MAPK3 and rheumatoid arthritis: Due to the phosphorylation of JNK, Erk1/2, and Akt signaling molecules [pathways involved in PDGF-BB signaling (16, 50)] and transformation to an aggressive phenotype [PDGF-BB playing an established role in promoting this phenotype (60, 64)] in HFLS-RA cells stimulated with Mφ-SN, we quantified PDGF-BB in Mφ-SN (U-937 derived SN).