BCR-ABL1-Associated Reduction of Beta Catenin Antagonist Chibby1 in Chronic Myeloid Leukemia

Abstract

Beta Catenin signaling is critical for the self-renewal of leukemic stem cells in chronic myeloid leukemia. It is driven by multiple events, enhancing beta catenin stability and promoting its transcriptional co-activating function. We investigated the impact of BCR-ABL1 on Chibby1, a beta catenin antagonist involved in cell differentiation and transformation. Relative proximity of the Chibby1 encoding gene (C22orf2) on chromosome 22q12 to the BCR breakpoint (22q11) lets assume its involvement in beta catenin activation in chronic myeloid leukemia as a consequence of deletions of distal BCR sequences encompassing one C22orf2 allele. Forty patients with chronic myeloid leukemia in chronic phase were analyzed for C22orf2 relocation and Chibby1 expression. Fluorescent in situ hybridization analyses established that the entire C22orf2 follows BCR regardless of chromosomes involved in the translocation. In differentiated hematopoietic progenitors (bone marrow mononuclear cell fractions) of 30/40 patients, the expression of Chibby1 protein was reduced below 50% of the reference value (peripheral blood mononuclear cell fractions of healthy persons). In such cell context, Chibby1 protein reduction is not dependent on C22orf2 transcriptional downmodulation; however, it is strictly dependent upon BCR-ABL1 expression because it was not observed at the moment of major molecular response under tyrosine kinase inhibitor therapy. Moreover, it was not correlated with the disease prognosis or response to therapy. Most importantly, a remarkable Chibby1 reduction was apparent in a putative BCR-ABL1+ leukemic stem cell compartment identified by a CD34+ phenotype compared to more differentiated hematopoietic progenitors. In CD34+ cells, Chibby1 reduction arises from transcriptional events and is driven by C22orf2 promoter hypermethylation. These results advance low Chibby1 expression associated with BCR-ABL1 as a component of beta catenin signaling in leukemic stem cells.

FOXM1 Transcription Factor: A New Component of Chronic Myeloid Leukemia Stem Cell Proliferation Advantage

“…Parental K562 BCR-ABL1þ cell line was maintained in RPMI 1640 medium (Lonza) supplemented with 10% fetal calf serum (FCS, Gibco), 1% L-Glutamine, and antibiotics in 5% CO 2 and fully humidified atmosphere at 37°C [Leo et al, 2013]. Imatinib (IM: 1 mM), BI6727 (1 mM), and thiostrepton (1 mM) were used to inhibit BCR-ABL1 TK, PLK1, and FOXM1, respectively.…”

“…Western blot (WB) and immunoprecipitation/immunoblotting (IP/ IB) analyses were performed on whole cell lysates and nuclear fractions according to published methods [Leo et al, 2013;Mancini et al, 2014]. The anti-b-catenin, anti-PLK1, anti-phospho-PLK1 (Thr210), and anti-phospho serine-Thr (Ser/Thr) antibodies were purchased from Cell Signaling Technology.…”

DNA Methyltransferase 1 Drives Transcriptional Down‐Modulation of β Catenin Antagonist Chibby1 Associated With the BCR‐ABL1 Gene of Chronic Myeloid Leukemia

“…β Catenin increase and its nuclear translocation result in the binding of β catenin with the T‐cell factor/lymphoid enhancer factor 1 (TCF/LEF1) transcription factors to form a transcriptionally active complex which triggers critical target genes for leukemic progenitor proliferative advantage [Henderson and Fagotto, ; Holland et al, ]. Our recent study established that a further component of β catenin activation is its antagonist CBY1 [Leo et al, ].…”

Leukemia stem cell immunophenotyping tool for diagnostic, prognosis, and therapeutics

“…This functional alteration leads to elevated proliferative, adhesive, and antiapoptotic potential (Kronenwett et al, ; Lemoli et al, ). Tyrosine kinase inhibitors, as would be expected, are effective for CML (Landberg et al, ), although in some cases, the translocation is not reciprocal, producing unbalanced altered chromosomes with particular outcomes (Leo et al, ).…”