Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.25.1 (proteasome)
 28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The leucine metabolite beta-hydroxy-beta-methylbutyrate (HMB) prevents muscle protein degradation in cancer-induced weight loss through attenuation of the ubiquitin-proteasome proteolytic pathway. To investigate the mechanism of this effect, the action of HMB on protein breakdown and intracellular signaling leading to increased proteasome expression by the tumor factor proteolysis-inducing factor (PIF) has been studied in vitro using murine myotubes as a surrogate model of skeletal muscle. A comparison has been made of the effects of HMB and those of eicosapentaenoic acid (EPA), a known inhibitor of PIF signaling. At a concentration of 50 mumol/L, EPA and HMB completely attenuated PIF-induced protein degradation and induction of the ubiquitin-proteasome proteolytic pathway, as determined by the "chymotrypsin-like" enzyme activity, as well as protein expression of 20S proteasome alpha- and beta-subunits and subunit p42 of the 19S regulator. The primary event in PIF-induced protein degradation is thought to be release of arachidonic acid from membrane phospholipids, and this process was attenuated by EPA, but not HMB, suggesting that HMB might act at another step in the PIF signaling pathway. EPA and HMB at a concentration of 50 mumol/L attenuated PIF-induced activation of protein kinase C and the subsequent degradation of inhibitor kappaBalpha and nuclear accumulation of nuclear factor kappaB. EPA and HMB also attenuated phosphorylation of p42/44 mitogen-activated protein kinase by PIF, thought to be important in PIF-induced proteasome expression. These results suggest that HMB attenuates PIF-induced activation and increased gene expression of the ubiquitin-proteasome proteolytic pathway, reducing protein degradation.
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PMID:Mechanism of the attenuation of proteolysis-inducing factor stimulated protein degradation in muscle by beta-hydroxy-beta-methylbutyrate. 1557 84

Loss of skeletal muscle is an important determinant of survival in patients with cancer-induced weight loss. The effect of the leucine metabolite beta-hydroxy-beta-methylbutyrate (HMB) on the reduction of body weight loss and protein degradation in the MAC16 model of cancer-induced weight loss has been compared with that of eicosapentaenoic acid (EPA), a recognized inhibitor of protein degradation. HMB was found to attenuate the development of weight loss at a dose greater than 0.125 g/kg accompanied by a small reduction in tumor growth rate. When EPA was used at a suboptimal dose level (0.6 g/kg) the combination with HMB seemed to enhance the anticachectic effect. Both treatments caused an increase in the wet weight of soleus muscle and a reduction in protein degradation, although there did not seem to be a synergistic effect of the combination. Proteasome activity, determined by the "chymotrypsin-like" enzyme activity, was attenuated by both HMB and EPA. Protein expression of the 20S alpha or beta subunits was reduced by at least 50%, as were the ATPase subunits MSS1 and p42 of the 19S proteasome regulatory subunit. This was accompanied by a reduction in the expression of E2(14k) ubiquitin-conjugating enzyme. The combination of EPA and HMB was at least as effective or more effective than either treatment alone. Attenuation of proteasome expression was reflected as a reduction in protein degradation in gastrocnemius muscle of cachectic mice treated with HMB. In addition, HMB produced a significant stimulation of protein synthesis in skeletal muscle. These results suggest that HMB preserves lean body mass and attenuates protein degradation through down-regulation of the increased expression of key regulatory components of the ubiquitin-proteasome proteolytic pathway, together with stimulation of protein synthesis.
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PMID:Attenuation of proteasome-induced proteolysis in skeletal muscle by {beta}-hydroxy-{beta}-methylbutyrate in cancer-induced muscle loss. 1566 4

Atrophy of skeletal muscle is common to a number of conditions, including cancer, sepsis, AIDS, renal failure, diabetes, severe trauma, and burns. In all cases, protein synthesis in skeletal muscle is depressed, whereas protein degradation is increased through an increase in activity and expression of the ubiquitin-proteasome proteolytic pathway. This pathway is not responsive to simple nutritional intervention. Certain agents, including glucocorticoids, cytokines, proteolysis-inducing factor (PIF), and oxidative stress, are thought to be responsible for the induction of the ubiquitin-proteasome pathway in skeletal muscle in catabolic conditions. Insulin suppresses activation of this pathway, and loss of insulin action in diabetes leads to muscle wasting. Cytokines, PIF, and reactive oxygen species (ROS) are thought to induce proteasome expression through activation of the transcription factor nuclear factor kappa B (NF-kappaB). Targets for therapeutic intervention include antagonists of the inducers of proteasome expression, intracellular signaling pathways leading to activation of NF-kappaB, and the enzymes inducing ubiquitin conjugation to the substrate protein (myosin), as well as the proteasome itself. Anticytokine and anti-PIF antibodies are effective in attenuating muscle protein degradation in certain experimental animal models,and glucocorticoid receptor antagonists are effective in the treatment of sepsis. Agents that inhibit NF-kappaB activation, such as resveratrol, thalidomide, ibuprofen, eicosapentaenoic acid, and beta-hydroxy-beta-methylbutyrate, are effective in the preservation of skeletal muscle mass in cachexia. These results suggest that the ubiquitin-proteasome pathway is an appropriate therapeutic target to prevent muscle wasting.
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PMID:The ubiquitin-proteasome pathway as a therapeutic target for muscle wasting. 1591 24

Cachexia involves progressive loss of adipose tissue and skeletal muscle mass and is common in a number of end-stage diseases. Cachexia causes weakness and immobility, reduces the quality of life of the patient, and eventually results in death. We reviewed the medical literature concentrating upon agents that have undergone clinical evaluation for the treatment of patients with cachexia. These agents are discussed, together with their mechanisms of action. Megestrol acetate, corticosteroids, eicosapentaenoic acid, and thalidomide have shown some success in the treatment of cachexia. beta-hydroxy-beta-methylbutyrate, cyclooxygenase inhibitors, adenosine 5'-triphosphate, and growth hormone are undergoing clinical evaluation. Appetite stimulants such as cannabinoids and antiserotonic agents have been shown to be ineffective in preventing progressive weight loss in cachexia. Much of the success in the treatment of cachexia has come from agents capable of blocking protein degradation through the ubiquitin-proteasome proteolytic pathway. Muscle mass can be increased when such agents are combined with agents that stimulate protein synthesis. In order to develop new agents, more fundamental research is required on the cellular mechanisms governing protein synthesis and degradation in skeletal muscle in cachexia.
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PMID:Clinical anticachexia treatments. 1655 27

The leucine metabolite beta-hydroxy-beta-methylbutyrate (HMB) has been extensively used as an ergogenic aid; particularly among bodybuilders and strength/power athletes, who use it to promote exercise performance and skeletal muscle hypertrophy. While numerous studies have supported the efficacy of HMB in exercise and clinical conditions, there have been a number of conflicting results. Therefore, the first purpose of this paper will be to provide an in depth and objective analysis of HMB research. Special care is taken to present critical details of each study in an attempt to both examine the effectiveness of HMB as well as explain possible reasons for conflicting results seen in the literature. Within this analysis, moderator variables such as age, training experience, various states of muscle catabolism, and optimal dosages of HMB are discussed. The validity of dependent measurements, clustering of data, and a conflict of interest bias will also be analyzed. A second purpose of this paper is to provide a comprehensive discussion on possible mechanisms, which HMB may operate through. Currently, the most readily discussed mechanism has been attributed to HMB as a precursor to the rate limiting enzyme to cholesterol synthesis HMG-coenzyme A reductase. However, an increase in research has been directed towards possible proteolytic pathways HMB may operate through. Evidence from cachectic cancer studies suggests that HMB may inhibit the ubiquitin-proteasome proteolytic pathway responsible for the specific degradation of intracellular proteins. HMB may also directly stimulate protein synthesis, through an mTOR dependent mechanism. Finally, special care has been taken to provide future research implications.
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PMID:Effects of beta-hydroxy-beta-methylbutyrate (HMB) on exercise performance and body composition across varying levels of age, sex, and training experience: A review. 1817 41

Both tumor necrosis factor-alpha (TNF-alpha)/interferon-gamma (IFN-gamma) and angiotensin II (ANG II) induced an increase in total protein degradation in murine myotubes, which was completely attenuated by treatment with beta-hydroxy-beta-methylbutyrate (HMB; 50 microM). There was an increase in formation of reactive oxygen species (ROS) within 30 min, as well as an increase in the activity of both caspase-3 and -8, and both effects were attenuated by HMB. Moreover, inhibitors of caspase-3 and -8 completely attenuated both ROS formation and total protein degradation induced by TNF-alpha/IFN-gamma and ANG II. There was an increased autophosphorylation of double-stranded RNA-dependent protein kinase (PKR), which was attenuated by the specific caspase-3 and -8 inhibitors. Neither ROS formation or protein degradation occurred in myotubes expressing a catalytically inactive PKR variant, PKRDelta6, in response to TNF-alpha/IFN-gamma, compared with myotubes expressing wild-type PKR, although there was still activation of caspase-3 and -8. HMB also attenuated activation of PKR, suggesting that it was important in protein degradation. Formation of ROS was attenuated by rotenone, an inhibitor of the mitochondrial electron transport chain, nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase, and SB 203580, a specific inhibitor of p38 mitogen-activated protein kinase (p38 MAPK), which also attenuated total protein degradation. Activation of p38 MAPK by PKR provides the link to ROS formation. These results suggest that TNF-alpha/IFN-gamma and ANG II induce muscle protein degradation by a common signaling pathway, which is attenuated by HMB, and that this involves the initial activation of caspase-3 and -8, followed by autophosphorylation and activation of PKR, which then leads to increased ROS formation via activation of p38 MAPK. Increased ROS formation is known to induce protein degradation through the ubiquitin-proteasome pathway.
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PMID:Mechanism of attenuation of muscle protein degradation induced by tumor necrosis factor-alpha and angiotensin II by beta-hydroxy-beta-methylbutyrate. 1884 Jul 62