EZH2 Inhibitor DZNep Induces Apoptosis In Adult T-Cell Leukemia/Lymphoma Cells By BCL2 Suppression Via Regulation Of Mir-181a

Adult T-cell leukemia/lymphoma (ATL) is a mature T-cell neoplasm originating from human T-cell leukemia virus type-1 (HTLV-1) infected cells. Its clinical behavior differs among patients and is sub-classified into 4 sub-types: smoldering and chronic as indolent subtypes, and acute and lymphoma as aggressive subtypes. Prognosis for patients with the aggressive subtypes is very poor with standard chemotherapy, thus a new therapeutic approach is urgently needed. Previously, we reported that EZH2, a part of the PRC2 complex, not only methylates histone, but also serves as a recruitment platform for DNA methyltransferases that methylate the promoter regions of target genes (tumor suppressor gene and miRNAs) and is overexpressed in ATL cells. We found that ATL cell lines were sensitive to DZNep (3-deazaneplanosin A), which has been shown to deplete EZH2 expression, and their proliferation was attenuated. In the present study, we clarified which target genes and miRNAs are involved in DZNep-induced ATL cell death.

We performed microarray analyses using the ATL cell lines KK1, SO4, LMY1, and KOB to compare their gene expression profiles between cells treated and untreated with DZNep. The results showed that BCL2 transcripts in ATL cell lines were commonly suppressed by DZNep. In accordance with those findings, quantitative PCR analysis revealed that BCL2 transcripts were suppressed in DZNep-treated as compared to untreated ATL cell lines. We also confirmed that EZH2 and BCL2 protein expressions were clearly suppressed in the ATL cell lines by DZNep. These findings indicated that DZNep suppresses BCL2 expression at the transcriptional level in ATL cells. In addition, we performed another set of microarray analyses for miRNA expression profiles using primary ATL cells obtained from ATL patients and CD4 positive T-cells from healthy volunteers. The ATL cells showed decreased expression levels of several miRNAs, such as miR-101, miR-126, and miR-181a. Importantly, miR-181a has been shown to be regulated by EZH2, while miR-181a is a candidate negative regulator of BCL2 expression. Quantification of miR-181a transcripts to determine whether miR-181a is induced by DZNep showed that miR-181a was up-regulated in ATL cells by DZNep. These results strongly support the notion that miR-181a is suppressed by EZH2 and that BCL2 expression is regulated by miR-181a in ATL cells. Together, our findings indicate a unique apoptotic pathway of BCL2 suppression via miR181a and that the EZH2 inhibitor DZNep may become a novel therapeutic agent for ATL.

No relevant conflicts of interest to declare.