Effects of aldosterone on RNA polymerase in rat heart and kidney nuclei

The absence of cardiomyopathy is accompanied by increased activities of CAT, MnSOD and GST in long-term diabetes in rats

The activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), the incidence of DNA damage, the activation of poly (ADP-ribose) polymerase-1 (PARP-1), a marker of DNA repair, and connective tissue growth factor (CTGF), a marker of tissue fibrosis, were examined in the hearts of rats for 16 weeks after diabetes induction by streptozotocin (STZ) administration. A 150% increase in CAT activity was detected at the end of the 2nd week post-STZ administration, and CAT activity remained 80% above the control level throughout 16 weeks. While total SOD and CuZn-SOD exhibited progressively decreasing activities, those of Mn-SOD and GST were elevated. Neither DNA strand breaks (apoptosis or necrosis) nor changes in PARP-1 activity and in CTGF levels (fibrosis) were observed in the diabetic heart. The absence of cardiomyopathy is accompanied with increased activities of CAT, MnSOD and GST.

Role of extracellular matrix proteins in heart function

The cardiac interstitium is populated by nonmyocyte cell types including transcriptionally active cardiac fibroblasts and endothelial cells. Since these cells are the source of many components of the cardiac extracellular matrix, and because changes in cardiac extracellular matrix are suspected of contributing to the genesis of cardiovascular complications in disease states such as diabetes, hypertension, cardiac hypertrophy and congestive heart failure, interest in the mechanisms of activation of fibroblasts and endothelial cells has led to progress in understanding these processes. Recent work provides evidence for the role of the renin-angiotensin-aldosterone system in the pathogenesis of abnormal deposition of extracellular matrix in the cardiac interstitium during the development of inappropriate cardiac hypertrophy and failure. The cardiac extracellular matrix is also known to change in response to altered cardiac performance associated with post-natal aging, and in response to environmental stimuli including intermittent hypoxia and abnormal nutrition. It is becoming clear that the extracellular matrix mainly consists of molecules of collagen types I and III; they form fibrils and provide most of the connective material for typing together myocytes and other structures in the myocardium and thus is involved in the transmission of developed mechanical force. The data available in the literature support the view that the extracellular matrix is a dynamic entity and alterations in this structure result in the development of heart dysfunction.

Purification and characterization of the activated mineralocorticoid receptor from rat myocardium

Cardiac cytosol from adrenalectomized rats was radiolabelled with 10 nM tritiated RU 26752, R 5020 or aldosterone, to saturate the mineralocorticoid receptor (MCR) in the presence of 1 microM RU 38486 to block the glucocorticoid and progestin receptors. Free steroids were removed by charcoal treatment and the radiolabelled cytosol was passed through a phosphocellulose column. The MCR peak in the phosphocellulose eluate was activated at 25 degrees C for 45 min, adsorbed onto the DNA-cellulose and finally extracted once each with buffers containing 1 M potassium chloride or 25 mM magnesium chloride. The pooled DNA-cellulose extracts, reequilibrated with 10 nM [3H]RU 26752, were resolved as a single, homogeneous band of 78 kDa upon polyacrylamide gel electrophoresis. Ion-exchange analysis of the purified MCR on DEAE-cellulose-52 revealed a single peak in the 0.017 M sodium phosphate region with both RU 26752 and R 5020, but aldosterone dissociated during this procedure. Molecular filtration on Ultrogel AcA-44 columns revealed a major 145 kDa peak, with some smaller components of 40 and 80 kDa. These hydrodynamic properties of the purified MCR are at variance with those of the native receptor in crude myocardial cytosol, and suggest that some post-translational modifications in vivo may be required for the expression of MCR-mediated responses.

Analysis of the mineralocorticoid receptor in rat heart with the aid of two new spirolactone derivatives

Two derivatives of spirolactone, synthesized in an effort to eliminate the obnoxious side effects of the native molecule, were employed to dissect various aspects of the MR structure and function in rat heart. The introduction of a propyl residue in position 7 of spirolactone produced a molecule (RU 26752) that exhibited an increased affinity for the agonist specific MR, and furthermore revealed an antagonist-specific MR population in the target organ heart but absent from nontarget lung and liver. The specificity for both sites increased when a methoxycarbonyl group was introduced in the 7 position (ZK 91587). RU 26752 labilized the MR at 35 degrees C but did not interfere with thermal activation assessed on DNA-cellulose and sucrose density gradients. ZK 91587 was even more effective in labilizing the MR and did not permit thermal activation at all. Whereas only one ionic species was observed with RU 26752 on DE-52 columns, two were evident with ZK 91587. Both antimineralocorticoids were bound to populations of two molecular sizes on Ultrogel columns. Thus, the nature of chemical substitution in the 7 position of spirolactone dramatically alters the receptor-mediated antisteroid action of the resulting molecule. Such differences may permit distinction between agonist versus the antagonist-specific receptor conformations, and could possibly be exploited for the eventual purification of the mineralocorticoid receptor from various organs.

Detection of corticosteroid type I binding sites in heart

Both high affinity (type I) and low affinity (type II) corticosteroid binding sites are detected in cytosolic extracts of atrial and ventricular tissue when [3H]aldosterone is used as the ligand. In the presence of RU-28362, which blocks binding of [3H]hormone to the low affinity type II sites, [3H]aldosterone binds to a single class of high affinity sites. The apparent Kd for binding of the hormone to the type I sites was 1.0 nM in atrial cytosol and 0.75 nM in ventricular cytosol. The concentration of type I sites in atrial (12 fmol/mg protein) and ventricular cytosols (11 fmol/mg protein) is comparable to reported values in renal (17-31 fmol/mg protein) cytosol. Activation of the type I hormone-receptor complexes to the DNA-binding form was examined using chromatography on DEAE-Sephadex anion-exchange resin. The unactivated hormone-receptor complex elutes at a concentration of 400 mM KCl. Following heat treatment (25 degrees C, 30 min) the [3H]aldosterone-receptor complex is transformed to a low salt eluting (200 mM KCl), DNA-binding form. Activation is blocked by inclusion of 10 mM sodium molybdate during heat treatment.

ATP-dependent activation of glucocorticoid-receptor complexes from the rat's heart

The effect of ATP on the cytosolic rat heart glucocorticoid receptor was studied by employing different methods for evaluation of the changes in molecular properties of the receptor, induced by activation. Incubation of triamcinolone acetonide labelled cytosol at 25 degrees C or with 10 mM ATP at 4 degrees C leads to the increase in the partition coefficient of the receptor in the aqueous dextran-polyethylene glycol two-phase system and also nuclear uptake of the complexes. The effect of ATP on the partition coefficient was more pronounced, compared with that of thermal treatment or dilution of the cytosol and totally inhibited by 10 mM sodium molybdate. The activating effect of ATP on the glucocorticoid-receptor complexes and sensitivity of this activation to sodium molybdate was also confirmed by DEAE-cellulose chromatography of cytosolic receptor preparations. The results suggest that ATP may be involved in the glucocorticoid receptor activation and through this regulates the translocation of complexes into the nucleus under in vivo conditions.

Glucocorticoid effects on newly synthesized proteins in muscle and non-muscle cells cultured from neonatal rat hearts

To analyze direct effects of steroids on the rates of synthesis (and/or degradation) of newly synthesized proteins of the rat heart, we have used high resolution two-dimensional gel electrophoresis and autoradiography. A collective steroid domain of nineteen proteins, comprising fifteen with an increased rate of synthesis and four with a decreased rate of synthesis, was consistently seen in cultures of cardiac muscle and non-muscle cells from neonatal rats following 24 h incubation with 10(-7) dexamethasone. Similarly, incubation with 10(-7) M sex steroids, mineralocorticoids, and other glucocorticoids including the highly selective compound RU26988, established the glucocorticoid-specificity of the response. Different subsets of this glucocorticoid domain were seen for collagenase- or trypsin-dispersed primary cultures of cardiac muscle and non-muscle cells or for passaged cultures of cardiac non-muscle cells. Six polypeptides were consistently induced in all cardiac cultures, regardless of cell morphology. Two polypeptides were consistently induced only in those cultures containing cardiac non-muscle cells, whereas protein l, of identical Mr(approximately 52K) and pI (approximately 5.3) to desmin, was induced only in cultures of spontaneously contractile cardiac muscle cells. The glucocorticoid domain proteins described herein represent direct steroid effects on cardiac cells and are therefore candidate mediators of physiological glucocorticoid effects on, for example, differentiation and contractility.

Nonenzymatic separation of myocardial cell nuclei from whole heart tissue

A simple and rapid nonenzymatic method has been developed to isolate myocardial cell nuclei from whole heart tissue. This method consists of a controlled disruption of cells followed by isopycnic gradient centrifugation. We have reviewed and compared our method to others more lengthy and laborious. By using a number of criteria, such as morphometric measurements, chemical composition, functional studies, specific nuclear protein markers, and mathematical analysis, we show that the nonenzymatic digestion method provides a most useful technique for the study of the biochemistry of the myocardial cell nucleus.

Fractionation of rat ventricular nuclei

Myocardial cells were isolated after treatment with collagenase (0.05%) and hyaluronidase (0.1%) by discontinuous-gradient centrifugation on 3% Ficoll. Nuclei derived from these myocardial cells were then fractionated on a discontinuous sucrose density gradient with the following steps: (I) 2.0M/2.3M, (II) 2.3M/2.4M, (III) 2.4M/2.5M, (IV) 2.5M/2.6M, and (V) 2.6M/2.85M. The myocardial nuclei were sedimented in the interfaces of gradient fractions (II) and (III). Nuclei from whole ventricles that had been treated with the enzymes before isolation sedimented into five major subsets of nuclei. These findings suggest that nuclei sedimented in the isopycnic gradient at fractions (II) and (III) are most probably derived from myocardial cells. However, this procedure is laborious and lengthy, and the recovery of myocardial-cell nuclei is low. An alternative method was developed to isolate an enriched fraction of myocardial-cell nuclei from whole ventricular tissue without exposing the tissues to enzyme digestion. These ventricular nuclei could be fractionated into five nuclear subsets by using the same discontinuous sucrose density gradient as that described above. The content of DNA, RNA and protein per nucleus for each band was determined. Although the DNA content per nucleus was constant (10pg), that of RNA varied from 1.5 to 4.5pg and that of protein from 16 to 24pg. Nuclei from each band were examined by light-microscopy: large nuclei occurred in the ligher regions whereas smaller nuclei were found in the denser regions of the gradient. From the size distribution pattern of myocardial-cell nuclei compared with that of total ventricular nuclei, it was found that nuclear subsets (II), (III), and (IV) were similar to myocardial nuclei. Electrophoretic analyses of the proteins solubilized in sodium dodecyl sulphate/phenol or Tris/EDTA/2-mercaptoethanol/phenol obtained from each nuclear subset indicate that these fractions are similar, with limited qualitative differences. These findings indicate that isolation of an enriched fraction of myocardial-cell nuclei could be achieved by discontinuous-sucrose-density-gradient centrifugation.

Nuclear proteins in the heart of the cardiomyopathic Syrian hamster. Phosphorylation of phenol-soluble nonhistone proteins

We examined incorporation of 32P into phenol-soluble nonhistone nuclear acidic proteins (NHNP) obtained from myolytic, hypertrophic, and failing phases of hamster cardiomyopathy. NHNP from these dystrophic hamster hearts were phosphorylated much less than their controls, despite a 9-fold increase in uptake of 32P into their nuclei. After fractionation of NHNP by isoelectrofocusing polyacrylamide gel electrophoresis, two major fractions focusing from pH 6.0 to 6.2 and 6.6 to 6.8 were highly phosphorylated in both the control and dystrophic hearts. The latter fraction was much more phosphorylated in the control. Two fractions of NHNP focusing at pH 4.9 and 5.1 were more highly phosphorylated in the dystrophic hearts than in the controls. Autoradiographs obtained from the two-dimensional polyacrylamide slab gel electrophoresis showed that two proteins (pH 4.9 and 5.1; mol wt 25,000 and 60,000, respectively) were highly phosphorylated in the dystrophic heart. There was no detectable phosphorylation of these proteins in the controls. These changes in the phosphorylation of cardiac NHNP may be important in determining the alteration of gene expression in hamster cardiomyopathy.

Role of RNA in the action of aldosterone on Na+ transport

Recent data describing the effects of aldosterone on the induction of messenger RNA (= mRNA) and ribosomal RNA (= rRNA) are reviewed. In the urinary bladder of the toad, aldosterone induces a few specific polyadenylated mRNAs (= poly(A)(+)mRNA) during the latent period, i.e., 30 to 60 min after hormone addition. Later i.e., 90 to 240 min after aldosterone addition, 18S and 28S cytoplasmic rRNA subunits are also induced. The effect of poly(A)(+)mRNA is mineralocorticoid-specific and correlates well with the aldosterone-dependent Na+ transport. Actinomycin D which inhibits both poly(A)(+)mRNA and nonpolyadenylated mRNA (= POLY(A)(-)mRNA) totally abolishes the response to aldosterone on Na+ transport. 3'deoxyadenosine (cordycepin), which inhibits poly(A)(+)mRNA but not poly(A)(-)mRNA, only inhibits 50 to 60% of the physiological response. These differential effects suggest that an intact poly(A)(-)mRNA pathway is also an important factor in mediating the action of aldosterone. In contrast, 3'deoxycytidine, which inhibits rRNA but not mRNA, does not impair the mineralocorticoid response, at least during the first 3 hr of aldosterone action.

Identification of nonhistone chromatin proteins in chromatin subunits

Rat liver chromatin was digested by micrococcal nuclease. More than 80% of the enzyme-digested chromatin could be recovered after centrifugation. Treatment with sodium deoxycholate and Triton X-100 at concentrations of 0.5% in the final chromatin suspension gave a higher recovery. Chromatin subunits were fractionated on a 5-30% linear sucrose density gradient. Approximately 35% of the chromatin subunits could be recovered from the gradient. Chromatin subunits and their DNA fragments were identified by gel electrophoresis and ultracentrifugation. The presence of nonhistone chromatin proteins (NHCP) in chromatin subunits was demonstrated by the following criteria: (i) Quantitative analysis showed that the mass ratio of histone to NHCP, in the presence or absence of detergents, was 1:0,25 or 1:0.1, respectively. (ii) After the removal of acid-soluble protein from the subunits, it was found that most of the phenol-soluble NHCP were similar to total chromatin NHCP. However, four major fractions of these phenol-soluble NHCP were found to be enriched in the subunits as identified by two-dimensional polyacrylamide gel electrophoresis. (iii) Experiments using an exchange of isotope-labeled and nonlabeled chromatin showed that NHCP were tightly bound to the chromatin subunits.

Actions of aldosterone on rRNA and Na+ transport in the toad bladder

Aldosterone increased methylation by [methyl-3H]methionine of nuclear ribosomal ribonucleic acid (rRNA) sedimenting at 18S, 28S, and 40S within 90 min and of 28S cytoplasmic RNA within 240 min of continuous exposure to the precursor and the hormone, in the toad bladder. In addition, incorporation of [14C]uridine into cytoplasmic 4S transfer RNA, and 18S and 28S rRNA was enhanced after 240 min of continuous exposure to the precursor and the hormone. Aldosterone had minimal effects on the 3H or 14C-labeled, acid-soluble pools. These results suggest that aldosterone augments the synthesis of rRNA at the transcriptional level. Ribosomes isolated 240 min after treatment of the toad bladder with aldosterone showed increased incorporation of [3H]-phenylalanine into peptides with both endogenous messenger RNA (mRNA) and exogenous mRNA (i.e., poly(uridylic acid) in an in vitro assay. Inhibition of reinitiation with NaF or poly (AUG) reduced the rate of amino acid polymerization by 45% but the aldosterone to control ratio remained significantly high. These results imply an increase in active ribosomes and perhaps in endogenous mRNA content. Our findings, however, do not distinguish between a steroid-dependent increase in the total number of active ribosomes and an increase in translational activity per ribosome.

Acetylation of nuclear proteins in the isolated perfused rat heart

Female rat hearts were maintained by retrograde perfusion under a hydrostatic pressure of 75 cm H2O. The perfused heart had a coronary flow of 8-9 ml/min and a heart rate of 220-240 beats/min. Recirculation of [3H]acetate (2 muCi/ml perfusate) for 20 min was sufficient to label nuclear proteins. Total nuclear proteins were separated into three major classes: (1) 0.14 M NaCl soluble nucleoplasmic proteins, (2) nucleohistones and (3) nonhistone residual proteins. Approximately 88-90% of the (3H)acetate incorporated was found in the nucleohistone fraction. Polyacrylamide-urea gel electrophoresis of the histones indicated that fraction f1 was not acetylated while f3 and f2al were highly acetylated, containing 75% of the total histone radioactivity. Fraction f2b + f2a2 was moderately acetylated contributing 20-25% of the radioactivity. Nucleohistones isolated from myocardial cells showed the same percentage distribution of (3H)acetate in the histone fractions as the whole heart. Acid hydrolysis followed by steam distillation released more than 95% of the acetyl groups from the two major nucleoproteins. These data suggest that the isolated perfused heart may provide a model system to study covalent modification of nucleoproteins under controlled physiological and biochemical conditions.

Kinetics of RNA labeling in toad bladder epithelium: effects of aldosterone and related steroids

Sucrose gradient analysis revealed an aldosterone-dependent increase in the incorporation of [(3)H]uridine into a nonmethylated, rapidly labeled RNA that sedimented at 9-12 S. This effect was antagonized by an anti-mineralocorticoid, spironolactone (SC 9420), and was not elicited either by a glucocorticoid, cortisol, or by the inactive isomer, 17-alpha-isoaldosterone. These findings are in accord with the inference that mRNA is induced by aldosterone during the latent period and that the induced mRNA mediates the action on sodium transport.

Isolation of nuclear acidic proteins from rat tissues. Characterization of acetylated liver nuclear acidic proteins

Nuclear acidic proteins isolated from rat brain, heart, kidney and liver showed similar, complex patterns on electrophoresis in sodium dodecyl sulphate-polyacrylamide gels. The contamination of nuclear acidic proteins by nuclear-membrane acidic proteins was found to the extent of 11%. Incorporation of [(3)H]acetate into the various nuclear acidic proteins in vivo, which were fractionated by polyacrylamide-gel electrophoresis, differed from tissue to tissue. Hydrolysis of these acetylated nuclear acidic proteins with 6m-HCl at 110 degrees C released 70% of the radioactivity, which indicated that labile acetyl groups had been incorporated into these proteins. Analysis of [(3)H]acetate-labelled nuclear acidic proteins revealed two acetylated amino acid residues, N(2)-acetylserine and N(2)-acetyl-lysine. The significance of the role played by nuclear acidic proteins in relation to gene regulation is discussed.