title: Intestinal cell kinase (ICK) promotes activation of mTOR complex 1 (mTORC1) through phosphorylation of Raptor Thr-908.
abstract: Intestinal cell kinase (ICK), named after its cloning origin, the intestine, is actually a ubiquitously expressed and highly conserved serine/threonine protein kinase. Recently we reported that ICK supports cell proliferation and G(1) cell cycle progression. ICK deficiency significantly disrupted the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) signaling events. However, the biological substrates that mediate the downstream signaling effects of ICK in proliferation and the molecular mechanisms by which ICK interacts with mTORC1 are not well defined. Our prior studies also provided biochemical evidence that ICK interacts with the mTOR/Raptor complex in cells and phosphorylates Raptor in vitro. In this report, we investigated whether and how ICK targets Raptor to regulate the activity of mTORC1. Using the ICK substrate consensus sequence [R-P-X-S/T-P/A/T/S], we identified a putative phosphorylation site, RPGT908T, for ICK in human Raptor. By mass spectrometry and a phospho-specific antibody, we showed that Raptor Thr-908 is a novel in vivo phosphorylation site. ICK is able to phosphorylate Raptor Thr-908 both in vitro and in vivo and when Raptor exists in protein complexes with or without mTOR. Although expression of the Raptor T908A mutant did not affect the mTORC1 integrity, it markedly impaired the mTORC1 activation by insulin or by overexpression of the small GTP-binding protein RheB under nutrient starvation. Our findings demonstrate an important role for ICK in modulating the activity of mTORC1 through phosphorylation of Raptor Thr-908 and thus implicate a potential signaling mechanism by which ICK regulates cell proliferation and division.
authors.affiliation: Department of Medicine, University of Virginia, Charlottesville, Virginia 22908, USA.
authors.forename: Di
authors.initials: D
authors.lastname: Wu
authors.forename: Jessica R
authors.initials: JR
authors.lastname: Chapman
authors.forename: Lifu
authors.initials: L
authors.lastname: Wang
authors.forename: Thurl E
authors.initials: TE
authors.lastname: Harris
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Shabanowitz
authors.forename: Donald F
authors.initials: DF
authors.lastname: Hunt
authors.forename: Zheng
authors.initials: Z
authors.lastname: Fu
mesh_terms: D041721:3T3-L1 Cells; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D018797:Cell Cycle Proteins; D049109:Cell Proliferation; D016384:Consensus Sequence; D016193:G1 Phase; D057809:HEK293 Cells; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D046912:Multiprotein Complexes; D016297:Mutagenesis, Site-Directed; D009479:Neuropeptides / Q000378:metabolism; D009842:Oligopeptides / Q000737:chemistry; D010446:Peptide Fragments / Q000737:chemistry; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D011506:Proteins / Q000378:metabolism*; D000076205:Ras Homolog Enriched in Brain Protein; D000076223:Regulatory-Associated Protein of mTOR; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D046912:Multiprotein Complexes; D009479:Neuropeptides; D009842:Oligopeptides; D010446:Peptide Fragments; D010750:Phosphoproteins; D011506:Proteins; C490211:RHEB protein, human; C463659:RPTOR protein, human; D000076205:Ras Homolog Enriched in Brain Protein; D000076223:Regulatory-Associated Protein of mTOR; D010769:Phosphothreonine; C097276:CILK1 protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D017346:Protein Serine-Threonine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; D020559:Monomeric GTP-Binding Proteins