Exon 3 of the α folate receptor gene contains a 5′ splice site which confers enhanced ovarian carcinoma specific expression

The human folate receptor (FR) is overexpressed in ovarian carcinoma. FR transcripts are heterogeneous due to the use of two promoters, P1 and P4, and alternative splicing of exon 3. RNase protection assay and RT-PCR revealed higher levels of the transcripts that include exon 3 in lines and specimens from ovarian carcinoma. A P1–chloramphenicol acetyltransferase (CAT) construct containing exon 3 demonstrated efficient reporter expression only in ovarian carcinoma. 5′ and 3′ deleted variants of the P1–CAT construct were analyzed by RT-PCR of the exogenous transcripts and reporter activity. A 5′ splice site and 35 bp downstream intronic region of exon 3 appeared to regulate enhanced FR expression in ovarian carcinoma.