MAP2K4 and Parkinson disease: The increased phosphorylation of c-Jun in the brain of MPTP-treated mice suggested an enhancement of c-Jun transcription through JNK activation (Zhou et al., 2015) as previously reported (Derijard et al., 1994), suggesting that MPTP-induced MKK4/JNK/c-Jun signaling is involved in DA neurons degeneration in PD.