Angiotensin-converting enzyme (CD143) in neoplastic germ cells

Angiotensin I-converting enzyme (ACE, CD143, Kininase II, EC 3.4.15.1) occurs in two isoforms; whereas the somatic isoform (sACE) appears in certain endothelial cells and some other cell types, the testicular isoform (tACE) was found in humans and various mammals only during spermiogenesis. An expression of ACE was reported formerly in some human seminomas, but its isoform type, cellular distribution, and pathogenetic meaning are not known. Therefore we analyzed normal human testes, 22 different testicular tumors, and 23 fetal and postnatal tissues of different stages of testicular development. By reverse transcriptase-polymerase chain reaction, ACE mRNA isoforms were assessed in homogenized tissue sections and in germ cells selectively isolated by laser-assisted cell picking. Immunohistochemistry was performed on consecutive sections using monoclonal antibodies specific to the human somatic isoform or both, sACE and tACE. In adult men, tACE was detectable in spermatids and spermatozoa, but normal spermatogonia and spermatocytes were not found to express ACE in any isoform. By contrast, both mRNA and protein of sACE were detectable in the cells of intratubular germ cell neoplasm, seminomas, and other testicular tumor types. Because sACE was also found in fetal germ cells, our findings point to profound differences in the regulation of ACE expression in fetal, mature adult, and neoplastic germ cells. They are in agreement with the concept that neoplastic germ cells phenotypically reflect an embryonic stage of cellular differentiation. Laser-assisted cell picking proved to be a reliable method to investigate differently regulated mRNA of cells which reside in close neighborhood within complex tissues.