The Btk inhibitor LFM-A13 is a potent inhibitor of Jak2 kinase activity

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Abstract
LFMA13, or α-cyano-β-hydroxy-β-methyl-N-(2,5-dibromophenyl)propenamide, was shown to inhibit Brutons tyrosine kinase (Btk). Here we show that LFM-A13 efficiently inhibits erythropoietin (Epo)-induced phosphorylation of the erythropoietin receptor, Janus kinase 2 (Jak2) and downstream signalling molecules. However, the tyrosine kinase activity of immunoprecipitated or in vitro translated Btk and Jak2 was equally inhibited by LFM-A13 in in vitro kinase assays. Finally, Epo-induced signal transduction was also inhibited in cells lacking Btk. Taken together, we conclude that LFM-A13 is a potent inhibitor of Jak2 and cannot be used as a specific tyrosine kinase inhibitor to study the role of Btk in Jak2-dependent cytokine signalling.