A NOVEL M(R)-32,000 NUCLEAR PHOSPHOPROTEIN IS SELECTIVELY EXPRESSED IN CELLS COMPETENT FOR SELF-RENEWAL

We investigated the association between expression of a novel M(r) 32, 000 nuclear phosphoprotein (pp32) and cell proliferation in vivo using the well-characterized physiological model of androgen-dependent rege neration of prostate in orchiectomized rats. pp32 is expressed at high levels in neoplastic cell lines and in certain anatomically defined s tem cell compartments of normal human tissues such as intestinal crypt epithelial cells. Immunohistochemistry and in situ hybridization were used to monitor pp32 expression in rat ventral prostatic epithelium f ollowing castration and androgen restoration. Castrated rats retained only 6% of prostate wet weight compared to intact controls but were ca pable of complete gland restoration upon androgen replacement. In inta ct controls, pp32 expression localized to small acini at the periphery of the gland and to rare basal cells in the central regions. Ten days following castration, there was a 3.5-fold enrichment in the frequenc y of pp32-positive cells with greater than 56% of remaining epithelial cells expressing pp32 protein. In situ hybridization showed that all remaining epithelial cells contained pp32 mRNA. Upon testosterone repl acement, pp32 expression and localization returned to that of intact c ontrols. In order to determine the association between pp32 expression and cell division, DNA synthesis was monitored by bromodeoxyuridine i ncorporation during prostate involution and regeneration. Bromodeoxyur idine incorporation peaked 3 days after androgen replacement and occur red diffusely throughout the gland. Thus, pp32-positive cells are anat omically distinguishable from the population of terminally differentia ting cells undergoing rapid expansion. Preliminary immunohistochemical studies of human prostatic neoplasia demonstrated increased expressio n of pp32 in human prostatic adenocarcinoma and prostatic intraepithel ial neoplasia compared to benign prostatic hypertrophy and normal huma n prostate. The highest degree of expression occurred in the higher Gl eason grades and prostatic intraepithelial neoplasia. This work sugges ts that pp32 is a nuclear protein which has a selective but presently undefined role in cells competent for self-renewal.