mTOR-raptor binds and activates SGK1 to regulate p27 phosphorylation.
The cell-cycle effects of mTORC1 are not fully understood. We provide evidence that mTOR-raptor phosphorylates SGK1 to modulate p27 function. Cellular mTOR activation, by refeeding of amino acid-deprived cells or by TSC2 shRNA, activated SGK1 and p27 phosphorylation at T157, and both were inhibited by short-term rapamycin treatment and by SGK1 shRNA. mTOR overexpression activated both Akt and SGK1, causing TGF-beta resistance through impaired nuclear import and cytoplasmic accumulation of p27. Rapamycin or raptor shRNA impaired mTOR-driven p70 and SGK1 activation, but not that of Akt, and decreased cytoplasmic p27. mTOR/raptor/SGK1 complexes were detected in cells. mTOR phosphorylated SGK1, but not SGK1-S422A, in vitro. SGK1 phosphorylated p27 in vitro. These data implicate SGK1 as an mTORC1 (mTOR-raptor) substrate. mTOR may promote G1 progression in part through SGK1 activation and deregulate the cell cycle in cancers through both Akt- and SGK-mediated p27 T157 phosphorylation and cytoplasmic p27 mislocalization.
Braman Family Breast Cancer Institute, Sylvester Comprehensive Cancer Center, University of Miami, Miami, FL 33136, USA.
Feng
F
Hong
Michelle D
MD
Larrea
Cheryl
C
Doughty
David J
DJ
Kwiatkowski
Rachel
R
Squillace
Joyce M
JM
Slingerland
D002453:Cell Cycle / Q000502:physiology*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004789:Enzyme Activation; D006706:Homeostasis; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism*; D007700:Kinetics; D008545:Melanoma; D010766:Phosphorylation; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism*; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases; D014162:Transfection; D000099184:Serum-Glucocorticoid Regulated Kinases
D017874:Immediate-Early Proteins; D018809:Proliferating Cell Nuclear Antigen; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins; D058570:TOR Serine-Threonine Kinases; D000099184:Serum-Glucocorticoid Regulated Kinases; C413374:p27 antigen; C546842:MTOR protein, human