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)

Interactions between inhibitors of the proteasome and histone deacetylases have been examined in human T-leukemia/lymphoma cells both in vitro and in vivo. Co-exposure of cells to bortezomib and suberoylanilide hydroxamic acid (SAHA) synergistically induces T-leukemia/lymphoma cells to undergo apoptosis, consistent with a significant increase in mitochondrial injury and caspase activation. These events are accompanied by inhibition of cyto-protective signaling pathways, including the nuclear factor (NF)-kappaB, Raf-1/mitogen-induced extracellular kinase (MEK)/extracellular signal-related kinase (ERK) and AKT pathways, and activation of stress-related cascades, including the stress-activated kinases c-jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38MAPK). Moreover, bortezomib in conjunction with SAHA efficiently induces apoptosis of primary T-leukemia/lymphoma cells and inhibits tumor growth in a murine xenograft model established with subcutaneous injection of Jurkat cells. Taken together, these findings confirm the synergistic anti-tumor effect of the proteasome and histone deacetylase inhibitors, and provide an insight into the future clinical applications of bortezomib-SAHA combining regimen in treating T-cell malignancies.
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PMID:The proteasome inhibitor bortezomib interacts synergistically with the histone deacetylase inhibitor suberoylanilide hydroxamic acid to induce T-leukemia/lymphoma cells apoptosis. 1928 31

Dysregulation of the ubiquitin-proteasome system (UPS) has been implicated in several types of tumorigenesis. Our previous studies have shown the potential role of Cdh1/APC in regulating tumor formation via governing the Skp2-p27-cyclinE/CDK2 axis. In this work, we used a xenograft mouse breast cancer model to identify the mechanism by which Cdh1/APC potentially suppresses tumor growth in vivo. Here, we report that depletion of Cdh1 results in a significant enhancement of the breast tumor proliferation, while elevated Cdh1 leads to suppression of breast tumor growth. Analysis of breast tissue arrays has indicated that higher levels of Cdh1 are associated with normal breast epithelial tissues whereas lower Skp2 expression and elevated p27 levels are detected. Conversely, the percentage of breast cancer tissues stained positive for Cdh1 and p27 are significantly lower with higher Skp2 levels. Thus, the E3 ligase, Cdh1/APC, may inhibit breast tumor growth via regulating Skp2-p27 mediated cell cycle progression.
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PMID:An in vivo study of Cdh1/APC in breast cancer formation. 1935 Jun 29

The majority of human tumors are angiogenesis dependent. Understanding the specific mechanisms that contribute to angiogenesis may offer the best approach to develop therapies to inhibit angiogenesis in cancer. Endothelial monocyte activating polypeptide-II (EMAP-II) is an anti-angiogenic cytokine with potent effects on endothelial cells (ECs). It inhibits EC proliferation and cord formation, and it suppresses primary and metastatic tumor growth in-vivo. However, very little is known about the molecular mechanisms behind the anti-angiogenic activity of EMAP-II. In the present study, we explored the molecular mechanism behind the anti-angiogenic activity exerted by this protein on ECs. Our results demonstrate that EMAP-II binds to the cell surface alpha5beta1 integrin receptor. The cell surface binding of EMAP-II results in its internalization into the cytoplasmic compartment where it interacts with its cytoplasmic partner PSMA7, a component of the proteasome degradation pathway. This interaction increases hypoxia-inducible factor 1-alpha (HIF-1alpha) degradation under hypoxic conditions. The degradation results in the inhibition of HIF-1alpha mediated transcriptional activity as well as HIF-1alpha mediated angiogenic sprouting of ECs. HIF-1alpha plays a critical role in angiogenesis by activating a variety of angiogenic growth factors. Our results suggest that one of the major anti-angiogenic functions of EMAP-II is exerted through its inhibition of the HIF-1alpha activities.
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PMID:Endothelial monocyte activating polypeptide-II modulates endothelial cell responses by degrading hypoxia-inducible factor-1alpha through interaction with PSMA7, a component of the proteasome. 1936 50

About two thirds of breast cancers in women are hormone-dependent and require estrogen for growth, its effects being mainly mediated through estrogen receptor alpha (ERalpha). Docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6) have opposite effects on carcinogenesis, with DHA suppressing and AA promoting tumor growth both in vitro and in vivo. However, the mechanism is not clear. Here, we examined whether the effect is mediated through changes in ERalpha distribution. MCF-7 cells, an ERalpha-positive human breast cancer cell line, was cultured in estrogen-free medium containing 0, 10 or 60 microM DHA or AA, then were stimulated with estradiol. DHA supplementation resulted in down-regulation of ERalpha expression (particularly in the extranuclear fraction), a reduction in phosphorylated MAPK, a decrease in cyclin D1 levels and an inhibition in cell viability. In contrast, AA had no such effects. The DHA-induced decrease in ERalpha expression resulted from proteasome-dependent degradation and not from decreased ERalpha mRNA expression. We propose that breast cancer cell proliferation is inhibited by DHA through proteasome-dependent degradation of ERalpha, reduced cyclin D1 expression and inhibition of MAPK signaling.
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PMID:Docosahexaenoic acid induces proteasome-dependent degradation of estrogen receptor alpha and inhibits the downstream signaling target in MCF-7 breast cancer cells. 1936 47

Bortezomib is a proteasome inhibitor that can synergize with interferon-alpha (IFN-alpha) to induce apoptosis in melanoma cells in vitro and inhibit tumor growth in vivo. We hypothesized that proteasome inhibition may be an effective means to sensitize melanoma cells to the direct effects of IFN-alpha. Pre-treatment of human melanoma cells with bortezomib led to significantly increased transcription of interferon-stimulated genes as determined by real-time PCR. Flow cytometric and immunoblot analyses indicated that the enhanced direct actions of IFN-alpha on melanoma cells were the result of prolonged phosphorylation of STAT1 (P-STAT1) on both the Tyrosine(701) and Serine(727) residues. In contrast, the enhanced IFN-alpha-induced P-STAT1 was not observed in peripheral blood mononuclear cells that were pre-treated with bortezomib. These data suggest that proteasome inhibition represents a mechanism to enhance the direct effects of IFN-alpha on melanoma cells thereby complementing its immunostimulatory properties.
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PMID:Bortezomib pre-treatment prolongs interferon-alpha-induced STAT1 phosphorylation in melanoma cells. 1939 96

Photodynamic therapy (PDT) is an approved therapeutic procedure that exerts cytotoxic activity toward tumor cells by inducing production of reactive oxygen species such as singlet oxygen. PDT leads to oxidative damage of cellular macromolecules, including proteins that undergo multiple modifications such as fragmentation, cross-linking, and carbonylation that result in protein unfolding and aggregation. Because the major mechanism for elimination of carbonylated proteins is their degradation by proteasomes, we hypothesized that a combination of PDT with proteasome inhibitors might lead to accumulation of carbonylated proteins in endoplasmic reticulum (ER), aggravated ER stress, and potentiated cytotoxicity toward tumor cells. We observed that Photofrin-mediated PDT leads to robust carbonylation of cellular proteins and induction of unfolded protein response. Pretreatment of tumor cells with three different proteasome inhibitors, including bortezomib, MG132, and PSI, gave increased accumulation of carbonylated and ubiquitinated proteins in PDT-treated cells. Proteasome inhibitors effectively sensitized tumor cells of murine (EMT6 and C-26) as well as human (HeLa) origin to PDT-mediated cytotoxicity. Significant retardation of tumor growth with 60% to 100% complete responses was observed in vivo in two different murine tumor models (EMT6 and C-26) when PDT was combined with either bortezomib or PSI. Altogether, these observations indicate that combination of PDT with proteasome inhibitors leads to potentiated antitumor effects. The results of these studies are of immediate clinical application because bortezomib is a clinically approved drug that undergoes extensive clinical evaluations for the treatment of solid tumors.
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PMID:Proteasome inhibition potentiates antitumor effects of photodynamic therapy in mice through induction of endoplasmic reticulum stress and unfolded protein response. 1943 17

The cyclin-dependent kinase inhibitor (CDK1) p27(kip1) is a negative regulator of cell cycling and has antitumor effects. In our previous study, the recombinant adenovirus expressing wild-type p27(kip1) (Adp27-wt) induced cell cycle arrest and apoptosis, and proved that p27 is a tumor suppressor gene like p53. Another adenovirus vector expressing mutant p27(kip1) (Adp27-mt), which inhibited degradation by the ubiquitin-proteasome system, showed increased protein stability and caused a stronger induction of apoptosis. Recently, the p27(kip1) protein binding with Jab1 (Jun activating binding protein 1) was found to translocate from the nucleus into the cytosol, and then become degraded by the 26S proteasome system. The inhibition of nuclear-cytoplasmic translocation increases the protein stability of p27(kip1) and p27(kip1) with a deletion of the Jab1-binding region (p27-jab-d) is not translocated and not degraded. Therefore, a new recombinant adenovirus (Adp27-jab-d) expressing p27-jab-d was made which was able to induce greater cytotoxicity. Adp27-jab-d inhibited the growth of human cholangiocarcinoma cell line (TFK-1) cells in vitro at 3.3 times (IC(50)) lower concentration than Adp27-wt. Moreover, in a xenografted severe combined immuno-deficient (SCID) mouse model injected with TFK-1 cells in the subcutaneous tissue, treatment by intratumor injection of Adp27-jab-d once a day for 3 days after the tumor was established, inhibited tumor growth more strongly than Adp27-wt or Adp27-mt and even induced tumor regression. However, the flow cytometric TUNEL assay showed little enhancement of apoptosis. Adp27-jab-d was thought to induce not only apoptosis but also necrosis, which was due to a specific effect of the Adp27-jab-d. Thus, by enhancing the cytotoxicity through inhibiting the translocaton of p27(kip1), p27(kip1) lacking the Jab1-binding region might be useful for cancer therapy. The control protein localization might also be a new target not only for cancer treatment, but also other diseases.
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PMID:Overexpression of adenovirus-mediated p27kip1 lacking the Jab1-binding region enhances cytotoxicity and inhibits xenografted human cholangiocarcinoma growth. 1952 60

Hepatocyte growth factor (HGF) inhibits the proliferation of several tumor cell lines and tumor growth in vivo. We showed previously that HGF induces cell cycle arrest at G1 in a human hepatoma cell line, HepG2, by up-regulating the expression of p16INK4a through strong activation of extracellular signal-regulated kinase (ERK). However, although essential, the activation was not sufficient for the up-regulation of p16. In this study, we examined regulatory mechanisms of p16 expression through a transcription factor, Ets, which has been shown previously to bind to the promoter. The treatment of HepG2 cells with HGF induced ERK-dependent phosphorylation of Ets, which leads to its activation, before the up-regulation of p16, suggesting that another factor suppresses Ets activity. We found that HGF reduces the amount of Id1, which is a dominant-negative inhibitor of Ets, leading to a decrease in Ets associated with Id1. Id1 was down-regulated via transcriptional regulation not via the ubiquitin-proteasome-mediated pathway. Inhibition of the HGF-induced high-intensity ERK activity had a modest effect on the Id1 down-regulation, and inhibition of the phosphatidylinositol 3-kinase pathway had no effect, showing that Id1 is regulated by ERK-dependent and -independent pathways other than the phosphatidylinositol 3-kinase pathway. Exogenously expressed Id1 suppressed the up-regulation of p16 by HGF and the antiproliferative effect of HGF. Knockdown of Id1 significantly enhanced the activity of the p16 promoter coordinately with the activation of ERK. Our results indicated that down-regulation of Id1 plays a key role in the inhibitory effect of HGF on cell proliferation and provides a molecular basis for cancer therapy with HGF.
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PMID:Id1 is down-regulated by hepatocyte growth factor via ERK-dependent and ERK-independent signaling pathways, leading to increased expression of p16INK4a in hepatoma cells. 1956 83

The proteasome and the autophagy systems are two evolutionarily conserved mechanisms for degrading intracellular materials. They are functionally coupled and suppression of the proteasome promotes autophagy. Although suppression of the proteasome leads to cell death, suppression of autophagy can be either prodeath or prosurvival. To understand the underlining mechanism of this dichotomy and its potential clinical implications, we treated various transformed and nontransformed human cells with proteasome inhibitors. We found that whether autophagy served a prosurvival role in this scenario was contingent on the cellular oncogenic status. Thus, autophagy suppression enhanced apoptosis induced by proteasome inhibitors in transformed cells, but not in nontransformed cells. Oncogenic transformation enhanced the ability of cells to initiate autophagy in response to stress, reflecting a stronger dependence of transformed cells on autophagy for survival. Indeed, a combined use of bortezomib, the only Food and Drug Administration-approved proteasome inhibitor for clinical use, and chloroquine, which inhibits autophagy by disturbing lysosomal functions, suppressed tumor growth more significantly than either agent alone in a xenograft model. These findings indicate that suppression of both intracellular degradation systems could constitute a novel strategy for enhanced cancer control in a tumor-specific way.
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PMID:Oncogenic transformation confers a selective susceptibility to the combined suppression of the proteasome and autophagy. 1958 39

The ubiquitin-proteasome system has a crucial role in maintaining and regulating cellular homeostasis including carcinogenesis. UBE2Q2, also designated Ubci, is one of the ubiquitin-conjugating enzymes (E2), and it has been reported that mRNA of UBE2Q2 is highly expressed in human head and neck squamous cell carcinoma, particularly hypopharyngeal carcinoma. However, the involvement of UBE2Q2 in carcinogenesis has not been fully elucidated. Most cases of head and neck carcinoma are treated with cis-diamminedichloroplatinum (II; CDDP) or docetaxel, which are the most effective chemotherapeutic agents against squamous cell carcinomas. Nevertheless, some head and neck cancers develop resistance to these drugs, although the causes and mechanisms remain unknown. In this study, we found high expression levels of UBE2Q2 in human head and neck carcinoma cell lines and cancer tissues by using an anti-UBE2Q2 antibody at the protein level. We also found that the expression level of UBE2Q2 is decreased in cell lines and cancer tissues that have resistance to CDDP or docetaxel and in cancer tissues treated with CDDP or docetaxel. Furthermore, we found that overexpression of UBE2Q2 affects cell proliferation and anchorage-independent cell growth. These findings suggest that UBE2Q2 is a novel oncosuppressor that inhibits tumor growth and is related to the resistance to anticarcinoma agents and that UBE2Q2 likely functions as a novel diagnostic tool and a potentially therapeutic target for head and neck squamous cell carcinoma.
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PMID:Ubiquitin-conjugating enzyme UBE2Q2 suppresses cell proliferation and is down-regulated in recurrent head and neck cancer. 1972 76


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