Bostwick and colleagues have suggested that prostatic intraepithelial neoplasia or PIN is the precursor of prostate cancer and that a significant percentage of men with PIN develop prostate cancer (Sakr, 1994; Bostwick, 1995b; Arakawa, 1995; Qian, 1995; Qian, 1997). Development of diagnostic markers for PIN would be of tremendous benefit to diagnosis of early stage disease. Recently, we have developed ‘DNA-protein’ binding assays for the identification of novel transcriptional regulatory proteins associated with PIN glands. Electrophoretic mobility assays (EMSAs) revealed that 1 DNA sequence (1 of 4096 sequences screened) specifically bound a ∼160 Kda protein over-expressed in PIN and not found in BPH, SV or PCA glands (n=11). The gene was cloned from a cDNA expression library by ‘in situ’ hybridization assays utilizing the 32P-labeled DNA sequence. Sequencing revealed that the gene encoding for the 160 Kda protein was ABCA5, a member of the superfamily of ATP-binding cassette (ABC) transporters of multi-drug resistant genes. RT-PCR assays indicated the mRNA was over-expressed by PIN tissue, but it was not present in BPH, or SV tissue. Rabbit polyclonal antibodies were raised against an n-terminal peptide (20 bases) and immunolabeling showed that the antibodies specifically labeled the cell junctions of glutaraldehyde fixed prostate cells in culture and labeled epithelial cells in sections of PIN tissue. Blinded studies with urine specimens from biopsed patients showed that ABCA5 was over-expressed in urine from patients with PIN (n=10), faintly expressed in PIN + PCA patients (n=8), and not expressed in PCA only (n=4) and BPH patients (n=10). The data suggest that ABCA5 is over-expressed by PIN and may be a urine diagnostic marker for detection of the disease. We are currently developing an ELISA test for ABCA5 utilizing urine specimens of biopsied patients.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]