Delineation of three different thyroid hormone-response elements in promoter of rat sarcoplasmic reticulum Ca2+ATPase gene. Demonstration that retinoid X receptor binds 5' to thyroid hormone receptor in response element 1

Thyroid hormone (3,5,3'-triiodothyronine) positively regulates transcription of the sarcoplasmic reticulum Ca2+ATPase gene in rat heart, and sequences within 559 nucleotides upstream from the transcription start site confer thyroid hormone responsiveness upon a reporter gene. In the present study, three thyroid hormone-response elements (TREs) are identified between nucleotides -485 and -190. Each TRE is active in transient transfection assays and specifically binds 3,5,3'-triiodothyronine receptors (TRs) alpha 1 and beta 1 alone and in combination with retinoid X receptors (RXRs) alpha and beta. TRE 1 is a direct repeat of two half-sites separated by four nucleotides; TREs 2 and 3 are inverted palindromes of two half-sites separated by four and six nucleotides, respectively. Methylation interference analysis of TRE 1 showed binding of a TR alpha 1 monomer to the 3' half-site, whereas the heterodimer contacts both half-sites. Subsequent studies employed TR beta and RXR alpha mutants in which their P-boxes were replaced with the P-box of the glucocorticoid receptor. Bandshifts of wild type and mutant proteins with either wild type TRE 1 or a mutant version, in which the 5' half-site was converted to a glucocorticoid response element half-site, demonstrated preferential binding of RXR to the 5' half-site and of TR to the 3' half-site of TRE 1.

Isolation of a novel inducible rat heat-shock protein (HSP70) gene and its expression during ischaemia/hypoxia and heat shock

Most of the members of the mammalian heat-shock protein (HSP) gene family have been studied and isolated from human and mouse cells. Few studies have concentrated on the HSPs of rat, a commonly used experimental animal. We have isolated and characterized a novel inducible rat HSP70 gene using an HSP70 cDNA sequence obtained from an ischaemic rat heart cDNA library. The isolated rat HSP70 gene was found to be a functional gene, as indicated by RNAase-protection and Northern-blot analysis. The deduced amino acid sequence of the inducible rat HSP70 exhibits a high degree of similarity to previously isolated mammalian inducible HSP70 gene products. Expression of the inducible HSP70 gene in rat myogenic cells (H9c2) is markedly increased after relatively short periods of hypoxia as well as by heat shock. Two heat-shock elements (HSE) are present in the rat HSP70 promoter. Transient transfection of rat HSP70 promoter/chloramphenicol acetyltransferase constructs into H9c2 cells shows that the presence of either of the two HSEs is sufficient for heat-shock inducibility. In contrast, induction of the rat HSP70/chloramphenicol acetyltransferase constructs by hypoxia is only detectable when both HSEs are present. This leads us to conclude that the induction of HSP70 by hypoxia and heat shock occurs through the same regulatory HSEs but the activation of the inducible HSP70 gene by heat shock is several-fold higher than by hypoxia.

Expression of inducible stress protein 70 in rat heart myogenic cells confers protection against simulated ischemia-induced injury

Myocardial ischemia markedly increases the expression of several members of the stress/heat shock protein (HSP) family, especially the inducible HSP70 isoforms. Increased expression of HSP70 has been shown to exert a protective effect against a lethal heat shock. We have examined the possibility of using this resistance to a lethal heat shock as a protective effect against an ischemic-like stress in vitro using a rat embryonic heart-derived cell line H9c2 (2-1). Myogenic cells in which the heat shock proteins have been induced by a previous heat shock are found to become resistant to a subsequent simulated ischemic stress. In addition, to address the question of how much does the presence of the HSP70 contribute to this protective effect, we have generated stably transfected cell lines overexpressing the human-inducible HSP70. Embryonal rat heart-derived H9c2(2-1) cells were used for this purpose. This stably transfected cell line was found to be significantly more resistant to an ischemic-like stress than control myogenic cells only expressing the selectable marker (neomycin) or the parental cell line H9c2(2-1). This finding implicates the inducible HSP70 protein as playing a major role in protecting cardiac cells against ischemic injury.

Identification of functional angiotensin II receptors on rat cardiac fibroblasts

BACKGROUND

Cardiac hypertrophy results in an increased deposition of the extracellular matrix (ECM) proteins fibronectin and collagen. Recent evidence indicates that angiotensin II (Ang II) might have an important role in the development of myocardial fibrosis accompanying cardiac hypertrophy. We sought to determine whether fibroblasts of cardiac origin (isolated from neonatal and adult animals) express receptors for Ang II and to examine the ability of this peptide to regulate fibronectin and collagen gene expression in a cultured adult cardiac fibroblast cell preparation.

METHODS AND RESULTS

Binding of 125I-Ang II to both neonatal and adult cardiac fibroblasts in culture was specific, reversible, and saturable, with the receptor evenly distributed over the cell population. Competition binding experiments with receptor-specific antagonists indicate that Ang II receptors found on both fibroblast types were of the AT1 subtype. Analysis of mRNA levels for the AT1 receptor indicates that adult cardiac fibroblasts express higher levels of the message than neonatal fibroblasts or cardiac myocytes. Addition of 10(-9) mol/L Ang II to adult cardiac fibroblasts resulted in an induction of ECM proteins above control levels, as determined through Northern blots and total collagen assays.

CONCLUSIONS

Results from this study indicate that neonatal and adult rat cardiac fibroblasts in culture express AT1 receptors for Ang II. Ang II stimulation of AT1 receptors results in an increased gene expression for ECM proteins. These data suggest that Ang II might have important regulatory roles over cardiac fibroblast function under normal and pathological conditions.

Cardiac function in thyroid disease: clinical features and management considerations

Thyroid disease is often manifested by cardiac abnormalities. The site of the cardiac actions of thyroid hormone, whether from a direct, nuclear effect or an extranuclear effect, remains to be established. Nuclear effects are delayed 1/2 to 1 hour after administration of thyroid hormone, require ongoing protein synthesis, and are thought to result from the binding of thyroid hormone to two separate isoforms of the nuclear thyroid hormone receptor. This binding, which is specific to thyroid hormone response elements, stimulates transcription and results in translation of specific enzymes or contractile proteins. Extranuclear effects may influence plasma membrane transport of calcium, sugar, and amino acids in addition to directly influencing mitochondria and are very rapid, occurring within minutes. It is possible that there exists an interaction between the adrenergic system and the thyroid hormone system, which may also contribute to the cardiac actions of thyroid hormone. This review highlights the clinical manifestations of thyroid disease and the mechanisms of thyroid hormone involved in the cardiac abnormalities.

Induction of HSP70 in cultured rat neonatal cardiomyocytes by hypoxia and metabolic stress

BACKGROUND

A cultured neonatal rat cardiomyocyte model is used to investigate the expression of the inducible heat shock protein 70 (HSP70i) during hypoxia/reoxygenation and metabolic stress.

METHODS AND RESULTS

The major HSP70i is increased in its expression at the mRNA and protein level in myocytes exposed to hypoxia/reoxygenation and metabolic stress by the addition of 2-deoxyglucose and sodium cyanide, which are inhibitors known to block ATP production. Surprisingly, the appearance of HSP70 mRNA precedes the intracellular ATP depletion caused by hypoxia, which is contrary to what we observe when the cardiomyocytes are subjected to metabolic stress.

CONCLUSIONS

It has been postulated recently that the decrease in intracellular ATP content in cells under stress may be the trigger that leads to the induction of HSP70i by reducing the pool of free HSP70, thus activating the stress response. Our results indicate that although this may be the case during metabolic stress, another route of activation must be used during the early stages of hypoxia in cardiomyocytes. The induction of HSP70i also appears to precede the onset of cellular damage as measured by the release of cytoplasmic enzymes and preincorporated arachidonic acid. This indicates that cardiomyocytes are able to respond to hypoxia/reoxygenation and metabolic stress with increased HSP70i production and points to a potential protective role of heat shock proteins during ischemia/reperfusion injury.

Surgical management of the thyroid nodule: patient selection based on the results of fine-needle aspiration cytology

To determine whether the routine use of fine-needle aspiration (FNA) cytology reduces the rate of unnecessary surgery, the surgical pathology of 54 thyroidectomy patients who had preoperative FNA was compared to the results obtained with 24 thyroidectomy patients who did not have preoperative FNA. Twenty-nine (85.3%) of the 34 patients who had a positive FNA were confirmed by histology to have a thyroid neoplasm; in 24 patients, the neoplasm was malignant. Two of the 17 patients who had a negative FNA but underwent thyroidectomy based on other factors were found to have thyroid cancer. Only 8 (33.3%) of the 24 surgical specimens of patients who did not have an FNA were found to be malignant. FNA had a sensitivity of 93.5% and a specificity of 75.0%. The results indicate that the routine use of FNA for patients with thyroid nodules reduces the incidence of unnecessary surgery. Furthermore, FNA alone is sufficient to identify most patients at risk and is, therefore, cost-effective. However, the presence of other findings suspicious of malignancy should preclude clinical decision making based on FNA alone.

Thyroid hormone response of slow and fast sarcoplasmic reticulum Ca2+ ATPase mRNA in striated muscle

The thyroid status markedly influences the contractile function of muscle, and changes in the activity of the Ca2+ ATPase of the sarcoplasmic reticulum (SR) contribute to these alterations. Two separate genes encode the major isoforms of SR Ca2+ ATPase. In fast skeletal muscle, sarcoplasmic endoplasmic reticulum Ca2+ ATPase type 1 (SERCa1) presents the major isoform, whereas in slow skeletal muscle SERCa type 2 (SERCa2) predominates. Cardiac muscle contains only SERCa2. To examine the mechanisms responsible for changes in contractile function, we quantitated SERCa1 and SERCa2 mRNA levels in fast extensor digitorum longus muscle (EDL), slow soleus muscle, and cardiac muscle in rats of different thyroid status. Hypothyroidism led in soleus to a marked decrease in SERCa1 mRNA and SERCa2 mRNA levels, in cardiac muscle SERCa2 mRNA decreased markedly, as previously shown by us, and in EDL SERCa1 mRNA decreased. These findings are compatible with a hypothyroidism induced decrease in SR Ca2+ ATPase activity and a delay in muscle relaxation. In contrast, SERCa2 mRNA of EDL, representing only a small percent of total SERCa mRNA in this muscle, increased to 175% of control values. Muscle specific and SERCa gene specific changes also occur after acute triiodothyronine (T3) administration to hypothyroid rats. T3 does not induce a significant change in SERCa1 or SERCa2 mRNA levels in soleus, but in the heart SERCa2 mRNA increases about 3-fold. In EDL, T3 increases SERCa1 mRNA from a hypothyroid level of 59 +/- 6% to 138 +/- 4% of control values but SERCa2 mRNA is decreased to 75 +/- 5% of control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective reduction of creatine kinase subunit mRNAs in striated muscle of diabetic rats

Creatine kinase (CK) is important for energy transfer and is composed of mitochondrial (mitCK), muscle (MCK), and brain (BCK) subunits, each being the product of separate nuclear genes. The concentrations of MCK and BCK mRNAs have been shown to decrease in streptozotocin-hypoinsulinemic rat hearts, and in this report, we examined in detail the diabetic effect on CK gene expression in cardiac muscle and in two types of skeletal muscle. The level of sarcomeric mitCK mRNA was not altered in the diabetic myocardium, but was reduced by 86 and 67% in diabetic slow-twitch soleus muscle and fast-twitch extensor digitorum longus (EDL) muscle, respectively. MCK mRNA was also lowered in diabetic soleus muscle by 56%, while it remained at control levels in diabetic EDL. In both skeletal muscles, at either state, BCK mRNA was not detectable. There was a 33% decrease in total CK activity in diabetic cardiac and soleus muscle, but not in EDL. Diabetes thus exerts a widespread, muscle type-dependent adverse effect on CK expression that we found to be insulin therapy revertible. This study adds to our understanding of defective energy transduction in diabetic muscle.

Cardiac hypertrophy-induced changes in mRNA levels for TGF-beta 1, fibronectin, and collagen

Cardiac hypertrophy induced by pressure overload is accompanied by increases in the deposition of extracellular matrix (ECM) proteins. We wanted to determine in this study whether changes in mRNA coding for transforming growth factor (TGF)-beta 1, TGF-beta 3, and the ECM proteins, fibronectin and collagen, occur during the early phases of cardiac hypertrophy. Steady-state mRNA levels were determined in sham-operated and thoracic-banded hypertrophied rat myocardium from 6 h to 30 days after surgery. TGF-beta 1 mRNA increased significantly (1.7-fold vs. control) 12 h after aortic banding, decreasing to control levels by 14 days. No significant changes were observed for TGF-beta 3 message. Fibronectin mRNA levels increased twofold at day 1 and peaked to approximately threefold at day 3. Type I and III collagen mRNA expression was similar to control levels at day 1 but increased significantly 3 days after banding. Cardiac hypertrophy also resulted in an induction of mRNA for an embryonic isoform of fibronectin (EIIIA+) that is generated through alternative splicing of the gene. These findings indicate that, with myocardial hypertrophy, mRNAs for fibronectin are increased as early as 1 day after banding, which may allow for an initial increase in the production of fibronectin followed by the deposition of collagen. These increased mRNA levels for the ECM proteins are preceded by marked increases in TGF-beta 1 mRNAs.

Iodide induces transforming growth factor beta 1 (TGF-beta 1) mRNA in sheep thyroid cells

We examined TGF-beta mRNA levels in primary sheep thyroid cell cultures to determine whether the inhibitory effects of iodide on thyroid cells could be explained by an induction of TGF-beta mRNA and if this induction was mediated by iodine organification. Thyroid cells were incubated with TSH and five additives (insulin, somatostatin, growth hormone, transferrin, and glycyl-L-histidyl-L-lysin) for 2-3 weeks and then were exposed to sodium iodide (NaI) or 1-methylimidazole-2-thiol (methimazole, MMI), or both for 72 h. Iodide at 10(-6) M and 10(-4) M significantly increased the amount of TGF-beta mRNA as determined by Northern blot analysis with a rat TGF-beta 1 cDNA probe. This increase in TGF-beta 1 mRNA was abolished by the addition of methimazole, an inhibitor of organification. These data indicate that the effects of iodide on thyroid growth and function may be mediated by a process that involves organification of iodide and increases in TGF-beta 1 mRNA levels.

Insulin responsiveness of CK-M and CK-B mRNA in the diabetic rat heart

Decreased cardiac performance is a known complication of diabetes mellitus, but the detailed molecular mechanisms that are responsible for this contractile abnormality are only incompletely explored, and cardiac gene products of known function, which are markedly and actively insulin responsive, have not been described. Recently, we found that creatine kinase (CK) enzyme activity and CK-M subunit mRNA levels are decreased in the heart of rats with experimental diabetes mellitus. These abnormalities could be restored to normal with chronic insulin administration. The CK-M and CK-B genes are expressed in the heart, and we wanted to determine whether diabetes also induces a change in CK-B mRNA levels. Quantitation of CK-M and CK-B mRNA levels on Northern blots with specific cDNA probes showed that, in diabetic hearts, CK-B mRNA levels represent only 19.8% of control levels and are more markedly depressed than CK-M mRNA levels, which are 46.5% of control values. Acute injection of insulin led to a significant 1.6-fold increase in CK-M mRNA and a 2.2-fold increase of CK-B mRNA 5 h after insulin injection. CK-M mRNA levels were restored to normal within 12 h, but 48 h were required to restore CK-B mRNA levels to normal values. After 1 mo of insulin therapy, CK-B mRNA levels had risen 9.7-fold, exceeding normal values by 90%, whereas CK-M mRNA levels were at the normal level as previously shown. CK enzyme activity showed only a small response to insulin administration 48 h postinjection. Diabetes leads therefore to a marked lowering of CK-M and CK-B mRNA levels in the rat heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of thyroid hormone and retinoic acid on slow sarcoplasmic reticulum Ca2+ ATPase and myosin heavy chain alpha gene expression in cardiac myocytes. Delineation of cis-active DNA elements that confer responsiveness to thyroid hormone but not to retinoic acid

The mRNA encoding the sarcoplasmic reticulum (SR) Ca2+ ATPase is highly influenced by thyroid hormone (T3) in the hearts of intact animals. We show here that this effect of T3 can be mimicked in primary neonatal rat cardiocytes, both in serum-containing and in serum-free media; the expression of SR Ca2+ ATPase mRNA is myocyte-specific and is also modulated by retinoic acid (RA). RA also induces myosin heavy chain (MHC) alpha-mRNA in this system. The induction of Ca2+ ATPase mRNA is sensitive to T3 (EC50 approximately 30 pM) and less sensitive to RA (EC50 approximately 2 nM). Transient transfection experiments utilizing various segments of the Ca2+ATPase promoter fused to the reporter gene chloramphenicol acetyltransferase (CAT) indicate a minimal thyroid hormone response element (TRE) between nucleotides -262 and -322, while sequences between -322 and -559 are required for maximal trans-activation. RA is not able to regulate these constructs. Likewise, a clear effect of T3 but no effect of RA was observed when the CAT gene was driven by a TRE derived from the rat alpha-MHC gene. In contrast, CAT expression was induced by either hormone when placed under the control of a synthetic palindromic TRE. Taken together, these results indicate that T3 and RA induce gene expression in primary cardiac myocytes, but through distinct response elements and/or mechanisms.

Age-induced decreases in the messenger RNA coding for the sarcoplasmic reticulum Ca2(+)-ATPase of the rat heart

Age-associated slowing of cardiac relaxation related to the decline in the Ca2+ pump function of cardiac sarcoplasmic reticulum (SR) has been previously described. It is unclear if the decreased Ca2+ pump function results from a lower amount of Ca2(+)-ATPase protein or a decreased pumping activity of the enzyme. To determine if these alterations could be mediated by changes in the amount of the protein itself, the level of the messenger RNA (mRNA) coding for the Ca2(+)-ATPase of the SR of Fischer rat hearts (4- and 30-month-old rats) were quantitated with a Northern blotting technique. We observed that the levels of SR Ca2(+)-ATPase mRNA were 60% lower in old rats as compared with young rats, suggesting that a quantitative reduction in the levels of the corresponding protein could occur during aging to explain the delayed diastolic relaxation documented in old animals as opposed to a change in the specific activity of this enzyme. The thyroid hormone responsiveness of SR Ca2(+)-ATPase mRNA has been previously established. We have found in this study that the thyroxine levels were consistently lower in old rats; however, this difference was relatively small (4.3 +/- 0.7 and 3.1 +/- 0.8 micrograms/dl [mean +/- SD), respectively, in young and old rats). In addition, no age-induced decrease in 3,5,3'-triiodothyronine levels was observed, suggesting that the aging process itself may be responsible for the changes in SR Ca2(+)-ATPase mRNA levels.

Biochemical basis of thyroid hormone action in the heart

Thyroid hormone-induced changes in cardiac function have been recognized for over 150 years; however, the biochemical basis of triiodothyronine (T3) action in the heart has been intensely investigated only during the last two decades. T3-induced changes in cardiac function can result from direct or indirect T3 effects. Direct T3 effects result from T3 action in the heart itself and are mediated by nuclear or extranuclear mechanisms. Extranuclear T3 effects, which occur independent of nuclear T3 receptor binding and increases in protein synthesis, influence primarily the transport of amino acids, sugars, and calcium across the cell membrane. Nuclear T3 effects are mediated by the binding of T3 to specific nuclear receptor proteins, which results in increased transcription of T3-responsive cardiac genes. The T3 receptor is a member of the ligand-activated transcription factor family and is encoded by cellular erythroblastosis A (c-erb A) genes. The c-erb A protein is the cellular homologue of the viral erythroblastosis A (v-erb A) protein, which causes red cell leukemia in chickens. Currently, three T3-binding isoforms of the c-erb protein and two non-T3-binding nuclear proteins that exert positive and negative effects on T3-responsive cardiac genes have been identified. T3 increases the heart transcription of the myosin heavy chain (MHC) alpha gene and decreases the transcription of the MHC beta gene, leading to an increase of myosin V1 and a decrease in myosin V3 isoenzymes. Myosin V1, which is composed of two MHC alpha, has a higher myosin ATPase activity than myosin V3, which contains two MHC beta. The globular head of myosin V1, with its higher ATPase activity, leads to a more rapid movement of the globular head of myosin along the thin filament, resulting in an increased velocity of contraction. T3 also leads to an increase in the speed of diastolic relaxation, which is caused by the more efficient pumping of the calcium ATPase of the sarcoplasmic reticulum (SR). This T3 effect results from T3-induced increases in the level of the mRNA coding for the SR calcium ATPase protein, leading to an increased number of calcium ATPase pump units in the SR. Overall, thyroid hormone leads to an increase in ATP consumption in the heart. In addition, less chemical energy of ATP is used for contractile purposes and more of it goes toward heat production, which causes a decreased efficiency of the contractile process in the hyperthyroid heart.

Diabetes decreases creatine kinase enzyme activity and mRNA level in the rat heart

Several of the adenosinetriphosphatase enzymes that are responsible for cardiac muscle contraction rely on high-energy phosphates supplied by the creatine kinase (CK) system. Experimental diabetes mellitus has been shown to cause a decrease in the maximal contractile performance of the heart. We postulated that the decrease in contractile performance may be explained in part by a decrease in CK enzyme activity. To evaluate this possibility, we determined the level of CK activity and isoenzyme distribution in ventricular homogenates from normal, diabetic, and insulin-treated diabetic rats. We found that total CK activity was decreased by 35% in diabetic hearts and that a 66% reduction in the cardiac-specific MB isoenzyme occurs. Using a cDNA probe for CK-muscle (M) RNA in Northern blot analysis, we determined that a 61.1% decrease in CK-M mRNA occurs in diabetes. Chronic insulin therapy for 1 mo restores CK-M mRNA levels and enzyme activity. In conclusion, diabetes-induced CK enzyme decreases are mediated in part by a lower level of CK-M mRNA that codes for the major CK-M subunit protein. Decreased performance of the CK system may contribute to diabetic cardiomyopathy.

Diabetes and thyroid-hormone-induced changes in cardiac function and their molecular basis

The heart is a major target organ for insulin and thyroid hormone action, and marked changes in cardiac function occur in patients with hyper- or hypothyroidism and diabetes mellitus. Cardiac contractility is increased in the hyperthyroid state and decreased in hypothyroidism, and changes in specific proteins mediating cardiac contraction accompany these alterations. Changes in thyroid status mediate their influence on cardiac function by a combination of direct thyroid hormone effects on the heart, alterations in the responsiveness of the cardiac sympathoadrenal system, and hemodynamic effects generated in the periphery. Cardiovascular complications of diabetes mellitus are a major contributor to mortality and morbidity in the diabetic population. In addition to cardiac small and large vessel disease, an autonomic neuropathy and a cardiomyopathy occur in diabetic patients. The cardiomyopathy results in congestive failure and is independent of large vessel disease. Studies in diabetic animal models point to a metabolic basis for the cardiomyopathy, which is accompanied by changes in specific contractile proteins.

Influence of thyroid hormone on myosin heavy chain mRNA and other messenger RNAs in the rat heart

The level of myosin heavy chain (MHC) alpha mRNA and of MHC-beta mRNA was quantitated in the rat heart using a specific cDNA probe. In hypothyroid and diabetic hearts MHC-beta mRNA predominates, whereas in normal hearts MHC-alpha mRNA represents 80% of all MHC mRNA. Administration of 0.2 mg T3/100 g body wt. to hypothyroid rats led to an increase in MHC-alpha mRNA beginning at 3 h after injection and continued to rise until at 24 h control level of MHC-alpha mRNA were reached. In contrast, after administration of 2 units regular insulin to diabetic rats, MHC-alpha mRNA levels showed a small but significant increase already 30 min after insulin administration reaching a peak at 3 h and returning to diabetic values 5 h after insulin. The T3 response of other cardiac mRNAs was quantitated using in vitro translation, separation of 35S methionine labeled translational products and their quantitation by digital matrix photometry. An mRNA (spot 72b) coding for a translational product with a Mr 81,000 and pI of 5.4 showed a 3-fold increase in its level 1 h after T3 administration. In view of the rapid response of spot 72b and the early response of MHC-alpha mRNA to insulin, it is currently unclear if the T3 response of MHC-alpha mRNA represents a primary effect of T3.

Ischemia induces changes in the level of mRNAs coding for stress protein 71 and creatine kinase M

Hyperthermia, hypoxia, and other conditions induce the appearance of heat shock or stress proteins in cells. We have previously shown that in the ischemic dog myocardium the level of a messenger RNA (mRNA) coding for a protein with migration characteristics similar to heat shock/stress protein 71 increases. Using a human heat-shock protein (hHSP) 70 genomic clone and anti-HSP70 antibodies as probes, we demonstrate in this report that heart stress protein (SP) 71 mRNA and its translational products (71 kDa polypeptides) are members of the stress protein family. In rabbit hearts, the ischemia-induced mRNAs translate into three isoforms with different isoelectric points (6.0, 6.1, and 6.15), in contrast to dog heart mRNA that translates into a protein with a pI of 5.8. The levels of SP71 mRNA in the dog and rabbit ischemic myocardium increased by sixfold and 18-fold, respectively. In the same samples, the levels of creatine kinase M mRNA decreased by about 40%, whereas those of myosin heavy chain mRNA remain unaltered. Our comparative analysis of three different mRNAs indicates that ischemia manifests its effects by differentially changing the levels of specific mRNAs coding for proteins with separate and distinct roles in the cell.

Cardiac response to pressure overload in the rat: the selective alteration of in vitro directed RNA translation products

As cardiac hypertrophy develops, total cardiac RNA and protein synthesis increase significantly. We have identified specific messenger RNAs that change in predominance with the induction of pressure-overload-stimulated cardiac hypertrophy. Total cardiac RNA was isolated from rats either undergoing cardiac hypertrophy secondary to subdiaphragmatic aortic constriction or subjected to sham surgery. The products translated in vitro were separated by two-dimensional gel electrophoresis and quantitated. The translation of four proteins decreased while the translation of four others increased in preparations from hypertrophied hearts compared with those from sham-treated rats. Two isoforms of creatine kinase M were translated in vitro. Only one of these isoforms decreased with cardiac hypertrophy, suggesting that the transcriptional or translational control for creatine kinase is much more complex than previously believed. Finally, since only eight of over 700 different translation products changed in relative predominance with cardiac hypertrophy, we conclude that the accumulation of existing RNA and protein products is the primary adaptive process responsible for cardiac hypertrophy.

Thyroid hormone markedly increases the mRNA coding for sarcoplasmic reticulum Ca2+-ATPase in the rat heart

Previous findings have shown that thyroid hormone markedly increases the speed of diastolic relaxation in the heart. This thyroid hormone-dependent change is also accompanied by an increased Ca2+ pumping ability in the sarcoplasmic reticulum. In an effort to determine the underlying cause of improved Ca2+ transport, mRNA levels of the slow Ca2+-ATPase of the sarcoplasmic reticulum were quantified on Northern blots. In hypothyroid rat hearts, the steady state level of Ca2+-ATPase mRNA was only 36% of control levels, whereas hyperthyroid rat heart mRNA levels were 136% of control. Ca2+-ATPase mRNA responded rapidly to T3, as the mRNA level was significantly increased by 2 h and normalized by 5 h after T3 injection into hypothyroid rats. The well established effect of thyroid hormone on improved myocardial contractility and increased speed of diastolic relaxation may in part relate to specific alterations in the level of the mRNA coding for Ca2+-ATPase, resulting in increased pump units.

Diabetes-induced changes of proteins synthesized by adult cardiac myocytes are partially reversed by insulin

In the rat heart diabetes mellitus leads to a change in myosin heavy chain (MHC) mRNAs and corresponding alterations in myosin isoenzymes as well as a decrease in total cardiac protein synthesis. However, it is still unknown whether cardiac proteins other than MHC are altered by diabetes and if so whether these abnormalities are mediated by insulin deficiency. To answer these questions we analyzed proteins synthesized by isolated cardiac myocytes in the presence or absence of insulin. Enzymatically dispersed adult cardiac myocytes from control and streptozotocin-induced diabetic rats were incubated in medium containing [35S]-methionine for 4 h; diabetic cells were incubated with or without the addition of 5 x 10(-7)M insulin. The labelled peptides were then separated by two-dimensional polyacrylamide gel electrophoresis and analyzed by fluorometry. The abundance of six individual polypeptides was consistently affected by diabetes: one protein was significantly decreased while four others were increased in diabetic myocytes. The remaining protein showed a shift in isoelectric point without a change in molecular weight possibly representing isoforms of a single polypeptide. The addition of insulin reverted the predominance of three proteins back to normal while it did not affect the other three at all. In conclusion diabetes induces changes in the abundance of a few proteins synthesized in vitro by cardiac myocytes and only half of them show an acute response to insulin.