Epigenetic down-regulation of BIM expression is associated with reduced optimal responses to imatinib treatment in chronic myeloid leukaemia.
BACKGROUND
Expression of the pro-apoptotic BCL-2-interacting mediator (BIM) has recently been implicated in imatinib-induced apoptosis of BCR-ABL1(+) cells. However, the mechanisms involved in the regulation of BIM in CML and its role in the clinical setting have not been established.


METHODS
We analysed the mRNA expression of BIM in 100 newly diagnosed patients with CML in chronic phase by Q-RT-PCR and the protein levels by Western blot analysis. Methylation status was analysed by bisulphite genomic sequencing and MSP. CML cell lines were treated with imatinib and 5-aza-2'-deoxycytidine, and were transfected with two different siRNAs against BIM and cell proliferation and apoptosis were analysed.


RESULTS
We demonstrated that down-regulation of BIM expression was present in 36% of the patients and was significantly associated with a lack of optimal response to imatinib as indicated by the decrease in cytogenetic and molecular responses at 6, 12 and 18 months in comparison with patients with normal BIM expression (p<0.05). Expression of BIM was mediated by promoter hypermethylation as demonstrated by restoration of BIM expression after treatment of CML cells with 5-aza-2'-deoxycytidine. Using CML cell lines with low and normal expression of BIM we further demonstrated that the expression of BIM is required for imatinib-induced CML apoptosis.


CONCLUSIONS
Our data indicate that down-regulation of BIM is epigenetically controlled by methylation in a percentage of CML patients and has an unfavourable prognostic impact, and that the combination of imatinib with a de-methylating agent may result in improved responses in patients with decreased expression of BIM.
San José-Eneriz
Edurne
E
Hematology Department and Area of Cell Therapy, Clinica Universitaria, Foundation for Applied Medical Research, University of Navarra, Pamplona, Spain.
Agirre
Xabier
X
Jiménez-Velasco
Antonio
A
Cordeu
Lucia
L
Martín
Vanesa
V
Arqueros
Victor
V
Gárate
Leire
L
Fresquet
Vicente
V
Cervantes
Francisco
F
Martínez-Climent
José A
JA
Heiniger
Anabel
A
Torres
Antonio
A
Prósper
Felipe
F
Roman-Gomez
Jose
J
D000328:Adult; D000970:Antineoplastic Agents / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis* / Q000235:genetics; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D000072224:Bcl-2-Like Protein 11; D001549:Benzamides; D049109:Cell Proliferation / Q000187:drug effects; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors; D000077209:Decitabine; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics*; D004353:Drug Evaluation, Preclinical / Q000379:methods; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D044127:Epigenesis, Genetic; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D008875:Middle Aged; D010879:Piperazines / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000235:genetics; D011743:Pyrimidines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D001549:Benzamides; D008565:Membrane Proteins; D010879:Piperazines; D011518:Proto-Oncogene Proteins; D011743:Pyrimidines; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D000077209:Decitabine; D000068877:Imatinib Mesylate; D015254:DNA Modification Methylases; D001374:Azacitidine