Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Neurotrophins activate multiple signaling pathways in neurons. However, the precise roles of these signaling molecules in cell survival are not well understood. In this report, we show that nerve growth factor (NGF) activates the transcription factors NF-kappaB and AP-1 in cultured sympathetic neurons. Activated NF-kappaB complexes were shown to consist of heterodimers of p50 and Rel proteins (RelA, as well as c-Rel), and NF-kappaB activation was found to occur independently of de novo protein synthesis but in a manner that required the action of the proteasome complex. Treatment with the NF-kappaB inhibitory peptide SN50 in the continuous presence of NGF resulted in dose-dependent induction of cell death. Under the conditions used, SN50 was shown to selectively inhibit NF-kappaB activation but not the activation of other cellular transcription factors such as AP-1 and cAMP response element-binding protein. Cells treated with SN50 exhibited morphological and biochemical hallmarks of apoptosis, and the kinetics of cell killing were accelerated relative to death induced by NGF withdrawal. Finally, experiments were conducted to test directly whether NF-kappaB could act as a survival factor for NGF-deprived neurons. Microinjection of cells with an expression plasmid encoding NF-kappaB (c-Rel) resulted in enhanced neuronal survival after withdrawal of NGF, whereas cells that were transfected with a vector encoding a mutated derivative of c-Rel lacking the transactivation domain underwent cell death to the same extent as control cells. Together, these findings suggest that the activation of NF-kappaB/Rel transcription factors may contribute to the survival of NGF-dependent sympathetic neurons.
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PMID:Nerve growth factor-dependent activation of NF-kappaB contributes to survival of sympathetic neurons. 985 73

Recent advances in our understanding of the molecular regulation of myeloma cells suggest novel strategies for treating multiple myeloma. Some myeloma cells express a 69 kD variant of Ku86, a heterodimer subunit that is essential for double-stranded DNA break repair. Presence of the variant impairs DNA repair; therefore normal Ku86 in myeloma cells confers resistance to therapy and may represent a therapeutic target. The upregulation of NF-kappaB-dependent interleukin-6 (IL-6) transcription and secretion that occurs following adhesion of myeloma cells to bone marrow stromal cells (BMSCs) may serve as a potential therapeutic target, as IL-6 is a growth and survival factor for myeloma cells. Accordingly, proteasome inhibitors inhibit activation of NF-kappaB and induce apoptosis of myeloma cells; they also inhibit the NF-kappaB-dependent up-regulation of IL-6 in BMSCs and related paracrine growth of adherent tumor cells. Therapeutic strategies may also target the mitogen-activated protein kinase (MAPK) pathway that is thought to mediate the IL-6-induced proliferation of myeloma cells. Vascular endothelial growth factor (VEGF) is also upregulated by adhesion of myeloma cells to BMSCs and may serve as a growth and/or survival factor for myeloma cells; preliminary studies suggest that VEGF receptor inhibitors may block proliferation of tumor cells. Thalidomide was recently used successfully to treat myeloma in patients whose disease was refractory to conventional treatment. An enhanced understanding of the mechanisms of action of thalidomide may result in the development of analogues with enhanced potency and fewer side effects. The potential mechanisms of action of thalidomide are reviewed, including antiangiogenic effects; direct effects of thalidomide on the growth and survival of myeloma cells and BMSCs; modulation of adhesive interactions; and regulation of secretion and bioactivity of cytokines. Immune-based strategies for treating multiple myeloma are also reviewed. Therapeutic obstacles include excessive toxicity after allografting, contaminating tumor cells in autografts, and the persistence of minimal residual disease (MRD) after high-dose therapy followed by allogenic or autologous stem cell transplantation. Allografting can be performed safely in myeloma, donor lymphocyte infusions (DLI) may effectively treat relapsed myeloma post allografting; and use of CD4+ T cell-enriched DLI may reduce the risk of graft-versus-host disease. Treatment with autografting is frequently compromised by MRD in the autograft and in the patient post myeloablative therapy. Adenoviral purging prior to autotransplantation and in vivo and ex vivo stimulation of autoimmune cells are discussed as potential approaches to address these problems.
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PMID:Novel biologically based therapies for myeloma. 1150 80

Multiple myeloma (MM) is characterized by the accumulation of malignant plasma cells in the bone marrow caused primarily by failure of normal homeostatic mechanisms to prevent the expansion of postgerminal center plasma cells. We have examined the molecular mechanisms that promote the survival of MM cells and have identified a key role for myeloid cell factor-1 (Mcl-1), an antiapoptotic member of the Bcl-2 family. These experiments were initiated by the observation that MM cells were exquisitely sensitive to culture in the presence of actinomycin D: caspase activation occurred within 3 hours of treatment and cells were not protected by interleukin-6, the main MM cell growth and survival factor. Actinomycin D-induced apoptosis was blocked by proteasome inhibitors, suggesting that a labile protein was required for MM cell survival. Further analysis demonstrated that Mcl-1 was likely to be the labile factor governing MM cell survival. Mcl-1 protein levels decreased rapidly after culture in the presence of actinomycin D in concordance with effector caspase activation, but addition of proteasome inhibitors reversed the loss of Mcl-1 and maintained cell viability. The levels of other antiapoptotic proteins, including Bcl-2 and members of the inhibitors-of-apoptosis family, were unaffected by these interventions. Furthermore, Mcl-1 antisense oligonucleotides caused a rapid down-regulation of Mcl-1 protein levels and the coincident induction of apoptosis, whereas overexpression of Mcl-1 delayed actinomycin D-induced apoptosis with kinetics that correlated with expression levels of Mcl-1. These data indicate that Mcl-1 expression is required for the survival of MM cells and may represent an important target for future therapeutics.
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PMID:Myeloid cell factor-1 is a critical survival factor for multiple myeloma. 1187 56

hnRNP A1 is a nucleocytoplasmic shuttling heterogeneous nuclear ribonucleoprotein that accompanies eukaryotic mRNAs from the active site of transcription to that of translation. Although the importance of hnRNP A1 as a regulator of nuclear pre-mRNA and mRNA processing and export is well established, it is unknown whether this is relevant for the control of proliferation, survival, and differentiation of normal and transformed cells. We show here that hnRNP A1 levels are increased in myeloid progenitor cells expressing the p210(BCR/ABL) oncoprotein, in mononuclear cells from chronic myelogenous leukemia (CML) blast crisis patients, and during disease progression. In addition, in myeloid progenitor 32Dcl3 cells, BCR/ABL stabilizes hnRNP A1 by preventing its ubiquitin/proteasome-dependent degradation. To assess the potential role of hnRNP A1 nucleocytoplasmic shuttling activity in normal and leukemic myelopoiesis, a mutant defective in nuclear export was ectopically expressed in parental and BCR/ABL-transformed myeloid precursor 32Dcl3 cells, in normal murine marrow cells, and in mononuclear cells from a CML patient in accelerated phase. In normal cells, expression of this mutant enhanced the susceptibility to apoptosis induced by interleukin-3 deprivation, suppressed granulocytic differentiation, and induced massive cell death of granulocyte colony-stimulating factor-treated cultures. In BCR/ABL-transformed cells, its expression was associated with suppression of colony formation and reduced tumorigenic potential in vivo. Moreover, interference with hnRNP A1 shuttling activity resulted in downmodulation of C/EBPalpha, the major regulator of granulocytic differentiation, and Bcl-X(L), an important survival factor for hematopoietic cells. Together, these results suggest that the shuttling activity of hnRNP A1 is important for the nucleocytoplasmic trafficking of mRNAs that encode proteins influencing the phenotype of normal and BCR/ABL-transformed myeloid progenitors.
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PMID:hnRNP A1 nucleocytoplasmic shuttling activity is required for normal myelopoiesis and BCR/ABL leukemogenesis. 1188 11

A number of malignant tumors interact with the host to cause a syndrome of cachexia, characterized by extensive loss of adipose tissue and skeletal muscle mass, but with preservation of proteins in visceral tissues. Although anorexia is frequently present, the body composition changes in cancer cachexia cannot be explained by nutritional deprivation alone. Loss of skeletal muscle mass is a result of depression in protein synthesis and an increase in protein degradation. The main degradative pathway that has been found to have increased expression and activity in the skeletal muscle of cachectic patients is the ubiquitin-proteasome proteolytic pathway. Cachexia-inducing tumors produce catabolic factors such as proteolysis-inducing factor (PIF), a 24 kDa sulfated glycoprotein, which inhibit protein synthesis and stimulate degradation of intracellular proteins in skeletal muscle by inducing an increased expression of regulatory components of the ubiquitin-proteasome proteolytic pathway. While the oligosaccharide chains in PIF are required to initiate protein degradation the central polypeptide core may act as a growth and survival factor. Only cachexia-inducing tumors are capable of elaborating fully glycosylated PIF, and the selectivity of production possibly rests with the acquisition of the necessary glycosylating enzymes, rather than expressing the gene for the polypeptide core. Loss of adipose tissue is probably the result of an increase in catabolism rather than a defect in anabolism. A lipid mobilizing factor (LMF), identical with the plasma protein Zn-alpha2-glycoprotein (ZAG) is found in the urine of cachectic cancer patients and is produced by tumors causing a decrease in carcass lipid. LMF causes triglyceride hydrolysis in adipose tissue through a cyclic AMP-mediated process by interaction with a beta3-adrenoreceptor. Thus, by producing circulating factors certain malignant tumors are able to interfere with host metabolism even without metastasis to that particular site.
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PMID:Tumor-host interactions. 1544 22

Elevated expression of the serine/threonine kinase Pim-1 increases the incidence of lymphomas in Pim-1 transgenic mice and has also been found to occur in some human cancers. Pim-1 acts as a cell survival factor and may prevent apoptosis in malignant cells. It was therefore of interest to understand to what extent maintenance and degradation of Pim-1 protein is affected by heat shock proteins (Hsp) and the ubiquitin-proteasome pathway in K562 and BV173 human leukemic cells. The half-life of Pim-1 protein in these cells was found to increase from 1.7 to 3.1 hours when induced by heat shock or by treating the cells with the proteasome inhibitor PS-341 (bortezomib). The Hsp90 inhibitor geldanamycin prevented the stabilization of Pim-1 by heat shock. Using immunoprecipitation, it was determined that Pim-1 is targeted for degradation by ubiquitin and that Hsp70 is associated with Pim-1 under these circumstances. Conversely, Hsp90 was found to protect Pim-1 from proteasomal degradation. A luminescence-based kinase assay showed that Pim-1 kinase bound to Hsp70 or Hsp90 remains active, emphasizing the importance of its overall cellular levels. This study shows how Pim-1 levels can be modulated in cells through degradation and stabilization.
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PMID:Pim-1 kinase stability is regulated by heat shock proteins and the ubiquitin-proteasome pathway. 1579 97

Neuregulins are a family of genes involved in key aspects of neural biology. Neuregulins 1, 2 and 3 (NRG1, NRG2 and NRG3) are expressed in the mammalian nervous system. It is well established that NRG1, with fifteen different splicing forms, is central for brain development and function. However, the biological relevance of NRG2 and NRG3 remains elusive. Here, we report the identification of a new isoform of NRG3 that is specifically expressed in the human embryonic central nervous system. Sequence alignment with the human genome suggests that this transcript is produced by alternative promoter usage. The encoded polypeptide is a type-I-glycosylated plasma membrane protein, which is shed into the extracellular space where it activates erbB4, a pivotal receptor for brain development. In addition, we show that the protein has a signal sequence that is cleaved after membrane insertion. Proteasome inhibition with Lactacystin enhances the expression of the protein, whereas impairment of ubiquitylation in the conditional mutant cell line ts20 protects the protein from degradation. These observations imply that the ubiquitin/proteasome pathway regulates biogenesis of the protein. We also show that recombinant neuregulin 3 acts as an oligodendrocyte survival factor by activating the phosphoinositide 3-kinase signalling pathway. Therefore, we report a new post-translationally regulated isoform of neuregulin 3 expressed in the developing human central nervous system with a role in oligodendrocyte survival.
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PMID:Characterization of a neural-specific splicing form of the human neuregulin 3 gene involved in oligodendrocyte survival. 1647 87

The 26S proteasome is a large multi-subunit protein complex found in the cytoplasm and nucleus of mammalian cells which plays a critical role in intracellular proteolysis. It has been found that the 26S proteasome degrades multiple important substrates which are associated with tumor growth and development. Emerging evidence demonstrates that proteasome inhibition is an innovative and effective approach for treating some human cancers. PS-341 (also known as Velcade or Bortezomib), a specific inhibitor of the 26S proteasome, has been approved for treating multiple myeloma by the FDA. PS-341 mainly exhibits its anti-cancer effect by inducing apoptosis, and has been found to affect several pro- and anti-apoptotic pathways. Activation of the transcription factor nuclear factor kappa B (NF-kappaB), a key survival factor, is dependent on the 26S proteasome. The inhibition of NF-kappaB by PS-341 has been found to induce apoptosis in several human cancer cells and is considered to be one of the primary targets of the PS-341 anti-tumor effect. More recently, studies have suggested that, in addition to the inhibition of pro-survivial NF-kappaB, PS-341 may induce apoptosis by stimulating pro-apoptotic endoplasmic reticulum stress through proteasome inhibition. In this review, we will mainly discuss recent progress on the elucidation of the molecular mechanism of PS-341-mediated apoptosis.
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PMID:Proteasome inhibitor induces apoptosis through induction of endoplasmic reticulum stress. 1686

Tribbles, an atypical protein kinase superfamily member, coordinates cell proliferation, migration, and morphogenesis during the development of Drosophila and Xenopus embryos. Although Tribbles are highly conserved throughout evolution, the physiological functions of mammalian Tribbles family remain largely unclear. Here we report that human TRB2 is a pro-apoptotic molecule that induces apoptosis of cells mainly of the hematopoietic origin. TRB2 mRNA is selectively induced by removal of granulocyte macrophage colony-stimulating factor (GM-CSF) or interleukin-2 from human erythroleukemia-derived TF-1 cell line or activated primary CD4(+) T cells, respectively. It is, however, not induced by many other treatments that trigger apoptosis of these two cell types. Overexpression of TRB2 activates many apoptotic events observed in GM-CSF-deprived TF-1 cells, including loss of mitochondrial membrane potential, Mcl-1 cleavage/degradation, and activation of Bax and a number of caspases. Specific knockdown of TRB2 significantly suppresses GM-CSF deprivation-induced apoptosis and all apoptotic events mentioned above. Finally, we demonstrate that TRB2-induced cleavage and degradation of Mcl-1 are mediated via a caspase-dependent but proteasome-independent mechanism, and overexpression of Mcl-1 or its upstream activator Akt can markedly overcome the apoptogenic effect of TRB2. Altogether, these results suggest that the TRB2-Mcl-1 axis plays an important role in survival factor withdrawal-induced apoptosis of TF-1 cells.
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PMID:Survival factor withdrawal-induced apoptosis of TF-1 cells involves a TRB2-Mcl-1 axis-dependent pathway. 1754 67

Fetal growth plate chondrocyte is a unique mesenchymal tissue, as it is avascular and hypoxic. Yet, chondrocytes not only survive in this environment, but also undergo all cellular processes (proliferation, growth arrest, differentiation, etc.) required for normal endochondral bone development. A crucial mediator of the adaptive response of cells to hypoxia is a transcription factor named hypoxia-inducible factor 1alpha (Hif-1alpha). One target of Hif-1alpha transcriptional activation is the angiogenic factor vascular endothelial growth factor (VEGF), whereas Hif-1alpha accumulation is controlled by the von Hippel-Lindau (VHL) tumor suppressor, an E3-ubiquitin ligase that induces its degradation by the proteasome. We, and others, demonstrated that each component of this pathway is a critical regulator of endochondral bone development. In particular, we previously established that Hif-1alpha is a survival factor for hypoxic chondrocytes, and that it also negatively regulates cell proliferation. Interestingly, we also showed that hypoxia increases extracellular matrix accumulation in a Hif-1alpha-dependent fashion. This suggested that Hif-1alpha could be critically important not only for cell survival and proliferation but also for cell differentiation. We recently demonstrated that Hif-1alpha is indeed a differentiation factor since it is required in mesenchymal cells both for early chondrogenesis, and for joint development.
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PMID:Fetal growth plate: a developmental model of cellular adaptation to hypoxia. 1805 35


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