Analysis of prostate-specific membrane antigen splice variants in LNCap cells

The prostate-specific membrane antigen (PSMA), a product of the folate hydrolase (FOLH1) gene, is highly expressed as a largely extracellular membrane-anchored protein in malignant prostate tissues and in nonprostatic tumor neovasculature. Treatment of prostate cancer LNCap cells with splice-switching oligonucleotides (SSOs) modulated splicing of FOLH1 pre-mRNA from the full-length PSMA splice variant to three splice variants: the cytoplasmic PSM', alternatively spliced at exon 1, and the previously unexamined PSMA Delta 6 and PSMA Delta 18 variants, which lack exons 6 and 18, respectively. Application of SSOs decreased membrane PSMA levels and increased PSM', PSMA Delta 6, and PSMA Delta 18 transcripts. As a result, PSM' protein was translocated to the cytoplasm, and switching to PSMA Delta 6 and PSMA Delta 18 downregulated PSMA expression. NAALADase assays showed that PSM' retained enzymatic activity. PSMA Delta 6 and PSMA Delta 18 were not active, presumably due to a change in a reading frame that eliminated the NAALDase active site or the dimerization domain or both in these proteins.