title: Calpain 2 regulates Akt-FoxO-p27(Kip1) protein signaling pathway in mammary carcinoma.
abstract: We investigated the role of the ubiquitously expressed calpain 2 isoform in breast tumor cell growth, migration, signaling, and tumorigenesis. RNAi-mediated knockdown of the capn2 transcript was used to manipulate expression of the catalytic subunit of calpain 2 in the AC2M2 mouse mammary carcinoma cell line. Stable knockdown of capn2 correlated with reduced in vitro proliferation rates, soft agar colony formation efficiency, and migration rates, indicating roles for calpain 2 in mitogenesis, survival, and motogenesis. Biochemical analysis showed increased levels of protein phosphatase 2A and reduced levels of activated Akt in calpain 2-deficient cells, and this correlated with increased levels of the FoxO3a target gene product p27(Kip1), a key regulator of cell proliferation. Calpain 2 deficiency in the AC2M2 cells correlated with enhanced nuclear localization of FoxO3a, consistent with it being in a derepressed state capable of regulating transcriptional targets. Orthotopically engrafted calpain 2 knockdown AC2M2 cells generated tumors with reduced growth rates and enhanced in vivo expression of p27(Kip1). In summary, calpain 2 deficiency correlated with reduced Akt activity, increased protein phosphatase 2A levels, derepression of FoxO3a, and enhanced expression of the p27(Kip1) tumor suppressor. These observations argue that calpain 2 promotes tumor cell growth both in vitro and in vivo through the PI3K-Akt-FoxO-p27(Kip1) signaling cascade. Inhibition of calpain 2 might therefore provide therapeutic benefits in the treatment of cancer.
authors.affiliation: Department of Pathology and Molecular Medicine, Queen's University, Division of Cancer Biology and Genetics, Queen's Cancer Research Institute, Kingston, Ontario K7L3N6, Canada.
authors.forename: Wai-chi
authors.initials: WC
authors.lastname: Ho
authors.forename: Larissa
authors.initials: L
authors.lastname: Pikor
authors.forename: Yan
authors.initials: Y
authors.lastname: Gao
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Elliott
authors.forename: Peter A
authors.initials: PA
authors.lastname: Greer
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism / Q000556:secondary; D015674:Mammary Neoplasms, Animal / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D008856:Microscopy, Fluorescence; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D047368:Tumor Burden / Q000235:genetics
chemical_list: D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; D050760:Cyclin-Dependent Kinase Inhibitor p27; D051057:Proto-Oncogene Proteins c-akt; D002154:Calpain; C570925:Capn2 protein, mouse