Clonal Evolution and Blast Crisis Correlate with Enhanced Proteolytic Activity of Separase in BCR-ABL b3a2 Fusion Type CML under Imatinib Therapy

PLoS One. 2015 Jun 18;10(6):e0129648. doi: 10.1371/journal.pone.0129648. eCollection 2015.

Abstract

Unbalanced (major route) additional cytogenetic aberrations (ACA) at diagnosis of chronic myeloid leukemia (CML) indicate an increased risk of progression and shorter survival. Moreover, newly arising ACA under imatinib treatment and clonal evolution are considered features of acceleration and define failure of therapy according to the European LeukemiaNet (ELN) recommendations. On the basis of 1151 Philadelphia chromosome positive chronic phase patients of the randomized CML-study IV, we examined the incidence of newly arising ACA under imatinib treatment with regard to the p210BCR-ABL breakpoint variants b2a2 and b3a2. We found a preferential acquisition of unbalanced ACA in patients with b3a2 vs. b2a2 fusion type (ratio: 6.3 vs. 1.6, p = 0.0246) concurring with a faster progress to blast crisis for b3a2 patients (p = 0.0124). ESPL1/Separase, a cysteine endopeptidase, is a key player in chromosomal segregation during mitosis. Separase overexpression and/or hyperactivity has been reported from a wide range of cancers and cause defective mitotic spindles, chromosome missegregation and aneuploidy. We investigated the influence of p210BCR-ABL breakpoint variants and imatinib treatment on expression and proteolytic activity of Separase as measured with a specific fluorogenic assay on CML cell lines (b2a2: KCL-22, BV-173; b3a2: K562, LAMA-84). Despite a drop in Separase protein levels an up to 5.4-fold increase of Separase activity under imatinib treatment was observed exclusively in b3a2 but not in b2a2 cell lines. Mimicking the influence of imatinib on BV-173 and LAMA-84 cells by ESPL1 silencing stimulated Separase proteolytic activity in both b3a2 and b2a2 cell lines. Our data suggest the existence of a fusion type-related feedback mechanism that posttranslationally stimulates Separase proteolytic activity after therapy-induced decreases in Separase protein levels. This could render b3a2 CML cells more prone to aneuploidy and clonal evolution than b2a2 progenitors and may therefore explain the cytogenetic results of CML patients.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Antineoplastic Agents / therapeutic use*
  • Blast Crisis / enzymology
  • Blast Crisis / genetics*
  • Blast Crisis / pathology
  • Cell Line, Tumor
  • Chromosome Aberrations
  • Chromosome Breakage
  • Clonal Evolution
  • Fusion Proteins, bcr-abl / genetics*
  • Humans
  • Imatinib Mesylate / therapeutic use*
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / drug therapy*
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / enzymology
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / genetics
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / pathology*
  • Middle Aged
  • Proteolysis
  • Separase / metabolism*
  • Young Adult

Substances

  • Antineoplastic Agents
  • Imatinib Mesylate
  • Fusion Proteins, bcr-abl
  • Separase

Grants and funding

WS received a grant from the Deutsche Krebshilfe (www.krebshilfe.de, 110625), RH obtained grants from Deutsche Krebshilfe (www.krebshilfe.de, 106642), Bundesministerium für Bildung und Forschung (www.bmbf.de, BMBF 01GI0270), Deutsche José-Carreras Leukämiestiftung (www.carreras-stiftung.de, DJCLS H09/01f, H06/04v, H03/01, R05/23), European Community (ec.europa.eu, LSHC-CT-2004-503216). Novartis (www.novartis.de, CSTI571ADE22). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors acknowledge financial support by the Open Access Publishing funding programme of the Ruprecht-Karls-Universität Heidelberg.