DEPTOR is a recently identified inhibitor of the mTOR kinase that is highly regulated at the posttranslational level. In response to mitogens, we found that DEPTOR was rapidly phosphorylated on three serines in a conserved degron, facilitating binding and ubiquitylation by the F box protein βTrCP, with consequent proteasomal degradation of DEPTOR. Phosphorylation of the βTrCP degron in DEPTOR is executed by CK1α after a priming phosphorylation event mediated by either the mTORC1 or mTORC2 complexes. Blocking the βTrCP-dependent degradation of DEPTOR via βTrCP knockdown or expression of a stable DEPTOR mutant that is unable to bind βTrCP results in mTOR inhibition. Our findings reveal that mTOR cooperates with CK1α and βTrCP to generate an auto-amplification loop to promote its own full activation. Moreover, our results suggest that pharmacologic inhibition of CK1 may be a viable therapeutic option for the treatment of cancers characterized by activation of mTOR-signaling pathways.
Bibliographical noteFunding Information:
The authors thank D. Foster, D. Sabatini, and W. Wei for reagents and W. Harper and W. Wei for sharing unpublished results. M.P. is grateful to T.M. Thor and K.E. Davidson for continuous support. J.R.S. is supported by the Mr. and Mrs. William G. Campbell Postdoctoral Fellowship in Memory of Carolyn Cabott from the American Cancer Society. This work was funded by grants to M.P. from the National Institutes of Health (R01-GM057587, R37-CA076584, and R21-CA161108) and the Multiple Myeloma Research Foundation. M.P. is an Investigator with the Howard Hughes Medical Institute.