Human prostate-specific transglutaminase: a new prostatic marker with a unique distribution pattern

Human prostate-specific transglutaminase (hTGp) is a cross-linking enzyme, the physiologic function of which has not been established unequivocally yet. To gain insight into its distribution, we raised antisera against hTGp. By using Western blotting analysis, we found that these antisera specifically recognize a 77-kDa protein in prostatic fluids, seminal plasmas, and prostatic tissues. The concentrations of hTGp in these fluids and tissues were found to be highly variable among individuals. Immunohistochemical examination of several formalin-fixed paraffin-embedded human tissues revealed an exclusive expression in the prostate. The histologic localization and distribution of hTGp within the prostate was assessed by studying multiple sections from tumor-containing prostatectomy specimens and needle biopsies. hTGp expression was entirely restricted to luminal epithelial cells. No basal epithelial cells or stromal cells were stained. Within the prostate, large areas without any hTGp-positive cells were seen. Immunopositive cells were present either in a scattered pattern or concentrated in single or multiple glands in which all luminal epithelial cells expressed hTGp. The latter staining pattern occurred frequently, but not exclusively, in the peripheral zone, whereas scattered expression was most often observed in the transitional zone. Expression of the hTGp protein could occasionally be observed in high-grade prostatic intraepithelial neoplasia, but was not detected in prostate carcinoma cells. The expression pattern as observed for hTGp has not been found thus far for any other prostate-specific marker.