Dysregulations of Expression of Genes of the Ubiquitin/SUMO Pathways in an In Vitro Model of Amyotrophic Lateral Sclerosis Combining Oxidative Stress and SOD1 Gene Mutation

Protein aggregates in affected motor neurons are a hallmark of amyotrophic lateral sclerosis (ALS), but the molecular pathways leading to their formation remain incompletely understood. Oxidative stress associated with age, the major risk factor in ALS, contributes to this neurodegeneration in ALS. We show that several genes coding for enzymes of the ubiquitin and small ubiquitin-related modifier (SUMO) pathways exhibit altered expression in motor neuronal cells exposed to oxidative stress, such as the CCNF gene mutated in ALS patients. Eleven of these genes were further studied in conditions combining oxidative stress and the expression of an ALS related mutant of the superoxide dismutase 1 (SOD1) gene. We observed a combined effect of these two environmental and genetic factors on the expression of genes, such as Uhrf2, Rbx1, Kdm2b, Ube2d2, Xaf1, and Senp1. Overall, we identified dysregulations in the expression of enzymes of the ubiquitin and SUMO pathways that may be of interest to better understand the pathophysiology of ALS and to protect motor neurons from oxidative stress and genetic alterations.

Reciprocal surface expression of arylsulfatase A and ubiquitin in normal and defective mammalian spermatozoa

Defective mammalian spermatozoa are marked on their surface by proteolytic chaperone ubiquitin. To identify potential ubiquitinated substrates in the defective spermatozoa, we resolved bull sperm protein extracts on a two-dimensional gel and isolated a 64-65-kDa spot (p64) corresponding to one of the major ubiquitin-immunoreactive bands observed in the one-dimensional Western blots. Immune serum raised against this protein recognized a prominent, possibly glycosylated band/spot in the range of 55-68 kDa, consistent with the original spot used for immunization. Internal sequences obtained by Edman degradation of this spot matched the sequence of arylsulfatase A (ARSA), the sperm acrosomal enzyme thought to be important for fertility. By immunofluorescence, a prominent signal was detected on the acrosomal surface (boar and bull) and on the sperm tail principal piece (bull). A second immune serum raised against a synthetic peptide corresponding to an immunogenic internal sequence (GTGKSPRRTL) of the porcine ARSA also labeled sperm acrosome and principal piece. Both sera showed diminished immunoreactivity in the defective bull spermatozoa co-labeled with an anti-ubiquitin antibody. Western blotting and image-based flow cytometry (IBFC) confirmed a reduced ARSA immunoreactivity in the immotile sperm fraction rich in ubiquitinated spermatozoa. Larger than expected ARSA-immunoreactive bands were found in sperm protein extracts immunoprecipitated with anti-ubiquitin antibodies and affinity purified with matrix-bound, recombinant ubiquitin-binding UBA domain. These bands did not show the typical pattern of ARSA glycosylation but overlapped with bands preferentially binding the Lens culinaris agglutinin (LCA) lectin. By both epifluorescence microscopy and IBFC, the LCA binding was increased in the ubiquitinated spermatozoa with diminished ARSA immunoreactivity. ARSA was also found in the epididymal fluid suggesting that in addition to intrinsic ARSA expression in the testis, epididymal spermatozoa take up ARSA on their surface during the epididymal passage. We conclude that sperm surface ARSA is one of the ubiquitinated sperm surface glycoproteins in defective bull spermatozoa. Defective sperm surface thus differs from normal sperm surface by increased ubiquitination, reduced ARSA binding, and altered glycosylation.

Ubiquitin chain elongation requires E3-dependent tracking of the emerging conjugate

Protein modification with ubiquitin chains is an essential signaling event catalyzed by E3 ubiquitin ligases. Most human E3s contain a signature RING domain that recruits a ubiquitin-charged E2 and a separate domain for substrate recognition. How RING-E3s can build polymeric ubiquitin chains while binding substrates and E2s at defined interfaces remains poorly understood. Here, we show that the RING-E3 APC/C catalyzes chain elongation by strongly increasing the affinity of its E2 for the distal acceptor ubiquitin in a growing conjugate. This function of the APC/C requires its coactivator as well as conserved residues of the E2 and ubiquitin. APC/C's ability to track the tip of an emerging conjugate is required for APC/C-substrate degradation and accurate cell division. Our results suggest that RING-E3s tether the distal ubiquitin of a growing chain in proximity to the active site of their E2s, allowing them to assemble polymeric conjugates without altering their binding to substrate or E2.

Ageing enhances alpha-synuclein, ubiquitin and endoplasmic reticular stress protein expression in the nigral neurons of Asian Indians

Accumulating evidences suggest that dopaminergic neuronal loss in the substantia nigra pars compacta (SNpc) during ageing and in Parkinson's disease (PD) is linked to neurodegenerative changes like exponential increase in alpha-synuclein expression and protein misfolding. Lewy body formation is also a quintessential observation in neurodegeneration and PD. In experimental models of PD, GRP78 a neuroprotective endoplasmic reticulum (ER) chaperone protein targets misfolded proteins for degradation and prevents release of caspase12 from the ER. Release of active caspase12 and its translocation to the nucleus induces ER mediated apoptosis. The effect of ageing on these proteins in human nigra is not known. We evaluated alpha-synuclein, caspase12, GRP78 and ubiquitin expression in the SNpc of Asian Indians, using immunohistochemistry and stereology. The number of alpha-synuclein and caspase12 immunoreactive neurons increased gradually with age whereas the number of GRP78-labeled neurons remained stable. In contrast, GRP78 protein expression was significantly upregulated with age, while alpha-synuclein and caspase12 increased slightly. An increase in the size and numbers of marinesco bodies was prominent after the sixth decade. The mild increase in alpha-synuclein expression and occurrence of marinesco bodies suggests ageing induced protein misfolding and GRP78 upregulation indicates presence of ER stress. The logarithmic upregulation of GRP78 could even be an indicator of neuroprotective or neuromodulatory response of ER to protein misfolding and initiation of unfolded protein response pathway. Since dopaminergic neurons are preserved in ageing Asian Indians, our study possibly signifies better proteasomal or ER response and partially explains the lower prevalence of PD in them.

Effect of the overexpression of mutant ubiquitin (K48R) on the cellular response induced by 4-hydroxy-2,3-trans-nonenal, an end-product of lipid peroxidation

Impairment of the ubiquitin-proteasome system (UPS) for degrading abnormal proteins leads to protein aggregates and increased protein oxidation/nitration. This study was performed to show that interference with polyubiquitination in the presence of 4-hydroxy-2,3-trans-nonenal (HNE) has similar consequences. Levels of polyubiquitin chains were not increased in NT-2 and SK-N-MC cells overexpressing a dominant-negative mutant form of ubiquitin (K48R) in response to HNE compared to wild-type transfectants. Increased oxidative (GSH, protein carbonyls and lipid peroxidation) and nitrative damage (nitric oxide production and elevated protein nitration) were aggravated in the mutant transfectants. These data show that initial oxidative/nitrative damage (due to HNE) and interference with ubiquitination (induced by mutant ubiquitin or HNE) can cause common characteristics of neurodegenerative diseases. These data suggest that impairment of the UPS at different levels may be a common mechanism in neurodegeneration and that more such defects remain to be identified.

Differential expression of LAMPs and ubiquitin in human thymus

Lysosome-associated membrane proteins 1 and 2 (LAMP-1 and LAMP-2) are implicated in a variety of normal and pathological processes. LAMP-2 is proposed to participate in chaperone-mediated autophagy.Autophagy regulates T-lymphocyte homeostasis by promoting both survival and proliferation. The biological importance of this process in the thymic gland and especially the involvement of LAMPs are far from being elucidated. The aim of the study was to examine the parallel expression of LAMPs and ubiquitin, a key molecule in autophagy, in normal human thymic glands and thymomas. The immunohistochemical expression of both markers was compared with that of cyclin D1--an important regulator of cell cycle progression. Novel evidence for differential expression of LAMPs and ubiquitin is presented. Most Hassal's corpuscules in thymoma were negative for LAMPs, but positive in normal thymus.Both lymphocytes and epithelial cells in pathological thymus showed higher intensity for LAMP-2 compared with LAMP-1. In thymoma, ubiquitin was more intensively positive in these cell types compared with the normal thymus, suggesting activated autophagy in the course of this pathological state. A deregulation in cyclin D1 expression in thymoma is also reported. The functional importance of these molecules in autophagy accompanying normal and pathological processes in the thymic gland is reviewed.

High yield expression and NMR characterization of Arkadia E3 ubiquitin ligase RING-H2 finger domain

E3 ubiquitin ligases play a key role in the recognition of target proteins and the degradation by 26S proteasomes. Arkadia is the first example of an E3 ubiquitin ligase that positively regulates TGF-beta family signaling. It has been shown to induce ubiquitin-dependent degradation of negative regulators of TGF-beta signaling through its C-terminal RING domain. Structural analysis of Arkadia RING domain is needed to elucidate its enzymatic properties. For such studies efficient production of pure and correctly folded Arkadia protein is required. Here we report the recombinant expression in Escherichia coli and purification of the C-terminal RING domain of Arkadia. NMR analysis of the soluble construct reveals a stable folded protein suitable for high resolution structural studies.

[Rpn4p is a positive and negative transcriptional regulator of the ubiquitin-proteasome system]

Ubiquitin-proteasome proteolytic system participates in metabolism of the majority of intracellular proteins and regulation of key cellular processes in eukaryotes. While the structure and functioning of this system is studied rather well, a little is known about regulation of its genes expression. At present time, the only regulatory system of transcription of proteasome genes is found in the yeast Saccharomyces cerevisiae. This system includes Rpn4p-proteasome-associated transcriptional regulator and its binding site called PACE (Proteasome Associated Control Element). To learn more about function of Rpn4p as a transcriptional regulator, there are following questions: 1) is the Rpn4p regulator for PACE-containing genes which encode for components of protein ubiquitinylation system 2) what is the contribution of Rpn4p in stress-activated level of mRNA of proteasome genes. In this work, using semiquantitative RT-PCR we have shown that deletion of RPN4 gene leads to decreasing in mRNA level of the genes of ubiqitination system RAD6, RAD23 and CDC48, while UBI4 mRNA level is increased in this strain. In the presence of alkylating agent methyl methanesulfonate or under heat shock we observed Rpn4 p-dependent elevation of mRNA level of the proteasomal genes RPT4 and RPNS. At the same time, CDC48 mRNA level is decreased in wild type yeast strain upon methyl methanesulfonate treatment. These data indicate that under normal or stress conditions Rpn4p may act as an activator or repressor for the genes of the ubiquitin-proteasome system.

[The connection between tumor and ubiquitin-ribosomal protein S27a, ubiquitin and ribosomal protein]

Ubiquitin-ribosomal protein S27a(UBRPS27a) is a fusion protein of Ubiquitin and ribosomal protein. The N-terminal is ubiquitin and C-termina is ribosomal protein S27a with a high conservative zinc finger domain of the C2-C2 type. When it was expressed in eukaryotes,The intact fusion protein were rapidly processed to free ubiquitin monomer and ribosomal protein S27a (RPS27a). Ubiquitin degradated proteins particularly and selectively in cell and RPS27a is indispensable for translation. This multifunctional ribosomal protein is expressed at high levels in a wide variety of actively proliferating cells and tumor tissues and is a representative characteristic of various tumor cells. In our preliminary study of this protein in the silkworm,RPS27a also be found express highly in actively proliferating cells. The precise functional role of each ribosomal protein is largely unknown and many ribosomal proteins have extraribosomal functions apart from the particle. In this article, we review the recent research on the connection between tumor and this fusion protein, Ubiquitin-Proteasome Pathway and ribosomal protein. These research may indicate the origin and development of tumor, provide the basis for clinical diagnosis of cancer and the novel therapeutic targets for the treatment of malignant tumors.

Tissue-specific regulation of ubiquitin (UbC) transcription by glucocorticoids: in vivo and in vitro analyses

In uremia, muscle wasting involves increased glucocorticoid production and activation of the ubiquitin-proteasome proteolytic pathway, including increased expression of ubiquitin. Previously, we reported that glucocorticoids stimulate ubiquitin transcription by a mechanism involving Sp1 in L6 muscle cells (Marinovic AC, Zheng B, Mitch WE, Price SR. J Biol Chem 277: 16673–16681, 2002). This finding was surprising because Sp1 is a general transcriptional activator. To better understand the mechanism of glucocorticoid-induced ubiquitin ( UbC) gene transcription, we examined whether this response occurs in many organs or uniquely in skeletal muscle. Glucocorticoid-responsive cells of different organs were transfected with a human UbC promoter-luciferase reporter plasmid; dexamethasone stimulated UbC reporter activity 220% ( P < 0.05) in L6 skeletal muscle cells but not in HepG2 hepatocytes, NRK kidney cells, CaCo-2 colon cells, or H9c2 cardiomyocytes. Transactivation of the Sp1-responsive SV40 viral promoter was also increased in muscle but not in other nonmuscle cells. The muscle-specific nature of the UbC response was confirmed in vivo in rats with insulin deficiency, a condition associated with high glucocorticoid production: UbC mRNA was elevated in skeletal muscle but not in liver, kidney, intestine, or heart. Electrophoretic mobility shift assays and in vivo genomic footprinting demonstrated that insulin deficiency increased Sp1 binding to GC-rich elements in the UbC promoter. Thus glucocorticoids increase UbC transcription by a mechanism involving Sp1 that is unique to muscle.

Increased expression of stress proteins in the surf clam Donax variabilis following hydrogen sulfide exposure

Endogenous free radical production and resulting oxidative damage may result from exposure to hypoxia, hyperoxia, or hydrogen sulfide. Previous investigations of sulfide-induced oxidative damage have produced conflicting results, perhaps because these studies utilized species presumably adapted to sulfide. We examined the effects of sulfide, hypoxia and hyperoxia on the surf clam Donax variabilis to test whether these stressors induce a cellular response to oxidative stress. These clams inhabit high-energy sandy beaches and are unlikely to have specific adaptations to these stressors. In duplicate flow-through experiments performed in fall and spring, clams were exposed to normoxia (22 kPa P(O(2))), hypoxia (10 kPa), hyperoxia (37 kPa), or sulfide with normoxia ( approximately 100 mumol L(-1), 22 kPa respectively) for 24 h. We quantified whole-animal expression of three antioxidants (Cu/Zn and Mn superoxide dismutases, glutathione peroxidase), a lipid peroxidation marker (4-hydroxy-2E-nonenol-adducted protein), a DNA repair enzyme (OGG1-m), four heat shock proteins (small Hsp, Hsp60, Hsp70, and mitochondrial Hsp70), ubiquitin, and actin. Clams exposed to sulfide showed upregulation of the greatest number of stress proteins and the pattern was consistent with a cellular response to oxidative stress. Furthermore, there was a marked seasonality, with greater stress protein expression in clams from the spring.

Life-cycle and growth-phase-dependent regulation of the ubiquitin genes of Trypanosoma cruzi

BACKGROUND

Trypanosoma cruzi, the causative agent of Chagas disease, exhibits a complex life cycle that is accompanied by the stage-specific gene expression. At the molecular level, very little is known about gene regulation in trypanosomes. Complex gene organizations coupled with polycistronic transcription units make the analysis of regulated gene expression difficult in trypanosomes. The ubiquitin genes of T. cruzi are a good example of this complexity. They are organized as a single cluster containing five ubiquitin fusion (FUS) and five polyubiquitin (PUB) genes that are polycistronically transcribed but expressed differently in response to developmental and environmental changes.

METHODS

Gene replacements were used to study FUS and PUB gene expression at different stages of growth and at different points in the life cycle of T. cruzi.

RESULTS

Based on the levels of reporter gene expression, it was determined that FUS1 expression was downregulated as the parasites approached stationary phase, whereas PUB12.5 polyubiquitin gene expression increased. Conversely, FUS1 expression increases when epimastigotes and amastigotes differentiate into trypomastigotes, whereas the expression of PUB12.5 decreases when epimastigotes differentiate into amastigotes and trypomastigotes.

CONCLUSIONS

Although the level of CAT activity in logarithmic growing epimastigotes is six- to seven-fold higher when the gene was expressed from the FUS1 locus than when expressed from the PUB12.5 locus, the rate of transcription from the two loci was the same implying that post-transcriptional mechanisms play a dominant role in the regulation of gene expression.

Expression of ubiquitin and proteasome in motorneurons and astrocytes of spinal cords from patients with amyotrophic lateral sclerosis

Proteasome, ubiquitin, GFAP and neurofilament were evaluated in motorneurons and astrocytes of spinal cords of ALS and control cases. ALS neurons exhibited ubiquitin positive inclusions and areas of strong immunoreaction for proteasome. Areas of proteasome stain were observed close to neurofilament positive proximal process enlargement. The percentage of neurons strongly immunoreacted, for proteasome was higher in ALS cases than in controls. Many astrocytes were positive for ubiquitin and proteasome. These results suggest that the ubiquitin-proteasome pathway is involved in the ALS pathogenesis and agree with the view that ALS is a disorder of protein aggregation that affects neurons and nonneuronal cells.

Up-regulation of genes for oxidative phosphorylation and protein turnover in diabetic mouse retina

Diabetic retinopathy is one of the most frequent complications of diabetes and is a leading cause of vision loss in adulthood. To better understand the molecular pathophysiology of diabetic retinopathy, we performed comprehensive gene expression analysis of the mouse retina under diabetic conditions with an in-house cDNA microarray system that was designed to be suitable for the small amount of RNA available from a single mouse retina. Diabetes was induced in male C57BL/6 mice by an intraperitoneal injection of streptozotocin, and the changes in retinal mRNA levels were examined in three pairs of diabetic and age-matched control mice at 1 and 3 months after the injection of streptozotocin. Northern blot analysis with amplified total cRNA confirmed the increase in mRNA levels of several selected genes. Most of the significantly up-regulated genes could be classified into two functional categories: oxidative phosphorylation and protein turnover. All mitochondrial DNA-encoded and most of the nuclear DNA-encoded genes for oxidative phosphorylation were up-regulated in the diabetic retina. This was in sharp contrast with a previous report of a down-regulation of these genes in skeletal muscles of streptozotocin-induced diabetic mice and type 2 diabetic humans. Genes for protein synthesis and ubiquitin were also up-regulated in the diabetic retina, suggesting the increase in turnover rates for at least a part of the protein population. Taken together, the diabetic retina appears to be in a state activated for intermediary metabolism, presumably because of an increase in insulin-independent glucose influx. These results provide insights into possible preventive and therapeutic intervention of diabetic retinopathy.

Lingering mysteries of ubiquitin-chain assembly

The small protein ubiquitin is often linked to substrates as a polymer. Such polymers vary in both linkage and length, which has important consequences for their function. Surprisingly, the mechanisms of ubiquitin-chain assembly are still not known. Deciphering them will shed light on why substrates differ in the extent and timing of polyubiquitin modification and how ancillary ubiquitination factors function.

Neuroprotection of Parkin against apoptosis is independent of inclusion body formation

Loss-of-function mutations in the parkin gene are known to result in autosomal recessive juvenile parkinsonism, which causes selective degeneration of nigrostriatal dopaminergic neurons in the absence of Lewy bodies. Here, we show that overexpression of parkin protects PC12 cells from neurotoxin of the proteasome inhibitor lactacystin and increases the accumulation of ubiquitin-protein conjugates and the formation of ubiquitin-positive inclusions induced by lactacystin. However, the protective effect of parkin against lactacystin-induced apoptosis is not associated with its ability to promote the formation of ubiquitinated inclusions. It is likely that Lewy body formation may be only a compensatory mechanism of dopaminergic neurons attempting to counteract toxicity, and not the ultimate cause of neuronal death.

Protein gene product 9.5 and ubiquitin are expressed in metabolically active epithelial cells of normal and pathologic human kidney

BACKGROUND

In a study initially designed to evaluate the specific protein gene product 9.5 expression in parietal epithelial cells of Bowman's capsule, a marked positivity was also observed in the tubular and collecting duct epithelial cells. Since protein gene product 9.5 is an important enzyme in the ubiquitin system of proteolysis, and plays a regulatory role in cell cycle and proliferation, its presence in specific segments of the nephron was of considerable interest.

METHODS

We investigated protein gene product 9.5 and ubiquitin expression in both normal and pathologic renal samples (more than 100 cases) using an immunohistochemical technique.

RESULTS

We found that protein gene product 9.5 and ubiquitin were constantly present in Bowman's capsule parietal cells and tubular/collecting duct epithelial cells, with the strongest positivity in metabolically active and proliferative conditions, such as tubular hypertrophy, cellular regeneration and crescent formation. Conversely, the expression of these molecules was attenuated in atrophic tubules. Podocytes were negative.

CONCLUSION

The diffuse presence of the protein gene product 9.5 and ubiquitin in normal and pathologic metabolically active epithelial cells of the nephron suggests that these proteins (and likely the whole ubiquitin-proteasome complex) play a fundamental role in the mechanism upregulating protein metabolism of the kidney and that its expression is correlated with activated cellular functions, like proliferation.

The ubiquitin–proteasome system in Creutzfeldt–Jakob and Alzheimer disease: Intracellular redistribution of components correlates with neuronal vulnerability

Creutzfeldt-Jakob (CJD) and Alzheimer disease (AD) are accompanied by selective neuronal loss in the brain. We examined the regional and subcellular immunolocalization of ubiquitin, proteasomal subunits, and the heat-shock protein Hsp72 in control, CJD, and AD cases. In control and non-affected areas of disease cases, 20S proteasomes, 19S regulatory subunits, S6a, S6b, and S10b exhibit mainly cytoplasmic, whereas S4 and S7 show predominantly nuclear localization. The intensity of immunostaining for ubiquitin, proteasomal subunits, and Hsp72 varies in different anatomical regions both in disease and control brains. Areas with weaker immunolabeling correspond to affected areas in CJD and AD. In disease cases, antibodies for 20S, S4, S6b, S7, and ubiquitin intensely immunolabel neuronal nuclei of vulnerable cells in affected areas. Our results suggest that the ubiquitin-proteasome system takes part in the pathogenesis of neurodegeneration. Ubiquitin, Hsp72, and proteasomal ATPases possibly play a role in protecting certain neuronal populations in CJD and AD.

A Novel Protein Specifically Interacting with Homer2 Regulates Ubiquitin-Proteasome Systems

Homer family proteins are encoded by three genes, homer1, 2 and 3. Most of these proteins are expressed constitutively in nervous systems and accumulated in postsynaptic regions. However, the functional significance of these proteins, especially the significance of the distinction among the proteins encoded by homer1, 2 and 3, is still obscure. In the present study, we isolated a cDNA clone encoding a novel protein by two-hybrid system screening using the C-terminal half of Homer2b as the bait. This protein, termed 2B28, has 297 amino acid residues and contains three major domains: a UBA domain, a coiled-coil region, and a UBX domain. When expressed in HEK293T cells, 2B28 showed colocalization with uniquitin and enhanced the expression levels of IkappaB or Homer1a proteins, which are known to be degraded by proteasomes, indicating that 2B28 is involved in ubiquitin-proteasome functions. 2B28 specifically interacted and colocalized with Homer2 proteins, but not with Homer1 proteins. So far, we have identified no counterpart of 2B28 for Homer1 experimentally or in the protein databases. These results suggest that the specific interaction of 2B28 with Homer2 may play a role in regulation of protein degradation by ubiquitin-proteasome systems and that this function may be specific to Homer2 proteins among Homer family proteins.

Transcriptional induction of Smurf2 ubiquitin ligase by TGF-β

Smad ubiquitination regulatory factor 2 (Smurf2), a ubiquitin ligase for Smads, plays critical roles in the regulation of transforming growth factor-beta (TGF-beta)-Smad signaling via ubiquitin-dependent degradation of Smad2 and Smad7. We found that TGF-beta stimulates Smurf2 expression. TGF-beta activated the Smurf2 promoter in a TGF-beta responsive cell lines, whereas IL-1alpha, PDGF and epidermal growth factor did not. TGF-beta-mediated Smurf2 promoter activation was inhibited by Smad7 or an activin receptor-like kinase 5 inhibitor but not by dominant negative Smad or disruption of Smad-binding elements in the promoter. Moreover, inhibition of the phosphatidil inositol 3 kinase (PI3K)/Akt pathway suppressed TGF-beta-mediated Smurf2 induction. These results suggest that TGF-beta stimulates Smurf2 expression by Smad-independent pathway such as PI3K/Akt pathway via TGF-beta receptor.

Morphological differences of intraneuronal ubiquitin-positive inclusions in the dentate gyrus and parahippocampal gyrus of motor neuron disease with dementia

Semiquantitative morphological analysis of cerebral intraneuronal ubiquitin-positive tau-negative inclusions, a pathologic marker for motor neuron disease with dementia (MND-D), was performed in the dentate gyrus and parahippocampal gyrus of 20 clinicopathologically confirmed patients with MND-D. The forms of the inclusions were tentatively classified into three types: (i) C-type, consisting of relatively large and intensely stained crescent or circular structures; (ii) L-type, showing fine linear structures around the nuclei; and (iii) G-type, showing faintly stained granular structures. The frequencies of the C-type, L-type and G-type was 0.5-9.3%,0.2-6.5% and 0-6.6% of dentate granule cells, respectively. In contrast to the dentate gyrus, almost all inclusions showed either the C-type or L-type form in the parahippocampal gyrus. A positive correlation was noted only between incidences of C-type inclusion of the dentate gyrus and that of the parahippocampal gyrus (r = 0.69, P < 0.05). The morphological differences of the inclusions probably reflect different stages of their formation.

Effect of ubiquitin expression on neuropathogenesis in a mouse model of familial amyotrophic lateral sclerosis

The ubiquitin-proteasome system (UPS) is a central component in the cellular defence against potentially toxic protein aggregates. UPS dysfunction is linked to the pathogenesis of both sporadic and inherited neurodegenerative diseases, including dominantly inherited familial amyotrophic lateral sclerosis (fALS). To investigate the role of the UPS in fALS pathogenesis, transgenic mice expressing mutant G9 3A Cu,Zn superoxide dismutase (SOD1) were crossed with transgenic mice expressing epitope tagged, wild-type or dominant-negative mutant ubiquitin (Ub(K48R)). RNase protection assays were used to confirm expression of the Ub transgenes in spinal cord and ubiquitin transgene levels were estimated to account for 9-12% of total ubiquitin. Mice expressing the G9 3A transgene exhibited neurological symptoms and histopathological changes typical of this model irrespective of ubiquitin transgene status. Impaired rotarod performance was observed in all G9 3A transgenics by 7 weeks of age irrespective of ubiquitin genotype. The presence of wild-type or mutant ubiquitin transgenes resulted in a small but significant delay in the onset of clinical symptoms and mild acceleration of disease progression, without influencing overall survival. These data suggest that relatively small changes in ubiquitin expression can influence the development of neurodegenerative disease and are consistent with a neuroprotective role for the UPS.

IGF-I stimulates muscle growth by suppressing protein breakdown and expression of atrophy-related ubiquitin ligases, atrogin-1 and MuRF1

Muscle atrophy results primarily from accelerated protein degradation and is associated with increased expression of two muscle-specific ubiquitin ligases (E3s): atrogin-1 and muscle ring finger 1 (MuRF1). Glucocorticoids are essential for many types of muscle atrophy, and their effects are opposite to those of insulin-like growth factor I (IGF-I) and insulin, which promote growth. In myotubes, dexamethasone (Dex) inhibited growth and enhanced breakdown of long-lived cell proteins, especially myofibrillar proteins (as measured by 3-methylhistidine release), while also increasing atrogin-1 and MuRF1 mRNA. Conversely, IGF-I suppressed protein degradation and prevented the Dex-induced increase in proteolysis. IGF-I rapidly reduced atrogin-1 expression within 1 h by blocking mRNA synthesis without affecting mRNA degradation, whereas IGF-I decreased MuRF1 mRNA slowly. IGF-I and insulin also blocked Dex induction of these E3s and several other atrophy-related genes ("atrogenes"). Changes in overall proteolysis with Dex and IGF-I correlated tightly with changes in atrogin-1 mRNA content, but not with changes in MuRF1 mRNA. IGF-I activates the phosphatidylinositol 3-kinase (PI3K)-Akt pathway, and inhibition of this pathway [but not the calcineurin-nuclear factor of activated T cell (NFAT) or the MEK-ERK pathway] increased proteolysis and atrogin-1 mRNA expression. Thus an important component of growth stimulation by IGF-I, through the PI3K-Akt pathway, is its ability to rapidly suppress transcription of the atrophy-related E3 atrogin-1 and other atrogenes and degradation of myofibrillar proteins.

Ubiquitin expression is up-regulated in human and rat skeletal muscles during aging

In this study, we have used two-dimensional electrophoresis, protein sequencing, immunoblotting, and immunohistochemistry to identify proteins that were differentially expressed during aging in human and rat skeletal muscles. Ubiquitin was identified. It was expressed at high levels in old fast-twitch muscles but at low levels in young fast-twitch muscles. It was also discovered that exogenous ubiquitin could suppress the growth of C2C12 cells, in vitro. The reduction in C2C12 cell growth was not attributed to an increase in apoptosis but to an inhibition in cell cycle entry. Furthermore, it was possible to induce muscles to degenerate in vivo by injecting a high dose of exogenous ubiquitin into young healthy skeletal muscles. These results suggest that hyperactivity of the ubiquitin-proteasome pathway is involved in the aging process of fast-twitch muscles. In addition, ubiquitin-dependent growth suppression in satellite cells may be associated with the poor healing potential of old skeletal muscles.

Markers of inflammation, proteolysis, and apoptosis in ESRD

BACKGROUND

Hemodialysis (HD) is associated with protein catabolism and augmented apoptosis. Although the effect of metabolic acidosis and inflammatory cytokines on activation of the ubiquitin-proteasome pathway and branched-chain keto acid dehydrogenase (BCKAD) is well known, the effect of HD on these pathways remains unexplored.

METHODS

Twelve patients with end-stage renal disease were studied before and during HD. Eight controls also were studied. Plasma levels of complement components and cytokines, interleukin-1 (IL-1), IL-6, and tumor necrosis factor-alpha (TNF-alpha) were measured. Messenger RNA (mRNA) levels of caspase-3, a mediator of apoptosis; ubiquitin, a marker of proteolysis; and BCKAD-E2, an enzyme regulating branched-chain amino acid oxidation, were estimated in skeletal muscle biopsy specimens by means of reverse-transcriptase polymerase chain reaction. Annexin-V expression was quantified by DNA array. Before the study, participants were placed on a 1.2-g/kg/d protein diet, and metabolic acidosis was corrected.

RESULTS

During HD, plasma IL-6 levels increased from 7.54 +/- 2.24 to 27.86 +/- 4.94 pg/dL (P < 0.001). Complement component, IL-1, and TNF-alpha levels did not change significantly during HD. mRNA levels of caspase-3 (0.50 +/- 0.01 versus 0.81 +/- 0.04), annexin-V (0.94 +/- 0.06 versus 1.48 +/- 0.05; P < 0.001), ubiquitin (1.10 +/- 0.03 versus 1.44 +/- 0.03), and BCKAD-E2 (0.47 +/- 0.01 versus 0.81 +/- 0.04) increased in muscle during HD compared with pre-HD values (P < 0.001). mRNA levels of ubiquitin (0.62 +/- 0.03) and BCKAD-E2 (0.58 +/- 0.02) were greater in controls than pre-HD values (P < 0.05). There were significant positive correlations between plasma IL-6 levels and expression of caspase-3, ubiquitin, and BCKAD-E2 genes.

CONCLUSION

HD causes activation of cytokines, which may mediate the increase in gene expression of caspase-3, ubiquitin, and BCKAD-E2 in skeletal muscles.

Failure in heat-shock protein expression in response to UBB+1 protein in progressive supranuclear palsy in humans

UBB+1 protein is an aberrant ubiquitin associated with progressive supranuclear palsy (PSP). It leads to proteasome inhibition, heat-shock protein (HSP) expression and apoptosis in cell cultures. Despite UBB+1 polyubiquitination (an indication of proteasome inhibition), we demonstrate that UBB+1 and HSP40/HSP70 immunoreactivity do not co-localize in the pons of patients with PSP. As HSPs are involved in both normal tau and proteasome function, these findings may be relevant to the aetiology of PSP and other tauopathies.

[Induction of chilling tolerance and heat shock protein synthesis in rice seedlings by heat shock]

Heat shock applied to germinated rice seeds increased the chilling tolerance of seedlings. Comparison with the control, brief heat shock applied before chilling at 4 degrees C for 2 days and recovery at 25 degrees C for another 2 days decreased the permeability of cellular membranes and increased the content of proline in rice seedlings. Heat shock applied before chilling also increased the activities of superoxide dismutase, catalase, and peroxidase and the content of ascorbate in rice seedlings. In contrast, the lipoxygenase activity and the malondialdehyde content in the heat-shocked rice seedlings were lower than those in the control. Germinated rice embryos synthesized heat shock proteins of Mr 78, 70, 64, 46, 38, 24, 17 and 16 kD during heat shock. The results of Western blot suggested that the binding protein (Bip) of HSP70 play an important role in protecting the rice seedling against chilling damage.

Ubiquitin and ubiquitin-related proteins in neurons and dendrites of brains of atypical Pick's disease without Pick bodies

Nine cases of atypical Pick's disease without Pick bodies were investigated immunohistochemically. Ubiquitin (ub)-positive and tau-negative structures were mainly found in the cerebral cortex and hippocampal dentate gyrus. In the cerebral cortex, most of the ub-positive structures had ub-positive dendrites in the neuropil, although some also showed diffuse ub-positive staining in the neuronal cytoplasm. These ub-positive structures were distributed throughout layers II-IIIab and layers V-VI. Granular cells of the dentate gyrus had ub-positive intraneuronal inclusions. When the numbers of ub-positive neurons and dendrites were evaluated in relation to the degree of neuronal loss in the cerebral cortex, the number of ub-positive neurons was significantly lower in regions showing very mild neuronal loss and higher in regions showing moderate neuronal loss. In contrast, ub-positive dendrites were detected even in cortical regions showing very mild neuronal loss. Immunoelectron-microscopically, ub-positive structures contained ub-positive ribosome-like granular components in the neuronal cytoplasm and dendrites, which were occasionally related to the rough endoplasmic reticulum and accompanied by a few filamentous components. Almost all ub-positive structures were positive for ub-binding protein p62 in double-immunostaining method. Some ub-positive or negative neurons in the cerebral cortex were positively immunolabeled with anti-ub ligase (Parkin) and anti-ub C-terminal hydrolase antibodies, whereas dendrites were not labeled by these antibodies. From the present study, it is suggested that in the cerebral cortex, these ubiquitinated proteins may firstly accumulate in the dendrites at the onset of neuronal degeneration, then appear in the neuronal cytoplasm before finally disappearing with neuronal loss.

Increased survival and neuroprotective effects of BN82451 in a transgenic mouse model of Huntington's disease

There is substantial evidence that excitotoxicity and oxidative damage may contribute to Huntington's disease (HD) pathogenesis. We examined whether the novel anti-oxidant compound BN82451 exerts neuroprotective effects in the R6/2 transgenic mouse model of HD. Oral administration of BN82451 significantly improved motor performance and improved survival by 15%. Oral administration of BN82451 significantly reduced gross brain atrophy, neuronal atrophy and the number of neuronal intranuclear inclusions at 90 days of age. These findings provide evidence that novel anti-oxidants such as BN82451 may be useful for treating HD.

Identification of novel ErbB3-interacting factors using the split-ubiquitin membrane yeast two-hybrid system

Analysis of membrane protein interactions is difficult because of the hydrophobic nature of these proteins, which often renders conventional biochemical and genetic assays fruitless. This is a substantial problem because proteins that are integral or associated with membranes represent approximately one-third of all proteins in a typical eukaryotic cell. We have shown previously that the modified split-ubiquitin system can be used as a genetic assay for the in vivo detection of interactions between the two characterized yeast transmembrane proteins, Ost1p and Wbp1p. This so-called split-ubiquitin membrane yeast two-hybrid (YTH) system uses the split-ubiquitin approach in which reconstitution of two ubiquitin halves is mediated by a protein-protein interaction. Here we converted the split-ubiquitin membrane YTH system into a generally applicable in vivo screening approach to identify interacting partners of a particular mammalian transmembrane protein. We have demonstrated the effectiveness of this approach by using the mammalian ErbB3 receptor as bait and have identified three previously unknown ErbB3-interacting proteins. In addition, we have confirmed one of the newly found interactions between ErbB3 and the membrane-associated RGS4 protein by coimmunoprecipitating the two proteins from human cells. We expect the split-ubiquitin membrane YTH technology to be valuable for the identification of potential interacting partners of integral membrane proteins from many model organisms.

Transcription profiling reveals mitochondrial, ubiquitin and signaling systems abnormalities in postmortem brains from subjects with a history of alcohol abuse or dependence

Alcohol abuse is a common human disorder with high rate of comorbidity with other psychiatric disorders. To identify candidate mechanisms for alcohol abuse, the expression of 12,626 genes was measured in postmortem temporal cortex from 11 subjects with a history of alcohol abuse or dependence, with or without other psychiatric diagnoses and compared pairwise with the expression in 11 nonalcoholic subjects matched for the other psychiatric diagnoses and demographics. Genes were defined to have altered expression in alcohol abuse if: 1) the gene showed decreased expression in at least 10 of 11 subjects with alcohol abuse, or showed increased expression in at least 10 of 11 subjects with this diagnosis compared to matched non-abusers (P < 0.007, chi(2)test); or 2) the difference in the mean abuser/non-abuser ratio for the gene from value of 1.0 was significant at P < 0.05 (one sample t-test). In subjects with a history of alcohol abuse or dependence, 163 genes were changed significantly. The most abundant and consistent changes were in gene families encoding mitochondrial proteins, the ubiquitin system, and signal transduction. These alterations indicate disturbances in energy metabolism and multiple signaling mechanisms in the temporal cortex of subjects with a history of alcohol abuse or dependence. We hypothesize that these mechanisms may be related to alcohol abuse traits or long-term effects of alcohol.

A wheat germ cell-free system is a novel way to screen protein folding and function

For high-throughput protein structural analysis, it is indispensable to develop a reliable protein overexpression system. Although many protein overexpression systems, such as that involving Escherichia coli cells, have been developed, the number of overexpressed proteins showing the same biological activities as those of the native proteins is limited. A novel wheat germ cell-free protein synthesis system was developed recently, and most of the proteins functioning in solution were synthesized as soluble forms. This suggests the applicability of this protein synthesis method to determination of the solution structures of functional proteins. To examine this possibility, we have synthesized two (15)N-labeled proteins and obtained (1)H-(15)N HSQC spectra for them. The structural analysis of these proteins has already progressed with an E. coli overexpression system, and (1)H-(15)N HSQC spectra for biologically active proteins have already been obtained. Comparing the spectra, we have shown that proteins synthesized with a wheat germ cell-free system have the proper protein folding and enough biological activity. This is the first experimental evidence of the applicability of the wheat germ cell-free protein synthesis system to high-throughput protein structural analysis.

Long-term expression of the uidA gene in Gladiolus plants under control of either the ubiquitin, rolD, mannopine synthase, or cauliflower mosaic virus promoters following three seasons of dormancy

UidA silencing did not occur following three seasons of dormancy for 23 independently transformed lines of Gladiolus plants carrying the bar- uidA fusion gene under control of either the cauliflower mosaic virus 35S (CaMV 35S), ubiquitin ( UBQ3), mannopine synthase ( mas2), or rolD promoters. The highest levels of GUS (beta-glucuronidase) expression were observed in callus, shoots, and roots of plants carrying the bar- uidA fusion gene under control of the CaMV 35S promoter and in shoots and roots of greenhouse-grown plants that contained the rolD promoter. There was no major difference in GUS expression when plants carrying the fusion gene driven by either the CaMV 35S, mas2, or UBQ3 promoters were grown in vitro as compared to growth in the greenhouse, although plants containing the rolD promoter expressed at 4- to 11-fold higher levels in shoots and roots, respectively, when grown in the greenhouse. The levels of GUS expression in greenhouse-grown plants were higher in roots than shoots for all four promoters. Of the 21 plants analyzed, 20 contained one to three copies of the bar- uidA fusion gene. Of the 23 plants analyzed, 11 had rearrangements of the transgene, but without apparent effects on levels of GUS expression.

Interactions between co-expressed Arabidopsis sucrose transporters in the split-ubiquitin system

BACKGROUND

The Arabidopsis genome contains nine sucrose transporter paralogs falling into three clades: SUT1-like, SUT2 and SUT4. The carriers differ in their kinetic properties. Many transport proteins are known to exist as oligomers. The yeast-based split ubiquitin system can be used to analyze the ability of membrane proteins to interact.

RESULTS

Promoter-GUS fusions were used to analyze the cellular expression of the three transporter genes in transgenic Arabidopsis plants. All three fusion genes are co-expressed in companion cells. Protein-protein interactions between Arabidopsis sucrose transporters were tested using the split ubiquitin system. Three paralogous sucrose transporters are capable of interacting as either homo- or heteromers. The interactions are specific, since a potassium channel and a glucose transporter did not show interaction with sucrose transporters. Also the biosynthetic and metabolizing enzymes, sucrose phosphate phosphatase and sucrose synthase, which were found to be at least in part bound to the plasma membrane, did not specifically interact with sucrose transporters.

CONCLUSIONS

The split-ubiquitin system provides a powerful tool to detect potential interactions between plant membrane proteins by heterologous expression in yeast, and can be used to screen for interactions with membrane proteins as baits. Like other membrane proteins, the Arabidopsis sucrose transporters are able to form oligomers. The biochemical approaches are required to confirm the in planta interaction.

[Construction of shuttle expression vector and expression of thymosin alpha 1 in Synechococcus sp. PCC7942]

The shutter expression vector pPREUT was constructed from the plasmid pPRS-1 containing the endogenous small plasmid of Plectonema boryanum. The expression elements such as heat shock gene groESL promoter, foreign gene Ub-thymosin alpha 1, rbcS polyA terminator and Kanamycin resistance gene were all included. The shutter plasmid pPREUT was directly transferred into Synechococcus sp. PCC7942. The transformants were obtained through Kanamycin screening. Southern blotting analysis showed that the shutter plasmid have been transferred into Synechococcus sp. PCC7942. After induction by heat shock(42 degrees C) for 30 min, the foreign protein UB-T alpha 1 was expressed efficiently, which reached 7.5% of total amount protein.

Mice expressing the alpha(1B)-adrenergic receptor induces a synucleinopathy with excessive tyrosine nitration but decreased phosphorylation

We had previously reported that systemic overexpression of the alpha(1B)-adrenergic receptor (AR) in a transgenic mouse induced a neurodegenerative disease that resembled the parkinsonian-like syndrome called multiple system atrophy (MSA). We now report that our mouse model has cytoplasmic inclusion bodies that colocalize with oligodendrocytes and neurons, are positive for alpha-synuclein and ubiquitin, and therefore may be classified as a synucleinopathy. Alpha-synuclein monomers as well as multimers were present in brain extracts from both normal and transgenic mice. However, similar to human MSA and other synucleinopathies, transgenic mice showed an increase in abnormal aggregated forms of alpha-synuclein, which also increased its nitrated content with age. However, the same extracts displayed decreased phosphorylation of alpha-synuclein. Other traits particular to MSA such as Purkinje cell loss in the cerebellum and degeneration of the intermediolateral cell columns of the spinal cord also exist in our mouse model but differences still exist between them. Interestingly, long-term therapy with the alpha(1)-AR antagonist, terazosin, resulted in protection against the symptomatic as well as the neurodegeneration and alpha-synuclein inclusion body formation, suggesting that signaling of the alpha(1B)-AR is the cause of the pathology. We conclude that overexpression of the alpha(1B)-AR can cause a synucleinopathy similar to other parkinsonian syndromes.

Intranuclear aggregation of nonexpanded ataxin-3 in marinesco bodies of the nonhuman primate substantia nigra

Marinesco bodies (MB) are intranuclear inclusion bodies predominantly found in melanin-pigmented neurons of the substantia nigra. MB are demonstrable not only in humans but also in nonhuman primates. In the present study MB of aged rhesus monkeys (Macaca mulatta; n = 15; mean age 16 years) and aged baboons (Papio anubis; n = 13; mean age 25 years) were examined immunohistochemically. MB were found to be immunoreactive for ubiquitin, a protein involved in initiation of proteasome-mediated proteolysis. We also demonstrate that MB in monkeys are intensely immunoreactive for the protein ataxin-3 as detected by using two monoclonal anti-ataxin-3 antibodies (1H9 and 2B6). The abnormally expanded form of this polyglutamine protein is known to be causally involved in spinocerebellar ataxia type 3 or Machado-Joseph disease. The monoclonal antibody 1C2 was employed to examine whether ataxin-3 in MB in monkeys contains such an abnormally expanded polyglutamine stretch. MB were consistently 1C2-immunonegative, indicating that they are composed of normal wild-type ataxin-3. In conclusion MB in nonhuman primates permit experimental examination of mechanisms involved in transnuclear localization, intranuclear aggregation, and ubiquitination of nonexpanded polyglutamine proteins.

Ultrastructure of nuclear aggregates formed by expressing an expanded polyglutamine

Intranuclear inclusions have been observed in the brains of patients affected with Huntington's disease (HD). Neuro 2A cells that transiently expressed HD exon 1 bearing 74 glutamine repeats linked to the green fluorescent protein (GFP) and the nuclear localization sequence (NLS) contained aggregates in nuclei. The aggregates were purified by fractionation with centrifugation followed by fluorescence-activated cell sorting (FACS). Heat treatment of the aggregate in an SDS sample buffer caused the dense aggregate cores to disappear and generated a basket-like structure composed of fibrils. Biochemical analysis of the aggregates revealed that the HD exon 1-GFP fusion protein was the major component. The heterogeneous nuclear ribonucleoproteins F and H, histones and ubiquitin were found to be associated with the aggregates. Our observations suggest that the N-terminal fragment of huntingtin may organize the skeletal structure of the aggregates and may disturb normal cellular functions by trapping other proteins within the aggregates.

Ubiquitin (UbC) expression in muscle cells is increased by glucocorticoids through a mechanism involving Sp1 and MEK1

The muscle protein catabolism present in rats with insulin-dependent diabetes and other catabolic conditions is generally associated with increased glucocorticoid production and mRNAs encoding components of the ubiquitin-proteasome system. The mechanisms that increase ubiquitin (UbC) expression have not been identified. We studied the regulation of UbC expression in L6 muscle cells because dexamethasone stimulates the transcription of this gene and others encoding components of the ubiquitin-proteasome pathway. Results of in vivo genomic DNA footprinting experiments indicate that a protein(s) binds to Sp1 sites approximately 50 bp upstream from the UbC transcription start site; dexamethasone changes the methylation pattern at these sites. Sp1 binds to DNA probes corresponding to the rat or human UbC promoter, and treating cells with dexamethasone increases this binding. Deletion and mutation analyses of the rat and human UbC promoters are consistent with an important role of Sp1 in UbC induction by glucocorticoids. Dexamethasone-induced ubiquitin expression is blocked by mithramycin, an inhibitor of Sp1 binding. UO126, a pharmacologic inhibitor of MEK1, also blocks UbC transcriptional activation by dexamethasone; L6 cells transfected to express constitutively active MEK1 exhibit increased UbC promoter activity. Thus, glucocorticoids increase UbC expression in muscle cells by a novel transcriptional mechanism involving Sp1 and MEK1.

Stress proteins induced by arsenic

The elevated expression of stress proteins is considered to be a universal response to adverse conditions, representing a potential mechanism of cellular defense against disease and a potential target for novel therapeutics. Exposure to arsenicals either in vitro or in vivo in a variety of model systems has been shown to cause the induction of a number of the major stress protein families such as heat shock proteins (Hsp). Among them are members with low molecular weight, such as metallotionein and ubiquitin, as well as ones with masses of 27, 32, 60, 70, 90, and 110 kDa. In most of the cases, the induction of stress proteins depends on the capacity of the arsenical to reach the target, its valence, and the type of exposure, arsenite being the biggest inducer of most Hsp in several organs and systems. Hsp induction is a rapid dose-dependent response (1-8 h) to the acute exposure to arsenite. Thus, the stress response appears to be useful to monitor the sublethal toxicity resulting from a single exposure to arsenite. The present paper offers a critical review of the capacity of arsenicals to modulate the expression and/or accumulation of stress proteins. The physiological consequences of the arsenic-induced stress and its usefulness in monitoring effects resulting from arsenic exposure in humans and other organisms are discussed.

Feline ubiquitin fusion protein genes

Using cDNA from a CRFK cell line as a template, PCR amplification was performed with the Ub1S and poly(dT) primers to isolate feline ubiquitin genes. Sequencing of the 495 bp PCR fragment revealed that the putative amino acids induced by this fragment gave a fusion protein consisting of a ubiquitin polypeptide (76 amino acids) and an extension protein of ribosomal proteins L40 (52 amino acids). The putative amino acid sequence of ubiquitin was identical to those of humans, rats and pigs. The recombinant glutathione S-transferase (GST)-feline ubiquitin fusion proteins were produced in Escherichia coli and purified. The fusion proteins had a molecular weight of about 42 kDa and were detected by immunoblot assay with rabbit anti-ubiquitin antiserum. The mRNAs from heat-shocked and non-heat-shocked cells were subjected to RT-PCR (Ub1S and poly(dT) primers) analysis. The molecular weights of the ubiquitinated proteins in heat-shocked CFRK cells were between 18 kDa and 24 kDa by immunoblot assay. These results suggested that there were more ubiquinated proteins in the heat-shocked CRFK cells than in the pre-heat-shocked cells.

[Effect of sepsis on the expression of ubiquitin and ubiquitinated protein in rat skeletal muscle]

OBJECTIVE

To study the regularity of ubiquitin and ubiquitinated protein expression in rat skeletal muscle during sepsis, and the molecular mechanism of enhancement in skeletal muscle protein catabolism.

METHODS

Wistar rats with sepsis were administered endotoxin peritoneally. The rats were randomly divided into 4 groups rats: 2, 6, 12 and 24 h after administration of endotoxin; each group (16) included normal controls. In vitro muscle incubation system with sufficient oxygen supply was used with amino acid automatic analyzer for detecting the proteolytic rate of the extensor digitorium longus(EDL) and soleus(SOL) muscle in the sample. The expression of ubiquitin and ubiquitinated protein in rat EDL muscle was determined by western blot.

RESULTS

Total proteolytic rate in the EDL muscle increased slightly at 2 and 6 h after administering endotoxin into the peritoneal cavity, and no significant difference at 12 and 24 h was observed. There was a progressive increase of 155% and 220% in myofibrillar proteolytic rate at 2 and 6 h, and 40% at 12 h, respectively, as compared with that of the normal controls. The expression of ubiquitin and ubiquitinated protein in the EDL muscle rose by 46% and 2.4 fold at 2 h and 6 h after administering endotoxin, while the ubiquitinated protein of high molecular weight was determined. No significant changes were noted in the expression of ubiquitin and ubiquitinated protein at 12 and 24 h.

CONCLUSION

The results indicate that activation of ubiquitin-proteasome pathway occurs in rat skeletal muscle during sepsis, and high expression of ubiquitin and ubiquitinated protein means that the substrate flowing into ubiquitin-proteasome pathway increases markedly, and then leads to muscle wasting.