Extracellular, circulating proteasomes and ubiquitin - incidence and relevance

Diagnostic value and prognostic significance of plasmatic proteasome level in patients with melanoma

Plasmatic proteasome (p-proteasome) also called circulating proteasome has recently been described as a tumor marker. We investigated the diagnostic and prognostic accuracies of p-proteasome levels in a melanoma population classified according to the American Joint Committee on Cancer staging system. Using an ELISA test, we measured p-proteasome levels in 90 patients and 40 controls between March 2003 and March 2008. The subunit composition of p-proteasomes was determined in metastatic melanoma by proteomic analysis. The mean p-proteasome levels were correlated with stages (P < 0.0001; r(S) = 0.664). They were significantly higher in patients with stage IV and stage III with lymph node metastasis (9187 ± 1294 and 5091 ± 454 ng/ml, respectively) compared to controls (2535 ± 187 ng/ml; P < 0.001), to stage I/II (2864 ± 166 ng/ml; P < 0.001) and to stage III after curative lymphadenectomy (2859 ± 271 ng/ml; P < 0.001). The diagnostic accuracy of p-proteasome was evaluated by receiver operating characteristic analysis. With a cut-off of 4300 ng/ml, diagnostic specificity and sensitivity of p-proteasome for regional or visceral metastases were respectively 96.3% and 72.2%. In univariate analysis, high p-proteasome levels (>4300 ng/ml) were significantly correlated with an increased risk of progression [hazard ratio (HR) = 7.34; 95% CI 3.54-15.21, P < 0.0001] and a risk of death (HR = 5.92; 95% CI 2.84-12.33, P < 0.0001). In multivariate analysis, high p-proteasome levels were correlated with a poorer clinical outcome in the subgroup analysis limited to patients with disease stages I, II and III. Proteomic analysis confirmed the presence of all proteasome and immunoproteasome subunits. Taken together, these results indicate that p-proteasomes are a new marker for metastatic dissemination in patients with melanoma.

Proteasomal regulation of pulmonary fibrosis

It is estimated that, combined, 400,000 people are diagnosed with idiopathic pulmonary fibrosis (IPF) or acute lung injury/acute respiratory distress syndrome annually in the United States, and both diseases are associated with an unacceptably high mortality rate. Although these disorders are distinct clinical entities, they share pathogenic mechanisms that may provide overlapping therapeutic targets. One example is fibroblast activation, which occurs concomitant with acute lung injury as well as in the progressive fibrosis of IPF. Both clinical entities are characterized by elevations of the profibrotic cytokine, transforming growth factor (TGF)-beta1. Protein degradation by the ubiquitin-proteasomal system modulates TGF-beta1 expression and signaling. In this review, we highlight the effects of proteasomal inhibition in various animal models of tissue fibrosis and mechanisms by which it may regulate TGF-beta1 expression and signaling. At present, there are no effective therapies for fibroproliferative acute respiratory distress syndrome or IPF, and proteasomal inhibition may provide a novel, attractive target in these devastating diseases.

Ubiquitin fragments: their known biological activities and putative roles

Ubiquitin (Ub) is involved in many key processes of cell biology. Identification of compounds that could interfere in the ubiquitination process is of importance. It could be expected that peptides derived from the Ub-binding regions might be able to interact with Ub receptors themselves and modify an ability of the Ub receptors interactions. This review summarizes current knowledge about known Ub-derived peptides and discusses putative activity of unexplored Ub fragments. Among identified biologically active Ub-derived peptides, its decapeptide fragment of the LEDGRTLSDY sequence was found to exhibit strong immunosuppressive effects on the cellular and humoral immune responses, comparable to that of cyclosporine. Some of the Ub fragments possess strong antibacterial and antifungal potency. In the search for new peptides that could interfere in the interaction of Ub with other proteins, we investigated the pentapeptide Ub sequences present in non-ubiquitin proteins. Based on examination of the Swiss-Prot database, we postulated that sequences of some Ub fragments often exist in other protein molecules. However, some of those motives are represented more frequently than others and could be involved in regulation of cellular processes related to Ub.

The G-Allele of the PSMA6-8C>G polymorphism is associated with poor outcome in multiple myeloma independently of circulating proteasome serum levels

INTRODUCTION

The proteasome system plays a crucial role in several malignant disorders, especially in multiple myeloma (MM). The G-allele of a single nucleotide polymorphism (SNP) -8C>G in the gene PSMA6, one of seven alpha-subunit genes of the 20S proteasome, was associated with myocardial infarction. Moreover, PSMA6 mRNA expression in human B-cell lines depended on genotypes. We investigated a potential role of this novel SNP in patients with MM.

METHODS

PSMA6 genotypes of 116 patients with MM were associated with survival. Circulating proteasome levels (CPL) dependent on -8C>G genotypes of 70 newly diagnosed patients were studied using an anti-20S proteasome enzyme-linked immunoabsorbant assay (ELISA).

RESULTS

Genotype distribution (69 CC, 44 CG, 3 GG) was compatible with Hardy-Weinberg equilibrium. Kaplan-Meier curves revealed a significant association of PSMA6-8C>G with 5-yr survival (P = 0.014). Median survival time was 43 months for the GG genotype and 50 months for the CG genotype. It was not reached within follow-up by the CC genotype (CC 5-yr survival rate 61.2%). Following hazard ratio (HR) for overall survival was calculated: G-allele vs. CC genotype: 2.038, 95% CI 1.14-3.65, P = 0.017. In multivariate analysis the G-allele was an independent prognostic factor (HR 2.1, P = 0.014). CPL were not significantly different between genotypes [mean CPL: CC 284.9 ng/mL vs. 303.3 ng/mL G-allele carriers (P = 0.709)].

CONCLUSIONS

These results suggest the G-allele of the PSMA6-8C>G polymorphism as a possible survival prognosticator.

Ontological evaluation of transcriptional differences between sperm of infertile males and fertile donors using microarray analysis

PURPOSE

To catalogue Gene Ontology terms in the sperm of infertile human males vs. donors of proven fertility by analyzing five samples from each of the two groups (five aliquots from fresh sperm and five post-swim-up).

METHODS

Microarray technology was employed to study the mRNA profile of both fresh and post-swim-up pooled samples from infertile males and donors.

RESULTS

Genes that were differentially expressed in the two populations and expressed in only one of two were analyzed to determine the gene products in terms of their associated Gene Ontology terms. Each group presented a different number and pattern of Gene Ontology terms.

CONCLUSIONS

We found differences in Gene Ontology terms between the two groups. These differences could potentially be employed to establish markers of fertility success and to identify cellular processes and complex systems related with male infertility.

Proteasomes in human bronchoalveolar lavage fluid after burn and inhalation injury

The purpose of this study was to determine whether 26S proteasome is detectable in human bronchoalveolar lavage fluid (BALF) and whether burn and inhalation injury is accompanied by changes in BALF proteasome content or activity. BALF was obtained on hospital admission from 28 patients with burn and inhalation injury (controls: 10 healthy volunteers). Proteasome concentrations were quantified by enzyme-linked immunosorbent assay, and their native molecular mass was assessed by gel filtration. Proteasome peptidase activity was measured using a chymotryptic-like peptide substrate in combination with epoxomicin (specific proteasome inhibitor). BALF protein was increased in patients (P<.001) and correlated positively with the degree of inhalation injury. The 20S/26S proteasomes were detectable in all BALF by enzyme-linked immunosorbent assay. Gel filtration confirmed the presence of intact 20S and 26S proteasome that was stable without soluble ATP/Mg. In all BALF chymotryptic-like activity was detectable and could be inhibited with epoxomicin by 60 to 70% (P<.01). Absolute amounts of 20S/26S proteasomes and proteasome activity were increased in patients (P<.001 for all). The relative BALF composition after injury was characterized by increased concentrations of 20S proteasome/mg protein (P=.0034 vs volunteers), decreased concentrations of 26S proteasome/mg protein (P=.041 vs volunteers), and reduced specific proteasome activity (P=.044 vs volunteers). The 26S proteasome per milligram and specific proteasome activity were even further reduced in patients who developed ventilator-associated pneumonia (P=.045 and P=.03 vs patients without ventilator-associated pneumonia). This study supports the novel concept that extracellular proteasomes could play a pathophysiological role in the injured lung and suggests that insufficient proteasome function may increase susceptibility for pulmonary complications.

Ventricular unloading is associated with increased 20s proteasome protein expression in the myocardium

BACKGROUND

The ubiquitin-proteasome system (UPS) breaks down misfolded and normal proteins, including cell cycle regulatory proteins involved in cardiac hypertrophy. Because congestive heart failure (CHF) increases cardiomyocyte cellular mass, indicative of increased protein synthesis and/or impaired breakdown, and ventricular unloading decreases cardiac hypertrophy and changes regulation of multiple molecular systems ("reverse cardiac remodeling"), we tested the hypothesis that ventricular unloading alters myocardial UPS.

METHODS

In 23 paired myocardial specimens (before and after unloading) ubiquitin, 20S proteasome, and cyclin D1 were investigated immunohistochemically and morphometrically quantified in relation to cardiomyocyte hypertrophy, DNA content, nuclear profile area and perimeter, and cyclin D1 protein expression. Moreover, 20S proteasome plasma concentrations were measured by enzyme-linked immunoassay (ELISA).

RESULTS

In CHF, sarcoplasmic 20S proteasome protein expression was significantly decreased compared with controls, but significantly increased after unloading. In contrast, sarcoplasmic ubiquitin protein was increased in CHF but significantly decreased after unloading, and both variables were inversely correlated. Cardiomyocyte 20S proteasome expression correlated inversely with cell size, mean DNA content, and cyclin D1, whereas ubiquitin protein expression was positively correlated with these parameters. The 20S proteasome plasma concentration was significantly increased after unloading.

CONCLUSIONS

Our data indicate that: (1) the UPS is depressed in CHF; and (2) this is reversed by ventricular unloading and associated with decreased cardiomyocyte hypertrophy, mean DNA content, and cell cycle regulatory proteins. The findings support the view that the UPS is involved in both the pathogenesis of cardiac hypertrophy and "reverse cardiac remodeling" after ventricular unloading.

On to the road to degradation: atherosclerosis and the proteasome

Protein metabolism is a central element of every living cell. The ubiquitin-proteasome system (UPS) is an integral part of the protein metabolism machinery mediating post-transcriptional processing and degradation of the majority of intracellular proteins. Over the past few years, remarkable progress has been made in our understanding of the role of the UPS in vascular biology and pathobiology, particularly atherosclerosis. This review reflects on the recent developments from the effects on endothelial cells and the initial stage of atherosclerosis to the effects on vascular smooth muscle and the progression stage of atherosclerosis and finally to the effects on cell viability and the complication stage of atherosclerosis. It will conclude with the integration of the available information in a synoptic view of the involvement of the UPS in atherosclerosis.

Copper-triggered aggregation of ubiquitin

Neurodegenerative disorders share common features comprising aggregation of misfolded proteins, failure of the ubiquitin-proteasome system, and increased levels of metal ions in the brain. Protein aggregates within affected cells often contain ubiquitin, however no report has focused on the aggregation propensity of this protein. Recently it was shown that copper, differently from zinc, nickel, aluminum, or cadmium, compromises ubiquitin stability and binds to the N-terminus with 0.1 micromolar affinity. This paper addresses the role of copper upon ubiquitin aggregation. In water, incubation with Cu(II) leads to formation of spherical particles that can progress from dimers to larger conglomerates. These spherical oligomers are SDS-resistant and are destroyed upon Cu(II) chelation or reduction to Cu(I). In water/trifluoroethanol (80∶20, v/v), a mimic of the local decrease in dielectric constant experienced in proximity to a membrane surface, ubiquitin incubation with Cu(II) causes time-dependent changes in circular dichroism and Fourier-transform infrared spectra, indicative of increasing β-sheet content. Analysis by atomic force and transmission electron microscopy reveals, in the given order, formation of spherical particles consistent with the size of early oligomers detected by gel electrophoresis, clustering of these particles in straight and curved chains, formation of ring structures, growth of trigonal branches from the rings, coalescence of the trigonal branched structures in a network. Notably, none of these ubiquitin aggregates was positive to tests for amyloid and Cu(II) chelation or reduction produced aggregate disassembly. The early formed Cu(II)-stabilized spherical oligomers, when reconstituted in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes and in POPC planar bilayers, form annular and pore-like structures, respectively, which are common to several neurodegenerative disorders including Parkinson's, Alzheimer's, amyotrophic lateral sclerosis, and prion diseases, and have been proposed to be the primary toxic species. Susceptibility to aggregation of ubiquitin, as it emerges from the present study, may represent a potential risk factor for disease onset or progression while cells attempt to tag and process toxic substrates.

Alveolar extracellular 20S proteasome in patients with acute respiratory distress syndrome

RATIONALE

Repair mechanisms resulting in alveolar protein degradation in acute respiratory distress syndrome (ARDS) are largely unknown.

OBJECTIVES

To test whether the 20S proteasome is present and functional in the alveolar space in patients with ARDS.

METHODS

Proteasome antigenic concentration in bronchoalveolar lavage (BAL) supernatants was measured by ELISA in patients with ARDS (n = 64), acute lung injury (ALI) (n = 8), sarcoidosis (n = 13), and in healthy subjects (n = 8). Cleavage of specific fluorogenic substrates (+/-epoxomicin), I(125) albumin degradation rate, and gel filtration were used to quantify and characterize proteasomal activity. The presence of proteasomes was confirmed independently by electron microscopic techniques.

MEASUREMENTS AND MAIN RESULTS

Proteasome concentrations in patients with ARDS were markedly increased (1,069 +/- 1,194 ng/ml) in comparison to healthy subjects (60.8 +/- 49.8; P < 0.001), ALI (154 +/- 43; P = 0.006), and sarcoidosis (97.6 +/- 42.2; P = 0.037). All fluorogenic substrates were hydrolyzed (Suc-LLVY-AMC, 3.6 +/- 8.8 pkat/mg; BZ-VGR-AMC, 1.8 +/- 3.1; Suc-LLE-AMC, 1 +/- 1.7) by BAL supernatants of patients with ARDS, with inhibition by epoxomicin (P = 0.0001), and the majority of proteolytic activity was detected in BAL supernatant. Maximum hydrolyzing activity occurred at 660 kD and 20S proteasome was seen microscopically after purification and being released by pneumocytes type II. Proteasomal activity and albumin degradation rate in patients with ARDS were approximately 17-fold lower than in healthy subjects. Proteasomal activity in normal BAL was inhibited by BAL aliquots from patients with ARDS but not by denatured BAL, and returned to normal by purification.

CONCLUSIONS

For the first time, we identified extracellular, biologically active 20S proteasome in the alveolar space of patients with ARDS in concentrations much higher than in normal subjects or in those with ALI.