Clinical Significance of WDR5 High Expression and Its Effect on Tumorigenesis in Adult Leukemia

Background: Mixed-lineage leukemia (MLL) functions within the context of a large multiprotein complex including MLL, WDR5, RbBP5, and ASH2L that is required for maximal enzymatic activity. Each component is required for full histone H3 trimethyl Lysine 4（H3K4me3） methyltransferase activity of the complex. The structure-function analysis shows that WDR5 mediates interaction between the MLL catalytic unit and the core complex, as well as the histone H3 substrate. Recently it is found that blocking MLL1-WDR5 interaction by an inhibitor could result in the complex disassembly, inhibition methyltransferase activity and suppression of proliferation of leukemia cells.  Despite our growing knowledge about MLL1 fusion proteins and leukemia, very little is known about the role of WDR5 in leukemia.

Methods: The WDR5 expression was determined by qPCR in acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) patients. The genome-wide binding profiling of WDR5 and H3K4me3 was obtained by ChIP-seq. The effect of WDR5 on its target gene expression, cell proliferation and apoptosis was observed by qPCR, WST-1 cell proliferation assay and Annexin V-PE staining following the flow cytometry analysis, respectively, in leukemic cells with WDR5 shRNA knockdown 

Results: WDR5 expression is significantly increased in adult ALL and AML compared to that of normal bone marrow control. WDR5 high expression is associated with high risk factors in the patients. Also, its high expression is associated with MLL1 high expression; particularly the patients with WDR5 high expression plus MLL1 high expression has poor complete remission (CR) rate. We further identified the global genomic binding of WDR5 in RS4:11 ALL and THP-1 AML cells by ChIP-seq and detected more than 2000 binding peaks in the two leukemia cell lines. We also examined global H3K4me3 peaks, analyzed the correlation of WDR5 peaks with H3K4me3 peaks and found the genomic co-localization of WDR5 binding with H3K4me3 enrichment. Moreover, WDR5 knockdown by shRNA suppressed the cell proliferation, induced apoptosis, inhibited the expression of WDR5 targets on oncogenesis and anti-apoptosis, blocked the H3K4me3 enrichment on the promoter of these targets. We also observed the positive correlation of WDR5 expression with its targets in B-ALL and AML cohort.

Conclusion: WDR5 has oncogenic effect and WDR5-mediated H3K4 methylation plays important role in the leukemogenesis