PTGER4 and systemic sclerosis: Finally, selective ligation of the EP4 receptor (via CAY10684) yielded a comparably diminished rise in cAMP in both cell types than PGE2 or butaprost, reaching under 50% of the forskolin response in SSc lung MFs and 20% in skin (Figure 3E), suggesting that EP4 ligation results in substantially lower AC activity compared to EP2.