Expression Of BMI-1and Its Functions In Osteosarcom

Background Osteosarcoma is the most common primary malignant bone tumor. Although the use of neoadjuvant chemotherapy and improvement in surgical technology have increased the5-year survival rate to65-75%, there are still many difficulties in diagnosis, treatment and prognosis of osteosarcoma, what’s more, until now the molecular mechanisms involved in the initiation and progression of osteosarcoma remain unclear. The search and identification of new therapeutic targets, predictive and prognostic factors is very important. BMI-1is a Polycomb group member which participates in many physiological processes as well as in a wide spectrum of cancers. However, there is no published report about the relationship between BMI-1and osteosarcoma.Objective To inhibit the gene expression of BMI-1with the RNA interference (RNAi) technique and explore its influence on the proliferation, invasion, cell cycle and chemosensitivity of osteosarcoma cell in vitro. To retrospectively investigate BMI-1expression in osteosarcoma in respect to clinicopathological features, therapeutic outcomes.Methods Lentivirus-mediated BMI-1-shRNA transfected into osteosarcoma cell line of SAOS-2and U20S, and BMI-1expression was examined by Real-time PCR and Western blotting after transfection. The biological features of transfected SAOS-2and U2OS including proliferation, invasion, cell cycle and chemosensitivity, were assessed by MTT assay, flowcytometer, transwell chamber invasive models and plate clone test. Paraffin sections from16patients with osteosarcoma,11patients with osteochondroma,9patients with chondrosarcoma,2patients with Ewing’s sarcoma and10patients with nontumorous bone tissue were examined for the expression of BMI-1by immunohistochemistry.Results The BMI-1expression was persistently and markedly reduced by lentivirus-mediated RNAi. Downregulation of BMI-1expression in osteosarcoma cells significantly suppressed their growth rates. Furthermore, we also observed that suppression of BMI-1could reduce the invasiveness of osteosarcoma cells and enhance their chemosensitivity. But there was no proof that the specific downregulation have function on cell cycle. All the results above showed the gene specificity through the rescue control test and manifested the cell line specificity. The positive expression rates of BMI-1in patients with osteosarcoma, chondrosarcoma, osteochondroma, Ewing’ s sarcoma and noncancerous bone tissue were12/16,6/9,1/11,1/2,0/10, respectively. And the positive expression rate of BMI-1in patients with osteosarcoma was significantly higher than those in cases of osteochondroma and noncancerous bone tissues respectively (P<0.05). The positive expression rates of BMI-1in patients with malignant bone tunor was significantly higher than those in cases of benign ones (P<0.05). There were not enough evidences to prove the relationship between expression of BMI-1protain and clinicopathological characteristics in osteosarcoma. In single variate survival analysis about the group of osteosarcoma, only the metastasis before surgery was significantly correlated with patient survival (P<0.05). In the Cox proportional hazard regression model of the group of osteosarcoma, all the items had no correlation with patient survival, but the pathologic grade, Enneking stage, reccurence and meatstasis after surgery, expression of BMI-1showed some effect.Conclusion In vitro study suggested that lentivirus-mediated RNAi silencing targeting BMI-1could induce potent antitumor activities and sensitivity of chemotherapy with Cisplatin in human osteosarcoma cell line. And BMI-1played an important role in malignant bone tumor inclouding osteosarcoma. BMI-1is possible served as a target for the diagnosis, treatment, prognosis of osteosarcoma. And we should do farther research about BMI-1and osteosarcoma.