In order to compare findings, the murine Jak1 and human JAK2 kinase domains were aligned and the relevant mutations highlighted. Notably, the JAK2 mutations E864K and V881A from this study cluster with the JAK1 mutations D895H, E897K, T901R, and L910Q in the b2 and b3 loop. The strongest mutation in the context of Jak2 V617F, G935R, clusters quite closely with the Jak1 mutation F958V/C/S/L and P960T/S in the kinase domain activation loop. This strong overlap suggests there are common WY 14643 50892-23-4 regions in the JAK kinases that are susceptible to mutations that confer inhibitor resistance. Two recent publications utilized a similar approach as this study: using mutagenesis of Jak2 V617F and incubation with ruxolitinib and mutagenized Jak2 R683G NSC 136476 Hedgehog inhibitor co-expressed with the Crlf2 receptor in BaF3 cells exposed to the BVB808 JAK2 inhibitor. The results of these mutagenesis screens have also been mapped on the mJak1/hJAK2 alignment. In sum, these studies discovered ten inhibitor-resistant mutations that cluster around the ATP-binding pocket. G935R was identified in all three groups, suggesting that G935 lies at a critical interface for inhibitor binding. Weigert et al. demonstrated that G935R displayed broad inhibitor-resistance using a wide panel of JAK2-selective inhibitors. Similarly, Y931C was isolated by both the Sattler and Weinstock groups, displayed broad inhibitor resistance. In contrast, the E864K mutation displayed narrow inhibitor resistance, suggesting that E864 is more inhibitor specific. The importance of the gatekeeper residue, M929, in Jak2 was verified by Deshpande et al. and our study, as the M929I mutation displayed resistance to JAK Inhibitor-1 and ruxolitinib. Other mutations were uniquely identified as resistant to JAK Inhibitor-I or ruxolitinib and may represent inhibitor-specific mutations. It is significant to note that all inhibitor-resistant mutations were identified in the Jak2 kinase domain and no allosteric mutations were isolated in the Jak2 pseudokinase or FERM domains. While our approach was a proof-of-concept screen that was not completed to saturation, there is considerable redundancy amongst the three reports, suggesting that fewer Jak2 residues may be critical in mediating inhibitor resistance when compared to the published BCR-ABL studies. Other JAKs have been targeted by small molecule inhibitors in the treatment of human disease. Inhibition of JAK3 has been explored as an alternative therapy to cyclosporine in transplant rejection and in treatment of rheumatoid arthritis, psoriasis, ulcerative colitis, Crohn��s disease, and dry eye syndrome. Promising clinical trial data have been observed for Tasocitinib and VX-509. In addition, Tasocitinib was also shown to be effective in inhibition of JAK3 and STAT5 activation in peripheral blood mononuclear cells isolated from Tcell leukemia and HTLV-associated myelopathy/tropical spastic paraparesis. The possibility of inhibitor resistance to these agents must not be overlooked.