MAPK1 and rheumatoid arthritis: In RA, JMJD3 was activated by ERK/MAPK signaling, and the increased JMJD3 led to a lower H3K27me3 mark on the promoter of the proliferating cell nuclear antigen (PCNA) gene, which resulted in the elevated transcription of PCNA and aggressive phenotype of RA (Jia et al. 2018).