Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0029463 (osteosarcoma)
 16,637 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The AF-2 helix of nuclear receptors is essential for ligand-activated transcription, and it may function to couple the receptor to transcriptional coactivator proteins. This domain also contacts components of the proteasome machinery, suggesting that nuclear receptors may be targets for proteasome-mediated proteolysis. In the present study, we demonstrate that mSUG1 (P45), a component of the 26S proteasome, interacts in a 1,25-(OH)2D3-dependent manner with the AF-2 domain of the vitamin D receptor (VDR). Furthermore, treatment of ROS 17/2.8 osteosarcoma cells with the proteasome inhibitors MG132 or beta-lactone increased steady-state levels of the VDR protein. In the presence cycloheximide (10 microg/ml), the liganded VDR protein was degraded with a half-life of approximately 8 h, and this rate of degradation was completely blocked by 0.05 mM MG132. The role of SUG1 -VDR interaction in this process was investigated in transient expression studies. Overexpression of wild-type mSUG1 in ROS17/2.8 cells generated a novel proteolytic VDR fragment of approximately 50 kDa, and its production was blocked by proteasome inhibitors or by a nonhydrolyzable ATP analog. Parallel studies with SUG1 (K196H), a mutant that does not interact with the VDR, did not produce the 50 kDa VDR fragment. Functionally, expression of SUG1 in a VDR-responsive reporter gene assay resulted in a profound inhibition of 1,25-(OH)2D3-activated transcription, while expression of SUG1 (K196H) had no significant effect in this system. These data show that the AF-2 domain of VDR interacts with SUG1 in a 1,25-(OH)2D3-dependent fashion and that this interaction may target VDR to proteasome-mediated degradation as a means to downregulate the 1,25-(OH)2D3-activated transcriptional response.
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PMID:Proteasome-mediated degradation of the vitamin D receptor (VDR) and a putative role for SUG1 interaction with the AF-2 domain of VDR. 983 Oct 79

E2F family of transcription factors regulates the transcription of genes required for DNA synthesis. E2F is itself controlled by a series of transcriptional and post-transcriptional pathways. Here we provide evidence that proteasome inhibitor-mediated E2F1 gene down-regulation is regulated by transcriptional events. Using the proteasome-specific inhibitors, MG132 and lactacystin, we show that the p53, the cdk inhibitors p21 and p27, and cyclin A are degraded by the ubiquitin-proteasome pathway in human osteosarcoma cells. Interestingly, the expression levels of E2F1 and E2F2 are down-regulated by proteasome inhibitors. E2F promoter and RT-PCR assay clearly demonstrated that proteasome inhibitors could reduce E2F transcriptional activation. However, MG132-induced repression of E2F1 and E2F2 is not associated with ROS generation.
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PMID:Transcriptional repression of E2F gene by proteasome inhibitors in human osteosarcoma cells. 1514 52

The human topoisomerase I- and p53-binding protein topors contains a highly conserved, N-terminal C3HC4-type RING domain that is homologous to the RING domains of known E3 ubiquitin ligases. We demonstrate that topors functions in vitro as a RING-dependent E3 ubiquitin ligase with the E2 enzymes UbcH5a, UbcH5c, and UbcH6 but not with UbcH7, CDC34, or UbcH2b. Additional studies indicate that a conserved tryptophan within the topors RING domain is required for ubiquitination activity. Furthermore, both in vitro and cellular studies implicate p53 as a ubiquitination substrate for topors. Similar to MDM2, overexpression of topors results in a proteasome-dependent decrease in p53 protein expression in a human osteosarcoma cell line. These results are similar to the recent finding that a Drosophila topors orthologue ubiquitinates the Hairy transcriptional repressor and suggest that topors functions as a ubiquitin ligase for multiple transcription factors.
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PMID:Topors functions as an E3 ubiquitin ligase with specific E2 enzymes and ubiquitinates p53. 1524 80

1-Methyl-4-phenylpyridinium ion (MPP(+)), an active metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, induces cell death and inhibition of cell proliferation in various cells. However, the mechanism whereby MPP(+) inhibits cell proliferation is still unclear. In this study, we found that MPP(+) suppressed the proliferation with accumulation in G(1) phase without inducing cell death in p53-deficient MG63 osteosarcoma cells. MPP(+) induced hypophosphorylation of retinoblastoma protein and rapidly down-regulated the protein but not mRNA levels of cyclin D1 in MG63 cells. The down-regulation of cyclin D1 protein was suppressed by a proteasome inhibitor, MG132. The cyclin D1 down-regulation by MPP(+) was also observed in p53-positive PC12, HeLa S3, and HeLa rho(0) cells, which are a subclone of HeLa S3 lacking mitochondrial DNA. Moreover, MPP(+) dephosphorylated Akt in PC12 cells, which was rescued by the pretreatment with nerve growth factor. In addition, the pretreatment with nerve growth factor or lithium chloride, a glycogen synthase kinase-3beta inhibitor, suppressed the cyclin D1 down-regulation caused by MPP(+). Our results demonstrate that MPP(+) induces cell cycle arrest independently of its mitochondrial toxicity or the p53 status of the target cells, but rather through the proteasome- and phosphatidylinositol 3-Akt-glycogen synthase kinase-3beta-dependent cyclin D1 degradation.
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PMID:Proteasome-dependent degradation of cyclin D1 in 1-methyl-4-phenylpyridinium ion (MPP+)-induced cell cycle arrest. 1524 82

The adenylate cyclase (AC)/cyclic AMP (cAMP)/cAMP-dependent protein kinase pathway controls many biological phenomena. The ubiquitin/proteasome system, controlling the levels of many proteins, modulates important cellular processes such as cell cycle and cell growth. Here we describe a novel mechanism for AC regulation by proteasome pathway. Pharmacological inhibition of proteasome function in human osteosarcoma U2OS cells results in up-regulation of AC activity, increase of levels of alpha subunit of heterotrimeric stimulatory GTP-binding proteins (alphas) and, remarkably, also in preventing of beta-adrenergic receptor-mediated down-regulation of alphas protein levels. Accumulation of alphas protein is also accompanied by the appearance of polyubiquitinated alphas species. Our results: (1) identify alphas protein as a novel proteasome substrate in mammalian cells; (2) indicate that proteasome might play a physiological role in controlling AC/cAMP mediated pathways by modulating the levels of Galphas protein; (3) suggest a role for the proteasome also in controlling alphas-mediated signaling pathways other than those affecting AC complex.
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PMID:Adenylate cyclase regulation via proteasome-mediated modulation of Galphas levels. 1533 22

A 97-kDa protein called valosin-containing protein (VCP) has been implicated in osteosarcoma metastasis and Paget's disease of bone, two conditions that complicate the course and outcome of orthopaedic surgery. High VCP gene expression is associated with high metastatic potential in osteosarcoma cells, while loss-of-function VCP mutations cause inclusion body myopathy associated with Paget's disease of bone and frontotemporal dementia (IBMPFD). VCP protein expression and regulation have not been examined in normal osteoblasts. The purpose of these studies was to characterize VCP protein expression in control and stressed untransformed osteoblasts. Proteins from confluent MC3T3-E1 mouse osteoblast-like cells were separated by 2D IEF/SDS-PAGE. An abundant spot with a M(r) of 94 kDa and a pI of 5.4 was identified as VCP by MALDI/ToF and peptide mass fingerprint analysis. High constitutive VCP protein expression in subconfluent and confluent resting and mildly physiologically stressed MC3T3-E1 cells was confirmed by Western blotting. When assessed by indirect immunofluorescence in fixed cells or Western blotting of subcellular fractions, VCP was more abundant in the cytoplasm than in the nucleus. Induction of mild physiological stress sufficient to stimulate the ubiquitin-proteasome pathway, which is partially dependent on VCP-mediated targeting of polyubiquitinylated substrates, did not affect steady-state VCP levels or distribution. Thus, VCP is a constitutively abundant protein in untransformed osteoblastic cells under all conditions tested. Such high levels of VCP protein expression in untransformed osteoblastic cells argue against a major causative role for it in metastasis, while the occurrence of Paget's disease in patients with missense VCP mutations supports a major role for VCP in normal osteoblast proliferation and regulation.
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PMID:Identification and characterization of valosin-containing protein (VCP/p97) in untransformed osteoblast-like cells. 1588 83

We report here that lysocellin, a polyether antibiotic from a streptomycete, induces G1 phase arrest in human osteosarcoma MG63 cells. Lysocellin up-regulates p21WAF1/Cip1 and down-regulates cyclin D1 at the mRNA level. In addition, cyclin D1 is down-regulated by the proteasome-dependent signal pathway in MG63 cells. In drug combination studies, we found that lysocellin treatment weakened the cytotoxic activity of etoposide in MG63 cells using a colony-formation assay. To study the in vivo efficacy of lysocellin, we isolated a novel compound related to lysocellin from the same streptomycete, and found that the novel drug is converted to lysocellin in vivo and decreases etoposide-induced alopecia in a neonatal rat model. We raise the possibility that this novel drug, named 'alopestatin', may be a promising agent against alopecia.
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PMID:Lysocellin, a metabolite of the novel drug 'alopestatin', induces G1 arrest and prevents cytotoxicity induced by etoposide. 1652 30

Because a limited study previously showed that alpha-synuclein (alpha-syn), the major pathogenic protein for Parkinson disease, was expressed in differentiating brain tumors as well as various peripheral cancers, the main objective of the present study was to determine whether alpha-syn might be involved in the regulation of tumor differentiation. For this purpose, alpha-syn and its non-amyloidogenic homologue beta-syn were stably transfected to human osteosarcoma MG63 cell line. Compared with beta-syn-overexpressing and vector-transfected cells, alpha-syn-overexpressing cells exhibited distinct features of differentiated osteoblastic phenotype, as shown by up-regulation of alkaline phosphatase and osteocalcin as well as inductive matrix mineralization. Further studies revealed that proteasome activity was significantly decreased in alpha-syn-overexpressing cells compared with other cell types, consistent with the fact that proteasome inhibitors stimulate differentiation of various osteoblastic cells. In alpha-syn-overexpressing cells, protein kinase C (PKC) activity was significantly decreased, and reactivation of PKC by phorbol ester significantly restored the proteasome activity and abrogated cellular differentiation. Moreover, activity of lysosome was up-regulated in alpha-syn-overexpressing cells, and treatment of these cells with autophagy-lysosomal inhibitors resulted in a decrease of proteasome activity associated with up-regulation of alpha-syn expression, leading to enhance cellular differentiation. Taken together, these results suggest that the stimulatory effect of alpha-syn on tumor differentiation may be attributed to down-regulation of proteasome, which is further modulated by alterations of various factors, such as protein kinase C signaling pathway and a autophagy-lysosomal degradation system. Thus, the mechanism of alpha-syn regulation of tumor differentiation and neuropathological effects of alpha-syn may considerably overlap with each other.
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PMID:alpha-Synuclein stimulates differentiation of osteosarcoma cells: relevance to down-regulation of proteasome activity. 1718 70

Bowman-Birk protease inhibitor (BBI) from soybean acts as a potential chemopreventive agent in several types of tumors. However, the mechanism is still unclear. The present study was undertaken to estimate a mechanism of BBI-dependent negative growth control of human osteosarcoma cell (U2OS cell). BBI had negative growth control of the cells via induction of connexin (Cx) 43, a tumor suppressor gene in U2OS cells. This negative growth control by BBI was abrogated under down-regulation of Cx43 induced by a Cx43 antisense nucleotide treatment. It was also found that the BBI-dependent induction of Cx43 was due to elevation of Cx43 mRNA and stabilization of Cx43 protein. Especially, BBI-dependent inhibition of chymotrypsin-like activity in proteasome contributed to stabilization of Cx43 protein. These results suggest that a major negative growth effect of BBI is based on the restoration of Cx43 expression in U2OS cells.
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PMID:Negative growth control of osteosarcoma cell by Bowman-Birk protease inhibitor from soybean; involvement of connexin 43. 1734 82

Mitochondrial abnormalities represent a major cytopathology in Huntington's disease (HD), a fatal neurodegenerative disease caused by CAG repeat expansions in the gene encoding huntingtin (Htt). In the present study, we investigated whether defects in the mitochondrial respiratory function are consequences of the expression of mutant Htt or they promote the formation of Htt aggregates. To take advantage of existing mitochondrial DNA mutants, we developed human osteosarcoma 143B cells expressing mutant Htt in an inducible manner and found that cells expressing mutant Htt but not wild-type Htt exhibited a reduced activity of complex III and an increased activity of complex IV. Conversely, pharmacological treatments that inhibited complex III activity significantly promoted the formation of Htt aggregates. This complex III-mediated modulation of Htt aggregates was also observed in a neuronal progenitor RN33B cell line transduced by lentivirus carrying mutant Htt. This effect of complex III inhibition on the Htt aggregates appeared to be mediated by the inhibition of proteasome activity, but not by ATP depletion or production of reactive oxygen species. Accordingly, complex III mutant cells also showed decreased proteasome activity. These results suggest the presence of a feedback system connecting the mitochondrial respiratory complex III and the production of Htt aggregates. Our results suggest that therapeutic interventions targeting complex III and/or proteasome could ameliorate the progress of HD.
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PMID:Extended polyglutamine repeats trigger a feedback loop involving the mitochondrial complex III, the proteasome and huntingtin aggregates. 1735 14


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