title: Selective inhibition of growth of tuberous sclerosis complex 2 null cells by atorvastatin is associated with impaired Rheb and Rho GTPase function and reduced mTOR/S6 kinase activity.
abstract: Inactivating mutations in the tuberous sclerosis complex 2 (TSC2) gene, which encodes tuberin, result in the development of TSC and lymphangioleiomyomatosis (LAM). The tumor suppressor effect of tuberin lies in its GTPase-activating protein activity toward Ras homologue enriched in brain (Rheb), a Ras GTPase superfamily member. The statins, 3-hydroxy-3-methylglutaryl CoA reductase inhibitors, have pleiotropic effects which may involve interference with the isoprenylation of Ras and Rho GTPases. We show that atorvastatin selectively inhibits the proliferation of Tsc2-/- mouse embryo fibroblasts and ELT-3 smooth muscle cells in response to serum and estrogen, and under serum-free conditions. The isoprenoids farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP) significantly reverse atorvastatin-induced inhibition of Tsc2-/- cell growth, suggesting that atorvastatin dually targets a farnesylated protein, such as Rheb, and a geranylgeranylated protein, such as Rho, both of which have elevated activity in Tsc2-/- cells. Atorvastatin reduced Rheb isoprenylation, GTP loading, and membrane localization. Atorvastatin also inhibited the constitutive phosphorylation of mammalian target of rapamycin, S6 kinase, and S6 found in Tsc2-/- cells in an FPP-reversible manner and attenuated the high levels of phosphorylated S6 in Tsc2-heterozygous mice. Atorvastatin, but not rapamycin, attenuated the increased levels of activated RhoA in Tsc2-/- cells, and this was reversed by GGPP. These results suggest that atorvastatin may inhibit both rapamycin-sensitive and rapamycin-insensitive mechanisms of tuberin-null cell growth, likely via Rheb and Rho inhibition, respectively. Atorvastatin may have potential therapeutic benefit in TSC syndromes, including LAM.
authors.affiliation: Pulmonary and Critical Care Division, Department of Medicine, Tupper Research Institute, Tufts-New England Medical Center, Boston, MA 02111, USA. gfinlay@tufts-nemc.org
authors.forename: Geraldine A
authors.initials: GA
authors.lastname: Finlay
authors.forename: Amy J
authors.initials: AJ
authors.lastname: Malhowski
authors.forename: Yingling
authors.initials: Y
authors.lastname: Liu
authors.forename: Barry L
authors.initials: BL
authors.lastname: Fanburg
authors.forename: David J
authors.initials: DJ
authors.lastname: Kwiatkowski
authors.forename: Deniz
authors.initials: D
authors.lastname: Toksoz
mesh_terms: D000818:Animals; D000069059:Atorvastatin; D048708:Cell Growth Processes / Q000187:drug effects / Q000235:genetics; D004347:Drug Interactions; D005260:Female; D006538:Heptanoic Acids / Q000494:pharmacology*; D008297:Male; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011106:Polyisoprenyl Phosphates / Q000494:pharmacology; D054876:Prenylation / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism*; D011758:Pyrroles / Q000494:pharmacology*; D000076205:Ras Homolog Enriched in Brain Protein; D051381:Rats; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D012717:Sesquiterpenes / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000172:deficiency* / Q000235:genetics; D020741:rho GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D006538:Heptanoic Acids; D009479:Neuropeptides; D011106:Polyisoprenyl Phosphates; D011758:Pyrroles; D000076205:Ras Homolog Enriched in Brain Protein; C490213:Rheb protein, mouse; D012717:Sesquiterpenes; C000624654:Tsc2 protein, mouse; C000624655:Tsc2 protein, rat; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C004808:farnesyl pyrophosphate; D000069059:Atorvastatin; D011494:Protein Kinases; C546843:mTOR protein, mouse; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins; D020741:rho GTP-Binding Proteins; C002963:geranylgeranyl pyrophosphate