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)

Beta-arrestin1, which regulates many aspects of seven transmembrane receptor (7TMR) biology, has also been shown to serve as an adaptor, which brings Mdm2, an E3 ubiquitin ligase to the insulin-like growth factor-1 receptor (IGF-1R), leading to its proteasome-dependent destruction. Here we demonstrate that IGF-1R stimulation also leads to ubiquitination of beta-arrestin1, which regulates vesicular trafficking and activation of ERK1/2. This beta-arrestin1-dependent ERK activity can occur even when the classical tyrosine kinase signaling is impaired. siRNA-mediated suppression of beta-arrestin1 in human melanoma cells ablates IGF-1-stimulated ERK and prolongs the G1 phase of the cell cycle. These data suggest that beta-arrestin-dependent ERK signaling by the IGF-1R regulates cell cycle progression and may thus be an important regulator of the growth of normal and malignant cells.
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PMID:Beta-arrestin and Mdm2 mediate IGF-1 receptor-stimulated ERK activation and cell cycle progression. 1730 58

The proteasome maintains cellular homeostasis by degrading oxidized and damaged proteins, a function known to be impaired during aging. The proteasome also acts in a regulatory capacity through E3 ligases to mediate the spatially and temporally controlled breakdown of specific proteins that impact biological processes. We have identified components of a Skp1-Cul1-F-Box E3 ligase complex that are required for the extended lifespan of Caenorhabditis elegans insulin/insulin-like growth factor-1-signaling (IIS) mutants. The CUL-1 complex functions in postmitotic, adult somatic tissues of IIS mutants to enhance longevity. Reducing IIS function leads to the nuclear accumulation of the DAF-16/FOXO transcription factor, which extends lifespan by regulating downstream longevity genes. These CUL-1 complex genes act, at least in part, by promoting the transcriptional activity of DAF-16/FOXO. Together, our findings describe a role for an important cellular pathway, the proteasomal pathway, in the genetic determination of lifespan.
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PMID:Regulation of Caenorhabditis elegans lifespan by a proteasomal E3 ligase complex. 1739 28

The E7 protein encoded by the oncogenic human papillomavirus type 16 has been shown to bind and inactivate insulin-like growth factor-binding protein-3 (IGFBP-3), the pro-apoptotic product of a tumour suppressor gene; however, the molecular mechanism underlying E7-induced inactivation of IGFBP-3 remained uncertain. In this study, we map the IGFBP-3-binding domain for E7 to the nuclear localization signal in the conserved C-terminal domain of IGFBP-3. Moreover, we demonstrate that both proteins interact in the nucleus and that E7 induces polyubiquitination and proteasome-dependent proteolysis of nuclear IGFBP-3 in cervical cancer cells. This leads to a dramatic shortening of the half-life of nuclear IGFBP-3, whereas the stability of an E7-non-binding IGFBP-3 mutant is not affected by E7. Finally, we show that E7-mediated destruction of nuclear IGFBP-3 correlates with the inhibition of IGFBP-3-induced apoptotic cell death. These data are consistent with E7-induced ubiquitin/proteasome-dependent inactivation of nuclear IGFBP-3.
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PMID:Human papillomavirus type 16 E7 oncoprotein inhibits apoptosis mediated by nuclear insulin-like growth factor-binding protein-3 by enhancing its ubiquitin/proteasome-dependent degradation. 1782 6

The insulin receptor substrate-1 (IRS-1), a docking protein of the type 1 insulin-like growth factor receptor (IGF-IR) plays a significant role in cell proliferation and differentiation. The expression of IRS-1 is down-regulated in mouse embryo fibroblasts (MEFs) with a deletion of caveolin-1 (cav1) genes (KO cells). Levels of IRS-1 mRNA are not affected. Re-introduction of cav1 into KO cells rescues IRS-1 expression. Stabilization of protein levels is reciprocal and a strict correlation between IRS-1 and cav1 levels was confirmed in five cell lines, and in mouse tissues. IRS-1 binds through its phosphotyrosine binding (PTB) domain to tyrosine 14 (Y14) of cav1, the residue phosphorylated by IGF-1 stimulation and by v-src. The down-regulation of IRS-1 in cav-/- cells occurs via the proteasome pathway. These results indicate a novel mechanism for the regulation of IRS-1 expression levels, an important finding in view of IRS-1 role in cell proliferation and transformation.
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PMID:Regulation of insulin receptor substrate-1 expression levels by caveolin-1. 1850 77

Oxidized low-density lipoprotein (LDL) is proatherogenic and induces smooth muscle cell apoptosis, which contributes to atherosclerotic plaque destabilization. We showed previously that oxidized LDL downregulates insulin-like growth factor-1 receptor in human smooth muscle cells and that this is critical for induction of apoptosis. To identify mechanisms, we exposed smooth muscle cells to 60 mug/ml oxidized LDL or native LDL and assessed insulin-like growth factor-1 receptor mRNA levels, protein synthesis rate, and receptor protein stability. Oxidized LDL decreased insulin-like growth factor-1 receptor mRNA levels by 30% at 8 h compared with native LDL, and this decrease was maintained for up to 20 h. However, insulin-like growth factor-1 receptor protein synthesis rate was not altered by oxidized LDL. Pulse-chase labeling experiments revealed that oxidized LDL reduced insulin-like growth factor-1 receptor protein half-life to 12.2+/-1.7 h from 24.4+/-4.7 h with native LDL. This destabilization of insulin-like growth factor-1 receptor protein was accompanied by enhanced receptor ubiquitination. Overexpression of dominant-negative Nedd4 prevented oxidized LDL-induced downregulation of insulin-like growth factor-1 receptor, suggesting that Nedd4 was the ubiquitin ligase that mediated receptor downregulation. However, the proteasome inhibitors lactacystin, MG-132, and proteasome inhibitor-1 failed to block oxidized LDL-induced downregulation of insulin-like growth factor-1 receptor. Thus oxidized LDL downregulates insulin-like growth factor-1 receptor by destabilizing the protein via Nedd4-enhanced ubiquitination, leading to degradation via a proteasome-independent pathway. This finding provides novel insights into oxidized LDL-triggered oxidant signaling and mechanisms of smooth muscle cell depletion that contribute to plaque destabilization and coronary events.
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PMID:The ubiquitin ligase Nedd4 mediates oxidized low-density lipoprotein-induced downregulation of insulin-like growth factor-1 receptor. 1872 65

Cyclin D dysregulation and overexpression is noted in the majority of multiple myeloma (MM) patients, suggesting its critical role in MM pathogenesis. Here, we sought to identify the effects of targeting cyclin D in MM. We first confirmed cyclin D mRNA overexpression in 42 of 64 (65%) patient plasma cells. Silencing cyclin D1 resulted in >50% apoptotic cell death suggesting its validity as a potential therapeutic target. We next evaluated P276-00, a clinical-grade small-molecule cyclin-dependent kinase inhibitor as a way to target the cyclins. P276-00 resulted in dose-dependent cytotoxicity in MM cells. Cell-cycle analysis confirmed either growth arrest or caspase-dependent apoptosis; this was preceded by inhibition of Rb-1 phosphorylation with associated downregulation of a range of cyclins suggesting a regulatory role of P276-00 in cell-cycle progression through broad activity. Proliferative stimuli such as interleukin-6, insulin-like growth factor-1 and bone-marrow stromal cell adherence induced cyclins; P276-00 overcame these growth, survival and drug resistance signals. Because the cyclins are substrates of proteasome degradation, combination studies with bortezomib resulted in synergism. Finally, in vivo efficacy of P276-00 was confirmed in an MM xenograft model. These studies form the basis of an ongoing phase I study in the treatment of relapsed/refractory MM.
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PMID:Preclinical activity of P276-00, a novel small-molecule cyclin-dependent kinase inhibitor in the therapy of multiple myeloma. 1915 76

Insulin receptor substrates (IRS)-1 and -2 are major substrates of insulin and type I insulin-like growth factor (IGF-I) receptor (IGF-IR) signaling. In this study, SH-EP human neuroblastoma cells are used as a model system to examine the differential roles of IRS-1 and IRS-2 on glucose-mediated apoptosis. In the presence of high glucose, IRS-1 underwent caspase-mediated degradation, followed by focal adhesion kinase (FAK) and Akt degradation and apoptosis. IRS-2 expression blocked all these changes whereas IRS-1 overexpression had no effect. In parallel, IRS-2, but not IRS-1, overexpression enhanced IGF-I-mediated Akt activation without affecting extracellular regulated kinase signaling. While IRS-1 was readily degraded by caspases, hyperglycemia-mediated IRS-2 degradation was unaffected by caspase inhibitors but blocked by proteasome and calpain inhibitors. Our data suggest that the differential degradation of IRS-1 and IRS-2 contributes to their distinct modes of action and the increased neuroprotective effects of IRS-2 in this report are due, in part, to its resistance to caspase-mediated degradation.
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PMID:Insulin receptor substrate (IRS)-2, not IRS-1, protects human neuroblastoma cells against apoptosis. 1925 21

The phosphatidylinositol 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) pathway mediates proliferation, survival, and drug resistance in multiple myeloma (MM) cells. Here, we tested the anti-MM activity of NVP-BEZ235 (BEZ235), which inhibits PI3K/Akt/mTOR signaling at the levels of PI3K and mTOR. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric survival assays showed that MM cell lines exhibited dose- and time-dependent decreased viability after exposure to BEZ235 (IC(50), 25-800 nmol/L for 48 hours). MM cells highly sensitive (IC(50), <25 nmol/L) to BEZ235 (e.g., MM.1S, MM.1R, Dox40, and KMS-12-PE) included both lines sensitive and resistant to conventional (dexamethasone, cytotoxic chemotherapeutics) agents. Pharmacologically relevant BEZ235 concentrations (25-400 nmol/L) induced rapid commitment to and induction of MM.1S and OPM-2 cell death. Furthermore, normal donor peripheral blood mononuclear cells were less sensitive (IC(50), >800 nmol/L) than the majority of MM cell lines tested, suggesting a favorable therapeutic index. In addition, BEZ235 was able to target MM cells in the presence of exogenous interleukin-6, insulin-like growth factor-1, stromal cells, or osteoclasts, which are known to protect against various anti-MM agents. Molecular profiling revealed that BEZ235 treatment decreased the amplitude of transcriptional signatures previously associated with myc, ribosome, and proteasome function, as well as high-risk MM and undifferentiated human embryonic stem cells. In vivo xenograft studies revealed significant reduction in tumor burden (P = 0.011) and survival (P = 0.028) in BEZ235-treated human MM tumor-bearing mice. Combinations of BEZ235 with conventional (e.g., dexamethasone and doxorubicin) or novel (e.g., bortezomib) anti-MM agents showed lack of antagonism. These results indicate that BEZ235 merits clinical testing, alone and in combination with other agents, in MM.
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PMID:Antimyeloma activity of the orally bioavailable dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor NVP-BEZ235. 1958 92

WTAP (Wilms tumor 1-associating protein) is a recently identified nuclear protein that is essential for mouse embryo development. The Drosophila homolog of WTAP, Fl(2)d, regulates pre-mRNA splicing; however, the role of WTAP in mammalian cells is uncertain. To elucidate a context for WTAP action, we screened growth and survival factors for their effects on WTAP expression in vascular smooth muscle cells (SMCs), a cell type previously found to express WTAP dynamically. This revealed that insulin-like growth factor-1 (IGF-1) uniquely reduced WTAP abundance. This decline in WTAP proved to be necessary for IGF-1 to confer its antiapoptotic properties, which were blocked by transducing the WTAP gene into SMCs. WTAP down-regulation by IGF-1 was mediated by an IGF-1 receptor-phosphatidylinositol 3-kinase-Akt signaling axis that directed WTAP degradation via a nuclear 26 S proteasome. Moreover, by promoting the degradation of WTAP, IGF-1 shifted the pre-mRNA splicing program for the survival factor, survivin, to reduce expression of survivin-2B, which is proapoptotic, and increase expression of survivin, which is antiapoptotic. Knockdown of survivin-2B rescued the ability of IGF-1 to promote survival when WTAP was overexpressed. These data uncover a novel regulatory cascade for human SMC survival based on adjusting the nuclear abundance of WTAP to define the splice variant balance among survivin isoforms.
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PMID:Nuclear degradation of Wilms tumor 1-associating protein and survivin splice variant switching underlie IGF-1-mediated survival. 1960 57

Muscle wasting is a prominent feature of end-stage renal disease and is associated with muscle weakness and poor physical functioning. Potential reasons for muscle wasting include advancing age, sedentary behavior, inflammation, poor nutritional intake, androgen deficiency, oxidative stress, metabolic acidosis, and insulin resistance. Each of these conditions can be associated with decreased protein synthesis, increased protein degradation, or both. The primary muscle protein synthesis pathway is the insulin insulin-like growth factor-1/phosphatidyl inositol-3 kinase/Akt pathway, which results in the phosphorylation of the mammalian target of rapamycin and subsequent increased protein synthesis. The major protein degradation pathway is the ubiquitin-proteasome system. This review discusses the ways in which end-stage renal disease tips the balance of protein turnover towards catabolism and the mechanisms by which various interventions may work to mitigate wasting or even cause anabolism.
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PMID:Anabolic and catabolic mechanisms in end-stage renal disease. 1980 Nov 38


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