DIFFERENTIATION-STAGE SPECIFIC EXPRESSION OF ONCOPROTEIN-18 IN HUMAN AND RAT PROSTATIC ADENOCARCINOMA

Oncoprotein 18 (Op18) is an intracellular phosphoprotein that has been shown to be overexpressed in a number of human malignancies. Tn the p resent report we have studied the pattern of Op18 expression in normal , hyperplastic, and malignant prostatic tissue as well as in rat prost atic tumor lines. One of the objectives of the present work was to est ablish whether the level of Op18 expression can be used as a prognosti c marker in human prostatic adenocarcinoma. To that end, sections from normal, hyperplastic, and malignant human prostatic tissue were exami ned by immunohistochemistry for expression of Op18. In the normal and hyperplastic prostate, Op18 expression was observed in basal glandular epithelial cells, whereas the columnar luminal epithelial cells were not stained by the anti Op18 antibodies. In highly differentiated pros tatic cancers occasional epithelial cells were stained, while in poorl y differentiated tumors most of the epithelial cells contained Op18 im munoreactivity. The staining pattern was similar in the primary prosta tic tumor and in the regional lymph node metastases. Most importantly, a limited survey of prostatic cancer patient samples (n = 40) showed a significant correlation between the fraction of Op18 immunoreactive cells and survival. Studies of a rat prostatic tumor model, showed tha t only a few cells were stained in the highly differentiated Dunning R 3327PAP tumor, while most cells were stained in the anaplastic AT1 rat prostatic tumor. Interestingly, castration of rats resulted in an inc reased Op18 immunoreactivity, within 14 days, in the highly differenti ated rat R3327PAP prostatic tumor. In conclusion, the level of Op18 ex pression seems to be related to cellular differentiation, histological grade, and survival in prostatic cancers. These findings show that Op 18 immunoreactivity may be useful as a prognostic marker in prostatic cancer. In addition it may help in the differentiation between highly differentiated prostatic tumors and non-malignant conditions. (C) 1995 Wiley-Liss, Inc.