Tissue-specific mechanisms for CCN2/CTGF persistence in fibrotic Gingiva -: Interactions between cAMP and MAPK signaling pathways, and prostaglandin E2-EP3 receptor mediated activation of the c-JUN n-terminal kinase

Prostaglandin E-2 blocks transforming growth factor TGF beta 1-induced CCN2/CTGF expression in lung and kidney fibroblasts. PGE(2) levels are high in gingival tissues yet CCN2/CTGF expression is elevated in fibrotic gingival overgrowth. Gingival fibroblast expression of CCN2/CTGF in the presence of PGE2 led us to compare the regulation of CCN2/CTGF expression in fibroblasts cultured from different tissues. Data demonstrate that the TGF beta 1-induced expression of CCN2/CTGF in human lung and renal mesangial cells is inhibited by 10 nM PGE2, whereas human gingival fibroblasts are resistant. Ten nM PGE2 increases cAMP accumulation in lung but not gingival fibroblasts, which require 1 mu M PGE2 to elevate cAMP. Micromolar PGE2 only slightly reduces the TGF beta 1-stimulated CCN2/CTGF levels in gingival cells. EP2 prostaglandin receptor activation with butaprost blocks the TGF beta 1-stimulated expression of CCN2/CTGF expression in lung, but not gingival, fibroblasts. In lung fibroblasts, inhibition of the TGF beta 1-stimulated CCN2/CTGF by PGE2, butaprost, or forskolin is due to p38, ERK, and JNK MAP kinase inhibition that is cAMP-dependent. Inhibition of any two MAPKs completely blocks CCN2/CTGF expression stimulated by TGF beta 1. These data mimic the inhibitory effects of 10 nM PGE2 and forskolin that were dependent on PKA activity. In gingival fibroblasts, the sole MAPK mediating the TGF beta 1-stimulated CCN2/CTGF expression is JNK. Whereas forskolin reduces TGF beta 1-stimulated expression of CCN2/CTGF by 35% and JNK activation in gingival fibroblasts, micromolar PGE2-stimulated JNK in gingival fibroblasts and opposes the inhibitory effects of cAMP on CCN2/CTGF expression. Stimulation of the EP3 receptor with sulprostone results in a robust increase in JNK activation in these cells. Taken together, data identify two mechanisms by which TGF beta 1-stimulated CCN2/CTGF levels in human gingival fibroblasts resist down-regulation by PGE2: (i) cAMP cross-talk with MAPK pathways is limited in gingival fibroblasts; (ii) PGE2 activation of the EP3 prostanoid receptor stimulates the activation of JNK.