BCL6 promotes the methotrexate-resistance by upregulating ZEB1 expression in children with acute B lymphocytic leukemia

OBJECTIVE: To investigate the effect of BCL6 on methotrexate-resistant children with acute B lymphoblastic leukemia (B-ALL) and its underlying mechanism. PATIENTS AND METHODS: Bone marrow samples of B-ALL children diagnosed at The Children & Women's Healthcare of Laiwu City from June 2014 to February 2017 were collected. Subjects were assigned into methotrexate-resistant group (n=8) and non-resistant group (n=32) according to the follow-up outcome. Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) was performed to detect expressions of BCL6 and E-cadherin in bone marrow tissues. Cell cycle and apoptosis of methotrexate-resistant B-ALL cells (BALL-1/MTXR cells) were detected after overexpression or inhibition of BCL6, respectively. Western blot was performed to determine the protein levels of E-cadherin and BCL6. The direct binding of BCL6 in the ZEB1 promoter region was verified by the ChIP (chromatin immunoprecipitation) assay. RESULTS: QRT-PCR showed a higher BCL6 expression in bone marrow samples of methotrexate-resistant group than that of the non-resistant group. Moreover, BCL6 was upregulated in BALL-1/MTXR cells than that of untreated B-ALL cells. After knockdown of BCL6 expression, we observed a decreased IC50, increased apoptosis, and arrested the cell cycle in BALL-1/MTXR cells. In addition, increased expression of E-cadherin was found in BALL-1/MTXR cells, which could be reversed by ZEB1 overexpression. ChIP assay suggested that BCL6 bound to the promoter region of ZEB1, so as to promote ZEB1 expression. CONCLUSIONS: BCL6 is overexpressed in the bone marrow of methotrexate-resistant children with B-ALL, which is capable of attenuating the sensitivity of B-ALL to methotrexate via promoting ZEB1 expression.