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 i...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 leukemogen-esis 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-termi-nally 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-bind-ing 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.展开更多
文摘肺癌是全球发病率与死亡率均位于第一位的恶性肿瘤。肺腺癌(lung adenocarcinoma,LUAD)大约占整个肺癌的40%。但是,目前对肺腺癌发生发展的机制尚未阐明。TCGA在线数据库GEPIA证实,免疫球蛋白超级家族成员9(immunoglobulin superfamily member 9,IGSF9)在肺腺癌中的平均表达量是6.56,其在正常癌旁组织中的平均表达量是0.55,提示IGSF9在肺腺癌中的表达量是正常癌旁组织的11.93倍。人类蛋白组学数据库也提示,IGSF9在肺腺癌中高表达。通过qRT-PCR检测IGSF9在肺腺癌细胞中的表达量,发现其在A549和H1299细胞中的表达量分别是其在BEAS-2B细胞中的4.17倍和6.6倍。细胞功能实验发现,过表达IGSF9,其LUAD细胞的增殖能力显著增加。平板克隆形成实验发现,在A549细胞中,对照组平板克隆大约有240个,过表达IGSF9后,该组细胞的平板克隆数大约是385个,实验组的克隆数目是对照组的1.60倍(P<0.01)。敲低IGSF9,则LUAD细胞增殖能力明显降低。平板克隆形成实验发现,在H1299细胞中,对照组平板克隆大约有320个,敲低IGSF9后,该组细胞的平板克隆数大约是164个,实验组的克隆数目仅为对照组的51.25%(P<0.01)。生物信息学预测结合后期研究证实,IGSF9可显著抑制叉头蛋白K2(forkhead box protein K2,FOXK2)的表达。MTS实验发现,过表达FOXK2可显著逆转IGSF9对LUAD细胞增殖的促进作用,而敲低FOXK2则可明显补偿敲低IGSF9对LUAD细胞的增殖抑制作用。这些结果提示,IGSF9通过下调FOXK2从而促进LUAD细胞的增殖。
基金the National Key R&D Program of China(No.2016YFA0501800 to D.Y.2016YFC1303303 to C.Y.)+5 种基金the NSFC Grant(No.31871431 and No.31821002 to D.Y.81572761,81772655 and 81972646 to Y.T.)the Innovative Research Team of High-Level Local Universities in Shanghai(to D.Y.)the Recruitment Program of Global Experts of China(Y.T.)the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning(V.T.)Shanghai Rising-Star Program(Y.T.).
文摘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 leukemogen-esis 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-termi-nally 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-bind-ing 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.
