Ku-0063794 is a specific inhibitor of the mammalian target of rapamycin (mTOR)
Résumé
mTOR stimulates cell growth by phosphorylating and promoting activation of AGC family kinases such as Akt, S6K and SGK. mTOR complex-1 (mTORC1) phosphorylates the hydrophobic motif of S6K, whereas mTORC2 phosphorylates the hydrophobic motif of Akt and SGK. Here we describe the small molecule Ku-0063794, which inhibits both mTORC1 and mTORC2 with an IC50 of ~10 nM, but does not suppress the activity of 76 other protein kinases or 7 lipid kinases including Class 1 PI 3-kinases at 1000-fold higher concentrations. Ku-0063794 is cell permeant, suppresses activation and hydrophobic motif phosphorylation of Akt, S6K and SGK, but not RSK, an AGC kinase not regulated by mTOR. Ku-0063794 also inhibited phosphorylation of the T-loop Thr308 residue of Akt phosphorylated by PDK1. We interpret this as implying phosphorylation of Ser473 promotes phosphorylation of Thr308 and/or induces a conformational change that protects Thr308 from dephosphorylation. In contrast, Ku-0063794 does not affect Thr308 phosphorylation in fibroblasts lacking essential mTORC2 subunits, suggesting that signalling processes have adapted to enable Thr308 phosphorylation to occur in the absence of Ser473 phosphorylation. We found that Ku-0063794 induced a much greater dephosphorylation of the mTORC1 substrate 4E-BP1 than rapamycin, even in mTORC2 deficient cells, suggesting a form of mTOR distinct from mTORC1 or mTORC2 phosphorylates 4E-BP1. Ku-0063794 also suppressed cell growth and induced a G1-cell cycle arrest. Our results indicate that Ku-0063794 will be useful in delineating the physiological roles of mTOR and may have utility in treatment of cancers in which this pathway is inappropriately activated.
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