Androgen-induced gene activation in the rat prostate

The role of androgen metabolism in the control of androgen action in the rat prostate

Recent results from a number of laboratories have led us to re-examine the role of 3 beta-androstanediol in the rat ventral prostate. Whereas previously 5 alpha-dihydrotestosterone and 3-beta androstanediol were thought to have distinctly separate effects on the prostate, we suggest that 3 beta-androstanediol serves only as an intermediate in the metabolism and removal of 5 alpha-dihydrotestosterone from the organ. In our view the action of androgens on the prostate are exerted exclusively through the binding of 5 alpha-dihydrotestosterone to the androgen receptor and its subsequent translocation to the nucleus. Differences in effects are related to the amount of 5 alpha-dihydrotestosterone available to the gland. 3 alpha-Hydroxysteroid dehydrogenase may play a critical role in modulating the level of 5 alpha-dihydrotestosterone available to the translocatable receptor.

Theoretical mechanisms for synthesis of carcinogen-induced embryonic proteins. V. The steroids

Since the induction of neoplastic cells by steroids has been well documented, an attempt is made to formulate a mechanism for explaining the resultant embryonic features of such tumour cells. Special emphasis is given to estrogen receptor complexes and their effect on chromatin proteins. Specifically a mechanism is presented for estradiol-17-beta and its ability to alter the gene expression (derepression) of mammary gland epithelial cells. In this model we explore the possible effects of small differences in receptor or repressor proteins associated with estrogens to translate quantitative steroid administration into qualitative cellular responses.

Comparative properties of rat liver chromatin in situ and in vitro at early stages after partial hepatectomy

The binding of acridine orange and ethidium bromide to rat liver chromatin increases by 30% one hour after partial hepatectomy, returns to the control level by the second hour and increases again by the sixth hour. The changes described were found in investigations carried out on whole cells, on isolated nuclei, and on chromatin preparation in vitro. Increased ligand binding disappears after the treatment of the one-hour chromatin with a 0.3 M NaCl solution, but such a treatment does not change the binding of ligands to chromatin obtained six hours after hepatectomy. The one-hour chromatin is characterized by elongation of distances between individual nucleosomes whereas the two-hour chromatin is the same as in control.

The role of nonhistone chromosomal proteins in the interaction of prostate chromatin with androgen.receptor complex

Rat prostate nonhistone chromatin proteins were fractionated by sequential extraction with 0.35 M NaCl and 2.0 M NaCl into 0.35 M NaCl-soluble, 2 M NaCl-soluble and -insoluble (residual) fractions. Interactions of [3H]dihydrotestosterone.receptor complex with reconstituted chromatin lacking one of these fractions and with reconstituted hybrid chromatin using spleen fractions indicate that binding of chromatin to androgen.receptor is largely determined by the residual fraction. The residual fraction of prostate also interacts directly with [3H]dihydrotestosterone.receptor complex target tissue-specifically similar to prostate chromatin. The DNA in the residual fraction is mostly bound by nonhistone proteins and the template activity of te residual DNA in transcription is severely restricted. These characteristics are discussed in relation to the acceptor role in the residual fraction in androgen action.

Androgenic regulation of elongation of polyribonucleotide chains on rat ventral-prostate chromatin

The kinetics of polyribonucleotide-chain elongation by rat ventral-prostate RNA polymerase B with homologous chromatin as a template were investigated. Chain elongation was measured under conditions wherein all initiation had occurred, no reinitiation took place and the reaction rate was constant. The kinetic behaviour of prostate RNA polymerase B was consistent with a mathematical model formulated for the multisubstrate enzyme. The addition of each nucleoside triphosphate was independent of the other three. The overall rate of chain elongation was lower when prostate chromatin from castrated rats was used than with prostate chromatin from normal rats. The inclusion of dihydrotestosterone-receptor complexes stimulated the rate of elongation. Androgenic effects did not appear to be directed towards the addition of individual nucleoside triphosphates, but probably towards one of the other major events in RNA-chain elongation, i.e., unwinding of DNA or movement of the enzyme along the template.