Troyer J K, Beckett M L, Wright G L
Department of Microbiology and Immunology, Virginia Prostate Center, Eastern Virginia Medical School, Norfolk 23501, USA.
Prostate. 1997 Mar 1;30(4):232-42. doi: 10.1002/(sici)1097-0045(19970301)30:4<232::aid-pros2>3.0.co;2-n.
Prostate-specific membrane antigen (PSMA) is a novel prostate biomarker overexpressed in poorly differentiated and metastatic prostate carcinomas and apparently upregulated following hormone-ablation therapy. PSMA appears to be a satisfactory target for antibody-directed imaging of prostate carcinomas despite the recent finding that the antigenic epitope recognized by monoclonal antibody (MAb) 7E11-C5 is found in the cytoplasmic domain of this transmembrane glycoprotein [Troyer et al.: Urol Oncol 1:29-37, 1995]. This finding prompted the present investigation to precisely define the cellular location of PSMA in the LNCaP prostate carcinoma cell line, the line used to generate MAb 7E11-C5.
Subcellular fractionation, immunofluorescence and immunoperoxidase staining of live and fixed cells, and immunoelectron microscopy were used to determine the localization of PSMA in LNCaP cells.
PSMA was found to be localized at the inner face of the plasma membrane as well as being associated with mitochondria. Staining of LNCaP cells, treated by serum starvation followed by serum stimulation, showed no changes in the typical cytoplasmic staining pattern.
The data suggest that the PSMA target epitope for antibody-directed imaging with MAb 7E11-C5 only becomes accessible upon apoptosis or necrosis. This further suggests that antibodies directed at the extracellular domain may enhance the sensitivity of antibody-directed imaging and therapy of prostate carcinomas by recognizing surface epitopes of PSMA on living cancer cells.
前列腺特异性膜抗原（PSMA）是一种新型的前列腺生物标志物，在低分化和转移性前列腺癌中过表达，并且在激素消融治疗后明显上调。尽管最近发现单克隆抗体（MAb）7E11-C5识别的抗原表位存在于这种跨膜糖蛋白的胞质结构域中，但PSMA似乎是前列腺癌抗体导向成像的一个令人满意的靶点[特罗耶等人：《泌尿肿瘤学》1:29 - 37，1995年]。这一发现促使本研究精确确定PSMA在LNCaP前列腺癌细胞系中的细胞定位，该细胞系用于产生MAb 7E11-C5。
采用亚细胞分级分离、活细胞和固定细胞的免疫荧光及免疫过氧化物酶染色以及免疫电子显微镜技术来确定PSMA在LNCaP细胞中的定位。
发现PSMA定位于质膜内表面以及与线粒体相关。对LNCaP细胞进行血清饥饿后再血清刺激处理，染色显示典型的胞质染色模式没有变化。
数据表明，用MAb 7E11-C5进行抗体导向成像的PSMA靶表位仅在细胞凋亡或坏死时才会暴露。这进一步表明，针对细胞外结构域的抗体可能通过识别活癌细胞上PSMA的表面表位来提高前列腺癌抗体导向成像和治疗的敏感性。
