do not mediate TGF1-stimulated CCN2/ CTGF expression in gingival fibroblasts. As glycogen synthase kinase-3 (GSK-3 ) can undergo phosphorylation by the PI3K/pathway, the effects of GSK-3 inhibitor kenpaullone and siRNA knockdown were investigated. Data in gingival fibroblasts indicate that kenpaullone attenuates TGF1-mediated CCN2/CTGF expression. Activation of the Wnt canonical pathways with Wnt3a, which inhibits GSK-3 , similarly inhibits TGF1-stimulated CCN2/CTGF expression. In contrast, inhibition of GSK-3 by Wnt3a does not inhibit, but modestly stimulates, CCN2/CTGF levels in primary human adult lung fibroblasts and is -catenin dependent, consistent with previous studies performed in other cell models. These data identify a novel pathway in gingival fibroblasts in which inhibition of GSK-3 attenuates CCN2/CTGF expression. In adult lung fibroblasts inhibition of GSK-3 modestly stimulates TGF1-regulated CCN2/CTGF expression. These studies have potential clinical relevance to the tissue specificity of drug-induced gingival overgrowth.