title: Calpain4 is required for activation of HER2 in breast cancer cells exposed to trastuzumab and its suppression decreases survival and enhances response.
abstract: Overactivation of HER2 and crosstalk of other HER family members contribute to a survival pathway of breast cancer cells exposed to trastuzumab, the therapeutic inhibitor of HER2 and thus, decrease response and promote resistance. We have explored the involvement of the intracellular cysteine protease calpain4, the common partner of isoforms calpain1 and calpain2, in the regulation of cell survival and trastuzumab-response. Increase of calpain4 expression and isoform activities were detected in breast cancer cells and HER2-positive tumors. Molecular analyses of parent and resistant cells suggested that perturbation of regulations, induced by calpain4 and of activities of HER2 and HER3, was associated with trastuzumab-resistance. The suppression of calpain4 destabilized calpain1 and calpain2, however, did not prevent the activation of HER2 and HER3 or cell proliferation in the absence of trastuzumab. To understand the significance, the survival of parent and trastuzumab-resistant cells in which calpain4 was suppressed, was assessed in the presence of trastuzumab; survival in each cell type was decreased and associated with a loss of HER2 and HER3 activity. Taken together, by contributing to the activation and the crosstalk of HER2, calpain4 promotes the survival pathway of breast cancer cells, and therefore, its suppression enhances trastuzumab-response and decreases resistance.
authors.affiliation: Department of Clinical Pathology, Pathology and Laboratory Medicine Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA. kulkars@ccf.org
authors.forename: Sucheta
authors.initials: S
authors.lastname: Kulkarni
authors.forename: Leya
authors.initials: L
authors.lastname: Saju
authors.forename: Carol
authors.initials: C
authors.lastname: Farver
authors.forename: Raymond
authors.initials: R
authors.lastname: Tubbs
mesh_terms: D061067:Antibodies, Monoclonal, Humanized / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020033:Protein Isoforms; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D020893:Receptor, ErbB-3 / Q000235:genetics / Q000378:metabolism; D000068878:Trastuzumab
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D002154:Calpain; D020033:Protein Isoforms; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3; D000068878:Trastuzumab; C527669:CAPNS1 protein, human