RESUMEN
Combination approaches are needed to strengthen and extend the clinical response to KRASG12C inhibitors (KRASG12Ci). Here, we assessed the antitumor responses of KRASG12C mutant lung and colorectal cancer models to combination treatment with a SOS1 inhibitor (SOS1i), BI-3406, plus the KRASG12C inhibitor, adagrasib. We found that responses to BI-3406 plus adagrasib were stronger than to adagrasib alone, comparable to adagrasib with SHP2 (SHP2i) or EGFR inhibitors and correlated with stronger suppression of RAS-MAPK signaling. BI-3406 plus adagrasib treatment also delayed the emergence of acquired resistance and elicited antitumor responses from adagrasib-resistant models. Resistance to KRASG12Ci seemed to be driven by upregulation of MRAS activity, which both SOS1i and SHP2i were found to potently inhibit. Knockdown of SHOC2, a MRAS complex partner, partially restored response to KRASG12Ci treatment. These results suggest KRASG12C plus SOS1i to be a promising strategy for treating both KRASG12Ci naive and relapsed KRASG12C-mutant tumors.
RESUMEN
KRAS inhibitors have demonstrated exciting preclinical and clinical responses, although resistance occurs rapidly. Here, we investigate the effects of KRAS-targeting therapies on the tumor microenvironment using a library of KrasG12D, p53-mutant, murine pancreatic ductal adenocarcinoma-derived cell lines (KPCY) to leverage immune-oncology combination strategies for long-term tumor efficacy. Our findings show that SOS1 and MEK inhibitors (SOS1i+MEKi) suppressed tumor growth in syngeneic models and increased intratumoral CD8+ T cells without durable responses. Single-cell RNA sequencing revealed an increase in inflammatory cancer-associated fibroblasts (iCAF), M2 macrophages, and a decreased dendritic cell (DC) quality that ultimately resulted in a highly immunosuppressive microenvironment driven by IL6+ iCAFs. Agonist CD40 treatment was effective to revert macrophage polarization and overcome the lack of mature antigen-presenting DCs after SOS1i+MEKi therapy. Treatment increased the overall survival of KPCY tumor-bearing mice. The addition of checkpoint blockade to SOS1i+MEKi combination resulted in tumor-free mice with established immune memory. Our data suggest that KRAS inhibition affects myeloid cell maturation and highlights the need for combining KRAS cancer-targeted therapy with myeloid activation to enhance and prolong antitumor effects. SIGNIFICANCE: Combination of SOS1 and MEK inhibitors increase T cell infiltration while blunting pro-immune myeloid cell maturation and highlights the need for combining KRAS cancer-targeted therapy with myeloid activation to enhance and prolong anti-tumor effects.
Asunto(s)
Carcinoma Ductal Pancreático , Inmunoterapia , Neoplasias Pancreáticas , Proteínas Proto-Oncogénicas p21(ras) , Proteína SOS1 , Microambiente Tumoral , Animales , Carcinoma Ductal Pancreático/tratamiento farmacológico , Carcinoma Ductal Pancreático/inmunología , Carcinoma Ductal Pancreático/patología , Ratones , Microambiente Tumoral/efectos de los fármacos , Microambiente Tumoral/inmunología , Neoplasias Pancreáticas/tratamiento farmacológico , Neoplasias Pancreáticas/inmunología , Neoplasias Pancreáticas/patología , Neoplasias Pancreáticas/genética , Proteína SOS1/genética , Proteína SOS1/metabolismo , Proteínas Proto-Oncogénicas p21(ras)/genética , Inmunoterapia/métodos , Línea Celular Tumoral , Inhibidores de Proteínas Quinasas/farmacología , Inhibidores de Proteínas Quinasas/uso terapéutico , Humanos , Inhibidores de Puntos de Control Inmunológico/farmacología , Inhibidores de Puntos de Control Inmunológico/uso terapéutico , Ratones Endogámicos C57BL , Linfocitos T CD8-positivos/inmunología , Linfocitos T CD8-positivos/efectos de los fármacos , FemeninoRESUMEN
Clinical effectiveness of KRAS G12C inhibitors (G12Cis) is limited both by intrinsic and acquired resistance, necessitating the development of combination approaches. We found that targeting proximal receptor tyrosine kinase (RTK) signaling using the SOS1 inhibitor (SOS1i) BI-3406 both enhanced the potency of and delayed resistance to G12Ci treatment, but the extent of SOS1i effectiveness was modulated by both SOS2 expression and the specific mutational landscape. SOS1i enhanced the efficacy of G12Ci and limited rebound RTK/ERK signaling to overcome intrinsic/adaptive resistance, but this effect was modulated by SOS2 protein levels. Survival of drug-tolerant persister (DTP) cells within the heterogeneous tumor population and/or acquired mutations that reactivate RTK/RAS signaling can lead to outgrowth of tumor initiating cells (TICs) that drive therapeutic resistance. G12Ci drug tolerant persister cells showed a 2-3-fold enrichment of TICs, suggesting that these could be a sanctuary population of G12Ci resistant cells. SOS1i re-sensitized DTPs to G12Ci and inhibited G12C-induced TIC enrichment. Co-mutation of the tumor suppressor KEAP1 limits the clinical effectiveness of G12Cis, and KEAP1 and STK11 deletion increased TIC frequency and accelerated the development of acquired resistance to G12Ci in situ. SOS1i both delayed acquired G12Ci resistance and limited the total number of resistant colonies regardless of KEAP1 and STK11 mutational status. These data suggest that SOS1i could be an effective strategy to both enhance G12Ci efficacy and prevent G12Ci resistance regardless of co-mutations.
RESUMEN
KRAS is a frequent driver in lung cancer. To identify KRAS-specific vulnerabilities in lung cancer, we performed RNAi screens in primary spheroids derived from a Kras mutant mouse lung cancer model and discovered an epigenetic regulator Ubiquitin-like containing PHD and RING finger domains 1 (UHRF1). In human lung cancer models UHRF1 knock-out selectively impaired growth and induced apoptosis only in KRAS mutant cells. Genome-wide methylation and gene expression analysis of UHRF1-depleted KRAS mutant cells revealed global DNA hypomethylation leading to upregulation of tumor suppressor genes (TSGs). A focused CRISPR/Cas9 screen validated several of these TSGs as mediators of UHRF1-driven tumorigenesis. In vivo, UHRF1 knock-out inhibited tumor growth of KRAS-driven mouse lung cancer models. Finally, in lung cancer patients high UHRF1 expression is anti-correlated with TSG expression and predicts worse outcomes for patients with KRAS mutant tumors. These results nominate UHRF1 as a KRAS-specific vulnerability and potential target for therapeutic intervention.
Asunto(s)
Adenocarcinoma del Pulmón , Proteínas Potenciadoras de Unión a CCAAT , Neoplasias Pulmonares , Ubiquitina-Proteína Ligasas , Animales , Humanos , Ratones , Adenocarcinoma del Pulmón/genética , Proteínas Potenciadoras de Unión a CCAAT/genética , Proteínas Potenciadoras de Unión a CCAAT/metabolismo , Transformación Celular Neoplásica/genética , Metilación de ADN , Epigénesis Genética , Neoplasias Pulmonares/genética , Proteínas Proto-Oncogénicas p21(ras)/genética , Proteínas Proto-Oncogénicas p21(ras)/metabolismo , Ubiquitina-Proteína Ligasas/genética , Ubiquitina-Proteína Ligasas/metabolismoRESUMEN
Efforts to improve the anti-tumor response to KRASG12C targeted therapy have benefited from leveraging combination approaches. Here, we compare the anti-tumor response induced by the SOS1-KRAS interaction inhibitor, BI-3406, combined with a KRASG12C inhibitor (KRASG12Ci) to those induced by KRASG12Ci alone or combined with SHP2 or EGFR inhibitors. In lung cancer and colorectal cancer (CRC) models, BI-3406 plus KRASG12Ci induces an anti-tumor response stronger than that observed with KRASG12Ci alone and comparable to those by the other combinations. This enhanced anti-tumor response is associated with a stronger and extended suppression of RAS-MAPK signaling. Importantly, BI-3406 plus KRASG12Ci treatment delays the emergence of acquired adagrasib resistance in both CRC and lung cancer models and is associated with re-establishment of anti-proliferative activity in KRASG12Ci-resistant CRC models. Our findings position KRASG12C plus SOS1 inhibition therapy as a promising strategy for treating both KRASG12C-mutated tumors as well as for addressing acquired resistance to KRASG12Ci.
RESUMEN
Zafra and colleagues developed new mouse models to study the role of specific KRAS mutations in pancreatic, lung, and colon cancer pathogenesis. Their studies clearly describe the distinct ability of these mutations to drive pathogenesis in a tissue-specific fashion.See related article by Zafra et al., p. 1654.
Asunto(s)
Oncogenes , Proteínas Proto-Oncogénicas p21(ras) , Animales , Carcinogénesis , Genes ras , Ratones , Mutación , Fenotipo , Proteínas Proto-Oncogénicas p21(ras)/genéticaRESUMEN
Activating mutations in RAS GTPases drive many cancers, but limited understanding of less-studied RAS interactors, and of the specific roles of different RAS interactor paralogs, continues to limit target discovery. We developed a multistage discovery and screening process to systematically identify genes conferring RAS-related susceptibilities in lung adenocarcinoma. Using affinity purification mass spectrometry, we generated a protein-protein interaction map of RAS interactors and pathway components containing hundreds of interactions. From this network, we constructed a CRISPR dual knockout library targeting 119 RAS-related genes that we screened for KRAS-dependent genetic interactions (GI). This approach identified new RAS effectors, including the adhesion controller RADIL and the endocytosis regulator RIN1, and >250 synthetic lethal GIs, including a potent KRAS-dependent interaction between RAP1GDS1 and RHOA. Many GIs link specific paralogs within and between gene families. These findings illustrate the power of multiomic approaches to uncover synthetic lethal combinations specific for hitherto untreatable cancer genotypes. SIGNIFICANCE: We establish a deep network of protein-protein and genetic interactions in the RAS pathway. Many interactions validated here demonstrate important specificities and redundancies among paralogous RAS regulators and effectors. By comparing synthetic lethal interactions across KRAS-dependent and KRAS-independent cell lines, we identify several new combination therapy targets for RAS-driven cancers.This article is highlighted in the In This Issue feature, p. 1775.
Asunto(s)
Neoplasias Pulmonares/genética , Proteómica/métodos , Proteínas ras/genética , HumanosRESUMEN
Cancer genomics studies have identified thousands of putative cancer driver genes1. Development of high-throughput and accurate models to define the functions of these genes is a major challenge. Here we devised a scalable cancer-spheroid model and performed genome-wide CRISPR screens in 2D monolayers and 3D lung-cancer spheroids. CRISPR phenotypes in 3D more accurately recapitulated those of in vivo tumours, and genes with differential sensitivities between 2D and 3D conditions were highly enriched for genes that are mutated in lung cancers. These analyses also revealed drivers that are essential for cancer growth in 3D and in vivo, but not in 2D. Notably, we found that carboxypeptidase D is responsible for removal of a C-terminal RKRR motif2 from the α-chain of the insulin-like growth factor 1 receptor that is critical for receptor activity. Carboxypeptidase D expression correlates with patient outcomes in patients with lung cancer, and loss of carboxypeptidase D reduced tumour growth. Our results reveal key differences between 2D and 3D cancer models, and establish a generalizable strategy for performing CRISPR screens in spheroids to reveal cancer vulnerabilities.
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Sistemas CRISPR-Cas/genética , Técnicas de Cultivo de Célula/métodos , Proliferación Celular/genética , Genoma Humano/genética , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/patología , Esferoides Celulares/patología , Adenocarcinoma/genética , Adenocarcinoma/metabolismo , Adenocarcinoma/patología , Secuencias de Aminoácidos , Animales , Carboxipeptidasas/antagonistas & inhibidores , Carboxipeptidasas/deficiencia , Carboxipeptidasas/genética , Carboxipeptidasas/metabolismo , Femenino , Humanos , Neoplasias Pulmonares/metabolismo , Ratones , Terapia Molecular Dirigida , Mutación , Fenotipo , Receptor IGF Tipo 1/química , Receptor IGF Tipo 1/metabolismo , Transducción de Señal , Esferoides Celulares/metabolismo , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Few therapies are currently available for patients with KRAS-driven cancers, highlighting the need to identify new molecular targets that modulate central downstream effector pathways. Here we found that the microRNA (miRNA) cluster including miR181ab1 is a key modulator of KRAS-driven oncogenesis. Ablation of Mir181ab1 in genetically engineered mouse models of Kras-driven lung and pancreatic cancer was deleterious to tumor initiation and progression. Expression of both resident miRNAs in the Mir181ab1 cluster, miR181a1 and miR181b1, was necessary to rescue the Mir181ab1-loss phenotype, underscoring their nonredundant role. In human cancer cells, depletion of miR181ab1 impaired proliferation and 3D growth, whereas overexpression provided a proliferative advantage. Lastly, we unveiled miR181ab1-regulated genes responsible for this phenotype. These studies identified what we believe to be a previously unknown role for miR181ab1 as a potential therapeutic target in 2 highly aggressive and difficult to treat KRAS-mutated cancers.
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Carcinogénesis/metabolismo , Neoplasias Pulmonares/metabolismo , MicroARNs/metabolismo , Familia de Multigenes , Neoplasias Experimentales/metabolismo , Neoplasias Pancreáticas/metabolismo , Proteínas Proto-Oncogénicas p21(ras)/metabolismo , ARN Neoplásico/metabolismo , Animales , Carcinogénesis/genética , Línea Celular Tumoral , Proliferación Celular , Humanos , Neoplasias Pulmonares/genética , Ratones , Ratones Noqueados , MicroARNs/genética , Neoplasias Experimentales/genética , Neoplasias Pancreáticas/genética , Proteínas Proto-Oncogénicas p21(ras)/genética , ARN Neoplásico/genéticaRESUMEN
Proinflammatory cytokines in the tumor microenvironment can promote tumor growth, yet their value as therapeutic targets remains underexploited. We validated the functional significance of the cardiotrophin-like cytokine factor 1 (CLCF1)-ciliary neurotrophic factor receptor (CNTFR) signaling axis in lung adenocarcinoma (LUAD) and generated a high-affinity soluble receptor (eCNTFR-Fc) that sequesters CLCF1, thereby inhibiting its oncogenic effects. eCNTFR-Fc inhibits tumor growth in multiple xenograft models and in an autochthonous, highly aggressive genetically engineered mouse model of LUAD, driven by activation of oncogenic Kras and loss of Trp53. Abrogation of CLCF1 through eCNTFR-Fc appears most effective in tumors driven by oncogenic KRAS. We observed a correlation between the effectiveness of eCNTFR-Fc and the presence of KRAS mutations that retain the intrinsic capacity to hydrolyze guanosine triphosphate, suggesting that the mechanism of action may be related to altered guanosine triphosphate loading. Overall, we nominate blockade of CLCF1-CNTFR signaling as a novel therapeutic opportunity for LUAD and potentially for other tumor types in which CLCF1 is present in the tumor microenvironment.
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Adenocarcinoma del Pulmón/tratamiento farmacológico , Proliferación Celular/genética , Subunidad alfa del Receptor del Factor Neurotrófico Ciliar/genética , Citocinas/genética , Adenocarcinoma del Pulmón/genética , Adenocarcinoma del Pulmón/patología , Animales , Línea Celular Tumoral , Subunidad alfa del Receptor del Factor Neurotrófico Ciliar/química , Citocinas/química , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Humanos , Interleucinas/genética , Ratones , Mutación/genética , Unión Proteica , Proteínas Proto-Oncogénicas p21(ras)/genética , Transducción de Señal/efectos de los fármacos , Microambiente Tumoral/efectos de los fármacos , Proteína p53 Supresora de Tumor/genética , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Resistance to platinum chemotherapy is a long-standing problem in the management of lung adenocarcinoma. Using a whole-genome synthetic lethal RNA interference screen, we identified activin signaling as a critical mediator of innate platinum resistance. The transforming growth factor-ß (TGFß) superfamily ligands activin A and growth differentiation factor 11 (GDF11) mediated resistance via their cognate receptors through TGFß-activated kinase 1 (TAK1), rather than through the SMAD family of transcription factors. Inhibition of activin receptor signaling or blockade of activin A and GDF11 by the endogenous protein follistatin overcame this resistance. Consistent with the role of activin signaling in acute renal injury, both therapeutic interventions attenuated acute cisplatin-induced nephrotoxicity, its major dose-limiting side effect. This cancer-specific enhancement of platinum-induced cell death has the potential to dramatically improve the safety and efficacy of chemotherapy in lung cancer patients.
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Activinas/metabolismo , Adenocarcinoma del Pulmón/tratamiento farmacológico , Neoplasias Pulmonares/tratamiento farmacológico , Platino (Metal)/uso terapéutico , Células A549 , Animales , Carboplatino/uso terapéutico , Línea Celular Tumoral , Supervivencia Celular/efectos de los fármacos , Folistatina/uso terapéutico , Humanos , Masculino , Ratones , Transducción de Señal/efectos de los fármacos , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Untargeted plasmid integration into mammalian cell genomes remains a poorly understood and inefficient process. The formation of plasmid concatemers and their genomic integration has been ascribed either to non-homologous end-joining (NHEJ) or homologous recombination (HR) DNA repair pathways. However, a direct involvement of these pathways has remained unclear. Here, we show that the silencing of many HR factors enhanced plasmid concatemer formation and stable expression of the gene of interest in Chinese hamster ovary (CHO) cells, while the inhibition of NHEJ had no effect. However, genomic integration was decreased by the silencing of specific HR components, such as Rad51, and DNA synthesis-dependent microhomology-mediated end-joining (SD-MMEJ) activities. Genome-wide analysis of the integration loci and junction sequences validated the prevalent use of the SD-MMEJ pathway for transgene integration close to cellular genes, an effect shared with matrix attachment region (MAR) DNA elements that stimulate plasmid integration and expression. Overall, we conclude that SD-MMEJ is the main mechanism driving the illegitimate genomic integration of foreign DNA in CHO cells, and we provide a recombination engineering approach that increases transgene integration and recombinant protein expression in these cells. Biotechnol. Bioeng. 2017;114: 384-396. © 2016 The Authors. Biotechnology and Bioengineering published by Wiley Periodicals, Inc.
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Cromatina/genética , Ingeniería Genética/métodos , Regiones de Fijación a la Matriz/genética , Proteínas Recombinantes/genética , Recombinación Genética/genética , Animales , Anticuerpos/química , Anticuerpos/genética , Anticuerpos/metabolismo , Células CHO , Cricetinae , Cricetulus , Técnicas de Silenciamiento del Gen , Humanos , Plásmidos/genética , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Transgenes/genéticaRESUMEN
In the canonical pathway of IFN-I-mediated signaling, phosphorylation of STAT1 and STAT2 leads to heterodimerization and interaction with IRF9. This complex, also known as IFN-stimulated gene factor 3 (ISGF3), then translocates into the nucleus and binds the IFN-I-stimulated response element (ISRE) leading to the activation of transcription of over 300 interferon stimulated genes (ISGs). In addition, STAT1 homodimers [known as γ-activated factor (GAF)] are formed and translocate to the nucleus, where they target genes containing the γ-activated sequence (GAS). The primary function of ISGF3 is to mediate a rapid and robust IFN-I activated response by regulating transient transcription of antiviral ISGs. This requires the quick assembly of ISGF3 from its pre-existing components STAT1, STAT2 and IRF9 and transport to the nucleus to bind ISRE-containing ISGs. The exact events that take place in formation, nuclear translocation and DNA-binding of active ISGF3 are still not clear. Over the years many studies have provided evidence for the existence of a multitude of alternative STAT2-containing (ISRE or GAS-binding) complexes involved in IFN-I signaling, emphasizing the importance of STAT2 in the regulation of specific IFN-I-induced transcriptional programs, independent of its involvement in the classical ISGF3 complex. This review describes the unique role of STAT2 in differential complex formation of unphosphorylated and phosphorylated ISGF3 components that direct constitutive and IFN-I-stimulated transcriptional responses. In addition, we highlight the existence of a STAT1-independent IFN-I signaling pathway, where STAT2/IRF9 can potentially substitute for the role of ISGF3 and offer a back-up response against viral infection.
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Interferón Tipo I/inmunología , Factor de Transcripción STAT2/inmunología , Transducción de Señal/inmunología , Transcripción Genética/inmunología , Virosis/inmunología , Animales , Humanos , Subunidad gamma del Factor 3 de Genes Estimulados por el Interferón/inmunología , Elementos de Respuesta/inmunologíaRESUMEN
DNA double stranded breaks (DSBs) are one of the most deleterious types of DNA lesions. The main pathways responsible for repairing these breaks in eukaryotic cells are homologous recombination (HR) and non-homologous end-joining (NHEJ). However, a third group of still poorly characterized DSB repair pathways, collectively termed microhomology-mediated end-joining (MMEJ), relies on short homologies for the end-joining process. Here, we constructed GFP reporter assays to characterize and distinguish MMEJ variant pathways, namely the simple MMEJ and the DNA synthesis-dependent (SD)-MMEJ mechanisms. Transfection of these assay vectors in Chinese hamster ovary (CHO) cells and characterization of the repaired DNA sequences indicated that while simple MMEJ is able to mediate relatively efficient DSB repair if longer microhomologies are present, the majority of DSBs were repaired using the highly error-prone SD-MMEJ pathway. To validate the involvement of DNA synthesis in the repair process, siRNA knock-down of different genes proposed to play a role in MMEJ were performed, revealing that the knock-down of DNA polymerase θ inhibited DNA end resection and repair through simple MMEJ, thus favoring the other repair pathway. Overall, we conclude that this approach provides a convenient assay to study MMEJ-related DNA repair pathways.
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Bioensayo , Roturas del ADN de Doble Cadena , Reparación del ADN por Unión de Extremidades , ADN Polimerasa Dirigida por ADN/genética , ADN/metabolismo , Animales , Secuencia de Bases , Células CHO , Cricetulus , ADN/química , ADN/genética , ADN Polimerasa Dirigida por ADN/metabolismo , Genes Reporteros , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Recombinación Homóloga , Datos de Secuencia Molecular , Plásmidos/química , Plásmidos/genética , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Homología de Secuencia de Ácido Nucleico , Transfección , ADN Polimerasa thetaRESUMEN
Eukaryotic cells respond to DNA breaks, especially double-stranded breaks (DSBs), by activating the DNA damage response (DDR), which encompasses DNA repair and cell cycle checkpoint signaling. The DNA damage signal is transmitted to the checkpoint machinery by a network of specialized DNA damage-recognizing and signal-transducing molecules. However, recent evidence suggests that DNA repair proteins themselves may also directly contribute to the checkpoint control. Here, we investigated the role of homologous recombination (HR) proteins in normal cell cycle regulation in the absence of exogenous DNA damage. For this purpose, we used Chinese Hamster Ovary (CHO) cells expressing the Fluorescent ubiquitination-based cell cycle indicators (Fucci). Systematic siRNA-mediated knockdown of HR genes in these cells demonstrated that the lack of several of these factors alters cell cycle distribution, albeit differentially. The knock-down of MDC1, Rad51 and Brca1 caused the cells to arrest in the G2 phase, suggesting that they may be required for the G2/M transition. In contrast, inhibition of the other HR factors, including several Rad51 paralogs and Rad50, led to the arrest in the G1/G0 phase. Moreover, reduced expression of Rad51B, Rad51C, CtIP and Rad50 induced entry into a quiescent G0-like phase. In conclusion, the lack of many HR factors may lead to cell cycle checkpoint activation, even in the absence of exogenous DNA damage, indicating that these proteins may play an essential role both in DNA repair and checkpoint signaling.
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Proteínas de Ciclo Celular/fisiología , Ciclo Celular/fisiología , Recombinación Homóloga/fisiología , Animales , Células CHO , Cricetinae , Cricetulus , Humanos , Proteínas RecombinantesRESUMEN
Evidence is accumulating for the existence of a signal transducer and activator of transcription 2 (STAT2)/interferon regulatory factor 9 (IRF9)-dependent, STAT1-independent interferon alpha (IFNα) signalling pathway. However, no detailed insight exists into the genome-wide transcriptional regulation and the biological implications of STAT2/IRF9-dependent IFNα signalling as compared with interferon-stimulated gene factor 3 (ISGF3). In STAT1-defeicient U3C cells stably overexpressing human STAT2 (hST2-U3C) and STAT1-deficient murine embryonic fibroblast cells stably overexpressing mouse STAT2 (mST2-MS1KO) we observed that the IFNα-induced expression of 2'-5'-oligoadenylate synthase 2 (OAS2) and interferon-induced protein with tetratricopeptide repeats 1 (Ifit1) correlated with the kinetics of STAT2 phosphorylation, and the presence of a STAT2/IRF9 complex requiring STAT2 phosphorylation and the STAT2 transactivation domain. Subsequent microarray analysis of IFNα-treated wild-type (WT) and STAT1 KO cells overexpressing STAT2 extended our observations and identified â¼120 known antiviral ISRE-containing interferon-stimulated genes (ISGs) commonly up-regulated by STAT2/IRF9 and ISGF3. The STAT2/IRF9-directed expression profile of these IFN-stimulated genes (ISGs) was prolonged as compared with the early and transient response mediated by ISGF3. In addition, we identified a group of 'STAT2/IRF9-specific' ISGs, whose response to IFNα was ISGF3-independent. Finally, STAT2/IRF9 was able to trigger an antiviral response upon encephalomyocarditis virus (EMCV) and vesicular stomatitis Indiana virus (VSV). Our results further prove that IFNα-activated STAT2/IRF9 induces a prolonged ISGF3-like transcriptome and generates an antiviral response in the absence of STAT1. Moreover, the existence of 'STAT2/IRF9-specific' target genes predicts a novel role of STAT2 in IFNα signalling.
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Subunidad gamma del Factor 3 de Genes Estimulados por el Interferón/metabolismo , Factor de Transcripción STAT1/deficiencia , Factor de Transcripción STAT2/metabolismo , Activación Transcripcional/fisiología , Animales , Antivirales/metabolismo , Línea Celular , Línea Celular Tumoral , Células HEK293 , Humanos , Subunidad gamma del Factor 3 de Genes Estimulados por el Interferón/genética , Ratones , Ratones Noqueados , Factor de Transcripción STAT1/genética , Factor de Transcripción STAT2/genéticaRESUMEN
Gene transfer and expression in eukaryotes is often limited by a number of stably maintained gene copies and by epigenetic silencing effects. Silencing may be limited by the use of epigenetic regulatory sequences such as matrix attachment regions (MAR). Here, we show that successive transfections of MAR-containing vectors allow a synergistic increase of transgene expression. This finding is partly explained by an increased entry into the cell nuclei and genomic integration of the DNA, an effect that requires both the MAR element and iterative transfections. Fluorescence in situ hybridization analysis often showed single integration events, indicating that DNAs introduced in successive transfections could recombine. High expression was also linked to the cell division cycle, so that nuclear transport of the DNA occurs when homologous recombination is most active. Use of cells deficient in either non-homologous end-joining or homologous recombination suggested that efficient integration and expression may require homologous recombination-based genomic integration of MAR-containing plasmids and the lack of epigenetic silencing events associated with tandem gene copies. We conclude that MAR elements may promote homologous recombination, and that cells and vectors can be engineered to take advantage of this property to mediate highly efficient gene transfer and expression.