J E Vivienne Watson

BACKGROUND: WFDC1/ps20 protein has been previously established as a growth suppressor of the prostate cancer cell line PC3. It maps to chromosome 16q23.1, a region of frequent loss of heterozygosity, familial association, and genomic loss in prostate cancer. We, therefore, chose to examine WFDC1/ps20 for mutations and expression changes in prostate cancer.METHODS: DNA from 21 prostate cancer patients and 5 prostate cancer cell lines was screened for mutations in the WFDC1/ps20 gene by sequencing PCR products of each exon. An SphI polymorphism in the 5′ UTR was screened in 23 tumors, 22 normal adjacent prostate tissue samples, and 35 control DNAs. Expression of WFDC1/ps20 in different tissue types was examined by Northern blot and by PCR across a multi‐tissue cDNA panel. Expression patterns of WFDC1/ps20 in primary tumors were examined by full‐length RT‐PCR and products were cloned and sequenced to identify novel splice forms. Quantitative RT‐PCR analysis of WFDC1/ps20 was performed in a separate cohort of matched tumor/benign tissues.RESULTS: No tumor‐associated mutations were identified in the coding region of WFDC1/ps20. A novel polymorphism was found in exon 6 in DNA from cell lines, tumors, and normal adjacent benign tissue. A novel splice form completely deleted for exon 3 was found in tumor and normal prostate RNA. Quantitative RT‐PCR demonstrated significant down regulation of WFDC1/ps20 in prostate tumors. Subdivision of normal tissue into stromal and epithelial compartments showed that WFDC1/ps20 expression correlates exponentially with the amount of stroma present.CONCLUSIONS: WFDC1/ps20 is down regulated but not frequently mutated in prostate cancer. It is expressed predominantly in the normal stroma of the prostate. We, therefore, propose that WFDC1/ps20 may not be a classical tumor suppressor gene, but might play a role in the maintenance of the normal extra cellular matrix milieu in the prostate.

We have constructed a high-resolution genomic microarray of human chromosome 16q, and used it for comparative genomic hybridization analysis of 16 prostate tumors. We demarcated 10 regions of genomic loss between 16q23.1 and 16qter that occurred in five or more samples. Mining expression array data from four independent studies allowed us to identify 11 genes that were frequently underexpressed in prostate cancer and that co-localized with a region of genomic loss. Quantitative expression analyses of these genes in matched tumor and benign tissue from 13 patients showed that six of these 11 (WWOX, WFDC1, MAF, FOXF1, MVD and the predicted novel transcript Q9H0B8 (NM_031476)) had significant and consistent downregulation in the tumors relative to normal prostate tissue expression making them candidate tumor suppressor genes.