Changes in the amount and distribution of prosomal subunits during the differentiation of U937 myeloid cells: high expression of p23K

Integrated multiscale analysis reveals complex gender-specific changes in lymphocytes of smokers

Environmental stressors induce specific physiological responses that can be measured in the blood, notably by morphological changes in lymphocytes. Tobacco being the best-known stress in terms of its impact on health, we studied the physiological properties of peripheral blood lymphocytes in a population of 33 healthy non-smokers and smokers. Proteasome amount, mitochondria energy levels, changes in membrane properties and cell and nuclear size were analyzed to obtain 28 parameters from two fluorescence-based techniques: flow cytometry and cell imaging. The results showed that none of the parameters alone identified gender and smoking status, but that statistical analysis of these parameters, whether or not combined with a third set of data, hematological data, can. Statistical analysis of selected parameters clearly discriminates between male and female samples, as well as smokers and non-smokers. Effects of tobacco smoke pollutants are more pronounced in female smokers than in other groups.

Ubiquitination and proteolysis in acute lung injury

Ubiquitination is a posttranslational modification that regulates a variety of cellular functions depending on timing, subcellular localization, and type of tagging, as well as modulators of ubiquitin binding leading to proteasomal or lysosomal degradation or nonproteolytic modifications. Ubiquitination plays an important role in the pathogenesis of acute lung injury (ALI) and other lung diseases with pathologies secondary to inflammation, mechanical ventilation, and decreased physical mobility. Particularly, ubiquitination has been shown to affect alveolar epithelial barrier function and alveolar edema clearance by targeting the Na,K-ATPase and epithelial Na(+) channels upon lung injury. Notably, the proteasomal system also exhibits distinct functions in the extracellular space, which may contribute to the pathogenesis of ALI and other pulmonary diseases. Better understanding of these mechanisms may ultimately lead to novel therapeutic modalities by targeting elements of the ubiquitination pathway.

Extracellular, circulating proteasomes and ubiquitin - incidence and relevance

The ubiquitin-proteasome system is the major pathway for intracellular protein degradation and is also deeply involved in the regulation of most basic cellular processes. Its proteolytic core, the 20S proteasome, has found to be attached also to the cell plasma membrane and certain observations are interpreted as to suggest that they may be released into the extracellular medium, e.g. in the alveolar lining fluid, epididymal fluid and possibly during the acrosome reaction. Proteasomes have also been detected in normal human blood plasma and designated circulating proteasomes; these have a comparatively low specific activity, a distinct pattern of subtypes and their exact origin is still enigmatic. In patients suffering from autoimmune diseases, malignant myeloproliferative syndromes, multiple myeloma, acute and chronic lymphatic leukaemia, solid tumour, sepsis or trauma, respectively, the concentration of circulating proteasomes has been found to be elevated, to correlate with the disease state and has even prognostic significance. Similarly, ubiquitin has been discovered as a normal component of human blood and seminal plasma and in ovarian follicular fluid. Increased concentrations were measured in diverse pathological situations, not only in blood plasma but also in cerebrospinal fluid, where it may have neuroprotective effects. As defective spermatozoa are covered with ubiquitin in the epididymal fluid, extracellular ubiquitination is proposed to be a mechanism for quality control in spermatogenesis. Growing evidence exists also for a participation of extracellular proteasomes and ubiquitin in the fertilization process.

High plasma proteasome levels are detected in patients with metastatic malignant melanoma

BACKGROUND

Proteasomes, nonlysosomal proteolytic structures, are implicated in cell growth and differentiation. An abnormal expression has been described in haematopoietic malignancies and in some solid tumours.

OBJECTIVES

To study the plasma proteasome levels in patients with malignant melanoma (MM) using an enzyme-linked immunosorbent assay (ELISA) technique, and to compare them with the values obtained in a normal population and in patients with severe psoriasis or chronic idiopathic urticaria (CIU).

METHODS

Plasma proteasome level was measured using a sandwich ELISA test in normal donors (n = 14), and in patients with stage I/II (n = 13), stage III (n = 6) and stage IV (n = 10) MM, severe psoriasis (n = 13) and CIU (n = 6). Tissue proteasome expression was also detected by immunohistology using a monoclonal antibody in paraffin-embedded samples of normal tissue, psoriasis skin and MM.

RESULTS

In normal donors, mean +/- SEM plasma proteasome concentration was 2138 +/- 221 ng mL(-1). Patients with stages III and IV MM exhibited a significantly higher value (3373 +/- 470 ng mL(-1) and 8931 +/- 1232 ng mL(-1), respectively). Values in patients with stage I/II MM and CIU were not significantly different from those in normal volunteers. Patients with severe psoriasis also exhibited increased values (3398 +/- 374 ng mL(-1)) but to a lesser extent than in patients with stage IV MM. There was a significant correlation of proteasome levels with serum lactate dehydrogenase in the MM group. Tissue expression as demonstrated by immunohistochemistry paralleled these findings. The strongest expression was seen on MM slides and to a lesser extent in psoriasis samples, the weakest expression being observed in normal skin.

CONCLUSIONS

Proteasomes are strongly expressed in cutaneous MM; high levels of circulating proteasomes are detected in patients with metastatic MM with a high melanoma burden, and at a lesser extent in psoriatic patients, which suggests proteasomes represent a marker more of nonspecific inflammation than of early cancer.

Development and evaluation of a sandwich ELISA for quantification of the 20S proteasome in human plasma

Because quantification of the 20S proteasome by functional activity measurements is difficult and inaccurate, we have developed an indirect sandwich enzyme-linked immunosorbent assays (ELISA) for quantification of the 20S proteasome in human plasma. This sandwich ELISA uses a combination of a monoclonal antibody (mcp 20) recognizing the C2-beta subunit of human 20S proteasome (Mr approximately 30,000) and a polyclonal rabbit anti-20S antibody which labels different subunits of the complex. The detection limit of the assay was established as 10 ng/ml (n=10, mean of zero standard+2 S.D.) and the recovery rate ranged from 96% to 104%. The within-run and between-run coefficients of variation (CV) ranges were 2.8-3.3 and 3.0-3.4, respectively. Using serial dilutions of plasma to which various amounts of purified 20S proteasome were added, a linear dose-response was observed between 102 and 2050 ng/ml with a slope of 1.004 and a coefficient of determination r(2) of 0.99. In a preliminary experiment performed on a limited number of patients, the present assay was used to quantify the 20S proteasome in plasma from healthy subjects (n=11) and from a limited number of patients with various diseases (two patients with each of the following diagnoses: acute myeloid leukaemia, chronic myeloproliferative syndromes, Hodgkin's disease and solid tumors). The average concentration of 20S proteasome in plasma from normal subjects was found to be 2319+/-237 ng/ml (n=11). With reference to this normal range, the plasma proteasome concentration was found to be increased in most of these pathological state and as high as 1200% when solid tumors had been detected. For patients with Hodgkin's disease, the changes were more variable whereas in patients with chronic lymphocytic leukaemia, the proteasome concentration was raised during the acute phase of disease and decreased during therapy. We suggest that this robust, accurate and highly reproducible assay could be used to quantify proteasome in human plasma and investigate its value as a biological marker for various malignant and nonmalignant diseases.

Inhibition of 20 S and 26 S proteasome activity by lithium chloride: impact on the differentiation of leukemia cells by all-trans retinoic acid

Lithium affects several enzymatic activities, however, the molecular mechanisms of lithium actions are not fully understood. We previously showed that LiCl interacts synergistically with all-trans-retinoic acid to promote terminal differentiation of WEHI-3B D(+) cells, a phenomenon accompanied by the recovery of the retinoid-induced loss of retinoic acid receptor alpha protein pools. Here, we demonstrate the effects of LiCl on proteasome-dependent degradation of retinoic acid receptor alpha proteins. LiCl alone, or in combination with all-trans-retinoic acid, increased cellular levels of ubiquitinated retinoic acid receptor alpha and markedly reduced chymotryptic-like activity of WEHI-3B D(+) 20 S and 26 S proteasome enzymes. Neither KCl nor all-trans-retinoic acid affected enzyme activity, whereas NaCl produced a modest reduction at relatively high concentrations. In addition, LiCl inhibited 20 S proteasome chymotryptic-like activity from rabbits but had no effect on tryptic-like activity of the 26 S proteasome. This effect has significant consequences in stabilizing the retinoic acid receptor alpha protein levels that are necessary to promote continued differentiation of leukemia cells in response to all-trans-retinoic acid. In support of this concept, combination of proteasome inhibitors beta-clastolactacystin or benzyloxycarbonyl-Leu-Leu-Phe with all-trans-retinoic acid increased differentiation of WEHI-3B D(+) cells in a manner that was analogous to the combination of LiCl and all-trans-retinoic acid.

Plasma proteasome level is a potential marker in patients with solid tumors and hemopoietic malignancies

BACKGROUND

Proteasomes are nonlysosomal proteolytic structures that have been implicated in cell growth and differentiation. Abnormal expression levels of proteasomes have been described in tumor cells, and proteasomes can be detected and measured in plasma. The objective of this study was to characterize differences in proteasome levels between normal, healthy donors and patients with neoplastic disease and to correlate the findings with clinical status and other biologic markers of disease spread.

METHODS

Plasma proteasome levels were measured using a sandwich enzyme-linked immunosorbent assay in normal donors (n = 73 donors) and in patients with solid tumors (n = 20 patients), acute leukemia (n = 35 patients), myeloproliferative (n = 37 patients) and myelodysplastic (n = 19 patients) syndromes, chronic lymphocytic leukemia (n = 44 patients), non-Hodgkin lymphoma (n =104 patients), Hodgkin disease (n = 14 patients), other lymphoid disorders (n = 17 patients), and multiple myeloma (n = 27 patients).

RESULTS

In the normal donors, the plasma proteasome concentration was 2356 ng/mL +/- 127 ng/mL. Patients with solid tumors exhibited a significantly higher value (7589 ng/mL +/- 2124 ng/mL), similar to the patients with myeloproliferative (4099 ng/mL +/- 498 ng/mL) and myelodysplastic (2922 ng/mL +/- 322 ng/mL) syndromes. Patients with lymphoproliferative disorders, in contrast, had significantly lower values than normal donors (1751 ng/mL +/- 107 ng/mL), except those in aggressive phase of the disease. This low level persisted in patients who were in complete remission. Proteasome levels decreased during the initial phase of treatment. Although there was a significant correlation with serum lactic dehydrogenase levels, frequent discrepancies were noted. There was no correlation with C-reactive protein or beta2-microglobulin levels, even in the group of patients with multiple myeloma.

CONCLUSIONS

The plasma proteasome level is a potential new tool for the monitoring of patients with neoplastic disease. It is not correlated solely with cell lysis and may be involved in the pathophysiology of disease progression.

Different proteasome subtypes in a single tissue exhibit different enzymatic properties

It is concluded from many experiments that mammalian tissues and cells must contain a heterogeneous population of 20 S proteasome complexes. We describe the purification and separation by chromatographic procedures of constitutive 20 S proteasomes, 20 S immuno-proteasomes and intermediate-type 20 S proteasomes from a given tissue. Our data demonstrate that each of these three groups comprises more than one subtype and that the relative ratios of the subtypes differ between different rat tissues. Thus, six subtypes could be identified in rat muscle tissue. Subtypes I and II are constitutive proteasomes, while subtypes V and VI comprise immuno-proteasomes. Subtypes III and IV belong to a group of intermediate-type proteasomes. The subtypes differ with regard to their enzymatic characteristics. Subtypes I-III exhibit high chymotrypsin-like activity and high peptidylglutamylpeptide hydrolysing activity, while these activities are depressed in subtypes IV-VI. In contrast, trypsin-like activity of subtypes IV-VI is enhanced in comparison to subtypes I-III. Importantly, the subtypes also differ in their preferential cleavage site usage when tested by digestion of a synthetic 25mer polypeptide substrate. Therefore, the characteristics of proteasomes purified from tissues or cells represent the average of the different subtype activities which in turn may have different functions in vivo.

Intracellular proteinases of invertebrates: calcium-dependent and proteasome/ubiquitin-dependent systems

Cytosolic proteinases carry out a variety of regulatory functions by controlling protein levels and/or activities within cells. Calcium-dependent and ubiquitin/proteasome-dependent pathways are common to all eukaryotes. The former pathway consists of a diverse group of Ca(2+)-dependent cysteine proteinases (CDPs; calpains in vertebrate tissues). The latter pathway is highly conserved and consists of ubiquitin, ubiquitin-conjugating enzymes, deubiquitinases, and the proteasome. This review summarizes the biochemical properties and genetics of invertebrate CDPs and proteasomes and their roles in programmed cell death, stress responses (heat shock and anoxia), skeletal muscle atrophy, gametogenesis and fertilization, development and pattern formation, cell-cell recognition, signal transduction and learning, and photoreceptor light adaptation. These pathways carry out bulk protein degradation in the programmed death of the intersegmental and flight muscles of insects and of individuals in a colonial ascidian; molt-induced atrophy of crustacean claw muscle; and responses of brine shrimp, mussels, and insects to environmental stress. Selective proteolysis occurs in response to specific signals, such as in modulating protein kinase A activity in sea hare and fruit fly associated with learning; gametogenesis, differentiation, and development in sponge, echinoderms, nematode, ascidian, and insects; and in light adaptation of photoreceptors in the eyes of squid, insects, and crustaceans. Proteolytic activities and specificities are regulated through proteinase gene expression (CDP isozymes and proteasomal subunits), allosteric regulators, and posttranslational modifications, as well as through specific targeting of protein substrates by a diverse assemblage of ubiquitin-conjugases and deubiquitinases. Thus, the regulation of intracellular proteolysis approaches the complexity and versatility of transcriptional and translational mechanisms.

Subcellular distribution and profiles of prosomes (proteasomes-MCP) during differentiation of human lymphoblastic cell line

The human lymphoblastoid leukemic cell line (CCRF-CEM) was induced to differentiate with phorbol 12-myristate 13-acetate (PMA). During differentiation, assessed by monitoring the cluster of differentiation (CD) profile, the prosome (proteasomes, multi-catalytic proteinase) distribution and composition were studied by microscopy, flow cytometry and Western blot analysis. Changes in prosome subunits were monitored using 3 monoclonal antibodies anti-p23K, p29K and p31K. There were changes in the subcellular distribution of prosome antigens in PMA treated cells compared to untreated cells. The amount of cytoplasmic prosomal antigens decreased during the first three days of differentiation and the membrane antigens increased; meanwhile there was an increase of p53 and no change in actin protein levels. As mitotic cyclins are degraded by the ubiquitin pathway and therefore via the prosome, the decrease observed in differentiated cells suggests that prosomes are involved in the cell cycle and thus in cell proliferation.

Changes in the subunit distribution of prosomes (MCP-proteasomes) during the differentiation of human leukemic cells

The subunit composition of cell-internal and surface prosomes during phorbol myristate acetate (PMA)-induced differentiation of human leukemic T lymphocytes (CCRF-CEM cell line) was studied in relation to clusters of differentiation (CD) markers. PMA inhibited cell growth and decreased the amounts of CD1a and CD4 while CD3, CD8, CD25, CD45, CD57 and MHCI increased it; the p53 anti-oncogene increased while actin levels remained constant. Cells incubated with the inducer PMA for 3 days and placed in fresh inhibitor-free medium resumed growth at a low rate, while the CD values slowly reverted to those of the initial phenotype. The presence and relative amounts of prosome subunits were analyzed by flow cytometry, light and fluorescent microscopy and Western blotting using 3 monoclonal antibodies (p25K, p27K and p30-33K MAbs). The decrease in cytoplasmic antigens on day 3 was remarkable (cells followed for 7 days) while increased surface antigens were observed. Changes in the subcellular distributions of prosome antigens, particularly the p25K and p30-33K subunit, were correlated with a partial arrest of the cell cycle. Interestingly, the composition of cell internal and surface prosomes showed different patterns of change.