Microseminoprotein, Prostate Associated (MSMP)

PSMP is highly conserved, sharing 91 to 94% amino acid identity with its rodent and dog homologs. RT-PCR of 27 human tissues detected PSMP expression only in trachea and, to a lesser extent, testis. PSMP was highly expressed in PC3 cells, but not in 2 other prostate cancer cell lines. Western blot analysis revealed an 18-kD PSMP protein in culture medium conditioned by PC3 cells. Lysates of PC3 cells also contained a 16-kD PSMP protein, suggesting that PSMP undergoes posttranslational modification prior to secretion. Immunohistochemical analysis and in situ hybridization showed strong expression of PSMP mRNA and protein in xenografted PC3 tumors from athymic nude mice. Immunohistochemical analysis of human prostate cancer specimens showed PSMP expression in the cytoplasm of both benign and malignant epithelial cells.