Human prostate-specific transglutaminase gene: promoter cloning, tissue-specific expression, and down-regulation in metastatic prostate cancer.

OBJECTIVES: To investigate the tissue-specific and differential expression of the human prostate-specific transglutaminase (pTGase) gene in metastatic prostate cancer (CaP) and to study how this gene is regulated in the prostate.
METHODS: Northern blot hybridization and polymerase chain reaction (PCR) were performed using RNA from a variety of organs to confirm prostate-specific expression of the gene. Relative quantitative reverse transcriptase-PCR (RT-PCR) was performed to investigate the differential expression of the gene among normal prostates and prostates with CaP and metastatic CaP. The pTGase gene promoter was cloned using genomic library screening and sequencing. Transfection experiments and chloramphenicol acetyltransferase (CAT) assays were performed to study the regulation of the gene.
RESULTS: Northern hybridization and RT-PCR confirmed that the gene is only expressed in the prostate. Relative quantitative RT-PCR demonstrated a loss of expression of the pTGase gene among men with CaP and higher Gleason grades. In metastatic CaP tissue from various sites, 86% of the samples lost expression of the gene. We cloned and sequenced a 1.4-kilobase promoter region of the pTGase gene. Transfection and CAT assay results supported the theory that certain elements in the -1 to -520 region are sufficient to direct prostate-specific expression of the gene. Additional elements in the -520 to -1400 region may also contribute to its prostate-specific expression.
CONCLUSIONS: The results of our study demonstrate that the human pTGase gene is only expressed in prostate tissue and that its expression is inhibited in most metastatic CaP. Prostate-specific expression of the gene is controlled by elements in the promoter region. The observed preferential loss of pTGase gene expression in metastatic CaP may be important to the pathogenesis and progression of this disease.