Nuclear acceptor sites for sex steroid hormone receptors in chromatin

A DNA-binding element for a steroid receptor-binding factor is flanked by dual nuclear matrix DNA attachment sites in the c-myc gene promoter

The receptor-binding factor (RBF) for the avian oviduct progesterone (Pg) receptor (PR) has previously been shown to be a unique 10-kDa nuclear matrix protein that generates high affinity PR-binding sites on avian DNA. This paper describes the use of Southwestern blot and DNA gel shift analyses with RBF protein to identify a minimal 54-base pair RBF-binding element in the matrix-associated region (MAR) of the Pg-regulated c-myc gene promoter. This element contains a 5'-GC-rich domain and a 3'-AT-rich domain, the latter of which has a homopurine/homopyrimidine structure. The gel shift assays required the generation of an RBF-maltose fusion protein (RBF-MBP), which specifically binds this element and is supershifted when the anti-RBF polyclonal antibody is added. Computer analysis of the full-length amino acid sequence for RBF predicts a DNA-binding motif involving a beta-sheet structure at the N-terminal domain. Southern blot analyses using nuclear matrix DNA suggests that there are dual MAR sites in the c-myc promoter, which flank an intervening domain containing the RBF element. The co-transfection of this MAR sequence, containing the RBF element and cloned into a luciferase reporter vector, together with an RBF expression vector construct, into steroid treated human MCF-7 cells, results in a decrease of the c-myc promoter activity relative to control transfections containing only the parent vector of the RBF expression construct. These data suggest that a unique chromatin/nuclear matrix structure, composed of the RBF-DNA element complex which is flanked by nuclear matrix attachment sites, serves to bind the PR and repress the c-myc promoter.

Nuclear matrix acceptor binding sites for steroid hormone receptors: a candidate nuclear matrix acceptor protein

Steroid/nuclear-hormone receptors are ligand-activated transcription factors that have been localized to the nuclear matrix. The classic model of hormone action suggests that, following activation, these receptors bind to specific "steroid response elements" on the DNA, then interact with other factors in the transcription initiation complex. However, evidence demonstrates the existence of specific chromatin proteins that act as accessory factors by facilitating the binding of the steroid receptors to the DNA. One such protein, the "receptor binding factor (RBF)-1", has been purified and shown to confer specific, high-affinity binding of the progesterone receptor to the DNA. Interestingly, the RBF-1 is localized to the nuclear matrix. Further, the RBF-1 binds specifically to a sequence of the c-myc proto-oncogene that has the appearance of a nuclear matrix attached region (MAR). These results, and other findings reviewed here, suggest that the nuclear matrix is involved intimately in steroid hormone-regulated gene expression.

Immunohistochemical localization of the avian progesterone receptor and its candidate receptor binding factor (RBF-1)

An avian oviduct nuclear matrix protein in the 6-10 kDa size range has been implicated to function in the cell-free nuclear binding of the avian oviduct progesterone receptor (PR). This protein, termed the receptor binding factor-1 (RBF-1), has been purified and partially characterized [Schuchard et al.: Biochemistry 30:4535-4542, 1991]. This paper describes the immunohistochemical co-localization of the RBF-1 and PR in the avian oviduct cell nuclei and rat reproductive cell nuclei using antibodies directed specifically against the RBF-1 and activated PR. In the undifferentiated oviduct, the immunoreactivities for both PR and RBF-1 were co-localized in the nuclei of only epithelial cells, but not the stromal cells or smooth muscle cells. In the partially differentiated oviduct of estrogen treated chicks, the immunoreactivity co-localized in the nuclei of not only epithelial but also glandular and stromal cells. Staining for the PR, but not RBF-1, was detected in the smooth muscle cells. The intensity of the PR but not the RBF-1 staining was markedly down-regulated in these cells at 2 and 6 h after treatment of the animals with progesterone (P). However, the band patterns for RBF-1 in the Western blots did show qualitative changes which may reflect P-induced posttranslational modifications which alter the epitope on the RBF-1. Interestingly, immunohistochemical analysis of several reproductive tissues of the rat showed that certain cell types in the uterus, ovary, and prostate displayed strong positive nuclear staining for an RBF-1-like antigen(s).(ABSTRACT TRUNCATED AT 250 WORDS)

The methyltrienolone binding protein of JEG-3 cells and human placenta is localized within the nucleus and is tightly associated with chromatin

Human placenta contains the methyltrienolone binding protein (MTBP), an androgen binding protein which is distinct from the androgen receptor. This study demonstrates that the human choriocarcinoma cell line (JEG-3) also contains the MTBP and that in both human placenta and JEG-3 cells the MTBP is located exclusively in the nucleus and in particular is associated with DNase 1 resistant chromatin.

Expression of actin and myosin heavy chain genes in skeletal, cardiac and uterine muscles of young and old rats

The steady-state levels of mRNA and transcription of alpha-skeletal actin (alpha-SKA) and adult myosin heavy chain (MHC) genes were measured in the skeletal, cardiac and uterine muscles of young (22-25 week) and old (123-135 week) female rats. The effects of 10(-8) M 17 beta-estradiol/dexamethasone/T3 alpha on their transcription were also studied. The data show that the alpha-SKA mRNA level is lower in the old skeletal muscle and uterus, but is higher in the old myocardium. The adult MHC mRNA level is not different in the three muscles of both the ages. The transcription of alpha-SKA gene is lower in the skeletal muscle and higher in the uterus of old rats. It is unaltered in the myocardium of old rats. The transcription of adult MHC gene is lower in the old uterus. The effects of hormones on transcription of both the genes are different in the three muscles. We show that the expression of alpha-SKA gene is tissue-specific and age-related. The over-expression of alpha-SKA gene in the old myocardium is possibly due to derepression of the gene caused by hypertrophy of cardiac myocytes, and continuous hemodynamic pressure overload on the old heart.

Biochemical and Immunocytochemical Assessment of Neural Progestin Receptors Following Estradiol Treatments that Eliminate the Sex Difference in Progesterone-Facilitated Lordosis in Guinea-Pigs

Abstract A single injection of estradiol benzoate (10 mug), while highly effective in ovariectomized female guinea-pigs, does not prime castrated males to display progesterone-facilitated lordosis. In contrast, adult males and females exhibit the same, high degree of progesterone-facilitated lordosis when primed with two, 2.0 mug injections of free estradiol-17ss (pulse regimen). We compared neural progestin receptor induction after these different estradiol treatments by in vitro radioligand binding assays and immunocyto-chemistry. Binding assays confirmed previous observations of lower concentrations of cytosol progestin receptors in the mediobasal hypothalamus-preoptic area in estradiol benzoate-treated males than in females. No such sex difference was observed in animals that had been exposed to the behaviorally effective estradiol pulse regimen; rather, hypothalamic-preoptic area progestin receptor concentrations in these animals did not differ from the low levels observed in males treated with the behaviorally ineffective estradiol benzoate regimen. Immunocytochemical analysis revealed progestin receptor-immunoreactivity in fewer cells in the medial preoptic nucleus-anterior hypothalamic nucleus, periventricular preoptic area and arcuate nucleus of estradiol pulse- as compared to estradiol benzoate-treated males and females. Estradiol benzoate treatment induced progestin receptor-immunoreactivity in more cells in the medial preoptic area and ventrolateral hypothalamus than estradiol pulses in males, but not in females. Surprisingly, in these regions estradiol benzoate-treated males had significantly more progestin receptor-immunoreactive cells than females. These experiments yield two major findings: First, as has been shown in rats, the display of progesterone-facilitated lordosis is not inflexibly differentiated according to sex in guinea-pigs. Furthermore, reduced concentrations of estradiol-induced progestin receptors in the hypothalamus and preoptic area cannot account for the lack of progesterone-facilitated lordosis that is observed following priming with estradiol benzoate in males. Secondly, in the medial preoptic area and ventrolateral hypothalamus of female guinea-pigs, estradiol pulses are as effective as estradiol benzoate in inducing progestin receptors. These observations, taken together with the finding of equal behavioral efficacy of the two estradiol treatments, are consistent with the hypothesis that estradiol-induced progestin receptors in these regions of the brain are involved in progesterone-facilitated lordosis in female guinea-pigs.

Selective expression of a normal action of the 1,25-dihydroxyvitamin D3 receptor in human skin fibroblasts with hereditary severe defects in multiple actions of that receptor

We evaluated three actions of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] in human skin fibroblasts to test for heterogeneity in hormone-response coupling. In fibroblasts from normal subjects the 1,25-(OH)2D3 concentrations for half-maximal effect (EC50) were: for mitogenic effect 0.0001-0.0005 nM, for antimitogenic effect 1 nM, and for induction of 25-OHD3 24-hydroxylase (24-OHase) 5 nM. To evaluate the effects of mutations presumed to be in the gene for the 1,25-(OH)2D3 receptor we examined cell lines representing four kindreds with hereditary resistance to 1,25-(OH)2D3 ("mutant" cell lines). In one mutant cell line all three 1,25-(OH)2D3 actions were severely abnormal. In one mutant cell line 24-OHase induction and mitogenic action were undetectable, but EC50 and maximal effect were normal for antimitogenic action of 1,25-(OH)2D3. In two mutant cell lines 24-OHase induction and antimitogenic actions were undetectable or severely impaired but mitogenic action were undetectable or severely impaired but mitogenic action was normal in EC50 and normal or increased in maximal effect. The mitogenic and antimitogenic actions in normal cells showed a similar profile of potency ratios for 1,25-(OH)2D3 and six analogues. Whenever a mutant cell showed a normal or even an abnormal mitogenic or antimitogenic effect of 1,25-(OH)2D3, these effects showed potency ratios similar to wild type, suggesting mediation by a similar 1,25-(OH)2D3 receptor. We conclude that three 1,25-(OH)2D3 actions show important differences in hormone response coupling indicated by differences in EC50 for 1,25-(OH)2D3 and by different consequences of receptor mutations.