Project description:Notch signaling regulates cell-fate decisions in several developmental processes and cell functions. However, a role for Notch in hepatic thrombopoietin (TPO) production remains unclear. We noted thrombocytopenia in mice with hepatic Notch1 deficiency, and so investigated TPO production and other features of platelets in these mice. We found that the liver ultrastructure and hepatocyte function were comparable between control mice and Notch1-deficient mice. However, the Notch1-deficient mice had significantly lower plasma TPO and hepatic TPO mRNA levels, concomitant with lower numbers of platelets and impaired megakaryocyte differentiation and maturation, which were rescued by addition of exogenous TPO. Additionally, JAK2/STAT3 phosphorylation was significantly inhibited in Notch1-deficient hepatocytes, consistent with the RNA-seq analysis. JAK2/STAT3 phosphorylation and TPO production was also impaired in cultured Notch1-deficient hepatocytes after treatment with desialylated platelets. Consistently, hepatocyte-specific Notch1 deletion inhibited JAK2/STAT3 phosphorylation and hepatic TPO production induced by administration of desialylated platelets in vivo. Interestingly, Notch1 deficiency downregulated the expression of HES5 but not HES1. Moreover, desialylated platelets promoted the binding of HES5 to JAK2/STAT3, leading to JAK2/STAT3 phosphorylation and pathway activation in hepatocytes. Hepatocyte Ashwell-Morell receptor (AMR) (asialoglycoprotein receptor 1, ASGR1) physically associates with Notch1 and inhibition of AMR impaired Notch1 signaling activation and hepatic TPO production. Furthermore, blockage of Dll4 on desialylated platelets inhibited hepatocyte Notch1 activation and HES5 expression, JAK2/STAT3 phosphorylation and subsequent TPO production. In conclusion, our study identifies a novel regulatory role of Notch1 in hepatic TPO production, indicating that it might be a target for modulating TPO level.
Project description:Somatic NOTCH1 mutations are found in ~60% of T lineage acute lymphoblastic leukemias (T-ALLs). Notch1 is cleaved by γ secretase to generate activated Notch intracellular domain (NICD) proteins. The NOTCH1 mutations found in T-ALL constitutively activate Notch1 signaling by increasing NICD levels. Genetic alterations in components of the Ras/PI3 kinase (PI3K)/Akt pathway are also highly prevalent in T-ALL, and often coexist with NOTCH1 mutations. Exposing a T-ALL cell line to the PI3 kinase (PI3K) inhibitor GDC-0941 generated drug resistant clones that down-regulated NICD expression. To address the in vivo relevance of this unexpected observation, we transplanted primary wild-type (WT) and KrasG12D mutant T-ALLs into recipient mice, and treated them with GDC-0941 alone and in combination with the MEK inhibitor PD0325901 (PD901). Although many leukemias responded dramatically to these targeted agents in vivo, drug-resistant clones invariably emerged. Multiple resistant T-ALLs lost NICD expression through mechanisms that included loss of Notch1 mutations found in the parental T-ALL. These GDC-0941-resistant leukemias exhibited reduced expression of many Notch1 target genes, elevated levels of phosphorylated Akt (pAkt), and displayed cross-resistance to γ secretase inhibitors (GSIs). Consistent with these data, inhibiting Notch1 activity in T-ALL cells enhanced PI3K signaling, providing a likely mechanism for in vivo selection against clones with Notch1 pathway activation. Thus, oncogenic Notch1 mutations that promote clonal outgrowth during malignant transformation unexpectedly “switch” to become deleterious during treatment with a PI3K inhibitor. These data advance our understanding of T-ALL pathogenesis and have implications for implementing new therapeutic regimens. We analyzed 28 mouse T-ALL samples obtained after in vivo treatment with GDC-0941 alone or GDC-0941 + PD0325901. These T-ALL samples are either Kras wild type or harbor a KrasG12D mutations.
Project description:Somatic NOTCH1 mutations are found in ~60% of T lineage acute lymphoblastic leukemias (T-ALLs). Notch1 is cleaved by γ secretase to generate activated Notch intracellular domain (NICD) proteins. The NOTCH1 mutations found in T-ALL constitutively activate Notch1 signaling by increasing NICD levels. Genetic alterations in components of the Ras/PI3 kinase (PI3K)/Akt pathway are also highly prevalent in T-ALL, and often coexist with NOTCH1 mutations. Exposing a T-ALL cell line to the PI3 kinase (PI3K) inhibitor GDC-0941 generated drug resistant clones that down-regulated NICD expression. To address the in vivo relevance of this unexpected observation, we transplanted primary wild-type (WT) and KrasG12D mutant T-ALLs into recipient mice, and treated them with GDC-0941 alone and in combination with the MEK inhibitor PD0325901 (PD901). Although many leukemias responded dramatically to these targeted agents in vivo, drug-resistant clones invariably emerged. Multiple resistant T-ALLs lost NICD expression through mechanisms that included loss of Notch1 mutations found in the parental T-ALL. These GDC-0941-resistant leukemias exhibited reduced expression of many Notch1 target genes, elevated levels of phosphorylated Akt (pAkt), and displayed cross-resistance to γ secretase inhibitors (GSIs). Consistent with these data, inhibiting Notch1 activity in T-ALL cells enhanced PI3K signaling, providing a likely mechanism for in vivo selection against clones with Notch1 pathway activation. Thus, oncogenic Notch1 mutations that promote clonal outgrowth during malignant transformation unexpectedly “switch” to become deleterious during treatment with a PI3K inhibitor. These data advance our understanding of T-ALL pathogenesis and have implications for implementing new therapeutic regimens.
Project description:Oncogenic mutations of KRAS are found in the most aggressive human tumors, including colorectal cancer. It has been suggested that oncogenic KRAS phosphorylation at Ser181 modulates its activity and favors cell transformation. Using non-phosphorylatable (S181A), phosphomimetic (S181D) and phospho/dephosphorylatable (S181) oncogenic KRAS mutants, we analyzed the role of this phosphorylation to the maintenance of tumorigenic properties of colorectal cancer cells. Our data show that the presence of phospho/dephosphorylatable oncogenic KRAS is required for preserving the epithelial organization of colorectal cancer cells in 3D cultures, and for supporting subcutaneous tumor growth in mice. Interestingly, gene expression differed according to the phosphorylation status of KRAS. In DLD-1 cells, CTNNA1 was only expressed in phospho/dephosphorylatable oncogenic KRAS expressing cells, correlating with cell polarization. Moreover, lack of oncogenic KRAS phosphorylation leaded to changes in expression of genes related to cell invasion, such as SERPINE1, PRSS1,2,3 and NEO1, and expression of phosphomimetic oncogenic KRAS resulted in diminished expression of genes involved in enterocyte differentiation, such as HNF4G. Finally, the analysis, in a public data set of human colorectal cancer, of the gene expression signatures associated to phosphomimetic and non-phosphorylatable oncogenic KRAS suggests that this post-translational modification regulates tumor progression in patients
Project description:The main oncogenic driver in T-lymphoblastic leukemia (T-LL) is NOTCH1, which activates genes by forming chromatin-associated Notch transcription complexes. Gamma-secretase (GSI) inhibitor treatment prevents NOTCH1 nuclear localization, but most genes with NOTCH1 binding sites are insensitive to GSI. Here, we demonstrate that fewer than 10% of NOTCH1 binding sites show dynamic changes in NOTCH1 occupancy when T-LL cells are toggled between the Notch-on and –off states with GSI. Dynamic NOTCH1 sites are functional, being highly associated with Notch target genes, are located mainly in distal enhancers, and frequently overlap with RUNX1 binding. In line with the latter association, we show that expression of IL7R, a gene with key roles in normal T cell development and in T-LL, is coordinately regulated by Runx factors and dynamic NOTCH1 binding to distal enhancers. Like IL7R, most Notch target genes and associated dynamic NOTCH1 binding sites co-occupy chromatin domains defined by constitutive binding of CCCTC binding factor (CTCF), which appears to restrict the regulatory potential of dynamic NOTCH1 sites. More remarkably, the majority of dynamic NOTCH1 sites lie in super-enhancers, distal elements with exceptionally broad and high levels of H3K27ac. Changes in Notch occupancy produces dynamic alterations in H3K27ac levels across the entire breadth of super-enhancers and in the promoters of nearby Notch target genes. These findings link regulation of super-enhancer function to NOTCH1, a master regulatory factor and potent oncoprotein in the context of immature T cells, and delineate a generally applicable roadmap for identifying functional Notch sites in cellular genomes. NOTCH1/RBPJ complexes binding dynamics in human T-LL
Project description:Senescence, a persistent form of cell cycle arrest, is often associated with a diverse secretome, which provides complex downstream functionality for senescent cells within the tissue microenvironment. We show that oncogene-induced senescence (OIS) is accompanied by a dynamic fluctuation of NOTCH1 activity, which drives a TGF-β-rich secretome, whilst suppressing the senescence-associated pro-inflammatory secretome through inhibition of C/EBPβ. NOTCH1 and NOTCH1-driven TGF-β contribute to ‘lateral induction of senescence’ through a juxtacrine NOTCH-JAG1 pathway. In addition, NOTCH1 inhibition during senescence facilitates upregulation of pro-inflammatory cytokines, promoting lymphocyte recruitment and senescence surveillance in vivo. Because enforced activation of NOTCH1 signalling confers a near mutually exclusive secretory profile compared to typical senescence, our data collectively indicate that the dynamic alteration of NOTCH1 activity during senescence dictates a functional balance between these two distinct secretomes: one representing TGF-β and the other pro-inflammatory cytokines, highlighting that NOTCH1 is a temporospatial controller of secretome composition.
Project description:The main oncogenic driver in T-lymphoblastic leukemia (T-LL) is NOTCH1, which activates genes by forming chromatin-associated Notch transcription complexes. Gamma-secretase (GSI) inhibitor treatment prevents NOTCH1 nuclear localization, but most genes with NOTCH1 binding sites are insensitive to GSI. Here, we demonstrate that fewer than 10% of NOTCH1 binding sites show dynamic changes in NOTCH1 occupancy when T-LL cells are toggled between the Notch-on and –off states with GSI. Dynamic NOTCH1 sites are functional, being highly associated with Notch target genes, are located mainly in distal enhancers, and frequently overlap with RUNX1 binding. In line with the latter association, we show that expression of IL7R, a gene with key roles in normal T cell development and in T-LL, is coordinately regulated by Runx factors and dynamic NOTCH1 binding to distal enhancers. Like IL7R, most Notch target genes and associated dynamic NOTCH1 binding sites co-occupy chromatin domains defined by constitutive binding of CCCTC binding factor (CTCF), which appears to restrict the regulatory potential of dynamic NOTCH1 sites. More remarkably, the majority of dynamic NOTCH1 sites lie in super-enhancers, distal elements with exceptionally broad and high levels of H3K27ac. Changes in Notch occupancy produces dynamic alterations in H3K27ac levels across the entire breadth of super-enhancers and in the promoters of nearby Notch target genes. These findings link regulation of super-enhancer function to NOTCH1, a master regulatory factor and potent oncoprotein in the context of immature T cells, and delineate a generally applicable roadmap for identifying functional Notch sites in cellular genomes.
Project description:Notch1 regulates gene expression by associating with the DNA-binding factor RBPJ and is oncogenic in murine and human T cell progenitors. Using ChIP-Seq, we find that in human and murine T-LL genomes Notch1 binds preferentially to promoters, to RBPJ binding sites, and near imputed ZNF143, Ets and Runx sites. ChIP-Seq confirmed that ZNF143 binds to ~40% of Notch1 sites. Notch1/ZNF143 sites are characterized by high Notch1 and ZNF143 signals, frequent co-binding of RBPJ (generally through sites embedded within ZNF143 motifs), strong promoter bias, and relatively low mean levels of activating chromatin marks. RBPJ and ZNF143 binding to DNA is mutually exclusive in vitro, suggesting RBPJ/Notch1 and ZNF143 complexes exchange on these sites in cells. K-means clustering of Notch1 binding sites and associated motifs identified conserved Notch1-Runx, Notch1-Ets, Notch1-RBPJ, Notch1-ZNF143, and Notch1-ZNF143-Ets clusters with different genomic distributions and levels of chromatin marks. Although Notch1 binds mainly to gene promoters, ~75% of direct target genes lack promoter binding and are presumably regulated by enhancers, which were identified near MYC, DTX1, IGF1R, IL7R and the GIMAP cluster. Human and murine T-LL genomes also have many sites that bind only RBPJ. Murine RBPJ âonlyâ sites are highly enriched for imputed REST sites, whereas human RPBJ âonlyâ sites lack REST motifs and are more highly enriched for imputed CREB sites. Thus, there is a conserved network of cis-regulatory factors that interacts with Notch1 to regulate gene expression in T-LL cells, as well as novel classes of divergent RBPJ âonlyâ sites that also likely regulate transcription.
Project description:Notch1 regulates gene expression by associating with the DNA-binding factor RBPJ and is oncogenic in murine and human T cell progenitors. Using ChIP-Seq, we find that in human and murine T-LL genomes Notch1 binds preferentially to promoters, to RBPJ binding sites, and near imputed ZNF143, Ets and Runx sites. ChIP-Seq confirmed that ZNF143 binds to ~40% of Notch1 sites. Notch1/ZNF143 sites are characterized by high Notch1 and ZNF143 signals, frequent co-binding of RBPJ (generally through sites embedded within ZNF143 motifs), strong promoter bias, and relatively low mean levels of activating chromatin marks. RBPJ and ZNF143 binding to DNA is mutually exclusive in vitro, suggesting RBPJ/Notch1 and ZNF143 complexes exchange on these sites in cells. K-means clustering of Notch1 binding sites and associated motifs identified conserved Notch1-Runx, Notch1-Ets, Notch1-RBPJ, Notch1-ZNF143, and Notch1-ZNF143-Ets clusters with different genomic distributions and levels of chromatin marks. Although Notch1 binds mainly to gene promoters, ~75% of direct target genes lack promoter binding and are presumably regulated by enhancers, which were identified near MYC, DTX1, IGF1R, IL7R and the GIMAP cluster. Human and murine T-LL genomes also have many sites that bind only RBPJ. Murine RBPJ M-CM-"M-BM-^@M-BM-^\onlyM-CM-"M-BM-^@M-BM-^] sites are highly enriched for imputed REST sites, whereas human RPBJ M-CM-"M-BM-^@M-BM-^\onlyM-CM-"M-BM-^@M-BM-^] sites lack REST motifs and are more highly enriched for imputed CREB sites. Thus, there is a conserved network of cis-regulatory factors that interacts with Notch1 to regulate gene expression in T-LL cells, as well as novel classes of divergent RBPJ M-CM-"M-BM-^@M-BM-^\onlyM-CM-"M-BM-^@M-BM-^] sites that also likely regulate transcription. Notch1, RBPJ, histone methylation ChIP-seq in human and mouse T-LL cell lines