title: Negative regulation of TSC1-TSC2 by mammalian D-type cyclins.
abstract: The metazoan cell cycle is driven by the timely and composite activities of cyclin-dependent kinases (CDKs). Among these, cyclin D- and cyclin E-dependent kinases phosphorylate the pRb family proteins during G(1) phase of the cell cycle and thereby advance cells beyond the restriction point. Increasing evidence suggests that cyclin D-dependent kinases might affect events other than Rb pathway-mediated entry into S phase, such as accumulation of cell mass. However, little is known about cyclin D activity toward Rb-independent pathway(s) or non-pRb substrates. In this article, we show that the tumor suppressor TSC2 is a cyclin D binding protein. Coexpression of cyclin D1-CDK4/6 in cultured cells leads to increased phosphorylation and decreased detection of both TSC2 and TSC1, and promotes the phosphorylation of the mTOR substrates, 4E-BP1 and S6K1, two key effectors of cell growth that are negatively regulated by the TSC1-TSC2 complex. At the cellular level, ectopic expression of cyclin D1 restores the cell size decrease caused by TSC1-TSC2 expression. Intriguingly, down-regulation of TSC proteins was also observed by the expression of a mutant cyclin D1 that is unable to bind to CDK4/6, or by the coexpression of cyclin D1 with either an INK4 inhibitor or with catalytically inactive CDK6, indicating that cyclin D may regulate TSC1-TSC2 independently of CDK4/6. Together, these observations suggest that mammalian D-type cyclins participate in cell growth control through negative regulation of TSC1-TSC2 function.
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, 27599, USA.
authors.forename: Sima J
authors.initials: SJ
authors.lastname: Zacharek
authors.forename: Yue
authors.initials: Y
authors.lastname: Xiong
authors.forename: Stuart D
authors.initials: SD
authors.lastname: Shumway
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D001859:Bone Neoplasms / Q000378:metabolism / Q000473:pathology; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6 / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16; D016193:G1 Phase; D005786:Gene Expression Regulation; D006801:Humans; D007668:Kidney / Q000378:metabolism; D012516:Osteosarcoma / Q000378:metabolism / Q000473:pathology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D016160:Retinoblastoma Protein / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; C087000:EIF4EBP1 protein, human; D010750:Phosphoproteins; D016160:Retinoblastoma Protein; C000624650:TSC1 protein, human; C000624653:TSC2 protein, human; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6