Electrophoretic Profiles of Nonhistone Nuclear Proteins of Human Hearts with Muscular Subaortic Stenosis

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1 Electrophoretic Profiles of Nonhistone Nuclear Proteins of Human Hearts with Muscular Subaortic Stenosis 53 CHOONG-CHIN LIEW, MICHAEL J. SOLE, MALCOLM D. SILVER, AND E. DOUGLAS WIGLE SUMMARY Muscular subaortic stenosis (MSS) is a genetically determined cardiomyopathy, whereas right ventricular infundibular hypertrophy (IH) apparently is an acquired condition. Since genetic expression in eukaryotic cells may be regulated primarily by DNA-associated proteins, we isolated and characterized the proteins of heart nuclei from nine patients with MSS, eight with IH, and two with normal (N) hearts. More than 50 proteins could be identified by two-dimensional polyacrylamide gel electrophoresis. Proteins in the entire region from ph 7.0 to 9.0 with molecular weights (M r ) ranging from 35,000 to 4,000 and a protein focusing from ph 5.2 to 5.3 with M r of 55,000 were strikingly reduced in MSS. Again the electrophoretic patterns of N and IH were similar. The electrophoretic patterns of nonhistone nuclear protein (NHNP) in MSS relative to N showed a striking resemblance to those demonstrated previously for the early stage (myolytic phase) of hamster cardiomyopathy relative to the matched control. Since NHNP interacting with DNA appears to play a major role in genetic expression, it is possible that some of the manifestations of MSS could be due to different components of NHNP in the affected hearts. Circ Res 46: 53-59, 980 Downloaded from by on October 5, 208 IDIOPATHIC hypertrophic cardiomyopathy is a primary disorder of heart muscle of unknown etiology characterized by a disproportionate hypertrophy of the ventricular septum and by the presence of a bizarre arrangement of hypertrophied myocardial fibers (Wigle and Silver, 978). One expression of hypertrophic cardiomyopathy is muscular (or hypertrophic) subaortic stenosis (MSS), a condition in which there is a dynamic obstruction to left ventricular outflow (Wigle et al., 962). In a very high percentage of cases of MSS, the trait is transmitted as an autosomal dominant (Braunwald et al., 964; Kariv et al., 97; Clark et al., 973). Genetic expression in eukaryotic cells may be regulated primarily by DNA-associated proteins (for reviews, see Allfrey, 97; Stein et al, 974; MacGillivray, 976; Bekhor, 978; Liew, 979). These DNA-associated proteins are known as chromosomal proteins (i.e., histones and nonhistone chromatin proteins). There is evidence that the chromosomal proteins play a significant role in dictating structural and functional properties of the eukaryotic genome (Allfrey et al., 974; Stein et al., 978). For example, the basic proteins (histones) have been shown to repress DNA-dependent RNA synthesis (Huang and Bonner, 962; Allfrey et al., 963) and are known to have a primary structural From the Departments of Clinical Biochemistry, Pathology, and Medicine, Toronto General Hospital, and Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada. This investigation was supported by grants from the Ontario Heart Foundation, Canada; U.S. Public Health Service (HL ); and the Medical Research Council of Canada. Address for reprints: Dr. C.C. Liew, Department of Clinical Biochemistry, Banting Institute, University of Toronto, Toronto, Ontario, Canada M5G L5. Received April, 979; accepted for publication December 2, 979. function which leads to restriction of the DNA template (e.g., Kornberg, 977). The most recent studies of chromatin structure indicate that histones are also involved in the packaging of the genome (Kornberg, 977; Felsenfeld, 978). On the other hand, nonhistone chromatin proteins (NHCP), or nonhistone nuclear proteins (NHNP), may be involved both in the maintenance of the genome and the regulation of genetic expression (e.g., Paul and Gilmour, 968; Teng et al., 97; Wang and Kostraba, 975; Stein et al., 976). Several lines of evidence (e.g., Gilmour and Paul, 973; Chiu and Hnilica, 978; Tsai et al., 976) have indicated that the highly heterogeneous and tissuespecific NHCP dictate the functional properties of genetic expression. In our previous studies (Liew and Sole, 978a, 978b), we demonstrated alterations in both the composition and phosphorylation of cardiac phenol-soluble NHNP in the hereditary cardiomyopathy of the Syrian hamster. This report extends these investigations to the human heart. We examined phenol-soluble NHNP from normal hearts and from the hearts of patients with MSS. In addition, we compared these proteins with those derived from hearts with infundibular hypertrophy (IH) as an acquired form of cardiac hypertrophy. Methods Myocardium from the left ventricular septum was obtained at surgery from nine patients with MSS who were undergoing ventriculomyotomy -myectomy (Wigle et al., 963; Morrow et al., 968). In six of the nine patients, there was a positive family history for hypertrophic cardiomyopathy, with Mendelian dominant inheritance. The family

2 54 CIRCULATION RESEARCH VOL. 46, No. 4, APRIL 980 Downloaded from by on October 5, 208 of one patient could not be traced, and in the families of the remaining two patients, there was no overt evidence of any heart muscle disorder, although specific screening procedures for hyper^o trophic cardiomyopathy (echocardiography) were not undertaken. All patients underwent surgery for symptomatic relief of longstanding angina pectoris, dyspnea, presyncope and/or syncope on exertion that was unresponsive to medical therapy with /3- adrenergic blockade. No patient suffered from congestive heart failure. Severe left ventricular hypertrophy, most marked in the ventricular septum, was documented in each patient by echocardiography, left ventricular cineangiography, and at the time of surgery. The specimens obtained at surgery were frozen immediately with liquid nitrogen and stored at 70 C until analysis. At least 2.0 g of tissue were required for the biochemical assay. Myocardial tissue from eight patients with IH (Tetralogy of Fallot or Infundibular Pulmonic Stenosis) was collected from the infundibulum at surgery in a similar manner. IH in these conditions is acquired either in postnatal life or during embryogenesis (congenital). In general, about g of tissue was obtained from each patient; therefore, a pool of four to five patients with MSS or IH was required for twodimensional polyacrylamide gel electrophoresis. Specimens from two patients with normal hearts were taken from cadaveric renal donors at the moment of cardiovascular arrest. Informed consent was obtained from relatives. The samples were frozen and kept under conditions identical to those for the MSS and IH samples. In preliminary experiments with normal heart tissue, the chromatin protein analysis showed no differences among samples taken from the septum, right ventricle, and the free wall of the left ventricle or between samples taken from the different types of lh. Isolation of Nuclei The frozen myocardium was placed in Medium A which contained 0.25 M sucrose, 0 mm Tris-HCl (ph 8.0), 3 HIM MgCl 2, and 0. mm phenylmethylsulfonylfluoride (PMSF), a protease inhibitor. The tissue was minced with scissors and homogenized for 2 seconds in 5 volumes of Medium A using a Polytron homogenizer (Brinkman Instruments) set at position 4. The homogenate was centrifuged at 2000 rpm for 0 minutes in a swinging bucket IEC- J-6 refrigerated centrifuge. The pellet was suspended in 20 volumes of Medium B which consisted of 0.% Triton X-00 in Medium A. The nuclear suspension was filtered through a layer of fine nylon and sieves of mesh in sizes of 20 and 320 /im, respectively. The filtrate was centrifuged at 2000 rpm for 0 minutes. The pellet was resuspended once with Medium A, recentrifuged, then suspended in 30 ml of 2.2 M sucrose containing mm MgCl 2,0 mm Tris-HCl (ph 8.0), and 0. mm PMSF and underlaid with 5 ml of the same solution. This suspension was centrifuged at 25,000 rpm for hour in a Beckman SW 27 rotor as described previously (Taylor and Liew, 976; Liew and Sole, 978a). The pellet then was suspended in Medium A and centrifuged at 2000 rpm in the IEC centrifuge prior to fractionation of the nuclear proteins. Part of the pellet was submitted for microscopy. Electron Microscopy For electron microscopy, the nuclear pellets were placed in 2-3 ml of % osmium tetroxide solution containing sucrose (Caulfield, 957) and centrifuged at 6000 rpm for 0 minutes. The supernatant was decanted. New osmium solution was added, and the nuclei were fixed for 2 hours. The nuclei then were washed in phosphate buffer, dehydrated through graded ethanol solutions, and embedded in an Epon-Araldite mixture. Thin sections, stained with uranyl acetate and lead citrate (Reynolds, 963), were examined in a Philips 200 electron microscope. Fractionation of Nuclear Proteins Nuclear proteins were fractionated into () nucleoplasmic proteins which are soluble in 0.4 M NaCl, (2) basic proteins (histones) which are soluble in 0.25 M HC, and (3) NHNP which are soluble in phenol (Suria and Liew, 974a). Acid-soluble nuclear proteins were fractionated by acid-urea polyacrylamide gel electrophoresis (Panyim and Chalkley, 969). Seventy-five micrograms of this protein were used for analysis. The gels were stained with 0.% amido black and destained electrophoretically. Acid-insoluble NHNP obtained from the phenol extraction method were dialyzed in 8 M urea, 0.02 M Tris-HCl (ph 8.4), and 0.% /?-mercaptoethanol containing 0.02 M glycine to prevent possible carbamylation during dialysis (Suria and Liew, 974b; Jackowski et al., 976). For one-dimensional polyacrylamide gel electrophoresis of isoelectrofocusing, the protein samples were mixed with 38.4% acrylamide,.6% iv,iv'-methylene-bis (acrylamide), 40% ampholine (ph 3.5-0), and 0.25% ammonium persulfate (in 0 M urea, freshly prepared) in proportions of.25:0.5:0.25:30 (by volume). The mixture was pipetted immediately into an acid washed glass tube (2.5 X 90 mm) to a height of 68 mm. After overlaying with water, the gel was left to polymerize for hour, followed by electrofocusing at 200 V for 5 hours. Gels were fixed overnight in 0% trichloroacetic acid (TCA) and stained semiquantitatively (Diezel et al., 972) in 0.% Coomassie blue-0% acetic acid. The ph gradients of the gels were determined as described previously (Suria and Liew, 974b). Sodium dodecyl sulfate (SDS)-polyacrylamide slab gel electrophoresis in the second dimension was prepared as described previously (Suria and Liew, 974b); Jackowski et al., 976). The following stock solutions were used to prepare the gel: (i)

3 NONHISTONE PROTEINS IN MSS/Liew et al. 65 TABLE Composition of Nuclear Proteins Nuclear suspension Histone NHNP Control MSS IH The results are expressed as jig/g heart tissue. Heart tissues from patients with MSS and IH were pooled for isolation of nuclei. Tissue for the control was obtained from the cadaveric renal donor with normal heart. Downloaded from by on October 5, 208 FIGURE Electron micrograph of heart nuclei. Nuclei were isolated from the left ventricle of a normal human heart (uranylacetate and lead citrate stain, 2400X). 38.9% aerylamide-.06% iv,iv'-methylene-bis (acrylamide) wt/vol; (ii).5 M Tris-HCl, ph 8.8; (iii) 0.5 M Tris-HCl, ph 6.8; (iv) 0% SDS; (v) 0.08% ammonium persulfate; and (vi).0% TEMED* (wt/ vol). The lower separating gel was prepared according to the following volume proportions: l(i):l(ii): 0.4(iv):.5(v):0.(vi) and the concentrating gel: 0.45(i):.0(iii):0.4(iv):.5(v):0.2(vi) and 0.45 parts of distilled water. After electrophoresis, the slab gels were fixed with 0% acetic acid-50% alcohol overnight. They were stained for 4 hours with 0.% Coomassie blue-0% acetic acid. Destaining of the gels was carried out in 25% ethanol-0% acetic acid. The gels were stored in 7% acetic acid. Determination of Protein and Molecular Weights Protein determination was carried out by the method of Lowry et al., (95) using bovine serum albumin as the standard. Molecular weights (M r ) of NHNP were estimated by protein markers, e.g., human carbonic anhydrase (29,000), ovalbumin (45,000), bovine serum albumin (67,000), and phosphorylase A (9,000). Results Isolated Nuclei Nuclei isolated from MSS, IH, and normal hearts were examined for their purity and composition. Light and electron micrographs showed the nuclei to be intact and free of cytoplasmic contamination (Fig. ). * iv,n,a'',/v'-tctramethylethylene-diamine. Fractionation of Nuclear Proteins The composition of nuclear DNA-associated proteins is presented in Table. About 50% of the nuclear proteins were histones. The histones were fractionated by acid-urea polyacrylamide gel electrophoresis as shown in Figure 2. The electrophoretic patterns for the three groups were identical. NHNP were fractionated by isoelectrofocusing in the first dimension and SDS-polyacrylamide slab gel electrophoresis in the second as shown in Figure 3. About 50 proteins were identified by two-dimensional polyacrylamide gel electrophoresis. In general, the electrophoretic patterns of IH and normal hearts were remarkably similar. However, there were distinct alterations in protein composition which distinguished MSS from both IH and normal (Fig. 3). For example, proteins (Ai) that were fo- H f - _ MSS IH N FIGURE 2 Fractionation of heart nucleohistone. Nucleohistone (50 ng) from normal (N) hearts and those with IH and MSS were fractionated by acid-urea polyacrylamide gel electrophoresis (Panyim and Chalkley, 969).

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5 NONHISTONE PROTEINS IN MSS/Liew et al. 57 M.W. 9 K- M.W. 9K- 67K- 67K- 45K- 29K- I -. _ N Downloaded from by on October 5, 208 f 29K I l I I 6 PH I 8 IH i I i i i i 6 7 FIGURE 4 Fractionation of acid-insoluble heart homogenate proteins. Acid-insoluble heart homogenate proteins (250 Hg), which were phenol-soluble, were fractionated by two-dimensional polyacrylamide gel electrophoresis. servativeness of heart NHNP between two species has not been previously reported. Our findings suggest that most of the heart NHNP are held in common by different species. This observation is not unexpected as myocardial cells in different species share similar enzymes and structural proteins. The high resolution of NHNP achieved by twodimensional polyacrylamide gel electrophoresis demonstrated differences in electrophoretic patterns between MSS, IH, and normal hearts. The observed differences in NHNP profiles were exactly reproducible from experiment to experiment. The alterations in NHNP composition between normal hearts and MSS were strikingly similar to those observed between normal hamster hearts and the very early stage of hamster cardiomyopathy. Specifically, proteins focusing in regions A4-A6 showed reductions in both MSS and hamster cardiomyopathy (Fig. 5) that were comparable to those of their respective controls. H It does not appear likely that our observations were due to traces of cytoplasmic proteins contaminating our nuclear preparations. Histological examination confirmed the purity of our nuclei. Although the contractile proteins constitute more than 80% of the cytoplasmic proteins of the myocardial cell, none of the altered NHNP exhibited electrophoretic characteristics similar to those of the major contractile proteins (Fig. 4). Furthermore, we have shown (by two-dimensional polyacrylamide gel electrophoresis) that the acid-insoluble, phenol-soluble proteins of whole heart homogenates (nuclei and cytoplasm) from MSS, IH, and normal hearts were comparable (Fig. 4). The contribution of nonmuscle cell nuclei is an important consideration in any comparative investigation of cardiac nuclear biochemistry. In this report, to evaluate the contribution of connective tissue, nuclei from both IH and normal hearts served as controls for MSS in our analysis. If our

6 58 CIRCULATION RESEARCH VOL. 46, No. 4, APRIL * - MSS 47K- Downloaded from by on October 5, PH 7 8 FIGURE 5 Comparison of cardiac NHNP isolated from control (C) and the early stage [myolytic phase (M)] of hamster cardiomyopathy and normal (N) and MSS human hearts. Fractions of interest demarcated by hatched boxes (see text). results were merely artifacts of increased connective tissue contamination, we would expect a gradual change between normal, IH, and MSS, assuming that the patients with MSS had more connective tissue than those with IH. Histological analysis of our tissue specimens did not demonstrate a significant increase in connective tissue from our patients with MSS as compared to IH. The electrophoretic patterns of both IH and normal were strikingly similar and clearly distinct from that of MSS. Furthermore, we have shown that the NHNP profile obtained from purified cardiac muscle cells of failing cardiomyopathic hamsters did not differ significantly from that obtained from unpurified whole heart nuclei (Liew and Sole, 978a). The particular function of any given NHNP identified by our analysis is, as yet, unknown. However, Suria and Liew (979) recently have shown in liver cells that a group of NHNP found in the region ph and M r of 35,000-40,000 plays an important role in the processing of mrna. This group of proteins (Ae) is strikingly reduced in MSS as compared to both the control and IH. These proteins are also known as ribonucleoprotein particles (e.g., Karn et al. 977; LeStourgeon et al. 978). It is possible that these differences in NHNP represent 3 4 PH alterations in the processing or maturation of mrna. Recent findings pertaining to intervening sequences of DNA and the processing of mrna (see review Darnell, 978) suggest that these proteins also may be involved in post-transcriptional events. We conclude that NHNP isolated from hearts of patients with MSS are quantitatively, and perhaps qualitatively, different from both normal and IH hearts. Furthermore, the electrophoretic patterns in both MSS and the very early stage of hamster cardiomyopathy show a striking resemblance. Since NHNP interacting with DNA appear to play a major role in genetic expression, it is possible that some of the manifestations of MSS could be due to a different constitution of NHNP in the affected hearts. Acknowledgments We are very grateful to Professor W.G. Bigelow and Dr. W.G. Williams for providing us with human tissues. The competent assistance of L. Suigu and J. Hwang are greatly appreciated. References Allfrey VG (97) Functional and metabolic aspects of DNAassociated proteins. In Histones and Nucleohistones, edited M

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