Differential expression of folate receptor α and reduced folate carrier and effect of folate in ovarian cancer

Abstract

Ovarian cancer is a common gynecological cancer world-wide and contributes to the highest mortality despite of advances in treatment modalities. There is increasing evidence that diet is a crucial factor in the development and progression of various human cancers. While folate is an essential nutrient required for the synthesis, repair, and functions of DNA, folate receptor α (FRα), one of folate transporters, was found to be overexpressed in cancers, indicating that uptake of folate by tumor cells enhance tumor growth. It is interesting to note that another folate transporter, reduced folate carrier (RFC), is essential for the uptake of both folates and antifolates. However, its expression in ovarian cancer is poorly defined. Thus, while folate may be vital for the growth of both normal and tumor cells, different mechanisms may be involved. In the present study, the expression levels of FRα and RFC as well as the functional impact of folate in ovarian cancer were investigated. By quantitative real-time PCR, the expression of FRα and RFC was examined in clinical samples of 33 ovarian cancers and their matched non-neoplastic tissue, as well as five benign and borderline ovarian tumours. The expression of FRα in 3 normal (HOSE-6-3, HSOE 11-12 and HOSE-17-1) and 5 cancerous (SKOV-3, OVCAR-3, OVCA 420, OVCA 429 and OVCA 433) ovarian cell lines was also assessed by real-time PCR and western blot analysis. By 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cell counting, effects of folate on proliferation in SKOV-3 was also determined after modulating folate level. By real-time PCR, significantly higher mRNA expression of FRα was detected in ovarian cancers (p<0.05). Inversely, RFC mRNA expression was significantly lower in ovarian cancers (p<0.05). FRα mRNA was significantly higher in higher stages ovarian cancers as compared with lower stages ovarian cancers and vice versa for RFC (p<0.05). Significantly higher mRNA expression of FRα was detected in non-mucinous ovarian cancers as compared with mucinous ovarian cancers (p<0.05). By real-time PCR and western blotting, relatively higher mRNA and protein expression of FRα were detected in SKOV-3 and OVCAR-3 as compared with 3 normal ovarian epithelial cell lines. Furthermore, evaluated cell proliferation level was observed in SKOV-3 after folate treatment. In conclusion, our results document that folate, FRα and RFC may be important differential regulators for the development and progression of ovarian cancer. Better understanding of their related mechanisms may bear potential impacts on the development of chemoprevention strategies.