Role of prostaglandin E2 EP receptors and cAMP in the expression of connective tissue growth factor

Wild-type (WT) Rat-1 fibroblasts express undetectable quantities of the prostaglandin E2 (PGE2) EP1, EP2, and EP3 receptor types and detectable amounts of the EP4 receptor. In the WT Rat-1, PGE2 enhances connective tissue growth factor (CTGF) mRNA. PGE2 does not stimulate cAMP production in these cells. However, forskolin induces cAMP production and ablates TGFβ-stimulated increases in CTGF mRNA. A similar pattern of CTGF expression in response to PGE2 and forskolin is observed in neonatal rat primary smooth muscle cell cultures. When WT Rat-1 cells are stably transfected with the EP2 receptor, PGE2 causes a sizable elevation in intracellular cAMP and ablates the TGFβ-stimulated increase in CTGF mRNA. PGE2 does not have this effect on cells expressing the EP1, EP3, or EP4 receptor subtypes. These results demonstrate the importance of the EP2 receptor and cAMP in the inhibition of TGFβ-stimulated CTGF production and suggest a role for PGE2 in increasing CTGF mRNA levels in the absence of the EP2 receptor. Involvement of inositol phosphate in this upregulation of CTGF expression by PGE2 is doubtful. None of the cell lines containing the four EP transfectants nor the WT Rat-1 cells responded to PGE2 with inositol phosphate production.