MAPK3 and myalgic encephalomeyelitis/chronic fatigue syndrome: However, the ERK kinase inhibitor (PD98059) not only decreased the phosphorylation of ERK1/2 (Figure 5(e)) but also alleviated oxidative stress and NOX4 protein expression induced by PRR overexpression in CFs (Figures 4(a)–4(c) and 5(e)).