Location of prostate-specific membrane antigen in the LNCaP prostate carcinoma cell line.
BACKGROUND
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Troyer
J K
JK
Department of Microbiology and Immunology, Virginia Prostate Center, Eastern Virginia Medical School, Norfolk 23501, USA.
Beckett
M L
ML
Wright
G L
GL
D001769:Blood; D002277:Carcinoma / Q000378:metabolism* / Q000473:pathology; D002462:Cell Membrane / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008928:Mitochondria / Q000378:metabolism; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D013347:Subcellular Fractions / Q000378:metabolism; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
D017430:Prostate-Specific Antigen