The histone H3 lysine 27 (H3K27) demethylase JMJD3 plays important roles in the transcriptional regulation of cell differentiation, development, the inflammatory response, and cancer. GSK-J2 is a pyridine regio-isomer of GSK-J1 which poorly inhibits JMJD3 (IC50 >100 μM), making it an appropriate negative control for in vitro studies involving GSK-J1. For in vivo research, cell-permeable prodrug forms of GSK-J1 and GSK-J2 are available as GSK-J4 and GSK-J5 , respectively. See the Structural Genomics Consortium (SGC) website for more information.