The Expression And Function Of Riboflavin Transporter 2 (RFT2) In Glioma

Objective: Glioma is the most common primary brain tumor in adults.Gliomas are highly aggressive and have no clear boundaries from adjacent normal tissue.As a consequence of these characteristics,treatments used to combat these gliomas including surgery and radiotherapy frequently fail.Moreover,due to resistance,the effects of chemotherapy are limited.Thus,more effective therapies based on new molecular targets are needed to establish novel therapeutic strategies for patients with glioma.Human riboflavin transporter 2(RFT2)is a member of the SLC52 family that has been shown to play a key role in riboflavin homeostasis.Recently,several studies have demonstrated that RFT2 is important in the development of several cancers,including esophageal squamous cell carcinoma(ESCC),gastric cancer and cervical cancer.Our study is to investigate the expression level and effects of RFT2 in human gliomas.We hope can provide new molecular targets for the treatment of glioma.Methods: In order to investigate the expression level of RFT2 in human gliomas and normal brain tissues,we performed immunohistochemistry(IHC)on 120 gliomas of different WHO grades,as well as on human brain tissue samples from 24 normal subjects.RFT2-siRNA-3 was used to knockdown the expression of RFT2 in LN308 and LN229 cells.To test the effects of RFT2 knockdown on tumor growth,migration,invasion and other phenotypic changes in vitro and vivo,we employed MTT assay,colony formation assay,flow cytometry analysis,Transwell assays,Western blot and a subcutaneous xenograft mouse model.Results: 1.RFT2 was overexpressed in glioma samples compared with normal brain tissues.Furthermore,RFT2 expression was correlated with World Health Organization(WHO)grade.2.In comparison to mock-transfected cells or cells transfected with scr-siRNA,knockdown of RFT2 in LN308 and LN229 cells significantly reduced cell viability(P<0.01)and resulted in a remarkable decrease in colony formation(P<0.01).Sliencing of RFT2 suppressed the growth of tumor xenografts in vivo(P<0.001).3.The percentage of cells in the G1/G0 stage increased significantly(P<0.05).The proportion of apoptotic cells was notably higher in cells transfected with RFT2-siRNA-3(P<0.05).Expression of proteins known to regulate cell cycle or apoptosis including p21,p27,Bcl-2 and Bax was notably altered in RFT2-depleted cells.4.Silencing of RFT2 impeded migration and invasion of glioma cells through suppression of MMP-2 and MMP-9 expression.Conclusion: In our study,we found that RFT2 was overexpressed in glioma samples compared with normal brain tissues.RFT2 expression was correlated with World Health Organization(WHO)grade.Silencing of RFT2 resulted in inhibition of glioma cell proliferation through promotion of cell cycle arrest and apoptosis.Furthermore,silencing of RFT2 impeded migration and invasion of glioma cells through suppression of MMP-2 and MMP-9 expression.In addition to blocking cell proliferation in vitro,reduction of RFT2 levels also decreased tumor growth in vivo.These data suggest that RFT2 could be an attractive therapeutic target for treatment of glioma.