title: Calpain-6 is an endothelin-1 signaling dependent protective factor in chemoresistant osteosarcoma.
abstract: Bone tumors strongly influence normal tissues and stimulate bone cells for the production of cytokines supporting proliferation and abnormal survival in cancer cells. We previously reported that the proteoglycan syndecan-2 controls the activity of various cytokines and growth factors and also modulates apoptosis and response to cytotoxic agents in osteosarcoma cell lines. Here, we show that syndecan-2 has a stronger tumor suppressor activity in vivo. We identify calpain-6 as a target gene downregulated by syndecan-2 in cells and in vivo. We demonstrate that calpain-6 expression in osteosarcoma cells depends on endothelin-1, a mediator of the tumor progression in bone. Syndecan-2 overexpression alters ERK1/2, PI3K/AKT and NFκB pathways that are calpain-6-promoting signals downstream of endothelin-1. Immunohistochemical analysis shows that calpain-6 is expressed in human bone tumors and metastases. A high expression of calpain-6 was specially found in recurrent osteosarcoma. Moreover, calpain-6 levels in primary tumors were inversely related to the response to chemotherapy. Consistently, calpain-6 was increased by doxorubicin and was found to be expressed at higher levels in doxorubicin-resistant U2OS osteosarcoma-derived cells as compared to responsive cells. Inhibition of calpain-6 with shRNA resulted in decreased proliferation, increased spontaneous apoptosis and increased sensitivity to doxorubicin and also methotrexate in responsive and resistant osteosarcoma cells. Taken together, our data show that syndecan-2 exerts its pro-apoptotic function through modulation of the endothelin-1/NFκB signaling and through downregulation of calpain-6, a protective factor that contributes to abnormal cell survival. Thus, this study identifies calpain-6 as a new possible therapeutic target in chemoresistant osteosarcoma.
authors.affiliation: Laboratory of Osteoblast Biology and Pathology, INSERM U606, Paris, F-75475, France.
authors.forename: Allison
authors.initials: A
authors.lastname: Marion
authors.forename: François-Xavier
authors.initials: FX
authors.lastname: Dieudonné
authors.forename: Ana
authors.initials: A
authors.lastname: Patiño-Garcia
authors.forename: Fernando
authors.initials: F
authors.lastname: Lecanda
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: Marie
authors.forename: Dominique
authors.initials: D
authors.lastname: Modrowski
mesh_terms: D017209:Apoptosis; D001859:Bone Neoplasms / Q000188:drug therapy / Q000473:pathology*; D002154:Calpain / Q000502:physiology*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D019332:Endothelin-1 / Q000502:physiology*; D006801:Humans; D016328:NF-kappa B / Q000502:physiology; D012516:Osteosarcoma / Q000188:drug therapy / Q000473:pathology*; D015398:Signal Transduction / Q000502:physiology*; D053669:Syndecan-2 / Q000502:physiology
chemical_list: D019332:Endothelin-1; D016328:NF-kappa B; D053669:Syndecan-2; D002154:Calpain