IN-VITRO AND EX-VIVO EXPRESSION OF NUCLEOLAR PROTEINS B23 AND P120 INBENIGN AND MALIGNANT EPITHELIAL LESIONS OF THE PROSTATE

The expression of two specific nucleolar antigens, p120 and B23, has b een investigated in the prostatic carcinoma cell line LNCaP as well as in 40 frozen and 40 formalin-fixed tissue samples of benign and malig nant prostatic lesions (15 benign hyperplasias, 5 grade 1, 15 grade 2, and 5 grade 3 carcinomas). In vitro, immunoreactivity of p120 was con fined to nucleoli of proliferating cells, with virtually no negative s taining during S and G(2)/M phases. Unlike p120, B23 was expressed in the nucleoli of all LNCaP cells independently of growth and cell cycle phases. Hence, B23 was detectable in all stromal as well as in normal and malignant epithelial prostatic cells, both in fresh and in formal in-fixed tissue sections after microwave treatment. In contrast, the i mmunoreactivity of p120 was almost completely restricted to the nucleo li of prostate carcinoma cells: frozen sections of benign prostatic hy perplasia (n = 15) were either totally negative for p120 (n = 13) or h ad a low percentage of positively stained cells (labeling index = 3.3% in 3 cases). In the carcinoma group 76% (19/25) of the specimens were p120 positive, and there was a significant rise of labeling index fro m 18.1% in grade 1 to 82.2% in grade 3 carcinomas (P < 0.001). In cont rast to B23, p120 could not be reliably demonstrated in formalin-fixed and paraffin-embedded tissue. We therefore conclude that anti-B23 is a general marker of nucleoli, whereas expression of p120 appears to co rrelate with ''hyperactivity'' of the nucleolus and provides a new too l for flow cytometrical and immunohistochemical assessment of nucleola r activity in tumor pathology.