ASXL1

ASXL1 Full Name

additional sex combs like transcriptional regulator 1

ASXL1 Introduction

ASXL1, also known as Additional Sex Combs Like 1, is a nuclear protein that functions as a scaffold for chromatin-modifying complexes, particularly those involved in the regulation of histone methylation and gene expression. The human ASXL1 gene is located on chromosome 20q11.21, spans approximately 28 kb, and contains 13 exons encoding a 1,541-amino-acid protein with a molecular weight of approximately 165 kDa. ASXL1 is a member of the ASXL family, which includes ASXL1, ASXL2, and ASXL3, all of which share a conserved N-terminal ASX homology domain (ASXH) and a C-terminal plant homeodomain (PHD) finger. ASXL1 is ubiquitously expressed in human tissues, with highest levels detected in the bone marrow, lymphoid tissues (spleen, thymus, lymph nodes), testis, and brain, and lower expression in the liver, kidney, and heart. Within the nucleus, ASXL1 associates with chromatin and serves as a core component of the polycomb repressive complex 1 (PRC1) and the enhancer of zeste homolog 2 (EZH2)-containing PRC2 complex, where it modulates their enzymatic activities. Unlike enzymes that directly add or remove histone modifications, ASXL1 lacks intrinsic catalytic activity but instead facilitates the recruitment and proper functioning of histone-modifying enzymes, including the deubiquitinase BAP1 (BRCA1-associated protein 1) and the methyltransferase EZH2.

Figure 1. ASXL1 in regulating the INK4B gene.

ASXL1 in Disease and Therapeutic Relevance
Genetic variations and dysregulation of ASXL1 are strongly associated with hematological malignancies, developmental disorders, and neurological diseases. Somatic mutations in the ASXL1 gene are among the most common genetic abnormalities in myeloid malignancies, including myelodysplastic syndromes (MDS), acute myeloid leukemia (AML), and chronic myelomonocytic leukemia (CMML), where mutant ASXL1 disrupts epigenetic regulation, leading to aberrant gene expression and malignant transformation. Germline mutations in ASXL1 are linked to Bohring-Opitz syndrome (BOS), a rare developmental disorder characterized by intellectual disability, developmental delay, and distinctive facial features. Additionally, ASXL1 dysregulation is implicated in neurological disorders such as autism spectrum disorder (ASD) and schizophrenia, where abnormal epigenetic regulation in the brain contributes to disease pathogenesis. The frequency of ASXL1 mutations is high in myeloid malignancies, with mutations detected in approximately 20–40% of MDS and CMML patients. ASXL1 holds therapeutic potential: targeting the epigenetic pathways regulated by ASXL1 could restore normal gene expression in cancer cells and diseased tissues, and ongoing research focuses on developing epigenetic therapies that modulate ASXL1 function for the treatment of myeloid malignancies and developmental disorders.

Role in Clonal Hematopoiesis and Age-Related Disease
ASXL1 mutations are also frequently found in clonal hematopoiesis of indeterminate potential (CHIP), a condition in which individuals without overt hematologic malignancy harbor a detectable somatic mutation in a fraction of their blood cells. ASXL1 mutations are among the top three most commonly mutated genes in CHIP (along with DNMT3A and TET2), with an estimated prevalence of 1-2% in individuals over 70 years of age. CHIP carriers have an increased risk of developing hematologic malignancies (MDS, AML, MPN), as well as an increased risk of cardiovascular disease, stroke, and all-cause mortality. The mechanism linking ASXL1-mutant CHIP to cardiovascular disease is thought to involve chronic inflammation: ASXL1-mutant macrophages and monocytes exhibit pro-inflammatory gene expression profiles (elevated IL-6, IL-1β, TNFα), which can accelerate atherosclerosis and promote thrombosis. This has led to the concept of "CHIP-related cardiovascular disease," where somatic mutations in hematopoietic cells contribute to non-hematologic disorders. Furthermore, ASXL1 mutations have been detected in other aging-related conditions, including idiopathic pulmonary fibrosis and chronic kidney disease, though the causal relationship remains to be established.

Alternate Names for ASXL1

ASXL1; additional sex combs like 1 (Drosophila); putative Polycomb group protein ASXL1; KIAA0978; Additional sex combs like 1 (Drosophila); Additional sex combs like protein 1; KIAA0978; Putative Polycomb group protein ASXL1; OTTHUMP00000030592; OTTHUMP00