DNA hypermethylation promotes the low expression of pro‐apoptotic BCL2L11 associated with BCR‐ABL1 fusion gene of chronic myeloid leukaemia

Abstract

DNA hypermethylation promotes the low expression of pro-apoptotic BCL2L11 associated with BCR-ABL1 fusion gene of chronic myeloid leukaemia BCL2L11 [BCL2-interacting mediator, (BIM)] is a member of the BH3-only death activator family and a key determinant of cell fate upon cytokine withdrawal. Its expression is regulated by transcriptional and post-transcriptional mechanisms, encompassing the class O forkhead transcription factor-3A (FOXO3A), which directs gene transcription by binding a consensus site at the BCL2L11 promoter, and extracellular signal-regulated kinases (ERK1/2), which dissociate the most abundant BCL2L11 EL isoform from pro-survival BCL2 proteins, concurrently targeting it for ubiquitylation and proteasomal degradation through phosphorylation at critical serine residues (Youle & Strasser, 2008). BCL2L11 downmodulation has a central role in the survival of clonal progenitors of chronic myeloid leukaemia (CML). It is contingent upon the BCR-ABL1 tyrosine kinase (TK) and mostly driven by a proteasome degradation pathway that hinders FOXO3A and BCL2L11 stability (Kuribara et al, 2004;Aichberger et al, 2009). Moreover, BCL2L11 re-expression has a key role in BCR-ABL1-expressing cell apoptosis in response to imatinib (IM) (Kuroda et al, 2006). Accordingly, BCL2L11 loss due to gene deletion polymorphism protects leukaemic cells from IM-induced death, hence contributing to intrinsic drug resistance (Ng et al, 2012). Low BCL2L11 expression in CML has been also ascribed to DNA hypermethylation at the gene promoter (Kuribara et al, 2004;Aichberger et al, 2005;San José-Eneriz et al, 2009). The putative role of epigenetic modifications in BCR-ABL1-associated BCL2L11 downmodulation is supported by our recent study proving the participation of 5 methylcytosine (5mC) hydroxylation in BCL2L11 transcriptional induction in response to IM (Mancini et al, 2012). Notably, the conversion of 5mC into 5 hydroxymethylcytosine (5hmC) impairs the chromatin recruitment of DNA methyltransferase (DNMT) 1, hence facilitating DNA de-methylation and gene re-expression Here we show that BCR-ABL1 TK is associated with DNMT1 enhanced recruitment at the BCL2L11 promoter and 5mC excess over 5hmC. Experiments were first perfomed in a cell clone (cl 3B, originated from the murine haematopoietic 32D cell line stably transduced with a temperature-sensitive BCR-ABL1 construct) kept at 33°C, the permissive temperature for BCR-ABL1 TK. Polymerase chain reaction (PCR) amplification of chromatin immuno-precipitation (ChIP) products obtained with an anti-DNMT1 antibody (Sigma, St Louis, MO, USA) revealed a significant reduction of DNMT1 at a 342 bp sequence of the BCL2L11 promoter (internal to a 358 bp region encompassing nucleotides À268 to +90) as 4-6 h of IM treatment (P < 0Á001 or less) paralleled the de-phosphorylation of BCR-ABL1 protein at a critical residue (Tyr 245 ) for enzymatic activity (Fig 1A). DNMT1 displacement was associated with a significant reduction of 5mC at the above-mentioned region of the BCL2L11 promoter paralleling t...

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Ponatinib treatment in chronic myeloid leukemia cell lines targets aurora kinase A/FOXM1 axis

“…6 In a series of previous studies, we ascribed the down-regulation of several tumor suppressor genes (the β-catenin antagonist Chibby, the pro-apoptotic BCL2-interacting mediator BIM, and GADD45a itself) to the hypermethylated state of promoter sequences controlling transcription rate. [7][8][9] Based on these observations, it will be worth trying the clinical advantage of combination approaches including epigenetic drugs for salvage therapy of multi-TKI-resistant CML patients. 10…”

DNA methylation polymerase chain reaction (PCR) array of apoptosis-related genes in pleomorphic adenomas of the salivary glands

“…[37][38][39] BCL2 L11 silencing has been described in cancers, such as lymphomas, leukemia, and renal cell carcinoma, but the molecular mechanisms driving this phenomenon are poorly understood. [40][41][42][43] Bell et al 44 evaluated the DNA methylation profile in salivary gland adenoid cystic carcinoma, and BCL2 L11 was among the hypermethylated genes in this salivary gland tumor. However, the impact of methylation in the transcription of this gene was not evaluated in their study.…”