Acute expression of human APOBEC3B in mice results in RNA editing and lethality.

BACKGROUND: RNA editing has been described as promoting genetic heterogeneity, leading to the development of multiple disorders, including cancer. The cytosine deaminase APOBEC3B is implicated in tumor evolution through DNA mutation, but whether it also functions as an RNA editing enzyme has not been studied. RESULTS: Here, we engineer a novel doxycycline-inducible mouse model of human APOBEC3B-overexpression to understand the impact of this enzyme in tissue homeostasis and address a potential role in C-to-U RNA editing. Elevated and sustained levels of APOBEC3B lead to rapid alteration of cellular fitness, major organ dysfunction, and ultimately lethality in mice. Importantly, RNA-sequencing of mouse tissues expressing high levels of APOBEC3B identifies frequent UCC-to-UUC RNA editing events that are not evident in the corresponding genomic DNA. CONCLUSIONS: This work identifies, for the first time, a new deaminase-dependent function for APOBEC3B in RNA editing and presents a preclinical tool to help understand the emerging role of APOBEC3B as a driver of carcinogenesis.

Generation of Human Lung Organoid Cultures from Healthy and Tumor Tissue to Study Infectious Diseases.

Respiratory viruses cause mild to severe diseases in humans every year, constituting a major public health problem. Characterizing the pathogenesis in physiologically relevant models is crucial for developing efficient vaccines and therapeutics. Here, we show that lung organoids derived from human primary or lung tumor tissue maintain the cellular composition and characteristics of the original tissue. Moreover, we show that these organoids sustain viral replication with particular infection foci formation, and they activate the expression of interferon-associated and proinflammatory genes responsible for mediating a robust innate immune response. All together, we show that three-dimensional (3D) lung organoids constitute a relevant platform to model diseases and enable the development of drug screenings. IMPORTANCE Three-dimensional (3D) human lung organoids reflect the native cell composition of the lung as well as its physiological properties. Human 3D lung organoids offer ideal conditions, such as timely availability in large quantities and high physiological relevance for reassessment and prediction of disease outbreaks of respiratory pathogens and pathogens that use the lung as a primary entry portal. Human lung organoids can be used in basic research and diagnostic settings as early warning cell culture systems and also serve as a relevant platform for modeling infectious diseases and drug development. They can be used to characterize pathogens and analyze the influence of infection on, for example, immunological parameters, such as the expression of interferon-associated and proinflammatory genes in the context of cancer. In our study, we found that cancer-derived lung organoids were more sensitive to influenza A virus infection than those derived from healthy tissue and demonstrated a decreased innate immune response.

Acquisition of chromosome instability is a mechanism to evade oncogene addiction.

Chromosome instability (CIN) has been associated with therapeutic resistance in many cancers. However, whether tumours become genomically unstable as an evolutionary mechanism to overcome the bottleneck exerted by therapy is not clear. Using a CIN model of Kras-driven breast cancer, we demonstrate that aneuploid tumours acquire genetic modifications that facilitate the development of resistance to targeted therapy faster than euploid tumours. We further show that the few initially chromosomally stable cancers that manage to persist during treatment do so concomitantly with the acquisition of CIN. Whole-genome sequencing analysis revealed that the most predominant genetic alteration in resistant tumours, originated from either euploid or aneuploid primary tumours, was an amplification on chromosome 6 containing the cMet oncogene. We further show that these tumours are dependent on cMet since its pharmacological inhibition leads to reduced growth and increased cell death. Our results highlight that irrespective of the initial CIN levels, cancer genomes are dynamic and the acquisition of a certain level of CIN, either induced or spontaneous, is a mechanism to circumvent oncogene addiction.

Plk1 overexpression induces chromosomal instability and suppresses tumor development.

Polo-like kinase 1 (Plk1) is overexpressed in a wide spectrum of human tumors, being frequently considered as an oncogene and an attractive cancer target. However, its contribution to tumor development is unclear. Using a new inducible knock-in mouse model we report here that Plk1 overexpression results in abnormal chromosome segregation and cytokinesis, generating polyploid cells with reduced proliferative potential. Mechanistically, these cytokinesis defects correlate with defective loading of Cep55 and ESCRT complexes to the abscission bridge, in a Plk1 kinase-dependent manner. In vivo, Plk1 overexpression prevents the development of Kras-induced and Her2-induced mammary gland tumors, in the presence of increased rates of chromosome instability. In patients, Plk1 overexpression correlates with improved survival in specific breast cancer subtypes. Therefore, despite the therapeutic benefits of inhibiting Plk1 due to its essential role in tumor cell cycles, Plk1 overexpression has tumor-suppressive properties by perturbing mitotic progression and cytokinesis.

Pan-cancer analysis distinguishes transcriptional changes of aneuploidy from proliferation.

Patterns of gene expression in tumors can arise as a consequence of or result in genomic instability, characterized by the accumulation of somatic copy number alterations (SCNAs) and point mutations (PMs). Expression signatures have been widely used as markers for genomic instability, and both SCNAs and PMs could be thought to associate with distinct signatures given their different formation mechanisms. Here we test this notion by systematically investigating SCNA, PM, and transcriptome data from 2660 cancer patients representing 11 tumor types. Notably, our data indicate that similar expression signatures can be derived from correlating gene expression with either SCNA or PM load. Gene sets related to cell growth and proliferation generally associated positively, and immunoregulatory gene sets negatively, with variant burden. In-depth analyses revealed several genes whose de-regulation correlates with SCNA but not with PM burden, yielding downstream effectors of TP53 and MYC signaling unique to high-SCNA tumors. We compared our findings to expression changes observed in two different cancer mouse models with persistent mitotic chromosomal instability, observing a decrease in proliferative expression signatures. Our results suggest that overexpression of cell-cycle-related genes are a characteristic of proliferation, and likely tumor evolution, rather than ongoing genomic instability.