SRSF2 Mutation Cooperates with ASXL1 Mutation to Promote the Development of Myeloproliferative Variant of Chronic Myelomonocytic Leukemia

Introduction:

Chronic myelomonocytic leukaemia (CMML) is a heterogenous haematopoietic stem cell (HSC) disorder characterized by sustained (>3 months) relative (≥10%) and absolute (≥0.5×109/L) monocytosis in peripheral blood (PB), and subclassified into two groups based on a white blood cell count (WBC) of PB: myelodysplastic CMML (MDS-CMML) (WBC<13×10⁹/L) and myeloproliferative CMML (MPN-CMML) (WBC ≥13×10⁹/L). CMML is a rare, age-related disease, has a poor prognosis and can easily transform into acute myeloid leukaemia (AML), especially MPN-CMML. Over 90% of CMML carry one or more somatic gene mutations, such as TET2, ASXL1, and SRSF2. As a well-known adverse prognostic factor of CMML, ASXL1 mutation frequently co-occurs with other gene mutations.

Methods:

A cohort of 66 CMML patients was defined according to WHO 2022 criteria from the Department of Haematology, Guangdong Provincial People's Hospital, within the last 6 years. The study was approved by the Ethnic Committee of Guangdong Provincial People's Hospital (GDREC2019041H).

Results:

In our study, we found that most patients with CMML had one or more gene mutations: 39 had the ASXL1 mutation (59%), 27 had the TET2 mutation (41%), and 26 had the SRSF2 mutation (39%) . ASXL1 mutation, an adverse prognostic molecular abnormality associated with CMML, always co-occurred with other gene mutations, approximately 86% of ASXL1 mutant patients. Among those co-occurring genes, RNA splicing factors, especially SRSF2 mutation, occurred most frequently (19/39, 48%) . Furthermore, patients of CMML that co-mutant with ASXL1 and SRSF2 (ASXL1/SRSF2 mutant) had worse outcomes, i.e., both overall survival and leukaemia-free survival, than patients with ASXL1 mutation only (ASXL1 mutant), SRSF2 mutation only (SRSF2 mutant), and ASXL1/SRSF2 wildtype (ASXL1/SRSF2 WT). Moreover, ASXL1/SRSF2 mutant patients were more likely to developed into MPN-CMML (13/19,68%) than other three genotypes, with increased cellularity of karyocytes and monocytes both in PB and BM.

To further identify the mechanisms of ASXL1/SRSF2 mutant-induced leukaemogenesis of CMML, we performed RNA-sequencing using BM cells collected from CMML patients with ASXL1/SRSF2 mutation, ASXL1 mutation, SRSF2 mutation, and ASXL1/SRSF2 WT. A significant difference in the transcriptome profile was observed amongst ASXL1/SRSF2 mutant patients compared with ASXL1/SRSF2 WT patients. Moreover, we performed differential expression analysis and found that ASXL1/SRSF2 mutant cells were particularly evident, exhibited 44.1% upregulated differentially expressed genes (DEGs) and 47.7% downregulated DEGs, specifically distinct from ASXL1 mutant and SRSF2 mutant cells. Gene set enrichment analysis (GSEA) of the RNA-seq data further revealed the upregulation of specific gene pathways in ASXL1/SRSF2 mutant cells when compared with ASXL1 and SRSF2 mutant cells, including TP53 associated regulation, tumor associated pathway, and haematopoiesis associated pathway, such as myeloid leukocyte differentiation & migration, myeloid leukocyte cytokine production, and HSC/HPC associated pathway. While histone & DNA modification, DNA repair, transcription and translation regulation, and cell death & senescence-associated pathways were downregulated .

Conclusion:

This study demonstrated that ASXL1 and SRSF2 mutations co-occurred frequently in CMML, and these patients had a greater likelihood of developing the MPN-CMML phenotype. Importantly, ASXL1/SRSF2 co-mutant patients with CMML had more adverse outcomes, compared to those with the other three genotypes. Mechanistically, the co-existence of SRSF2 and ASXL1 mutation induces an increase in a biased commitment to myeloid development myeloid lineage commitment and upregulated tumorigenicity-associated genes, whereas cell death & senescence-associated pathways were downregulated. Future studies assessing the mechanism of monocytosis and specific therapies for ASXL1/SRSF2 mutant patients are ongoing.

Disclosures

No relevant conflicts of interest to declare.

No relevant conflicts of interest to declare.