Combinatorial in vivo genome editing identifies widespread epistasis and an accessible fitness landscape during lung tumorigenesis
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ABSTRACT: Lung adenocarcinoma, the most common subtype of lung cancer, is genomically complex, with tumors containing tens to hundreds of non-synonymous mutations. However, little is understood about how genes interact with each other to enable the evolution of cancer in vivo, largely due to a lack of methods for investigating genetic interactions in a high-throughput and quantitative manner. Here, we employed a novel platform to generate tumors with all pairwise inactivation of ten diverse tumor suppressor genes within an autochthonous mouse model of oncogenic KRAS-driven lung cancer. By quantifying the fitness of tumors with every single and double mutant genotype, we show that most tumor suppressor genetic interactions exhibited negative epistasis, with diminishing returns on tumor fitness. In contrast, Apc inactivation showed positive epistasis with the inactivation of several other genes, including synergistic effects on tumor fitness in combination with Lkb1 or Nf1 inactivation. Sign epistasis was extremely rare, suggesting a surprisingly accessible fitness landscape during lung tumorigenesis. These findings greatly expand our understanding the evolutionary interactions that drive tumorigenesis in vivo.
Project description:LKB1 is among the most frequently altered tumor suppressors in lung adenocarcinoma. Inactivation of Lkb1 accelerates the growth and progression of oncogenic KRAS-driven lung tumors in mouse models. However, the molecular mechanisms by which LKB1 constrains lung tumorigenesis and whether the aggressive cancer state that stems from Lkb1 deficiency can be reverted remains unknown. To identify the processes governed by LKB1 in vivo, we generated an allele which enables Lkb1 inactivation during tumor development and subsequent Lkb1 restoration in established tumors. Restoration of Lkb1 in oncogenic KRAS-driven lung tumors suppressed proliferation and promoted tumor stasis. Lkb1 restoration activated targets of C/EBP transcription factors and drove the transition of neoplastic cells from a progenitor-like state to a less proliferative alveolar type II cell-like state. We show that C/EBP transcription factors govern a subset of genes that are induced by LKB1 and depend upon NKX2-1. We also demonstrate that a defining factor of the alveolar type II lineage, C/EBPα, constrains oncogenic KRAS-driven lung tumor growth. Thus, we uncover a role for a critical tumor suppressor in the regulation of key lineage-specific transcription factors, thereby constraining lung tumor development through the enforcement of differentiation.
Project description:Cancer genome sequencing has uncovered substantial complexity in the mutational landscape of tumors. Given this complexity, experimental approaches are necessary to establish the impact of combinations of genetic alterations on tumor biology and to uncover genotype-dependent effects on drug sensitivity. In lung adenocarcinoma, EGFR mutations co-occur with many putative tumor suppressor gene alterations, however the extent to which these alterations contribute to tumor growth and their response to therapy in vivo has not been explored experimentally. By integrating a novel mouse model of oncogenic EGFR-driven Trp53-deficient lung adenocarcinoma with multiplexed CRISPR–Cas9-mediated genome editing and tumor barcode sequencing, we quantified the effects of inactivation of ten putative tumor suppressor genes. Inactivation of Apc, Rb1, or Rbm10 most strongly promoted tumor growth. Unexpectedly, inactivation of Lkb1 or Setd2 – which were the strongest drivers of tumor growth in an oncogenic Kras-driven model – reduced EGFR-driven tumors growth. These results were consistent with the relative frequency of these tumor suppressor gene alterations in human EGFR and KRAS-driven lung adenocarcinomas. Furthermore, Keap1 inactivation reduced the sensitivity of tumors to osimertinib in the EGFRL858R;p53flox/flox model. Importantly, in human EGFR/TP53 mutant lung adenocarcinomas, mutations in the KEAP1 pathway correlated with decreased time on tyrosine kinase inhibitor treatment. Our study highlights how genetic alterations can have dramatically different biological consequences depending on the oncogenic context and that the fitness landscape can shift upon drug treatment.
Project description:Inherited mutation in LKB1 results in the Peutz-Jeghers syndrome (PJS), characterized by intestinal hamartomas and a modestly increased frequency of gastrointestinal and breast cancer1. Somatic inactivation of LKB1 occurs in human lung adenocarcinoma2-4, but its tumor suppressor role in this tissue is unknown. Here we show that somatic Lkb1 deficiency strongly cooperates with somatic K-rasG12D activating mutation to accelerate the development of mouse lung tumorigenesis. Lkb1 deficiency in the setting of K-rasG12D mutation (K-ras Lkb1L/L) was associated with decreased tumor latency and increased tumor aggressiveness including metastasis. Furthermore, tumors from K-ras Lkb1L/L mice demonstrated histologies--squamous, adenosquamous and large cell--not seen with K-rasG12D mutation, Ink4a/Arf inactivation, or p53 inactivation alone or in combination. Experiments in vitro suggest that LKB1 suppresses lung tumorigenesis and progression through both p16INK4a-ARF-p53 dependent and independent mechanisms. These data indicate that LKB1 regulates lung tumor progression and differentiation. Keywords: cancer research To analyze the role of LKB1 in lung cancer progression and differentiation, we have dissected the lung tumors from mice with/without lkb1 loss and performed the microarray analyses to compare their gene expression pattern. In addition, we have also performed microarray analysis in both A549 and H2126 cell lines after reconsistitution of either wt-lkb1 or the kinase dead form of lkb1 (lkb1-KD) to confirm what we observed from in vivo studies.
Project description:Inherited mutation in LKB1 results in the Peutz-Jeghers syndrome (PJS), characterized by intestinal hamartomas and a modestly increased frequency of gastrointestinal and breast cancer1. Somatic inactivation of LKB1 occurs in human lung adenocarcinoma2-4, but its tumor suppressor role in this tissue is unknown. Here we show that somatic Lkb1 deficiency strongly cooperates with somatic K-rasG12D activating mutation to accelerate the development of mouse lung tumorigenesis. Lkb1 deficiency in the setting of K-rasG12D mutation (K-ras Lkb1L/L) was associated with decreased tumor latency and increased tumor aggressiveness including metastasis. Furthermore, tumors from K-ras Lkb1L/L mice demonstrated histologies--squamous, adenosquamous and large cell--not seen with K-rasG12D mutation, Ink4a/Arf inactivation, or p53 inactivation alone or in combination. Experiments in vitro suggest that LKB1 suppresses lung tumorigenesis and progression through both p16INK4a-ARF-p53 dependent and independent mechanisms. These data indicate that LKB1 regulates lung tumor progression and differentiation. Keywords: cancer research
Project description:Tumorigenesis is a multistep process that results from the sequential accumulation of mutations in key oncogene and tumor-suppressor pathways. The quest to personalize cancer medicine based on targeting these underlying genetic abnormalities presupposes that sustained inactivation of tumor suppressors and activation of oncogenes are required for tumor maintenance. Mutations in the p53 tumor-suppressor pathway are a hallmark of cancer and significant efforts toward pharmaceutical reactivation of mutant p53 pathways are underway1-3. Here we show that restoration of p53 in established murine lung tumors leads to significant but incomplete tumor cell loss specifically in malignant adenocarcinomas but not in adenomas. Also, we define amplification of MAPK signaling as a critical determinant of malignant progression. The differential response to p53 restoration depends on activation of the Arf tumor suppressor downstream of hyperactive MAPK signaling. We propose that p53 naturally limits malignant progression by responding to increased oncogenic signaling, but is unresponsive to low levels of oncogene activity that are sufficient for early stages of lung tumor development. These data suggest that restoration of pathways important in tumor progression, as opposed to initiation, may lead to incomplete tumor regression due to the stage-heterogeneity of tumor cell populations. 18 tumors of different grade and treatment status. 6 treated grade 3, 4 treated grade2, 4 untreated grade3, 4 untreated grade2
Project description:Tumorigenesis is a multistep process that results from the sequential accumulation of mutations in key oncogene and tumor-suppressor pathways. The quest to personalize cancer medicine based on targeting these underlying genetic abnormalities presupposes that sustained inactivation of tumor suppressors and activation of oncogenes are required for tumor maintenance. Mutations in the p53 tumor-suppressor pathway are a hallmark of cancer and significant efforts toward pharmaceutical reactivation of mutant p53 pathways are underway1-3. Here we show that restoration of p53 in established murine lung tumors leads to significant but incomplete tumor cell loss specifically in malignant adenocarcinomas but not in adenomas. Also, we define amplification of MAPK signaling as a critical determinant of malignant progression. The differential response to p53 restoration depends on activation of the Arf tumor suppressor downstream of hyperactive MAPK signaling. We propose that p53 naturally limits malignant progression by responding to increased oncogenic signaling, but is unresponsive to low levels of oncogene activity that are sufficient for early stages of lung tumor development. These data suggest that restoration of pathways important in tumor progression, as opposed to initiation, may lead to incomplete tumor regression due to the stage-heterogeneity of tumor cell populations. 3 cell lines each treated with Tamoxifen or EtOH vehicle. Tamoxifen treatment results in reactivation of p53 expression
Project description:Functional analysis in mouse models is necessary to establish the involvement of a set of genetic variations in tumor development. Many lung cancer models have been developed using genetic techniques to create gain- or loss-of-function alleles in genes involved in tumorigenesis; however, because of their labor- and time-intensive nature, these models are not suitable for quick and flexible hypothesis testing. Here we introduce a lung mutagenesis platform that utilizes CRISPR/Cas9 RNPs delivered via cationic polymers. This approach allows for the simultaneous inactivation of multiple genes. We validate the effectiveness of this system by targeting a group of tumor suppressor genes, specifically Rb1, Rbl1, Pten, and Trp53. chosen for their potential to cause lung tumors. This polymer-based delivery platform enables the modeling of lung tumorigenesis independently of the genetic background, simplifying and expediting the process without the need for modifying the mouse germline or creating custom viral vectors.