The a isoform of the Folate Receptor (FR), a cell surface glycoprotein that mediates the uptake of folates and antifolates, is selectively expressed in nonmucinous carcinomas. Knowledge concerning the transcriptional regulation of the a FR gene might shed insight into the mechanism(s) underlying the relative overexpression of the FR in ovarian tumors. The gene is composed of seven exons and is transcribed from at least two promoters: one (P1) is located upstream from exon 1 and the other (P4) is upstream from exon 4. Differential promoter usage and alternative splicing of 5′ flanking exons yield distinct mRNA species that share a common open reading frame and 3′ UTR but that contain unique 5′ termini. RNase protection assays performed utilizing P1- and P4-specific riboprobes on total RNA from six ovarian carcinoma cell lines reveals that P1 transcripts are more abundant than P4 transcripts. Although nuclear extracts from expressing and non-expressing cell lines support transcription from the P1 and P4 promoters as determined by in vitro transcription assays, only the ovarian carcinoma cell lines support transcription from the P1 and P4 promoters in vivo. As determined by gel shift assays, only the sizes of radiolabeled P1 DNA-protein complexes were different between the expressing and non-expressing cell lines, while no differences were detected using radiolabeled P4 promoter sequences. Based on these results, we hypothesize the presence of tissue-specific elements, probably related to the chromatin structure, that contribute to the selective P1 and P4 promoter activation in ovarian carcinoma cells. Partially supported by AIRC/FIRC.
|Publication status||Published - 1997|
ASJC Scopus subject areas
- Agricultural and Biological Sciences (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Cell Biology