title: Rapamycin requires AMPK activity and p27 expression for promoting autophagy-dependent Tsc2-null cell survival.
abstract: Tuberous sclerosis complex (TSC) disease results from inactivation of the TSC1 or TSC2 gene, and is characterized by benign tumors in several organs. Because TSC tumorigenesis correlates with hyperactivation of mTORC1, current therapies focus on mTORC1 inhibition with rapamycin or its analogs. Rapamycin-induced tumor shrinkage has been reported, but tumor recurrence occurs on withdrawal from rapamycin. Autophagy has been associated with development of TSC tumors and with tumor cell survival during rapamycin treatment. mTORC1 and AMPK directly inhibit and activate autophagy, respectively. AMPK is hyperactivated in TSC cells and tumors, and drives cytoplasmic sequestration of the cell-cycle inhibitor p27KIP (p27). Whether AMPK and p27 are involved in rapamycin-induced autophagy and survival of TSC cells remain unexplored. Here, we show that inhibition of AMPK by compound C or by shRNA-mediated depletion of LKB1 reduces activation of autophagy by rapamycin in Tsc2-null cells. Similarly, shRNA-mediated depletion of p27 inhibited rapamycin-induced autophagy. In support of p27 lying downstream of AMPK on the activation of autophagy in Tsc2-null cells, a p27 mutant that preferentially localizes in the cytosol recovered the effect of rapamycin on autophagy in both p27- and LKB1-depleted cells, but a nuclear p27 mutant was inactive. Finally, we show that p27-dependent activation of autophagy is involved in Tsc2-null cell survival under rapamycin treatment. These results indicate that an AMPK/p27 axis is promoting a survival mechanism that could explain in part the relapse of TSC tumors treated with rapamycin, exposing new avenues for designing more efficient treatments for TSC patients.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
authors.forename: Tania
authors.initials: T
authors.lastname: Campos
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
authors.forename: Javiera
authors.initials: J
authors.lastname: Ziehe
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
authors.forename: Francisco
authors.initials: F
authors.lastname: Fuentes-Villalobos
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
authors.forename: Orlando
authors.initials: O
authors.lastname: Riquelme
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
authors.forename: Daniela
authors.initials: D
authors.lastname: Peña
authors.affiliation: Advanced Center for Chronic Disease (ACCDiS), Facultad de Ciencias Químicas y Farmacéuticas & Facultad de Medicina, Universidad de Chile, Santiago, Chile; Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, Santiago, Chile.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Troncoso
authors.affiliation: Advanced Center for Chronic Disease (ACCDiS), Facultad de Ciencias Químicas y Farmacéuticas & Facultad de Medicina, Universidad de Chile, Santiago, Chile; Department of Internal Medicine (Cardiology Division), University of Texas Southwestern Medical Center, Dallas, TX, USA.
authors.forename: Sergio
authors.initials: S
authors.lastname: Lavandero
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
authors.forename: Violeta
authors.initials: V
authors.lastname: Morin
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
authors.forename: Roxana
authors.initials: R
authors.lastname: Pincheira
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile. Electronic address: arcastro@udec.cl.
authors.forename: Ariel F
authors.initials: AF
authors.lastname: Castro
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D001343:Autophagy / Q000187:drug effects* / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D015151:Immunoblotting; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D034622:RNA Interference; D020123:Sirolimus / Q000494:pharmacology*; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000172:deficiency* / Q000235:genetics
chemical_list: D000903:Antibiotics, Antineoplastic; C493961:Cdkn1b protein, mouse; C000624654:Tsc2 protein, mouse; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D055372:AMP-Activated Protein Kinases; D020123:Sirolimus
keywords: AMPK; Cell survival; Rapamycin; Tuberous sclerosis complex; mTOR; p27