Role of αvβ3 integrin in the action of osteopontin in cancer cells

• Main Authors: I-Shan Hsieh, 謝宜珊
• Other Authors: Wen-Mei Fu
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/c3z7nn

博士 === 國立臺灣大學 === 藥理學研究所 === 103 === Osteopontin, known as a secreted phosphoprotein, has a functional RGD domain and acts as a regulator of cytoskeleton dynamics and gene expression. Extracellular osteopontin functions through its interaction with cell surface receptors, including various integrins (αvβ1, αvβ3, αvβ5, α4β1, and α9β1) and CD44. Binding of osteopontin to these receptors can elicit a wild range of functions, such as cell adhesion, survival, and migration. Osteopontin is overexpressed in various cancers and has a crucial role in all stages of cancer. Elevated ostoepontin has been correlated with poor survival of patients with cancer in different tumor types. Accordingly, clinical studies have shown high osteopontin plasma concentration in patients with metastatic tumors compared with normal samples. Here we investigated the role of osteopontin in drug resistance, cancer cell survival and cancer therapy. It was found that osteopontin was upregulated in hypoxic human prostate cancer cells and osteosarcoma cells. Glucose transporters were also regulated in the hypoxia condition. Osteopontin upregulated drug transporter-p-glycoprotein expression in prostate cancer cells. P-glycoprotein is a subfamily of ATP-binding cassette transporter (ABC transporter). Cancer cells overexpressing ABC transporters actively pump out a variety of compounds from cells and decrease the therapeutic effects of chemotherapeutic agents. Using daunomycin, a chemotherapeutic agent with autofluorescence, to evaluate the ABC transporter pump activity, and osteopontin was found to increase the drug pumping-out activity. Long-term treatment with low-dose of daunomyain contributed to a drug resistance condition and further enhanced the overexpression of osteopontin. Released osteopontin inhibited daunomycin-induced cell death, which was antagonized by αvβ3 antibody. Knockdown of endogenous osteopontin potentiated the daunomycin-induced apoptosis. Furthermore, knockdown of osteopontin also enhanced the cell death caused by other chemotherapeutic drugs, including paclitaxel, doxorubicin, actinomycin-D and rapamycin, which are also the p-glycoprotein substrate. The animal studies showed that osteopontin knockdown enhanced the cytotoxic action of daunomycin. These results indicate that osteopontin is a potential therapeutic target for cancer therapy to reduce the drug resistance in sensitive tumors. On the other hand, 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. According to the results shown above studies, we know that osteopontin plays an important role in drug resistance and influences cancer cells survival during cancer therapy via integrin αvβ3. We thus investigated the effect of integrin antagonist, Rhodostomin mutant-RGD-related proteins, HSA (C34S)-ARLDDL, PEG-ARLDDL, ARLDDL and KKKRT-ARGDNP, in cancer therapy. During treatment of these four RGD-related proteins, they can inhibit prostate cancer, melanoma, osteosarcoma tumor growth, effectively. The inhibition of tumor growth effect is more significant when combination RGD-protein combined with chemotherapy drug of daunomycin. The RGD-proteins also can inhibit cancer cell adhesion and angiogenesis. αvβ3 integrin is highly expressed in some tumor cells and involved in tumor progression. Osteopontin and RGD-related proteins influence tumor growth, cell adhesion, survival via αvβ3 integrins. αvβ3 integrin can be a good target for cancer therapy. Our studies demonstrate that inhibition of αvβ3 integrin with RGD-related proteins or in combination with chemotherapy improve the anticancer efficacy. This may be a new strategy for cancer therapy.