Androgen ablation-induced programmed death of prostatic glandular cells does not involve recruitment into a defective cell cycle or p53 induction

Proliferating cells characteristically undergo programmed (i.e. apoptotic) death if their progression through the cell cycle is sufficiently perturbed. To determine whether androgen ablation-induced programmed death of prostatic glandular cells involves apoptosis triggered by recruitment of nonproliferating cells into a perturbed cell cycle, rat ventral prostates were assessed temporally after castration for several stereotypical molecular stigmata of entry into the proliferative cell cycle. Northern blot analysis was used to assess levels of transcripts from genes characteristically activated 1) during the transition from quiescence (G₀) into G₁ of the proliferative cell cycle (cyclin-D1 and cyclin-C), 2) during the transition from G₁ to S (cyclin-E, cdk2, thymidine kinase, and H₄-histone), and 3) during progression through S (cyclin-A). Although levels of each of these transcripts increased as expected in prostatic glandular epithelial cells stimulated to proliferate by the administration of exogenous androgen to previously castrated rats, levels of the same transcripts decreased in prostatic glandular cells induced to undergo apoptosis after androgen withdrawal. Northern and Western blot analyses also demonstrated that there was no increase in prostatic p53 messenger RNA or protein content per cell after androgen ablation. Likewise, after castration, there was no enhanced prostatic expression of the WAF1/CIP1 gene, a gene whose expression is known to be induced in both a p53-dependent and -independent manner during recruitment from G₀ into G₁. In addition, androgen ablation-induced apoptosis of prostatic glandular cells was not accompanied by retinoblastoma protein phosphorylation, which is characteristic of progression into late G₁. Nuclear run-on assays demonstrated that there was no increase in the prostatic rate of transcription of the c-myc and c-fos genes after castration. These results demonstrate that prostatic glandular cells undergo programmed death in G₀ without recruitment into the G₁ phase of a defective cell cycle, and that an increase in p53 protein or its function is not involved in this death process.