ANDROGENIC REGULATION OF PHOSPHORYLATION AND STABILITY OD NUCLEOLAR PROTEIN NUCLEOLIN IN RAT VENTRAL PROSTATE

Nucleolin is an abundant nucleolar phosphoprotein which has been impli cated as a factor in various stages of ribosome synthesis, including t ranscription. Since androgens exert a profound effect on the rRNA synt hesis in the target organ prostate, we have examined the nature of and rogenic regulation of the amount and phosphorylation of nucleolin in t his tissue. Phosphorylation of prostatic nucleolin is catalyzed in par t by heparin-sensitive casein kinase 2 (CK-2) and by another (heparin- insensitive) protein kinase. Both the amount and phosphorylation of pr ostatic nucleolin are profoundly sensitive to androgens. Rapid reducti on in the level and phosphorylation of nucleolin occurs following andr ogen deprivation, which corresponds to the ensuing cessation of prosta tic growth leading to involution. Further, the loss of nucleolin phosp horylation and its degradation appear to be concordant. Administration of a single injection of 5 alpha-dihydrotestosterone to castrated ani mals causes an early increase in the amount and phosphorylation of nuc leolin, starting in the prereplicative phase in the prostatic cell nuc leus. These data suggest that early androgenic regulation of nucleolin expression and phosphorylation may play a role in nucleolar control m echanisms relevant to prostatic cell growth. (C) 1994 Wiley-Liss, Inc.