The role of folate receptor alpha in cancer development, progression and treatment: cause, consequence or innocent bystander?
Folate receptor alpha (FRalpha) is a membrane-bound protein with high affinity for binding and transporting physiologic levels of folate into cells. Folate is a basic component of cell metabolism and DNA synthesis and repair, and rapidly dividing cancer cells have an increased requirement for folate to maintain DNA synthesis, an observation supported by the widespread use of antifolates in cancer chemotherapy. FRalpha levels are high in specific malignant tumors of epithelial origin compared to normal cells, and are positively associated with tumor stage and grade, raising questions of its role in tumor etiology and progression. It has been suggested that FRalpha might confer a growth advantage to the tumor by modulating folate uptake from serum or by generating regulatory signals. Indeed, cell culture studies show that expression of the FRalpha gene, FOLR1, is regulated by extracellular folate depletion, increased homocysteine accumulation, steroid hormone concentrations, interaction with specific transcription factors and cytosolic proteins, and possibly genetic mutations. Whether FRalpha in tumors decreases in vivo among individuals who are folate sufficient, or whether the tumor's machinery sustains FRalpha levels to meet the increased folate demands of the tumor, has not been studied. Consequently, the significance of carrying a FRalpha-positive tumor in the era of folic acid fortification and widespread vitamin supplement use in countries such as Canada and the United States is unknown. Epidemiologic and clinical studies using human tumor specimens are lacking and increasingly needed to understand the role of environmental and genetic influences on FOLR1 expression in tumor etiology and progression. This review summarizes the literature on the complex nature of FOLR1 gene regulation and expression, and suggests future research directions.
Kelemen
Linda E
LE
Department of Health Sciences Research, Mayo Clinic College of Medicine, Rochester, MN 55905, USA. L.Kelemen@post.harvard.edu
D000818:Animals; D002170:Canada; D002352:Carrier Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004273:DNA, Neoplasm / Q000378:metabolism; D019587:Dietary Supplements; D018450:Disease Progression; D058975:Folate Receptor 1; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D012739:Gonadal Steroid Hormones / Q000097:blood; D006710:Homocysteine / Q000378:metabolism; D006801:Humans; D009154:Mutation; D009369:Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D011379:Prognosis; D011956:Receptors, Cell Surface / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014481:United States
D002352:Carrier Proteins; D004273:DNA, Neoplasm; C548696:FOLR1 protein, human; D058975:Folate Receptor 1; D058973:Folate Receptors, GPI-Anchored; D012739:Gonadal Steroid Hormones; D011956:Receptors, Cell Surface; D014157:Transcription Factors; D006710:Homocysteine; D005492:Folic Acid