MAPK4 and pachyonychia congenita: COX-2 is highly expressed in several human cancers and cancer cell lines, including PC tumor cells, and activates the PGE2/EGFR pathway, leading to cell proliferation via extracellular signal-regulated kinase 2 (ERK2) activation.49,50 A study by Zhu et al. demonstrated that miRNA-136 suppressed PC cell proliferation and invasion by targeting mitogen-activated protein kinase 4 (MAP2K4a) in vitro51.