title: Regulation of metformin response by breast cancer associated gene 2.
abstract: Adenosine monophosphate-activated protein kinase (AMPK), a master regulator of cellular energy homeostasis, has emerged as a promising molecular target in the prevention of breast cancer. Clinical trials using the United States Food and Drug Administration (FDA)-approved, AMPK-activating, antidiabetic drug metformin are promising in this regard, but the question of why metformin is protective for some women but not others still remains. Breast cancer associated gene 2 (BCA2/Rabring7/RNF115), a novel Really Interesting New Gene (RING) finger ubiquitin E3 ligase, is overexpressed in >50% of breast tumors. Herein, we report that BCA2 is an endogenous inhibitor of AMPK activation in breast cancer cells and that BCA2 inhibition increases the efficacy of metformin. BCA2 overexpression inhibited both basal and inducible Thr172 phosphorylation/activation of AMPKα1, while BCA2-specific small interfering RNA (siRNA) enhanced phosphorylated AMPKα1 (pAMPKα1). The AMPK-suppressive function of BCA2 requires its E3 ligase-specific RING domain, suggesting that BCA2 targets some protein controlling (de)phosphorylation of AMPKα1 for degradation. Activation of AMPK by metformin triggered a growth inhibitory signal but also increased BCA2 protein levels, which correlated with AKT activation and could be curbed by an AMPK inhibitor, suggesting a potential feedback mechanism from pAMPKα1 to pAkt to BCA2. Finally, BCA2 siRNA, or inhibition of its upstream stabilizing kinase AKT, increased the growth inhibitory effect of metformin in multiple breast cancer cell lines, supporting the conclusion that BCA2 weakens metformin's efficacy. Our data suggest that metformin in combination with a BCA2 inhibitor may be a more effective breast cancer treatment strategy than metformin alone.
authors.affiliation: Department of Oncology and Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, MI.
authors.forename: Daniela
authors.initials: D
authors.lastname: Buac
authors.affiliation: Department of Oncology and Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, MI.
authors.forename: Fathima R
authors.initials: FR
authors.lastname: Kona
authors.affiliation: Department of Biological Sciences and Anatomic Pathology, University of Toronto Sunnybrook Health Sciences Centre, Toronto, Ontario.
authors.forename: Arun K
authors.initials: AK
authors.lastname: Seth
authors.affiliation: Department of Oncology and Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, MI ; Departments of Pharmacology and Pathology, Wayne State University School of Medicine, Detroit, MI.
authors.forename: Q Ping
authors.initials: QP
authors.lastname: Dou
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D008687:Metformin / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011499:Protein Processing, Post-Translational; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012265:Ribonucleotides / Q000494:pharmacology; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide; D000970:Antineoplastic Agents; D008687:Metformin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D012265:Ribonucleotides; D044767:Ubiquitin-Protein Ligases; C506934:RNF115 protein, human; C526180:PRKAA1 protein, human; C031143:AICA ribonucleotide