MK2 SUMOylation inhibits kinase activity. (A) The effect of SUMOylation on MK2 kinase activity was evaluated by in vitro assays using recombinant HSP27 as a substrate. A representative autoradiogram is shown, along with a SUMOylation assay to show MK2 SUMOylation expression levels. For details, please see “Methods.” Note the increase of HSP27 phosphorylation by MK2-K339R (lane 5) versus WT-MK2 (lane 3). Also note the inhibition of HSP27 phosphorylation by SUMOylated WT-MK2 (lane 6) and that this effect was not seen in the SUMOylation-deficient K339R mutant (lane 8). (B) Densitometry quantification of HSP27 phosphorylation. (A-B) Representative images from 1 of 3 independent experiments and quantitative data are shown (n = 3). Values are means ± SEM. *P < .05; **P < .01.