Monoclonal antibody to prostate cancer nuclear matrix protein (PRO:4- 216) recognizes nucleophosmin/B23

BACKGROUND. The nuclear protein B23, nucleophosmin, is an RNA- associated nucleolar phosphoprotein reported to be more abundant in malignant and growing cells than in normal nondividing cells. We examined the levels of B23 in fresh human prostate tissue and in five human prostate cancer cell lines with monoclonal antibodies (mAb) to nucleophosmin (α-B23) and to human prostate cancer nuclear matrix proteins (PRO:4-216). METHODS. mAb PRO:4-216 and mAb α-B23 were used for protein level detection. Nuclear matrix proteins (NMPs) were prepared from prostate tumor and five human prostate cancer cell lines: LNCaP, TSU, DU145, PC-3, and PPC-1. The NMPs were run on one- dimensional and two-dimensional (2D) electrophoresis gels for Western blot analysis with the two mAbs. Histologic sections from paraffin-embedded normal and cancerous prostate tissue were stained immunohistochemically with both mAbs. RESULTS. PRO:4-216 and B23 mAbs identified a 40-kD protein (pI ~5.0) by Western blot analysis in the human prostate cancer cell lines and on two- dimensional blots of human prostate cancer NMPs. Immunohistochemical staining demonstrated large punctate nuclear dots in most cancer nuclei, while staining of normal tissue was less intense or absent. Predominant reactivity was of epithelial nuclei, with some minor reactivity of stromal nuclei. Red blood cells (RBCs) and white blood cells (WBCs) were routinely negative. CONCLUSIONS. PRO:4-216, previously characterized as recognizing prostate cancer nuclear matrix proteins, recognized B23/nucleophosmin. PRO:4-216 and α-B23 showed intense immunohistochemical staining of B23/nucleophosmin in cancer nuclei compared to adjacent normal cells in paraffin-embedded prostate tissue. This preliminary study showed the potential of B23 as a tumor marker for human prostate cancer.