title: Sestrin2 modulates AMPK subunit expression and its response to ionizing radiation in breast cancer cells.
abstract: BACKGROUND
  The sestrin family of stress-responsive genes (SESN1-3) are suggested to be involved in regulation of metabolism and aging through modulation of the AMPK-mTOR pathway. AMP-activated protein kinase (AMPK) is an effector of the tumour suppressor LKB1, which regulates energy homeostasis, cell polarity, and the cell cycle. SESN1/2 can interact directly with AMPK in response to stress to maintain genomic integrity and suppress tumorigenesis. Ionizing radiation (IR), a widely used cancer therapy, is known to increase sestrin expression, and acutely activate AMPK. However, the regulation of AMPK expression by sestrins in response to IR has not been studied in depth.
  
  
  RESULTS
  Through immunoprecipitation we observed that SESN2 directly interacted with the AMPKα1β1γ1 trimer and its upstream regulator LKB1 in MCF7 breast cancer cells. SESN2 overexpression was achieved using a Flag-tagged SESN2 expression vector or a stably-integrated tetracycline-inducible system, which also increased AMPKα1 and AMPKβ1 subunit phosphorylation, and co-localized with phosphorylated AMPKα-Thr127 in the cytoplasm. Furthermore, enhanced SESN2 expression increased protein levels of LKB1 and AMPKα1β1γ1, as well as mRNA levels of LKB1, AMPKα1, and AMPKβ1. Treatment of MCF7 cells with IR elevated AMPK expression and activity, but this effect was attenuated in the presence of SESN2 siRNA. In addition, elevated SESN2 inhibited IR-induced mTOR signalling and sensitized MCF7 cells to IR through an AMPK-dependent mechanism.
  
  
  CONCLUSIONS
  Our results suggest that in breast cancer cells SESN2 is associated with AMPK, it is involved in regulation of basal and IR-induced expression and activation of this enzyme, and it mediates sensitization of cancer cells to IR.
authors.affiliation: Research Department, Juravinski Cancer Center, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Toran
authors.initials: T
authors.lastname: Sanli
authors.forename: Katja
authors.initials: K
authors.lastname: Linher-Melville
authors.forename: Theodoros
authors.initials: T
authors.lastname: Tsakiridis
authors.forename: Gurmit
authors.initials: G
authors.lastname: Singh
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D001943:Breast Neoplasms / Q000201:enzymology* / Q000473:pathology / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D004789:Enzyme Activation / Q000528:radiation effects; D005260:Female; D006801:Humans; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation / Q000528:radiation effects; D011485:Protein Binding / Q000528:radiation effects; D021122:Protein Subunits / Q000378:metabolism*; D011839:Radiation, Ionizing; D015398:Signal Transduction / Q000528:radiation effects; D013347:Subcellular Fractions / Q000378:metabolism / Q000528:radiation effects; D000084622:Sestrins
chemical_list: D055372:AMP-Activated Protein Kinases; D009687:Nuclear Proteins; D021122:Protein Subunits; C465398:SESN2 protein, human; D000084622:Sestrins