Leo Elisa, Mancini Manuela, Aluigi Michela, Luatti Simona, Castagnetti Fausto, Testoni Nicoletta, Soverini Simona, Santucci Maria Alessandra, Martinelli Giovanni
Istituto di Ematologia "Lorenzo e Ariosto Seràgnoli", Dipartimento di Medicina Specialistica Diagnostica e Sperimentale - DIMES, University of Bologna - Medical School, Bologna, Italy.
PLoS One. 2013 Dec 10;8(12):e81425. doi: 10.1371/journal.pone.0081425. eCollection 2013.
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.
β-连环蛋白信号传导对于慢性粒细胞白血病中白血病干细胞的自我更新至关重要。它由多个事件驱动，增强β-连环蛋白的稳定性并促进其转录共激活功能。我们研究了BCR-ABL1对Chibby1的影响，Chibby1是一种参与细胞分化和转化的β-连环蛋白拮抗剂。位于22号染色体q12上的Chibby1编码基因（C22orf2）与BCR断点（22q11）相对接近，推测由于包含一个C22orf2等位基因的远端BCR序列缺失，它参与了慢性粒细胞白血病中的β-连环蛋白激活。对40例慢性期慢性粒细胞白血病患者进行了C22orf2重排和Chibby1表达分析。荧光原位杂交分析表明，整个C22orf2均跟随BCR，无论涉及易位的染色体如何。在30/40例患者的分化造血祖细胞（骨髓单个核细胞组分）中，Chibby1蛋白表达降低至低于参考值（健康人外周血单个核细胞组分）的50%。在这种细胞环境中，Chibby1蛋白减少不依赖于C22orf2转录下调；然而，它严格依赖于BCR-ABL1表达，因为在酪氨酸激酶抑制剂治疗下达到主要分子反应时未观察到这种情况。此外，它与疾病预后或治疗反应无关。最重要的是，与分化程度更高的造血祖细胞相比，在通过CD34+表型鉴定的假定BCR-ABL1+白血病干细胞区室中，Chibby1明显减少。在CD34+细胞中，Chibby1减少源于转录事件，并由C22orf2启动子高甲基化驱动。这些结果将与BCR-ABL1相关的低Chibby1表达推进为白血病干细胞中β-连环蛋白信号传导的一个组成部分。
