title: mTORC2 is required for proliferation and survival of TSC2-null cells.
abstract: Mutational inactivation of the tumor suppressor tuberous sclerosis complex 2 (TSC2) constitutively activates mTORC1, increases cell proliferation, and induces the pathological manifestations observed in tuberous sclerosis (TS) and in pulmonary lymphangioleiomyomatosis (LAM). While the role of mTORC1 in TSC2-dependent growth has been extensively characterized, little is known about the role of mTORC2. Our data demonstrate that mTORC2 modulates TSC2-null cell proliferation and survival through RhoA GTPase and Bcl2 proteins. TSC2-null cell proliferation was inhibited not only by reexpression of TSC2 or small interfering RNA (siRNA)-induced downregulation of Rheb, mTOR, or raptor, but also by siRNA for rictor. Increased RhoA GTPase activity and P-Ser473 Akt were inhibited by siRNA for rictor. Importantly, constitutively active V14RhoA reversed growth inhibition induced by siRNA for rictor, siRNA TSC1, reexpression of TSC2, or simvastatin. While siRNA for RhoA had a modest effect on growth inhibition, downregulation of RhoA markedly increased TSC2-null cell apoptosis. Inhibition of RhoA activity downregulated antiapoptotic Bcl2 and upregulated proapoptotic Bim, Bok, and Puma. In vitro and in vivo, simvastatin alone or in combination with rapamycin inhibited cell growth and induced TSC2-null cell apoptosis, abrogated TSC2-null tumor growth, improved animal survival, and prevented tumor recurrence by inhibiting cell growth and promoting apoptosis. Our data demonstrate that mTORC2-dependent activation of RhoA is required for TSC2-null cell growth and survival and suggest that targeting both mTORC2 and mTORC1 by a combination of proapoptotic simvastatin and cytostatic rapamycin shows promise for combinational therapeutic intervention in diseases with TSC2 dysfunction.
authors.affiliation: Pulmonary, Allergy and Critical Care Division, Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Elena A
authors.initials: EA
authors.lastname: Goncharova
authors.forename: Dmitry A
authors.initials: DA
authors.lastname: Goncharov
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Wittaya
authors.initials: W
authors.lastname: Pimtong
authors.forename: Stephen
authors.initials: S
authors.lastname: Lu
authors.forename: Irene
authors.initials: I
authors.lastname: Khavin
authors.forename: Vera P
authors.initials: VP
authors.lastname: Krymskaya
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000924:Anticholesteremic Agents / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation; D002470:Cell Survival; D002478:Cells, Cultured; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000378:metabolism; D000076225:Mechanistic Target of Rapamycin Complex 2; D051379:Mice; D018345:Mice, Knockout; D008819:Mice, Nude; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009368:Neoplasm Transplantation; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D051381:Rats; D000076223:Regulatory-Associated Protein of mTOR; D019821:Simvastatin / Q000378:metabolism; D020123:Sirolimus / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000924:Anticholesteremic Agents; D002352:Carrier Proteins; D007166:Immunosuppressive Agents; D046912:Multiprotein Complexes; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; C540162:Rptor protein, mouse; C000624653:TSC2 protein, human; C000624654:Tsc2 protein, mouse; C000624655:Tsc2 protein, rat; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C525637:rictor protein, mouse; D019821:Simvastatin; D000076225:Mechanistic Target of Rapamycin Complex 2; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020742:rhoA GTP-Binding Protein; D020123:Sirolimus