title: Association of CAD, a multifunctional protein involved in pyrimidine synthesis, with mLST8, a component of the mTOR complexes.
abstract: BACKGROUND
  mTOR is a genetically conserved serine/threonine protein kinase, which controls cell growth, proliferation, and survival. A multifunctional protein CAD, catalyzing the initial three steps in de novo pyrimidine synthesis, is regulated by the phosphorylation reaction with different protein kinases, but the relationship with mTOR protein kinase has not been known.
  
  
  RESULTS
  CAD was recovered as a binding protein with mLST8, a component of the mTOR complexes, from HEK293 cells transfected with the FLAG-mLST8 vector. Association of these two proteins was confirmed by the co-immuoprecipitaiton followed by immunoblot analysis of transfected myc-CAD and FLAG-mLST8 as well as that of the endogenous proteins in the cells. Analysis using mutant constructs suggested that CAD has more than one region for the binding with mLST8, and that mLST8 recognizes CAD and mTOR in distinct ways. The CAD enzymatic activity decreased in the cells depleted of amino acids and serum, in which the mTOR activity is suppressed.
  
  
  CONCLUSIONS
  The results obtained indicate that mLST8 bridges between CAD and mTOR, and plays a role in the signaling mechanism where CAD is regulated in the mTOR pathway through the association with mLST8.
authors.affiliation: Biosignal Research Center, Kobe University, Kobe, 657-8501, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Nakashima
authors.forename: Ippei
authors.initials: I
authors.lastname: Kawanishi
authors.forename: Sumiko
authors.initials: S
authors.lastname: Eguchi
authors.forename: Eugene Hsin
authors.initials: EH
authors.lastname: Yu
authors.forename: Satoshi
authors.initials: S
authors.lastname: Eguchi
authors.forename: Noriko
authors.initials: N
authors.lastname: Oshiro
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Yoshino
authors.forename: Ushio
authors.initials: U
authors.lastname: Kikkawa
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Yonezawa
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D001221:Aspartate Carbamoyltransferase / Q000235:genetics / Q000378:metabolism*; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / Q000235:genetics / Q000378:metabolism*; D004080:Dihydroorotase / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D057809:HEK293 Cells; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D010766:Phosphorylation; D011485:Protein Binding; D011743:Pyrimidines / Q000096:biosynthesis / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000076242:mTOR Associated Protein, LST8 Homolog
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; C033626:CAD trifunctional enzyme; C555285:MLST8 protein, human; D046912:Multiprotein Complexes; D011743:Pyrimidines; D000076242:mTOR Associated Protein, LST8 Homolog; D001221:Aspartate Carbamoyltransferase; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D004080:Dihydroorotase; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing); C030986:pyrimidine