title: Osteopontin upregulates the expression of glucose transporters in osteosarcoma cells.
abstract: Osteosarcoma is the most common primary malignancy of bone. Even after the traditional standard surgical therapy, metastasis still occurs in a high percentage of patients. Glucose is an important source of metabolic energy for tumor proliferation and survival. Tumors usually overexpress glucose transporters, especially hypoxia-responsive glucose transporter 1 and glucose transporter 3. Osteopontin, hypoxia-responsive glucose transporter 1, and glucose transporter 3 are overexpressed in many types of tumors and have been linked to tumorigenesis and metastasis. In this study, we investigated the regulation of glucose transporters by osteopontin in osteosarcoma. We observed that both glucose transporters and osteopontin were upregulated in hypoxic human osteosarcoma cells. Endogenously released osteopontin regulated the expression of glucose transporter 1 and glucose transporter 3 in osteosarcoma and enhanced glucose uptake into cells via the αvβ3 integrin. Knockdown of osteopontin induced cell death in 20% of osteosarcoma cells. Phloretin, a glucose transporter inhibitor, also caused cell death by treatment alone. The phloretin-induced cell death was significantly enhanced in osteopontin knockdown osteosarcoma cells. Combination of a low dose of phloretin and chemotherapeutic drugs, such as daunomycin, 5-Fu, etoposide, and methotrexate, exhibited synergistic cytotoxic effects in three osteosarcoma cell lines. Inhibition of glucose transporters markedly potentiated the apoptotic sensitivity of chemotherapeutic drugs in osteosarcoma. These results indicate that the combination of a low dose of a glucose transporter inhibitor with cytotoxic drugs may be beneficial for treating osteosarcoma patients.
authors.affiliation: Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: I-Shan
authors.initials: IS
authors.lastname: Hsieh
authors.affiliation: Department of Orthopedic Surgery, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Rong-Sen
authors.initials: RS
authors.lastname: Yang
authors.affiliation: Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Wen-Mei
authors.initials: WM
authors.lastname: Fu
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D001859:Bone Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D003630:Daunorubicin / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D005472:Fluorouracil / Q000494:pharmacology; D051246:Glucose Transport Proteins, Facilitative / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051272:Glucose Transporter Type 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D051274:Glucose Transporter Type 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D049990:Membrane Transport Modulators / Q000494:pharmacology; D008727:Methotrexate / Q000494:pharmacology; D053495:Osteopontin / Q000378:metabolism*; D012516:Osteosarcoma / Q000378:metabolism*; D010693:Phloretin / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D000970:Antineoplastic Agents; D051246:Glucose Transport Proteins, Facilitative; D051272:Glucose Transporter Type 1; D051274:Glucose Transporter Type 3; D039302:Integrin alphaVbeta3; D049990:Membrane Transport Modulators; C495677:SLC2A1 protein, human; C495687:SLC2A3 protein, human; D053495:Osteopontin; D005047:Etoposide; D010693:Phloretin; D005472:Fluorouracil; D008727:Methotrexate; D003630:Daunorubicin