The role of the Soluble Folate Receptor Alpha in cancer development

Abstract

Folates are essential vitamins for cell growth and replication which shows an important role of folates in development of embryos, deficits may result in congenital malfunctions. In order to avoid diseases such as neural tube defects (NTD) due to folate deficiency during pregnancy, different countries approved the folic acid supplementation and fortification of foods. As a result NTD development decreased, but adverse effects have been reported for several years. Some studies have shown that folic acid elevates the growth of pre-existing tumours when supplied. To understand folic acid uptake from cells and cancer development, we have been focused on one of the transport mechanisms, folate receptor alpha (FRα), is highly restricted to certain tissues and is upregulated in several cancers. Previous experiments performed at Department of Molecular Biology and Genetics (University of Aarhus) have shown that folic acid activates STAT3 oncogene via the FRα. Furthermore FRα can be found bound to membrane by GPI-anchored or as a soluble protein (sFRα). This soluble form has been associated with cancer because of its high concentration in serum of patients with cancer and poor folates levels, whereas healthy individuals exhibit low sFRα concentrations and high folates levels. Results demonstrated that the soluble FRα is able to activate STAT3 gene via transsignaling independently of its membrane-bound counterpart. Earlier analysis were performed to investigate the effect of folic acid on tumour development and it was found that folic acid cause elevated growth of pre-existing tumours when folic acid doses are similar to those from fortified foods. The high FRα expression in breast tumours suggested that it contributes to tumour development. Consequently, larger tumours expressed higher levels of STAT3 protein. The aim of this project was to study the sFRα expression and how is it involved in cancer development through the transsignaling process prior proposed. Before starting to investigate the soluble protein is necessary to study its predecessor FRα. We show here that FRα is expressed at higher levels in cancer cells and we expect to find this protein in its soluble form (sFRα). In addition, the PI-PLC, an activator of phospholipase C, is used in to demonstrate its ability to release FRα by cleavage of GPI-anchored proteins. Levels of the soluble FR were lower and precipitations were performed to detect proteins at higher concentrations. Additionally, to analyse protein concentrations in tumours, a group of mice fed a high or low folic acid diet were analysed. After find out which of them were PyMT mice (MT protein develops cancer) tumours from one of these mice together with serum from previously analysed mice were extracted. From tumours cell cultures were generated to study expression levels of FRα, and from serum sFRα levels were investigated. From tumours cultures no FRα was detected but the soluble protein was found in serum although it was not possible to measure the protein concentration. The higher expression of FRα in cancer cells shows its involvement in disease development. Moreover, the soluble protein presence confirms its expression and even though concentration was not determined the preliminary data suggest that FRα levels increase when tumours are bigger and so the expression of FRα proteins is larger in these tumours than in small tumours from mice fed a low folic acid diet. Further studies will focused on determine sFRα levels and its effect on tumour development.