Particulate cytoplasmic structures with high concentration of ubiquitin-proteasome accumulate in myeloid neoplasms

Abstract

BackgroundIncreased plasma levels of proteasome have been associated with various neoplasms, especially myeloid malignancies. Little is known of the cellular origin and release mechanisms of such proteasome. We recently identified and characterized a novel particulate cytoplasmic structure (PaCS) showing selective accumulation of ubiquitin-proteasome system (UPS) components. PaCSs have been reported in some epithelial neoplasms and in two genetic disorders characterized by hematopoietic cell dysplasia and increased risk of leukemia. However, no information is available about PaCSs in hematopoietic neoplasms.MethodsPaCSs were investigated by ultrastructural, immunogold, and immunofluorescence analysis of bone marrow (BM) biopsies and peripheral blood (PB) cell preparations of 33 consecutive, untreated, or relapsed patients affected by different hematopoietic neoplasms. BM and PB samples from individuals with non-neoplastic BM or healthy donors were studied as controls. Granulocytes and platelet proteasome content was measured by immunoblotting and plasma proteasome levels by ELISA.ResultsPaCSs with typical, selective immunoreactivity for polyubiquitinated proteins and proteasome were widespread in granulocytic cells, megakaryocytes, and platelets of patients with myeloproliferative neoplasms (MPN). In acute myeloid leukemia and myelodysplastic syndromes (MDS), PaCSs were only occasionally detected in blast cells and were found consistently in cells showing granulocytic and megakaryocytic maturation. Conversely, PaCSs were poorly represented or absent in non-neoplastic hematopoietic tissue or lymphoid neoplasms. In MPN granulocytes and platelets, the presence of PaCSs was associated with increased amounts of proteasome in cell lysates. PaCSs were often localized in cytoplasmic blebs generating PaCSs-filled plasma membrane vesicles observable in the BM intercellular space. In MPN and MDS, accumulation of PaCSs was associated with significant increase in plasma proteasome. Immunogold analysis showed that PaCSs of myeloid neoplasia selectively concentrated the chaperone proteins Hsp40, Hsp70, and Hsp90. ConclusionsPaCSs accumulate in cells of myeloid neoplasms in a lineage- and maturation-restricted manner; in particular, they are widespread in granulocytic and megakaryocytic lineages of MPN patients. PaCSs development was associated with excess accumulation of polyubiquitinated proteins, proteasome, and chaperone molecules, indicating impairment of the UPS-dependent protein homeostasis and a possible link with Hsp90-related leukemogenesis. A mechanism of PaCSs discharge by leukemic cells could contribute to increased plasma proteasome of MPN and MDS.Electronic supplementary materialThe online version of this article (doi:10.1186/s13045-015-0169-6) contains supplementary material, which is available to authorized users.

Proteasome 19S RP and translation preinitiation complexes are secreted within exosomes upon serum starvation

“…As schematized in Figure , one might imagine that formation of PSG‐like structures facilitates 20S CP release in the extracellular space. As a matter of fact, such enrichment of proteasomes in cytosolic structures named PaCS (Particle‐rich Cytoplasmic Structure) and further release by plasma membrane blebbing has already been described . In our purification flow chart, part of the proteasome has been found in the 20 000 g pellet, which might indicate release of such microvesicles (not shown).…”

MEK1 signaling promotes self-renewal and tumorigenicity of liver cancer stem cells via maintaining SIRT1 protein stabilization

“…More and more evidence show that ubiquitin-proteasome pathway is associated with cancer [ 45 , 46 ]. People find that TGF-β treatment lead to protein degradation of PTHrP through the ubiquitin-proteasome-dependent pathway [ 47 ].…”

Proteasome-Rich PaCS as an Oncofetal UPS Structure Handling Cytosolic Polyubiquitinated Proteins. In Vivo Occurrence, in Vitro Induction, and Biological Role

“…It may also be detected under confocal microscopy by proteasome immunofluorescence of tissue sections or glass-adhering cells, provided that they are fixed in formaldehyde-glutaraldehyde/osmium tetroxide solutions [ 17 , 21 , 22 ]. In addition to proteasome particles, the PaCS also shows selective immunoreactivity for several Hsps [ 23 , 24 ] and for the pUbP-specific FK1 antibody [ 25 ] that, coupled with unreactivity for antibodies directed against K63-linked pUbPs, suggests K48-linked pUbPs as likely partners of the PaCS proteasome ( Figure 2 ). Indeed, PaCS′ simultaneous concentration of Hsp70 and Hsp90, with their established role in misfolded/denatured-protein recognition and triage [ 12 , 13 ], together with K48-linked pUbPs [ 26 , 27 ] and proteasome particles, points to PaCS, an essentially cytosolic structure, as a UPS center handling cytosolic proteins.…”

“…However, it should be recalled that several additional molecules are known to interact with UPS inside the cells, among which ubiquitin-activating enzyme E1 [ 28 ], E2 and E3 ligases [ 11 ], and deubiquitinases [ 29 ]. E1 and, especially, Hsps have been found to be highly concentrated inside PaCSs [ 17 , 23 , 24 ]. Hsp90 seems relevant in this respect as it has been shown to bind and stabilize a large number of so-called “client proteins” forming multiple complexes where they escape degradation [ 30 ].…”