Tumor-derived neomorphic mutations in ASXL1 impairs the BAP1-ASXL1-FOXK1/K2 transcription network

Additional sex combs-like 1 (ASXL1) interacts with BRCA1-associated protein 1 (BAP1) deubiquitinase to oppose the polycomb repressive complex 1 (PRC1)-mediated histone H2A ubiquitylation. Germline BAP1 mutations are found in a spectrum of human malignancies, while ASXL1 mutations recurrently occur in myeloid neoplasm and are associated with poor prognosis. Nearly all ASXL1 mutations are heterozygous frameshift or nonsense mutations in the middle or to a less extent the C-terminal region, resulting in the production of C-terminally truncated mutant ASXL1 proteins. How ASXL1 regulates specific target genes and how the C-terminal truncation of ASXL1 promotes leukemogenesis are unclear. Here, we report that ASXL1 interacts with forkhead transcription factors FOXK1 and FOXK2 to regulate a subset of FOXK1/K2 target genes. We show that the C-terminally truncated mutant ASXL1 proteins are expressed at much higher levels than the wild-type protein in ASXL1 heterozygous leukemia cells, and lose the ability to interact with FOXK1/K2. Specific deletion of the mutant allele eliminates the expression of C-terminally truncated ASXL1 and increases the association of wild-type ASXL1 with BAP1, thereby restoring the expression of BAP1-ASXL1-FOXK1/K2 target genes, particularly those involved in glucose metabolism, oxygen sensing, and JAK-STAT3 signaling pathways. In addition to FOXK1/K2, we also identify other DNA-binding transcription regulators including transcription factors (TFs) which interact with wild-type ASXL1, but not C-terminally truncated mutant. Our results suggest that ASXL1 mutations result in neomorphic alleles that contribute to leukemogenesis at least in part through dominantly inhibiting the wild-type ASXL1 from interacting with BAP1 and thereby impairing the function of ASXL1-BAP1-TF in regulating target genes and leukemia cell growth.

Effect of sex combing protein 1 on proliferation and differentiation of osteoblasts in inflammatory microenvironment / 中国组织工程研究

BACKGROUND: Studies have shown that the loss of sex combing protein 1 (Asxl1) can lead to the occurrence of bone dysplasia and bone defects, but the relationship between this factor and bone destruction in the microenvironment of apical periodontitis has not been reported. OBJECTIVE: To study the effect of Asxl1 on proliferation and differentiation of osteoblasts in an inflammatory microenvironment. METHODS: MC3T3-E1 cells were excited by lipopolysaccharide to establish an in vitro inflammatory microenvironment. The best concentration and optimal action time of lipopolysaccharide were screened by cell counting kit-8 test. MC3T3-E1 cells were then stimulated with 20 mg/L lipopolysaccharide for 24 hours. The expression levels of Asxl1 protein and mRNA were detected by immunofluorescence and real-time PCR, respectively. After lipopolysaccharide stimulated the formation of inflammatory microenvironment, Asxl1-Si RNA was transfected for 24 hours, cell counting kit-8 was applied to detect the activity of cell proliferation, and real-time PCR was used to detect the expression levels of Asxl1 and osteogenic related genes ALP and RUNX2 mRNA. RESULTS AND CONCLUSION: After lipopolysaccharides stimulation of MC3T3-E1 cells, the expression levels of Asxl1 protein and mRNA were decreased. Under the inflammatory microenvironment, the proliferation activity of MC3T3-E1 cells transfected with Asxl1-Si RNA for 24 hours was significantly decreased, and the expression levels of Asxl1, ALP and RUNX2 mRNA were markedly decreased. These findings indicate that Asxl1 may influence the proliferation and differentiation of osteoblasts by involvement in the process of inflammatory reaction, thereby participating in bone destruction.

A de novo truncating mutation in ASXL1 associated with segmental overgrowth

Mutations in genes involved in chromatin remodelling have been implicated in broad phenotypes of congenital abnormalities and neurodevelopment. However, limited genotype–phenotype correlations are available for some of the rarestgenetic disorders that affect chromatin regulation. We hereby describe a 12-year-old girl presented at birth with severe hypotonia, developmental delay, a mid-line capillary malformation and distinctive craniofacial features. During the natural history of her disease, the girl developed severe spasticity and drug-resistant seizures, leading to a diagnosis of Bohring–Opitz syndrome (BOS). We performed whole-exome sequencing (WES) and identified a de novo mutation in ASXL1 (c.2033dupG) which results in the introduction of a premature stop codon (p.R678fs*6). ASXL1 encodes a polycomb repressive complex protein implicated in chromatin regulation and de novo mutations are a known cause of BOS. Phenotypes with segmental craniofacial overgrowth associated to midline capillary malformations enlarge the clinical spectrum of BOS at onset and further expand the differential diagnosis in ASXL1 mutation carriers.

Poor Prognostic Implication of ASXL1 Mutations in Korean Patients With Chronic Myelomonocytic Leukemia

BACKGROUND: Molecular genetic abnormalities are observed in over 90% of chronic myelomonocytic leukemia (CMML) cases. Recently, several studies have demonstrated the negative prognostic impact of ASXL1 mutations in CMML patients. We evaluated the prognostic impact of ASXL1 mutations and compared five CMML prognostic models in Korean patients with CMML. METHODS: We analyzed data from 36 of 57 patients diagnosed as having CMML from January 2000 to March 2016. ASXL1 mutation analysis was performed by direct sequencing, and the clinical and laboratory features of patients were compared according to ASXL1 mutation status. RESULTS: ASXL1 mutations were detected in 18 patients (50%). There were no significant differences between the clinical and laboratory characteristics of ASXL1-mutated (ASXL1+) CMML and ASXL1-nonmutated (ASXL1−) CMML patients (all P>0.05). During the median follow-up of 14 months (range, 0–111 months), the overall survival (OS) of ASXL1+ CMML patients was significantly inferior to that of ASXL1− CMML patients with a median survival of 11 months and 19 months, respectively (log-rank P=0.049). An evaluation of OS according to the prognostic models demonstrated inferior survival in patients with a higher risk category according to the Mayo molecular model (log-rank P=0.001); the other scoring systems did not demonstrate a significant association with survival. CONCLUSIONS: We demonstrated that ASXL1 mutations, occurring in half of the Korean CMML patients examined, were associated with inferior survival. ASXL1 mutation status needs to be determined for risk stratification in CMML.

Mutations of ASXL1 gene in myelodysplastic syndromes / 白血病·淋巴瘤

Objective To investigate the mutations of epigenetic regulation factor ASXL1 gene in myelodysplastic syndrome(MDS).Methods Mutation analysis of ASXL1 gene in 53 de novo MDS patients and 20 healthy persons was performed by using polymerase chain reaction(PCR)followed by sequence analysis at DNA level.The clinical and laboratory characteristics were compared in MDS patients with ASXL1 gene mutation and ASXL1 wild type.ASXL1 mutation in mRNA level was detected by using reverse transcription PCR(RT-PCR)followed by sequence analysis.Results ASXL1 gene mutations were observed in 9 cases(16.9%)of 53 MDS patients.6 mutation types were detected,including 4 frameshift mutations types(2 cases with p.Glu635ArgfsX15,3 cases with p.Gly646TrpfsX12,1 case with p.Ala640GlyfsX14 and 1 case with p.Gly790TrpfsX10)and 2 nonsense mutation types(1 case with p.Gln1063X and 1 case with p.Gln695X).All the mutations were heterozygous,and p.Gly790TrpfsX10 and p.Gln695X were new mutation types.In addition,a single nucletide polymorphism(SNP)p.Gly652Ser was also detected in 4 cases with MDS.5 cases of p.G652S SNP and 1 case of p.Leu1173Leu SNP were detected in 20 healthy people.Frameshift mutation(p.Gly646TrpfsX12)could be detected at mRNA level by using RT-PCR.Differences were not observed in red blood cell counts,white blood cell counts,platelet counts,hemoglobin levels,reticulocyte,neutrophil granulocyte,the peripheral blood lymphocytes percentage,T-cell subsets in the peripheral blood,the proportion of primitive cell in the marrow and MDS types between the patients with ASXL1 gene mutation and ASXL1 wild type patients(P >0.05).Conclusion There is a high frequency of ASXL1 gene mutation in MDS patients,which can be detected at mRNA level.

Mutations of ASXL1 gene in myelodysplastic syndromes / 白血病·淋巴瘤

Objective To investigate the mutations of epigenetic regulation factor ASXL1 gene in myelodysplastic syndrome(MDS).Methods Mutation analysis of ASXL1 gene in 53 de novo MDS patients and 20 healthy persons was performed by using polymerase chain reaction(PCR)followed by sequence analysis at DNA level.The clinical and laboratory characteristics were compared in MDS patients with ASXL1 gene mutation and ASXL1 wild type.ASXL1 mutation in mRNA level was detected by using reverse transcription PCR(RT-PCR)followed by sequence analysis.Results ASXL1 gene mutations were observed in 9 cases(16.9%)of 53 MDS patients.6 mutation types were detected,including 4 frameshift mutations types(2 cases with p.Glu635ArgfsX15,3 cases with p.Gly646TrpfsX12,1 case with p.Ala640GlyfsX14 and 1 case with p.Gly790TrpfsX10)and 2 nonsense mutation types(1 case with p.Gln1063X and 1 case with p.Gln695X).All the mutations were heterozygous,and p.Gly790TrpfsX10 and p.Gln695X were new mutation types.In addition,a single nucletide polymorphism(SNP)p.Gly652Ser was also detected in 4 cases with MDS.5 cases of p.G652S SNP and 1 case of p.Leu1173Leu SNP were detected in 20 healthy people.Frameshift mutation(p.Gly646TrpfsX12)could be detected at mRNA level by using RT-PCR.Differences were not observed in red blood cell counts,white blood cell counts,platelet counts,hemoglobin levels,reticulocyte,neutrophil granulocyte,the peripheral blood lymphocytes percentage,T-cell subsets in the peripheral blood,the proportion of primitive cell in the marrow and MDS types between the patients with ASXL1 gene mutation and ASXL1 wild type patients(P >0.05).Conclusion There is a high frequency of ASXL1 gene mutation in MDS patients,which can be detected at mRNA level.

Correlation of Genomic Characteristic with Disease Progression in Polycythemia Vera / 天津医药

Objective To screen mutations in genes including ASXL1, TET2, IDH1, IDH2, SETBP1, MPL515, JAK2 exon 12 and JAK2V617 in 135 polycythemia vera (PV) patients. To assess progreasson and genomics characteristics post polycythemic myelofibrosis. Methods DNA sequencing of ASXL1(Exon12),TET2 (Exons 3-11),IDH1(Exon4),IDH2(Ex-on4),SEPBP1(Exon4),JAK2 exon 12 and MPL515 (Exon 10) genes were carried out using Sanger method. JAK2V617 muta-tion was detected by allele-specific PCR in patients with PV. In the mean time, the mutation load of JAK2V617F allele (V617F%) was evaluated by real-time PCR using Tagman MGB probe. Then, the significant of gene mutations and clinical outcomes of post-PV Myelofibrosis(PPMF)was analyzed. To study risk factors of PPMF, logistic regression were employed. Results ASXL1, TET2, IDH1, IDH2 were mutated in 7.69%(8/104), 5.26%(1/19) , 0.08%(1/120) and 0.08%(1/121) of all PV patient respectively. JAK2 was mutated in 82.22%(111/135) of PV patients with mutation rate of exon12 of 2.96%(4/135) and there were no mutation of MPL515 and SETBP1 in PV patients. ASXL1 mutation was found in 31.82%(7/22) PPMF patients. Spearman analysis showed that ASXL1 is correlated with JAK2V617F (V617F%) (rs=0.298,P=0.002). The hemo-globin was lower in patients with ASXL1 mutation than patient without mutation (wild type). Leukocyte count, V617F%>50%rate, thrombosis and PPMF were higher in patients with ASXL1 mutation than that of ASXL1 wild type(P＜0.05). ASXL1 mu-tation, V617F%>50% rate and splenomegaly were all risk factors of PPMF. Conclusion ASXL1 mutation is the risk-fac-tor of PPMF and may promote V617F%by some mechanism.