Functional effect of point mutations in the alpha-folate receptor gene of CABA I ovarian carcinoma cells

The alpha -folate receptor (alpha FR) is overexpressed in 90% of nonmucinou s ovarian carcinomas. In addition to the known role of alpha FR binding and mediating the internalization of folates, functional interaction of alpha FR with signaling molecules was recently shown. To identify a model to stud y the role of alpha FR in ovarian carcinoma, we characterized the alpha FR gene in the ovarian carcinoma cell line CABA I in comparison to a reference line, IGROV1. In CABA I cells, Northern blot analysis revealed an alpha FR transcript of the expected length and FACS analysis indicated receptor exp ression on the cell membrane; however, RNase protection assay revealed no s pecific signals. Southern blot and genomic PCR analysis suggested the prese nce of a rearrangement(s) involving the 5' region of the gene in CABA I cel ls as compared to IGROV1 cells. Cloning and sequencing of CABA I alpha FR c DNA revealed several point mutations. The partitioning of alpha FR in membr ane microdomains from CABA I cells and its association with regulatory mole cules was comparable to that of IGROV1 cells. By contrast, the alpha FR exp ressed on the CABA I cell membrane bound folic acid with lower affinity, an d ectopic expression of the corresponding cDNA in CHO cells confirmed impai red folic acid binding. Thus, CABA I cells may provide a tool to delineate functional domains of the alpha FR. J. Cell. Biochem. 81:488-498, 2001. (C) 2001 Wiley-Liss, Inc.