GSK-J1 is selective for H3K27 demethylases of the KDM6 subfamily and specifically binds to endogenous JMJD3. GSK-J1 inhibits TNF-α production by human primary macrophages in an H3K27-dependent manner. GSK-J1 inhibits the demethylase activity of KDM5C with 8.5-fold increased potency compared with that of KDM5B at 1 mM α-ketoglutarate, with IC50 of 11 μM and 94 μM, respectively.