Prostate Specific Membrane Antigen (PSMA) is highly expressed in prostate cancer and the neovasculature of nearly all non-prostate cancers. Its levels may be highest in androgen-independent prostate cancers although the function of PSMA in oncogenesis and/or prostate cancer progression is unknown. The two predominant PSMA splice variants include a membrane-bound full length PSMA and a cytosolic PSMA' which lacks the encoded transmembrane domain located at the end of exon 1. The PSMA:PSMA' mRNA ratio in prostate cancer is substantially higher than that of normal prostate and benign prostate hyperplasia. A lesser known PSMA splice variant lacking exon 6 should produce a truncated and presumably inactive protein. To alter expression of PSMA splice variants we have targeted both the downstream 5' splice site of PSMA's exon 1 and the 5' splice site of exon 6 with two 18-mer antisense 2'-O-methyl splice-switching oligonucleotides (SSOs). The SSO targeted to exon 1 induces the simultaneous downregulation of PSMA and upregulation of PSMA' mRNA in the LnCap prostate cancer cell line, the other decreases mRNA levels of PSMA without increasing PSMA' levels. Splice switching resulted in concomitant changes at the protein level. Both SSO treatments gave led to a decrease in cell proliferation. A marked increase in apoptosis was measured by PARP cleavage assay; the PSMA5'A1 SSO was more efficient at apoptosis induction. Functional studies of PSMA's dipeptidase activity after splice switching are being carried out. This research may link PSMA's ability to hydrolyze poly-glutamyl folate providing readily-transportable mono-glutamyl folate with cell cycle progression concerning purine and methionine metabolism and the one carbon cycle in prostate cancer and tumor neovasculature. Further, a comparison between results from the two SSO treatments will help distinguish which effects are due to changes in PSMA's intracellular localization.