Additional Sex Comb-like (ASXL) Proteins 1 and 2 Play Opposite Roles in Adipogenesis via Reciprocal Regulation of Peroxisome Proliferator-activated Receptor γ

Abstract

Our previous studies have suggested that the mammalian additional sex comb-like 1 protein functions as a coactivator or repressor of retinoic acid receptors in a cell-specific manner. Here, we investigated the roles of additional sex comb-like 1 proteins in regulating peroxisome proliferator-activated receptors (PPARs). In pulldown assays in vitro and in immunoprecipitation assays in vivo, ASXL1 and its paralog, ASXL2, interacted with PPAR␣ and PPAR␥. In 3T3-L1 preadipocyte cells, overexpression of ASXL1 inhibited the induction of PPAR␥ activity by rosiglitazone, as shown by transcription assays, and completely suppressed adipogenesis, as shown by Oil Red O staining. In contrast, overexpression of ASXL2 greatly enhanced rosiglitazone-induced PPAR␥ activity and enhanced adipogenesis. Deletion of the heterochromatin protein 1 (HP1)-binding domain from ASXL1 caused the mutant protein to enhance adipogenesis similarly to ASXL2, indicating that HP1 binding is required for the adipogenesis-suppressing activity of ASXL1. Adipocyte differentiation was associated with a gradual decrease in ASXL1 expression but did not affect ASXL2 expression. Knockdown of ASXL1 and ASXL2 had reciprocal effects on adipogenesis. In chromatin immunoprecipitation assays in 3T3-L1 cells, ASXL1 occupied the promoter of the PPAR␥ target gene aP2 together with HP1␣ and Lys-9-methylated histone H3, whereas ASXL2 occupied the aP2 promoter together with histone-lysine N-methyltransferase MLL1 and Lys-9-acetylated and Lys-4-methylated H3 histones. Finally, microarray analysis demonstrated that ASXL1 represses, whereas ASXL2 increases, the expression of adipogenic genes, most of which are PPAR␥ targets. These results suggest that members of the additional sex comb-like family provide complex regulation of adipogenesis via differential modulation of PPAR␥ activity.

Myelodysplastic syndromes are induced by histone methylation–altering ASXL1 mutations

“…Additional sex combs-like 1 (ASXL1) is 1 of 3 mammalian homologs of the Drosophila additional sex combs (Asx), and plays critical roles both in activation and suppression of Hox genes in axial patterning through regulating the polycomb group and trithorax group proteins (1)(2)(3)(4). ASXL1 is mutated in patients with the entire spectrum of myeloid malignancies including 11%-21% of patients with myelodysplastic syndrome (MDS) (5-8), 10%-15% of patients with myeloproliferative neoplasms (MPNs), 5%-25% of patients with acute myeloid leukemia (AML) (5,7), and 43%-58% of patients with chronic myelomonocytic leukemia (CMML) (6,7,9,10).…”

The BAP1/ASXL2 Histone H2A Deubiquitinase Complex Regulates Cell Proliferation and Is Disrupted in Cancer

“…A, comparison between BAP1 and UCH37. tsUCH37 of the worm T. spiralis, whose crystal structure was recently reported (38), was aligned with human UCH37 and BAP1. The functionally conserved domains between BAP1 and tsUCH37 are shown in the left panel.…”

ASXL1 mutations identify a high-risk subgroup of older patients with primary cytogenetically normal AML within the ELN Favorable genetic category

“…44 The ASXL1 protein modulates gene expression induced by retinoic acid receptors (RARs) and peroxisome proliferator-activated receptors, at least in part through affecting histone methylation. 45,46 Thereby, ASXL1 is involved in pathways controlling cell proliferation and differentiation in the hematopoietic system and other tissues. 44 Most reported ASXL1 mutations are predicted to truncate the protein before the RAR-binding domain ( Figure 1A), but it is largely unknown how this affects gene expression in AML.…”