Recently, inhibition of Ser217/221 phosphorylation by GSK1120212/JTP-74057 in enzyme assay and cancer cells was studied by MS analysis, and it has been shown that phosphorylation of Ser217 site but not or less of Ser221 site is preferentially inhibited by this compound [30] These previous findings and results in this study highly suggest that JTP-74057, but not PD0325901, interacts with Ser217 of u-MEK and is able to fix its inactive structure resistant of phosphorylation mediated by upper kinases such as Raf. The gene discussed is RAF1; the disease is cancer.