title: Rheb activates AMPK and reduces p27Kip1 levels in Tsc2-null cells via mTORC1-independent mechanisms: implications for cell proliferation and tumorigenesis.
abstract: Tuberous sclerosis complex (TSC) is an autosomally inherited disorder that causes tumors to form in many organs. It is frequently caused by inactivating mutations in the TSC2 tumor-suppressor gene. TSC2 negatively regulates the activity of the GTPase Rheb and thereby inhibits mammalian target of rapamycin complex 1 (mTORC1) signaling. Activation of mTORC1 as a result of lack of TSC2 function is observed in TSC and sporadic lymphangioleiomyomatosis (LAM). TSC2 deficiency has recently been associated with elevated AMP-activated protein kinase (AMPK) activity, which in turn correlated with cytoplasmic localization of p27Kip1 (p27), a negative regulator of cyclin-dependent kinase 2 (Cdk2). How AMPK in the absence of TSC2 is stimulated is not fully understood. In this study, we demonstrate that Rheb activates AMPK and reduces p27 levels in Tsc2-null cells. Importantly, both effects occur largely independent of mTORC1. Furthermore, increased p27 levels following Rheb depletion correlated with reduced Cdk2 activity and cell proliferation in vitro, and with inhibition of tumor formation by Tsc2-null cells in vivo. Taken together, our data suggest that Rheb controls proliferation of TSC2-deficient cells by a mechanism that involves regulation of AMPK and p27, and that Rheb is a potential target for TSC/LAM therapy.
authors.affiliation: Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, CA, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Lacher
authors.forename: R
authors.initials: R
authors.lastname: Pincheira
authors.forename: Z
authors.initials: Z
authors.lastname: Zhu
authors.forename: B
authors.initials: B
authors.lastname: Camoretti-Mercado
authors.forename: M
authors.initials: M
authors.lastname: Matli
authors.forename: R S
authors.initials: RS
authors.lastname: Warren
authors.forename: A F
authors.initials: AF
authors.lastname: Castro
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology; D051357:Cyclin-Dependent Kinase 2 / Q000032:analysis / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000032:analysis / Q000378:metabolism*; D005260:Female; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008819:Mice, Nude; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D046912:Multiprotein Complexes; D009479:Neuropeptides / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D000076205:Ras Homolog Enriched in Brain Protein; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000032:analysis / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D046912:Multiprotein Complexes; D009479:Neuropeptides; D011506:Proteins; C490211:RHEB protein, human; D000076205:Ras Homolog Enriched in Brain Protein; C000624653:TSC2 protein, human; C000624654:Tsc2 protein, mouse; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D051357:Cyclin-Dependent Kinase 2; D055372:AMP-Activated Protein Kinases; D020559:Monomeric GTP-Binding Proteins