ANDROGENIC REGULATION OF THE EXPRESSION AND PHOSPHORYLATION OF PROSTATIC NUCLEOLAR PROTEIN-B23

Protein B23 is a nucleolar and nuclear matrix phosphoprotein which has been implicated in ribosomal assembly and/or rRNA processing. Since a ndrogen action in the prostate is accompanied by early changes in rRNA synthesis, we have investigated androgenic regulation of protein B23 expression and phosphorylation in rat ventral prostatic nuclei. The mR NA for prostatic protein B23 was relatively stable and decreased only after several days of androgen deprivation. However, androgen deprivat ion resulted in a rapid change in the amount and phosphorylation of pr otein B23 in prostatic nuclei, which was reversed on administration of androgens to orchiectomized animals. Phosphorylation of protein B23 a ppears to be catalyzed primarily by casein kinase 2 (CK-2). Early andr ogenic changes in phosphorylation of protein B23 appear to relate more to modulations in the protein kinase activity than in the amount of p rotein B23. The androgen mediated enhancement in the amount of protein B23 and its phosphorylation precedes the cellular proliferative phase following androgen administration to castrated rats, and appear to be temporally concordant with the rRNA synthesis in the tissue. The andr ogen mediated changes in the amount and phosphorylation of protein B23 are specific to the prostate and are not detected in the liver nuclei . Thus, androgenic regulation of the amount and phosphorylation of pro static protein B23 may be related to the early changes associated with androgen mediated growth of the gland.