[Early Structural Valve Deterioration of Trifecta Aortic Bioprosthesis:Report of a Case].

Trifecta, an externally mounted bovine pericardial bioprosthetic aortic valve, provides excellent hemodynamic performance;however, early structural deterioration of this valve has been reported. A 60-year-old man with progressive dyspnea was admitted to the emergency unit of our institution. Seven years prior, he underwent aortic valve replacement with 23-mm Trifecta valve. Severe aortic valve regurgitation and stenosis due to structural valve deterioration was diagnosed and redo aortic valve replacement using an Inspiris valve was performed. Intraoperative findings revealed a large laceration in the left coronary cusp adjacent to the non coronary-left coronary commissure and leaflet calcification. Further, circumferential fibrous pannus ingrowth at the inflow portion was also noted. To avoid anticoagulation therapy and repeat surgery, mitral valve plasty and left atrial appendage clipping were performed simultaneously. Postoperative course was uneventful, and he was transferred to a rehabilitation facility on 36th postoperative day.

Safety and efficacy of a simple cardiotomy suction system as a blood salvage procedure during off-pump coronary artery bypass surgery.

The ideal blood-salvaging strategies for off-pump coronary artery bypass graft procedures have not been determined. We developed a new blood-salvaging system that uses a cardiotomy suction. The purpose of this study was to examine the efficacy of this novel method. This was a retrospective study involving 50 consecutive patients undergoing off-pump coronary artery bypass grafting. In 25 patients, a simple cardiotomy suction system was used (cardiotomy suction group). These individuals were compared with 25 historical cohorts who were treating with the conventional cell saver system (cell saver group). There was no in-hospital mortality in either group. In the cell saver group, there was one major complication (stroke) and two minor complications (saphenous vein graft occlusion, superficial wound infection). In the cardiotomy suction group, there was one minor complication (subclinical pulmonary emboli). The cardiotomy suction group received significantly fewer transfused RBC (cardiotomy: 0.56 ± 1.4 units vs. cell saver: 2.46 ± 3.3 units, p = 0.005). The serum total protein and albumin levels were significantly higher in the cardiotomy group. Our newly developed simple cardiotomy suction system, when compared with the conventional cell saver system, produced similar clinical results and attenuated postoperative hemodilution. Our system may emerge as a preferable alternative for blood salvage during off-pump coronary artery bypass grafting.

Cockayne syndrome B protein regulates recruitment of the Elongin A ubiquitin ligase to sites of DNA damage.

Elongin A performs dual functions as the transcriptionally active subunit of RNA polymerase II (Pol II) elongation factor Elongin and as the substrate recognition subunit of a Cullin-RING E3 ubiquitin ligase that ubiquitylates Pol II in response to DNA damage. Assembly of the Elongin A ubiquitin ligase and its recruitment to sites of DNA damage is a tightly regulated process induced by DNA-damaging agents and α-amanitin, a drug that induces Pol II stalling. In this study, we demonstrate (i) that Elongin A and the ubiquitin ligase subunit CUL5 associate in cells with the Cockayne syndrome B (CSB) protein and (ii) that this interaction is also induced by DNA-damaging agents and α-amanitin. In addition, we present evidence that the CSB protein promotes stable recruitment of the Elongin A ubiquitin ligase to sites of DNA damage. Our findings are consistent with the model that the Elongin A ubiquitin ligase and the CSB protein function together in a common pathway in response to Pol II stalling and DNA damage.

[A Case of Rapidly Advancing G-CSF Producing Pleomorphic Carcinoma of the Breast Appearing as an Inflammatory Breast Cancer].

We report a rare case of pleomorphic carcinoma of the breast, suspected of being a granulocyte-colony stimulating factor (G-CSF)producing tumor, in a 75-year-old woman. She presented with a red and swollen breast, 3 weeks after undergoing core needle biopsy(CNB). Her leukocyte counts and C-reactive protein(CRP)levels were markedly high. At first, she was suspected to have an abscess and was initiated on a course of antibiotics. However, her condition rapidly deteriorated; therefore, she underwent an emergency mastectomy. Despite undergoing postoperative radiation therapy, 2 months after the operation, multiple metastatic foci were found in the lungs and liver, and she died of the disease 3 months after her first visit. After the operation, her leukocyte count had quickly returned to normal, but it increased as the disease progressed. These findings support the conclusion that this carcinoma was producing G-CSF. The final pathological diagnosis was G-CSF producing pleomorphic carcinoma of the breast.

Assembly of the Elongin A Ubiquitin Ligase Is Regulated by Genotoxic and Other Stresses.

Elongin A performs dual functions in cells as a component of RNA polymerase II (Pol II) transcription elongation factor Elongin and as the substrate recognition subunit of a Cullin-RING E3 ubiquitin ligase that has been shown to target Pol II stalled at sites of DNA damage. Here we investigate the mechanism(s) governing conversion of the Elongin complex from its elongation factor to its ubiquitin ligase form. We report the discovery that assembly of the Elongin A ubiquitin ligase is a tightly regulated process. In unstressed cells, Elongin A is predominately present as part of Pol II elongation factor Elongin. Assembly of Elongin A into the ubiquitin ligase is strongly induced by genotoxic stress; by transcriptional stresses that lead to accumulation of stalled Pol II; and by other stimuli, including endoplasmic reticulum and nutrient stress and retinoic acid signaling, that activate Elongin A-dependent transcription. Taken together, our findings shed new light on mechanisms that control the Elongin A ubiquitin ligase and suggest that it may play a role in Elongin A-dependent transcription.

A correlation of reactive oxygen species accumulation by depletion of superoxide dismutases with age-dependent impairment in the nervous system and muscles of Drosophila adults.

The theory that accumulation of reactive oxygen species (ROS) in internal organs is a major promoter of aging has been considered negatively. However, it is still controversial whether overexpression of superoxide dismutases (SODs), which remove ROS, extends the lifespan in Drosophila adults. We examined whether ROS accumulation by depletion of Cu/Zn-SOD (SOD1) or Mn-SOD (SOD2) influenced age-related impairment of the nervous system and muscles in Drosophila. We confirmed the efficient depletion of Sod1 and Sod2 through RNAi and ROS accumulation by monitoring of ROS-inducible gene expression. Both RNAi flies displayed accelerated impairment of locomotor activity with age and shortened lifespan. Similarly, adults with nervous system-specific depletion of Sod1 or Sod2 also showed reduced lifespan. We then found an accelerated loss of dopaminergic neurons in the flies with suppressed SOD expression. A half-dose reduction of three pro-apoptotic genes resulted in a significant suppression of the neuronal loss, suggesting that apoptosis was involved in the neuronal loss caused by SOD silencing. In addition, depletion of Sod1 or Sod2 in musculature is also associated with enhancement of age-related locomotion impairment. In indirect flight muscles from SOD-depleted adults, abnormal protein aggregates containing poly-ubiquitin accumulated at an early adult stage and continued to increase as the flies aged. Most of these protein aggregates were observed between myofibril layers. Moreover, immuno-electron microscopy indicated that the aggregates were predominantly localized in damaged mitochondria. These findings suggest that muscular and neuronal ROS accumulation may have a significant effect on age-dependent impairment of the Drosophila adults.

Transcriptional properties of mammalian elongin A and its role in stress response.

Elongin A was shown previously to be capable of potently activating the rate of RNA polymerase II (RNAPII) transcription elongation in vitro by suppressing transient pausing by the enzyme at many sites along DNA templates. The role of Elongin A in RNAPII transcription in mammalian cells, however, has not been clearly established. In this report, we investigate the function of Elongin A in RNAPII transcription. We present evidence that Elongin A associates with the IIO form of RNAPII at sites of newly transcribed RNA and is relocated to dotlike domains distinct from those containing RNAPII when cells are treated with the kinase inhibitor 5,6-dichloro-1-ß-d-ribofuranosylbenzimidazole. Significantly, Elongin A is required for maximal induction of transcription of the stress response genes ATF3 and p21 in response to several stimuli. Evidence from structure-function studies argues that Elongin A transcription elongation activity, but not its ubiquitination activity, is most important for its function in induction of transcription of ATF3 and p21. Taken together, our data provide new insights into the function of Elongin A in RNAPII transcription and bring to light a previously unrecognized role for Elongin A in the regulation of stress response genes.

Degradation of p21Cip1 through anaphase-promoting complex/cyclosome and its activator Cdc20 (APC/CCdc20) ubiquitin ligase complex-mediated ubiquitylation is inhibited by cyclin-dependent kinase 2 in cardiomyocytes.

Cyclin-dependent kinase inhibitor p21Cip1 plays a crucial role in regulating cell cycle arrest and differentiation. It is known that p21Cip1 increases during terminal differentiation of cardiomyocytes, but its expression control and biological roles are not fully understood. Here, we show that the p21Cip1 protein is stabilized in cardiomyocytes after mitogenic stimulation, due to its increased CDK2 binding and inhibition of ubiquitylation. The APC/CCdc20 complex is shown to be an E3 ligase mediating ubiquitylation of p21Cip1 at the N terminus. CDK2, but not CDC2, suppressed the interaction of p21Cip1 with Cdc20, thereby leading to inhibition of anaphase-promoting complex/cyclosome and its activator Cdc20 (APC/CCdc20)-mediated p21Cip1 ubiquitylation. It was further demonstrated that p21Cip1 accumulation caused G2 arrest of cardiomyocytes that were forced to re-enter the cell cycle. Taken together, these data show that the stability of the p21Cip1 protein is actively regulated in terminally differentiated cardiomyocytes and plays a role in inhibiting their uncontrolled cell cycle progression. Our study provides a novel insight on the control of p21Cip1 by ubiquitin-mediated degradation and its implication in cell cycle arrest in terminal differentiation.

Mammalian Elongin A complex mediates DNA-damage-induced ubiquitylation and degradation of Rpb1.

The Elongin complex stimulates the rate of transcription elongation by RNA polymerase II (pol II) by suppressing transient pausing of the pol II at many sites along the DNA. Elongin is composed of a transcriptionally active A subunit and two small regulatory B and C subunits, which can form an isolable Elongin BC subcomplex. Here, we have shown that both the ubiquitylation and proteasomal degradation of the largest subunit of pol II (Rpb1) following UV-irradiation are significantly suppressed in Elongin A-deficient cells; however, in both cases suppression is rescued by transfection of wild-type Elongin A. Moreover, we have demonstrated that the Elongin A-Elongin BC complex is capable of assembling with the Cul5/Rbx2 module, and that this hetero-pentamer complex efficiently ubiquitylates Rpb1 in vitro. Mechanistic studies indicate that colocalization of Elongin A and Cul5 in cells and the interaction of Elongin A with the Ser5-phosphorylated form of Rpb1 are strongly enhanced following UV-irradiation. Taken together, our results suggest that mammalian Elongin A is directly involved in ubiquitylation and degradation of Rpb1 following DNA damage.

The reduced left ventricular stroke volume does not fully recover after pulmonary valve replacement in patients with repaired tetralogy of Fallot.

OBJECTIVES: The present study was conducted to investigate the decrease in left ventricular stroke volume index (LVSVI) that is caused by pulmonary regurgitation-induced right heart dysfunction and its clinical implications before and after pulmonary valve replacement (PVR). METHODS: Between January 2010 and December 2019, 30 adults who underwent surgical PVR for chronic pulmonary regurgitation with right ventricular dilation late after tetralogy of Fallot (TOF) repair were included. All patients were evaluated using cardiac magnetic resonance before PVR. The median interval from TOF repair to PVR was 29 [25th, 75th percentile: 25, 37] years. The median pulmonary regurgitation fraction and right ventricular end-diastolic volume index were 56 [48, 66] % and 203 [187, 239] ml/m2. Twenty-three patients (76.7%) were re-evaluated 1 year after PVR. RESULTS: Before PVR, the median LVSVI was 40 [35, 46] ml/beat/m2. A lower LVSVI was associated with a longer interval from TOF repair to PVR (r = -0.40, P = 0.029) and a lower right ventricular ejection fraction (r = 0.52, P = 0.004). A lower LVSVI was not associated with a higher right ventricular end-diastolic volume index. LVSVI remained unchanged after PVR. The patients were subdivided into Normal-stroke volume index (SVI) and Subnormal-SVI groups using the preoperative LVSVI cut-off value of 35 mL/beat/m2. Compared with the Normal-SVI group, the Subnormal-SVI group had a higher incidence of ablation therapy before PVR (4.7 vs 2.3 patient-years, P = 0.044). After PVR, LVSVI in the Subnormal-SVI group was still lower (40 [34, 42] vs 44 [42, 47] ml/beat/m2, P = 0.038) despite the right ventricular end-diastolic volume index normalization. There was no difference in the clinical event incidence between the 2 groups during the follow-up period. Brain natriuretic peptide level in the Subnormal-SVI group was higher within 3 years after PVR (P = 0.046). CONCLUSIONS: Reduced left ventricular stroke volume did not fully recover after PVR. PVR for patients with repaired TOF should be performed before the left ventricular stroke volume begins to decrease.

Interstage management of pulmonary blood flow after the Norwood procedure with right ventricle-to-pulmonary artery conduit.

OBJECTIVES: Our goal was to assess the efficacy of managing pulmonary blood flow from the Norwood procedure with a right ventricle-to-pulmonary artery (RV-PA) conduit until stage 2 palliation (S2P). METHODS: Among 48 consecutive patients undergoing the Norwood procedure between 2008 and 2018, 40 (83.3%) patients who survived to discharge were included in this study. The primary diagnosis was hypoplastic left heart syndrome in 28 (70%) patients and hypoplastic left heart syndrome variant in 12 (30%) patients. All patients received bilateral pulmonary artery banding. The median age and weight at the time of the Norwood procedure were 41 (25th-75th percentiles: 27-89) days and 3.2 (2.7-3.9) kg, respectively. In keeping with institutional strategy, S2P was undertaken when body weight exceeded 5.0 kg, and normal gross motor development was confirmed. RESULTS: The RV-PA conduit was clipped in 28 (70%) patients during the perioperative period of the Norwood procedure, then partial unclipping was performed in 8 (20%) patients and full unclipping was performed in 20 (50%) patients. Before S2P, the median pulmonary-to-systemic blood flow ratio was 1.0 (0.7-1.3). The median age and weight at the time of S2P were 10.7 (9.0-12.9) months and 6.3 (5.5-7.1) kg, respectively. The survival rate 5 years after Norwood discharge was 85.3%. Pre-S2P pulmonary-to-systemic blood flow ratio was linearly correlated with greater interstage changes in systemic atrioventricular valve regurgitation (R2 = 0.223, P = 0.004). CONCLUSIONS: Interstage management of pulmonary blood flow by RV-PA conduit clipping and gradual unclipping provided good interstage outcomes. The median pulmonary-to-systemic blood flow ratio could be controlled to 1.0 at pre-S2P catheter examination.

NRBP1-Containing CRL2/CRL4A Regulates Amyloid ß Production by Targeting BRI2 and BRI3 for Degradation.

Alzheimer's disease (AD) is a progressive neurodegenerative disease caused by accumulations of Aß peptides. Production and fibrillation of Aß are downregulated by BRI2 and BRI3, which are physiological inhibitors of amyloid precursor protein (APP) processing and Aß oligomerization. Here, we identify nuclear receptor binding protein 1 (NRBP1) as a substrate receptor of a Cullin-RING ubiquitin ligase (CRL) that targets BRI2 and BRI3 for degradation. Moreover, we demonstrate that (1) dimerized NRBP1 assembles into a functional Cul2- and Cul4A-containing heterodimeric CRL through its BC-box and an overlapping cryptic H-box, (2) both Cul2 and Cul4A contribute to NRBP1 CRL function, and (3) formation of the NRBP1 heterodimeric CRL is strongly enhanced by chaperone-like function of TSC22D3 and TSC22D4. NRBP1 knockdown in neuronal cells results in an increase in the abundance of BRI2 and BRI3 and significantly reduces Aß production. Thus, disrupting interactions between NRBP1 and its substrates BRI2 and BRI3 may provide a useful therapeutic strategy for AD.

Radiation therapy for recurrent cardiac undifferentiated pleomorphic sarcoma after three operations.

We report the case of a 57-year-old female suffering from recurrent malignant undifferentiated pleomorphic sarcoma of the left atrium. Metastasis to the posterior mediastinum was detected upon first presentation. Incomplete resections were carried out twice before mitral valve replacement was finally performed. The tumor recurred 16 months later and was treated with radiation therapy, which has proved to be effective in bringing about tumor regression for 2 years, to date. The patient has survived for 7 years since the first surgery.

iNOS as a Driver of Inflammation and Apoptosis in Mouse Skeletal Muscle after Burn Injury: Possible Involvement of Sirt1 S-Nitrosylation-Mediated Acetylation of p65 NF-κB and p53.

Inflammation and apoptosis develop in skeletal muscle after major trauma, including burn injury, and play a pivotal role in insulin resistance and muscle wasting. We and others have shown that inducible nitric oxide synthase (iNOS), a major mediator of inflammation, plays an important role in stress (e.g., burn)-induced insulin resistance. However, it remains to be determined how iNOS induces insulin resistance. Moreover, the interrelation between inflammatory response and apoptosis is poorly understood, although they often develop simultaneously. Nuclear factor (NF)-κB and p53 are key regulators of inflammation and apoptosis, respectively. Sirt1 inhibits p65 NF-κB and p53 by deacetylating these transcription factors. Recently, we have shown that iNOS induces S-nitrosylation of Sirt1, which inactivates Sirt1 and thereby increases acetylation and activity of p65 NF-κB and p53 in various cell types, including skeletal muscle cells. Here, we show that iNOS enhances burn-induced inflammatory response and apoptotic change in mouse skeletal muscle along with S-nitrosylation of Sirt1. Burn injury induced robust expression of iNOS in skeletal muscle and gene disruption of iNOS significantly inhibited burn-induced increases in inflammatory gene expression and apoptotic change. In parallel, burn increased Sirt1 S-nitrosylation and acetylation and DNA-binding capacity of p65 NF-κB and p53, all of which were reversed or ameliorated by iNOS deficiency. These results indicate that iNOS functions not only as a downstream effector but also as an upstream enhancer of burn-induced inflammatory response, at least in part, by Sirt1 S-nitrosylation-dependent activation (acetylation) of p65 NF-κB. Our data suggest that Sirt1 S-nitrosylation may play a role in iNOS-mediated enhanced inflammatory response and apoptotic change, which, in turn, contribute to muscle wasting and supposedly to insulin resistance after burn injury.

Drosophila Ogg1 is required to suppress 8-oxo-guanine accumulation following oxidative stress.

Reactive oxygen species (ROS) generated during energy production processes are a major cause of oxidative DNA damage. A DNA glycosylase encoded by the Ogg1 gene removes oxidized guanine bases and is widely conserved. However, the biological role of the gene in individual organisms has not yet been characterized in Drosophila, which is a suitable model to study the influence of oxidative damage on senescence. Here, we performed a genetic analysis to confirm that Ogg1 plays an essential role in the removal of 8-oxo-guanines from nuclei. We first confirmed by quantitative real-time PCR that Ogg1 mRNA expression was reduced by 30-55% in Ogg1 mutants and in flies expressing inducible Ogg1 dsRNA compared to control flies. We then showed that additional accumulation of 8-oxo-guanines occurred in the nuclei of epithelial midgut cells after paraquat feeding in flies with downregulated Ogg1 expression. We confirmed that a transposon possessing the UAS sequence was integrated in the 5'-UTR of the Ogg1 alleles and that it is oriented in the same transcriptional direction as the gene. Using the Gal4/UAS system, which enables us to induce ectopic expression in Drosophila, we induced overexpression of Ogg1 by 40-fold. We observed a lower amount of 8-oxo-guanine in the midgut epithelial cells of adults overexpressing Ogg1. These genetic data strongly suggest that the Drosophila Ogg1 ortholog CG1795 plays an essential role in the suppression of 8-oxo-guanines, consistent with its role in other organisms. Although adult flies with reduced Ogg1 expression failed to show elevated sensitivity to paraquat, those with Ogg1 overexpression showed resistance to oxidative stress by paraquat feeding and had a significantly longer lifespan in normal feeding conditions. These observations are consistent with the hypothesis that oxidative DNA damage by ROS accumulation is a major contributor to senescence.

Transcriptional elongation factor elongin A regulates retinoic acid-induced gene expression during neuronal differentiation.

Elongin A increases the rate of RNA polymerase II (pol II) transcript elongation by suppressing transient pausing by the enzyme. Elongin A also acts as a component of a cullin-RING ligase that can target stalled pol II for ubiquitylation and proteasome-dependent degradation. It is not known whether these activities of Elongin A are functionally interdependent in vivo. Here, we demonstrate that Elongin A-deficient (Elongin A(-/-)) embryos exhibit abnormalities in the formation of both cranial and spinal nerves and that Elongin A(-/-) embryonic stem cells (ESCs) show a markedly decreased capacity to differentiate into neurons. Moreover, we identify Elongin A mutations that selectively inactivate one or the other of the aforementioned activities and show that mutants that retain the elongation stimulatory, but not pol II ubiquitylation, activity of Elongin A rescue neuronal differentiation and support retinoic acid-induced upregulation of a subset of neurogenesis-related genes in Elongin A(-/-) ESCs.

Functional characterization of a mammalian transcription factor, Elongin A.

Elongin A is the transcriptionally active subunit of the Elongin complex that strongly stimulates the rate of elongation by RNA polymerase II (pol II) by suppressing the transient pausing of the polymerase at many sites along the DNA template. We have recently shown that Elongin A-deficient mice are embryonic lethal, and mouse embryonic fibroblasts (MEFs) derived from Elongin A(-/-) embryos display not only increased apoptosis but also senescence-like phenotypes accompanied by the activation of p53. To further understand the function of Elongin A in vivo, we have carried out the structure-function analysis of Elongin A and identified sequences critical to its nuclear localization and direct interaction with pol II. Moreover, we have analyzed the replication fork movement in wild-type and Elongin A(-/-) MEFs, and shown the possibility that the genomic instability observed in Elongin A(-/-) MEFs might be caused by the replication fork collapse due to Elongin A deficiency.

Burn injury impairs insulin-stimulated Akt/PKB activation in skeletal muscle.

The molecular bases underlying burn- or critical illness-induced insulin resistance still remain unclarified. Muscle protein catabolism is a ubiquitous feature of critical illness. Akt/PKB plays a central role in the metabolic actions of insulin and is a pivotal regulator of hypertrophy and atrophy of skeletal muscle. We therefore examined the effects of burn injury on insulin-stimulated Akt/PKB activation in skeletal muscle. Insulin-stimulated phosphorylation of Akt/PKB was significantly attenuated in burned compared with sham-burned rats. Insulin-stimulated Akt/PKB kinase activity, as judged by immune complex kinase assay and phosphorylation status of the endogenous substrate of Akt/PKB, glycogen synthase kinase-3beta (GSK-3beta), was significantly impaired in burned rats. Furthermore, insulin consistently failed to increase the phosphorylation of p70 S6 kinase, another downstream effector of Akt/PKB, in rats with burn injury, whereas phosphorylation of p70 S6 kinase was increased by insulin in controls. The protein expression of Akt/PKB, GSK-3beta, and p70 S6 kinase was unaltered by burn injury. However, insulin-stimulated activation of ERK, a signaling pathway parallel to Akt/PKB, was not affected by burn injury. These results demonstrate that burn injury impairs insulin-stimulated Akt/PKB activation in skeletal muscle and suggest that attenuated Akt/PKB activation may be involved in deranged metabolism and muscle wasting observed after burn injury.

S-nitrosylation-dependent inactivation of Akt/protein kinase B in insulin resistance.

Inducible nitric-oxide synthase (iNOS) has been implicated in many human diseases including insulin resistance. However, how iNOS causes or exacerbates insulin resistance remains largely unknown. Protein S-nitrosylation is now recognized as a prototype of a redox-dependent, cGMP-independent signaling component that mediates a variety of actions of nitric oxide (NO). Here we describe the mechanism of inactivation of Akt/protein kinase B (PKB) in NO donor-treated cells and diabetic (db/db) mice. NO donors induced S-nitrosylation and inactivation of Akt/PKB in vitro and in intact cells. The inhibitory effects of NO donor were independent of phosphatidylinositol 3-kinase and cGMP. In contrast, the concomitant presence of oxidative stress accelerated S-nitrosylation and inactivation of Akt/PKB. In vitro denitrosylation with reducing agent reactivated recombinant and cellular Akt/PKB from NO donor-treated cells. Mutated Akt1/PKBalpha (C224S), in which cysteine 224 was substituted by serine, was resistant to NO donor-induced S-nitrosylation and inactivation, indicating that cysteine 224 is a major S-nitrosylation acceptor site. In addition, S-nitrosylation of Akt/PKB was increased in skeletal muscle of diabetic (db/db) mice compared with wild-type mice. These data suggest that S-nitrosylation-mediated inactivation may contribute to the pathogenesis of iNOS- and/or oxidative stress-involved insulin resistance.

Inducible nitric-oxide synthase and NO donor induce insulin receptor substrate-1 degradation in skeletal muscle cells.

Chronic inflammation plays an important role in insulin resistance. Inducible nitric-oxide synthase (iNOS), a mediator of inflammation, has been implicated in many human diseases including insulin resistance. However, the molecular mechanisms by which iNOS mediates insulin resistance remain largely unknown. Here we demonstrate that exposure to NO donor or iNOS transfection reduced insulin receptor substrate (IRS)-1 protein expression without altering the mRNA level in cultured skeletal muscle cells. NO donor increased IRS-1 ubiquitination, and proteasome inhibitors blocked NO donor-induced reduction in IRS-1 expression in cultured skeletal muscle cells. The effect of NO donor on IRS-1 expression was cGMP-independent and accentuated by concomitant oxidative stress, suggesting an involvement of nitrosative stress. Inhibitors for phosphatidylinositol-3 kinase, mammalian target of rapamycin, and c-Jun amino-terminal kinase failed to block NO donor-induced IRS-1 reduction, whereas these inhibitors prevented insulin-stimulated IRS-1 decrease. Moreover iNOS expression was increased in skeletal muscle of diabetic (ob/ob) mice compared with lean wild-type mice. iNOS gene disruption or treatment with iNOS inhibitor ameliorated depressed IRS-1 expression in skeletal muscle of diabetic (ob/ob) mice. These findings indicate that iNOS reduces IRS-1 expression in skeletal muscle via proteasome-mediated degradation and thereby may contribute to obesity-related insulin resistance.