Studies on the mode of oestrogenic inhibition of hepatic synthesis of alpha2u-globulin and its corresponding messenger ribonucleic acid in rat liver

1. The possible mechanism of the oestrogenic inhibition of the androgen-dependent synthesis of alpha2u-globulin in rat liver was explored by a correlative study of the amounts of alpha2u-globulin, its corresponding mRNA and circulating testosterone in oestrogen-treated male rats. 2. Daily treatments of mature male rats with oestradiol-17beta (10 microgram/100g body wt.) decreased and ultimately stopped the hepatic synthesis of alpha2u-globulin as determined by both hepatic and urinary concentrations of the protein. The oestrogen-mediated decrease in the hepatic synthesis of alpha2u-globulin was correlated with a decrease in the mRNA for this protein. 3. Withdrawal of oestrogen resulted in the recovery of alpha2u-globulin synthesis and an increase in mRNA for alpha2u-globulin. 4. At higher doses of oestradiol-17beta (50 microgram/100g body wt.), synthesis of alpha2u-globulin was totally suppressed. In addition, this treatment resulted in an extended period of androgen-insensitivity during which treatment with androgens induced synthesis of neither alpha2u-globulin nor its corresponding mtrna. 5. it is concluded that the oestrogenic inhibition of alpha2u-globulin synthesis is mediated by an oestrogen-dependent decrease in the hepatic content of translatable mRNA for alpha2u-globulin.

Early events in the steroidal regulation of alpha2mu globulin in rat liver. Evidence for both androgenic and estrogenic induction

1. A double-antibody radioimmunoassay for alpha2mu globulin has been developed. With the help of this highly sensitive radoimmunoassay the early effects of both androgen and estrogen treatments on the hepatic synthesis of alpha2mu globulin in the rat have been investigated. 2. Results show that the earlier observation of the long lag period in the androgenic induction of alpha2mu globulin is more apparent than real. 3. Single injections of either 5alpha-dihydrotestosterone(5alpha-dihydro-17beta-hydroxy-4-androsten-3-one) or its physiological antagonist estradiol-17beta (1,3,5(10)-estratriene-3,17beta-idol) to castrated female rats resulted in the induction of alphamu globulin reaching maximum hepatic level of the protein between 6--9 h after the hormone administration. Administration of cycloheximide 15 prior to hormone treatment blocked both androgenic andestrogenic induction of alpha2mu globulin. 4. Daily pretreatments with 5alphamu-dihydrotestosterone increased the sensitivity of subsequent androgenic response to alpha2muglobulin synthesis. On the other hand, daily pretreatments with estradiol 17beta decreased and ultimately abolished the estrogenic induction of alpha2mu globulin. 5. The possible mechanism of both androgenic and estrogenic induction of alpha2mu globulin in rat liver mediated through a sex-hormone-binding protein with dual affinity for both dihydrotestosterone and estradiol has been suggested.

Effect of cyproterone acetate on androgen-dependent synthesis of alpha2u globulin in rats

Cyproterone acetate (CA, 2-5 mg/100 g body wt) inhibited androgenic induction of alpha2u globulin in spayed rats. In mature male rats, which normally produce alpha2u globulin, ten daily injections of CA did not inhibit synthesis of this protein. Long-term treatment of mature male rats (two injections every week for 12 weeks) showed only slight inhibition of alpha2u synthesis after 10 weeks of CA treatment. CA also failed to compete with 5alpha-dihydrotestosterone for the cytosol androgen-binding protein of male rat liver. The inhibitory effect of CA on the primary induction of alpha2u globulin in the spayed rat and its lack of effect on continued synthesis of this protein in maximally induced mature male rats are consistent with the hypothesis of a two-step mechanism for androgenic regulation of alpha2u synthesis, an initial CA-sensitive step followed later by a CA-insensitive step.

Effect of estrogen on gene expression in the chick oviduct. In vitro transcription of the ovalbumin gene in chromatin

RNA was transcribed from chromatin isolated from chick oviduct and spleen by using RNA polymerase from Escherichia coli. RNA was also transcribed from whole chick DNA using E. coli RNA polymerase. DNA complementary to ovalbumin messenger RNA (cDNAov) was then used as a hybridization probe to estimate the concentration of ovalbumin messenger RNA sequences (mRNAov) in these in vitro transcripts. Although chromatin from unstimulated chick oviduct was capable of substantial RNA synthesis, no detectable mRNAov sequences could be found in the transcript. Likewise, mRNAov sequences could not be found in RNA synthesized from spleen chromatin using E. coli RNA polymerase. However, chromatin from estrogen-stimulated chick oviducts was capable of supporting synthesis of ovalbumin mRNA. We estimate that approximately 0.01% of the RNA synthesized from estrogen-stimulated chromatin was mRNAov sequences. When RNA synthesized from chick DNA was tested with the cDNAov probe, mRNAov sequences could be detected in a concentration of approximately 10% that found in the RNA transcript from estrogen-stimulated chromatin. This was as expected if the ovalbumin gene is considered to be in the "open or derepressed" region of the estrogen-stimulated oviduct chromatin. Chromatin isolated from chicks withdrawn from hormone for 12 days was only capable of supporting mRNAov synthesis in vitro at a level of 5 to 10% of that observed in chromatin prepared from estrogen-stimulated chicks, thus indicating the requirement for estrogen to maintain the ovalbumin gene in the available or "open" state in the majority of oviduct cells. These data militate against post-transcriptional control as the primary mechanism of steroid hormone regulation of specific mRNA synthesis in the chick oviduct system, and favor primary gene derepression as the most likely mechanism for estrogen induction of ovalbumin synthesis.

Estrogenic inhibition of the hepatic synthesis of alpha2u globulin in the rat

The hepatic synthesis of the androgen-dependent urinary protein in the rat, called alpha2u globulin, is strongly inhibited by estrogens. In mature male rats, treatment with estradiol-17beta (0.5 mug/g body weight) completely inhibits alpha2u synthesis within 6-7 days. Following withdrawal of estrogen treatment alpha 2u synthesis is not reinitiated for approximately 20 days. Parabiotic joining of estrogen-suppressed male rats with their normal littermates within this lag period fails to change the preparabiotic pattern of alpha2u synthesis in the respective partners. Besides estradiol-17beta, other estrane derivatives such as estrone, estriol and estradiol-17alpha were also found to inhibit the synthesis of alpha2u globulin. All of the above estrane derivatives which inhibit alpha2u synthesis are also found to inhibit the uptake of 5alpha-dihydrotestosterone by the hepatic cytosol androgen binding protein of the mature male rat. Unlike cycloheximide, a known translational inhibitor, estradiol-17beta does not inhibit alpha 2u synthesis in the perfused rat liver.

Hormonal regulation of the hepatic messenger RNA levels for alpha2u globulin

The messenger RNA rat alpha2u globulin has been identified and quantitated in a cell-free translational system derived from Krebs II ascites cells. Hepatic tissue of the mature male rats which normally produce alpha2u globulin was also found to contain a high level of alpha2u mRNA. Approximately 1.6 per cent of all poly(A) containing RNA of the adult male rat liver could be accounted for alpha2u messenger activity. Female rats do not produce alpha2u globulin and no alpha2u mRNA activity could be detected in the poly(A) containing RNA fraction obtained from the livers of these animals. However, androgen treatment to spayed female rats was found to induce the parallel appearance to both alpha2u globulin and its corresponding mRNA. Both hypophysectomy and adrenalectomy which are known to reduce the level of alpha2u globulin in the urine of male rats were found also to reduce the hepatic level of alpha2u mRNA. The results indicate that hormonal control of alpha2u globulin synthesis in rat liver is achieved primarily through regulation of its translatable mRNA level and that more than one hormone may participate in this regulation.

Androgen-dependent synthesis of aplha-2u globulin in the rat: role of the pituitary gland

Hypophysectomy completely abolished the androgen-dependent synthesis of α2u globulin in adult rats. Experiments with adrenalectomized and thyroidectomized adult male rats showed that these endocrine ablations also reduced the daily urinary output of α2u globulin to about 10% or less than those of the pre-operative values. The effects of adrenalectomy and thyroidectomy on α2u output could be reversed to normal with the supplementation of corticosterone and thyroxine respectively. However, none of the pituitary hormones administered alone or along with testosterone was able to reverse the effect of hypophysectomy. Simultaneous treatment with growth hormone, corticosterone and thyroxine along with testosterone was required for the complete reversal of the effect of hypophysectomy. It is concluded that the androgenic induction of α2u globulin is dependent on the synergistic effects of growth and developmental hormones such as growth hormone, thyroxine and corticosterone.

Immunofluorescent localization of 2u -globulin in the hepatic and renal tissues of rat

α2u-Globulin is an androgen-inducible rat urinary protein of hepatic origin. Examination of adult male rat liver sections with rhodamine-labeled anti-α2u-antiserum showed that the liver parenchymal cells are the site of α2u-globulin synthesis and that all of the parenchymal cells contain this protein. Immunofluorescent localization of α2u-globulin in male kidney sections revealed the existence of the protein in the cells of proximal convoluted tubules, in the loop of Henle as well as in the distal convoluted tubule. The collecting ducts did not bind the fluorescent labeled antibody. Intraperitoneally administered rhodamine-labeled α2u-globulin was found to be localized only in the kidney tubules in particulate form. It is concluded that α2u-globulin after its synthesis and release from the hepatic parenchymal cells is filtered into the renal tubular lumen and that both kinds of convoluted tubules as well as the loop of Henle are actively involved in α2u reabsorption.