title: Particulate cytoplasmic structures with high concentration of ubiquitin-proteasome accumulate in myeloid neoplasms.
abstract: BACKGROUND
  Increased 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.
  
  
  METHODS
  PaCSs 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.
  
  
  RESULTS
  PaCSs 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.
  
  
  CONCLUSIONS
  PaCSs 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.
authors.affiliation: Department of Internal Medicine, IRCCS Policlinico San Matteo Foundation and University of Pavia, Pavia, Italy. alessandro.pecci@unipv.it.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Pecci
authors.affiliation: Department of Molecular Medicine, University of Pavia, Pavia, Italy. vittorio.necchi@unipv.it.|Centro Grandi Strumenti, University of Pavia, Pavia, Italy. vittorio.necchi@unipv.it.
authors.forename: Vittorio
authors.initials: V
authors.lastname: Necchi
authors.affiliation: Department of Internal Medicine, IRCCS Policlinico San Matteo Foundation and University of Pavia, Pavia, Italy. serena.barozzi@gmail.com.
authors.forename: Serena
authors.initials: S
authors.lastname: Barozzi
authors.affiliation: Department of Molecular Medicine, University of Pavia, Pavia, Italy. agostina.vitali@unipv.it.
authors.forename: Agostina
authors.initials: A
authors.lastname: Vitali
authors.affiliation: Pathologic Anatomy Section, Department of Diagnostic Medicine, IRCCS Policlinico San Matteo Foundation, Pavia, Italy. e.boveri@smatteo.pv.it.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Boveri
authors.affiliation: Hematology Section, Department of Oncology and Hematology, IRCCS Policlinico San Matteo Foundation, Pavia, Italy. chiara.elena1@gmail.com.
authors.forename: Chiara
authors.initials: C
authors.lastname: Elena
authors.affiliation: Hematology Section, Department of Oncology and Hematology, IRCCS Policlinico San Matteo Foundation, Pavia, Italy. p.bernasconi@smatteo.pv.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Bernasconi
authors.affiliation: Department of Internal Medicine, IRCCS Policlinico San Matteo Foundation and University of Pavia, Pavia, Italy. p.noris@smatteo.pv.it.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Noris
authors.affiliation: Department of Molecular Medicine, University of Pavia, Pavia, Italy. solciae@smatteo.pv.it.|Pathologic Anatomy Section, Department of Diagnostic Medicine, IRCCS Policlinico San Matteo Foundation, Pavia, Italy. solciae@smatteo.pv.it.
authors.forename: Enrico
authors.initials: E
authors.lastname: Solcia
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002675:Child, Preschool; D022083:Cytoplasmic Structures; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009196:Myeloproliferative Disorders / Q000235:genetics* / Q000473:pathology; D046988:Proteasome Endopeptidase Complex / Q000235:genetics*; D025801:Ubiquitin / Q000235:genetics*
chemical_list: D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex