ASXL1/2 mutations and myeloid malignancies

Myeloid malignancies develop through the accumulation of genetic and epigenetic alterations that dysregulate hematopoietic stem cell (HSC) self-renewal, stimulate HSC proliferation and result in differentiation defects. The polycomb group (PcG) and trithorax group (TrxG) of epigenetic regulators act antagonistically to regulate the expression of genes key to stem cell functions. The genes encoding these proteins, and the proteins that interact with them or affect their occupancy at chromatin, are frequently mutated in myeloid malignancies. PcG and TrxG proteins are regulated by Enhancers of Trithorax and Polycomb (ETP) proteins. ASXL1 and ASXL2 are ETP proteins that assemble chromatin modification complexes and transcription factors. ASXL1 mutations frequently occur in myeloid malignancies and are associated with a poor prognosis, whereas ASXL2 mutations frequently occur in AML with t(8;21)/RUNX1-RUNX1T1 and less frequently in other subtypes of myeloid malignancies. Herein, we review the role of ASXL1 and ASXL2 in normal and malignant hematopoiesis by summarizing the findings of mouse model systems and discussing their underlying molecular mechanisms.

Automated summary

Myeloid malignancies are caused by the accumulation of genetic and epigenetic alterations that interfere with hematopoietic stem cell (HSC) self-renewal, increase HSC proliferation, and cause differentiation defects. The polycomb group (PcG) and trithorax group (TrxG) of epigenetic regulators play opposing roles in regulating the expression of genes essential for stem cell functions. The genes encoding these proteins and the proteins that interact with them or affect their presence on chromatin are frequently mutated in myeloid malignancies. Enhancers of Trithorax and Polycomb (ETP) proteins regulate PcG and TrxG proteins. ASXL1 and ASXL2, which are ETP proteins, form chromatin modification complexes and transcription factors. ASXL1 mutations are often found in myeloid malignancies and are associated with a poor prognosis, while ASXL2 mutations are more common in AML with t(8;21)/RUNX1-RUNX1T1 and less frequent in other subtypes of myeloid malignancies.