Most antigenic peptides presented by MHC class I molecules result from the degradation of intracellular proteins by the proteasome. In lymphoid tissues and cells exposed to IFNγ, the standard proteasome is replaced by the immunoproteasome, in which all of the standard catalytic subunits β1, β2, and β5 are replaced by their inducible counterparts β1i, β2i, and β5i, which have different cleavage specificities. The immunoproteasome thereby shapes the repertoire of antigenic peptides. The existence of additional forms of proteasomes bearing a mixed assortment of standard and inducible catalytic subunits has been suggested. Using a new set of unique subunit-specific antibodies, we have now isolated, quantified, and characterized human proteasomes that are intermediate between the standard proteasome and the immunoproteasome. They contain only one (β5i) or two (β1i and β5i) of the three inducible catalytic subunits of the immunoproteasome. These intermediate proteasomes represent between one-third and one-half of the proteasome content of human liver, colon, small intestine, and kidney. They are also present in human tumor cells and dendritic cells. We identified two tumor antigens of clinical interest that are processed exclusively either by intermediate proteasomes β5i ) or by intermediate proteasomes β1i-β5i (MAGE-A10 [254][255][256][257][258][259][260][261][262] ). The existence of these intermediate proteasomes broadens the repertoire of antigens presented to CD8 T cells and implies that the antigens presented by a given cell depend on their proteasome content.antigen processing | antigenic peptide | immunoproteasome | tumor antigen | MAGE

The immunoproteasome (IP) is usually viewed as favoring the production of antigenic peptides presented by MHC class I molecules, mainly because of its higher cleavage activity after hydrophobic residues, referred to as the chymotrypsin-like activity. However, some peptides have been found to be better produced by the standard proteasome. The mechanism of this differential processing has not been described. By studying the processing of three tumor antigenic peptides of clinical interest, we demonstrate that their differential processing mainly results from differences in the efficiency of internal cleavages by the two proteasome types. Peptide gp100209–217 (ITDQVPSFV) and peptide tyrosinase369–377 (YMDGTMSQV) are destroyed by the IP, which cleaves after an internal hydrophobic residue. Conversely, peptide MAGE-C2336–344 (ALKDVEERV) is destroyed by the standard proteasome by internal cleavage after an acidic residue, in line with its higher postacidic activity. These results indicate that the IP may destroy some antigenic peptides due to its higher chymotrypsin-like activity, rather than favor their production. They also suggest that the sets of peptides produced by the two proteasome types differ more than expected. Considering that mature dendritic cells mainly contain IPs, our results have implications for the design of immunotherapy strategies.

We recently described two proteasome subtypes that are intermediate between the standard proteasome and the immunoproteasome. They contain only one (β5i) or two (β1i and β5i) of the three inducible catalytic subunits of the immunoproteasome. They are present in tumor cells and abundant in normal human tissues. We described two tumor antigenic peptides that are uniquely produced by these intermediate proteasomes. In this work, we studied the production by intermediate proteasomes of tumor antigenic peptides known to be produced exclusively by the immunoproteasome (MAGE-A3114–122, MAGE-C242–50, MAGE-C2336–344) or the standard proteasome (Melan-A26–35, tyrosinase369–377, gp100209–217). We observed that intermediate proteasomes efficiently produced the former peptides, but not the latter. Two peptides from the first group were equally produced by both intermediate proteasomes, whereas MAGE-C2336–344 was only produced by intermediate proteasome β1i-β5i. Those results explain the recognition of tumor cells devoid of immunoproteasome by CTL recognizing peptides not produced by the standard proteasome. We also describe a third antigenic peptide that is produced exclusively by an intermediate proteasome: peptide MAGE-C2191–200 is produced only by intermediate proteasome β1i-β5i. Analyzing in vitro digests, we observed that the lack of production by a given proteasome usually results from destruction of the antigenic peptide by internal cleavage. Interestingly, we observed that the immunoproteasome and the intermediate proteasomes fail to cleave between hydrophobic residues, despite a higher chymotrypsin-like activity measured on fluorogenic substrates. Altogether, our results indicate that the repertoire of peptides produced by intermediate proteasomes largely matches the repertoire produced by the immunoproteasome, but also contains additional peptides.

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The proteasome is responsible for selective degradation of proteins. It exists in mammalian cells under four main subtypes, which differ by the combination of their catalytic subunits: the standard proteasome (β1–β2–β5), the immunoproteasome (β1i–β2i–β5i) and the two intermediate proteasomes (β1–β2–β5i and β1i–β2–β5i). The efficiency of the four proteasome subtypes to degrade ubiquitinated or oxidized proteins remains unclear. Using cells expressing exclusively one proteasome subtype, we observed that ubiquitinated p21 and c-­myc were degraded at similar rates, indicating that the four 26S proteasomes degrade ubiquitinated proteins equally well. Under oxidative stress, we observed a partial dissociation of 26S into 20S proteasomes, which can degrade non-ubiquitinated oxidized proteins. Oxidized calmodulin and hemoglobin were best degraded in vitro by the three β5i-containing 20S proteasomes, while their native forms were not degraded. Circular dichroism analyses indicated that ubiquitin-independent recognition of oxidized proteins by 20S proteasomes was triggered by the disruption of their structure. Accordingly, β5i-containing 20S proteasomes degraded unoxidized naturally disordered protein tau, while 26S proteasomes did not. Our results suggest that the three β5i-containing 20S proteasomes, namely the immunoproteasome and the two intermediate proteasomes, might help cells to eliminate proteins containing disordered domains, including those induced by oxidative stress.

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Summary:lesions, and magnetic resonance imaging of the bone marrow was normal. Electrocardiogram and echocardiography AL amyloidosis is an infiltrative disorder characterized were normal. by the extracellular deposition of insoluble fibrillarThe patient had an HLA-identical sister. As first-line immunoglobulin light chains whose production results therapy, an allogeneic BMT was performed on 24 August from a plasma cell dyscrasia. Treatment with melphalan 1995. Conditioning consisted of melphalan, 140 mg/m 2 , has resulted in an improvement in a few patients.and TBI (800 cGy, single dose). GVHD prophylaxis Recently, intensive chemotherapy followed by autologincluded CsA and MTX. The immediate post-grafting perous or syngeneic stem cell support has been shown to iod was uneventful. Grade I GVHD progressing to grade II offer potential benefit. Allogeneic stem cell support after developed on day 30 post-transplant. Methylprednisolone, intensive therapy would retain the benefits of autolog-2 mg/kg/day for 10 days, followed by tapering of the dose, ous transplantation, with the additional advantages of was effective. The monoclonal component was no longer a tumor-free graft and of a possible graft-versus-tumor detected in blood and urine on 25 October 1995. On effect. We report a patient with AL amyloidosis and sig-17 November 1995 the bone marrow was normal, without nificant proteinuria. She improved after an allogeneic abnormal plasma cells and without B cell monoclonality on bone marrow transplantation.Southern blot analysis. There was full chimerism as demonKeywords: amyloidosis; allogeneic BMT strated by RLFP. The proteinuria gradually decreased. At 18 months post-BMT, the proteinuria was 1.3 g/24 h (Figure 1), and there was no ankle oedema. Immunoelectrophoresis of the urine did not show a monoclonal band. At Case report the time of writing, the performance status of the patient is 100%. There is limited chronic skin and liver GVHD, A 56-year-old woman noticed ankle oedema in November well controlled by CsA. The patient declined a repeat 1994. A superficial thrombophlebitis led to a blood test in renal biopsy. January 1995. There was an increase in serum gammaglobulins (2.5 g/dl), with an IgG lambda monoclonal component (2.2 g/dl). The IgA concentration was 132 mg/dl, and the IgM 88 mg/dl. The serum creatinine was 0.8 mg/dl, and the blood count was normal. The serum albumin was 4.2 g/dl. Twenty-four hour proteinuria was 9.15 g. Analysis of the urinary proteins showed a mixed proteinuria, with an IgG lambda monoclonal immunoglobulin in the urine. Bone marrow examination showed 23% plasma cells, with membrane IgG lambda monoclonality. No amyloid deposition was seen in the bone marrow biopsy. The serum beta-2-microglobulin level was 2.3 mg/l, and serum CRP level Ͻ0.2 mg/dl. Renal biopsy showed an infiltration of arteries and mesangium by eosinophilic deposits which showed the characteristic green birefringence under polarized light by Congo red stain. Immunofluorescence showed strong staining of the deposits by ant...

Background Most recent trials evaluating extensive screening strategies for occult cancer in patients with unprovoked venous thromboembolism have failed, because, among other reasons, of an overall low rate of occult cancer. The RIETE investigators recently proposed a score aimed at identifying a subgroup at higher risk. Methods We retrospectively computed the RIETE score for all patients included in the MVTEP study, which evaluated the accuracy of [¹⁸F]fluorodeoxyglucose-positron emission tomography in the screening of occult cancer in patients with unprovoked venous thromboembolism. Performance of the RIETE score was assessed according to the proportion of patients classified in each risk group, and the corresponding rates of cancer diagnosis. Results Among the 386 patients included in the analysis, 136 patients (35.3%) were classified as high risk by the RIETE score. Cancer was diagnosed in 16 (11.8%) of them, whereas it was diagnosed in nine (3.6%) of the 250 patients with a low RIETE cancer score: odds ratio of 3.6 (95% confidence interval [CI] 1.53-8.32). The area under the receiver operating characteristic curve was 0.63 (95% CI 0.51-0.74). Conclusion The RIETE score seems to be able to identify a subgroup at high risk for cancer (10%) in our specific dataset of patients with unprovoked venous thromboembolism.