Down-regulation of MTSS1 is associated with a poor prognosis in acute myeloid leukemia and differentially affects responses to different drugs

Acute myeloid leukemia (AML) is an aggressive malignancy of hematopoietic cells. Despite recent approvals of targeted drugs, chemotherapy with cytosine arabinoside (araC) and an anthracycline like daunorubicin remains an important pillar of treatment. In a previous work, we have shown that MTSS1 is down-regulated at relapse compared to diagnosis of AML and its down-regulation was previously implicated in aggressiveness of solid tumors. Our results showed that MTSS1 expression was regulated by methylation and reduced by araC and daunorubicin. Experimental down-regulation rendered human AML cell lines more resistant to araC, daunorubicin, and eight additional drugs. In contrast, venetoclax, a BCL2 inhibitor, was more effective towards cells with low MTSS1 expression. A CRISPR/Cas9-mediated knock-out of the MTSS1 gene was used to generate insight into the molecular changes induced by the down-regulation of MTSS1. The knock-out led to the deregulation of > 900 genes which included numerous target genes of transcription factors with a confirmed role in hematopoiesis and AML. A gene ontology analysis of the differentially expressed genes revealed that genes linked to transcription, cell cycle, and immune response were strongly affect. In summary, down-regulation of MTSS1 is associated with primary and secondary chemotherapy resistance in AML. In experimental models, it confers refractoriness to several cytotoxic drugs, yet sensitizes cells to venetoclax, pointing towards ways to overcome therapy resistance in MTSS1low AML. Gene expression profiles of TF-1 MTSS1 knock-out pools and TF-1 control pools, in triplicate for the knock-out and duplicate for the control, using Illumina HiSeq 2500. MTSS1 was knocked-out in TF-1 cells by CRISPR/Cas9 and pools of 4 clones each were preapred.