KRAS and YAP1 converge to regulate EMT and tumor survival.

Cancer cells that express oncogenic alleles of RAS typically require sustained expression of the mutant allele for survival, but the molecular basis of this oncogene dependency remains incompletely understood. To identify genes that can functionally substitute for oncogenic RAS, we systematically expressed 15,294 open reading frames in a human KRAS-dependent colon cancer cell line engineered to express an inducible KRAS-specific shRNA. We found 147 genes that promoted survival upon KRAS suppression. In particular, the transcriptional coactivator YAP1 rescued cell viability in KRAS-dependent cells upon suppression of KRAS and was required for KRAS-induced cell transformation. Acquired resistance to Kras suppression in a Kras-driven murine lung cancer model also involved increased YAP1 signaling. KRAS and YAP1 converge on the transcription factor FOS and activate a transcriptional program involved in regulating the epithelial-mesenchymal transition (EMT). Together, these findings implicate transcriptional regulation of EMT by YAP1 as a significant component of oncogenic RAS signaling.

ß-Catenin-driven cancers require a YAP1 transcriptional complex for survival and tumorigenesis.

Wnt/ß-catenin signaling plays a key role in the pathogenesis of colon and other cancers; emerging evidence indicates that oncogenic ß-catenin regulates several biological processes essential for cancer initiation and progression. To decipher the role of ß-catenin in transformation, we classified ß-catenin activity in 85 cancer cell lines in which we performed genome-scale loss-of-function screens and found that ß-catenin active cancers are dependent on a signaling pathway involving the transcriptional regulator YAP1. Specifically, we found that YAP1 and the transcription factor TBX5 form a complex with ß-catenin. Phosphorylation of YAP1 by the tyrosine kinase YES1 leads to localization of this complex to the promoters of antiapoptotic genes, including BCL2L1 and BIRC5. A small-molecule inhibitor of YES1 impeded the proliferation of ß-catenin-dependent cancers in both cell lines and animal models. These observations define a ß-catenin-YAP1-TBX5 complex essential to the transformation and survival of ß-catenin-driven cancers.

Cancer vulnerabilities unveiled by genomic loss.

Due to genome instability, most cancers exhibit loss of regions containing tumor suppressor genes and collateral loss of other genes. To identify cancer-specific vulnerabilities that are the result of copy number losses, we performed integrated analyses of genome-wide copy number and RNAi profiles and identified 56 genes for which gene suppression specifically inhibited the proliferation of cells harboring partial copy number loss of that gene. These CYCLOPS (copy number alterations yielding cancer liabilities owing to partial loss) genes are enriched for spliceosome, proteasome, and ribosome components. One CYCLOPS gene, PSMC2, encodes an essential member of the 19S proteasome. Normal cells express excess PSMC2, which resides in a complex with PSMC1, PSMD2, and PSMD5 and acts as a reservoir protecting cells from PSMC2 suppression. Cells harboring partial PSMC2 copy number loss lack this complex and die after PSMC2 suppression. These observations define a distinct class of cancer-specific liabilities resulting from genome instability.

Identification of resistance mechanisms to small-molecule inhibition of TEAD-regulated transcription.

The Hippo tumor suppressor pathway controls transcription by regulating nuclear abundance of YAP and TAZ, which activate transcription with the TEAD1-TEAD4 DNA-binding proteins. Recently, several small-molecule inhibitors of YAP and TEADs have been reported, with some entering clinical trials for different cancers with Hippo pathway deregulation, most notably, mesothelioma. Using genome-wide CRISPR/Cas9 screens we reveal that mutations in genes from the Hippo, MAPK, and JAK-STAT signaling pathways all modulate the response of mesothelioma cell lines to TEAD palmitoylation inhibitors. By exploring gene expression programs of mutant cells, we find that MAPK pathway hyperactivation confers resistance to TEAD inhibition by reinstating expression of a subset of YAP/TAZ target genes. Consistent with this, combined inhibition of TEAD and the MAPK kinase MEK, synergistically blocks proliferation of multiple mesothelioma and lung cancer cell lines and more potently reduces the growth of patient-derived lung cancer xenografts in vivo. Collectively, we reveal mechanisms by which cells can overcome small-molecule inhibition of TEAD palmitoylation and potential strategies to enhance the anti-tumor activity of emerging Hippo pathway targeted therapies.

CRISPR-Cas13d screens identify KILR, a breast cancer risk-associated lncRNA that regulates DNA replication and repair.

BACKGROUND: Long noncoding RNAs (lncRNAs) have surpassed the number of protein-coding genes, yet the majority have no known function. We previously discovered 844 lncRNAs that were genetically linked to breast cancer through genome-wide association studies (GWAS). Here, we show that a subset of these lncRNAs alter breast cancer risk by modulating cell proliferation, and provide evidence that a reduced expression on one lncRNA increases breast cancer risk through aberrant DNA replication and repair. METHODS: We performed pooled CRISPR-Cas13d-based knockdown screens in breast cells to identify which of the 844 breast cancer-associated lncRNAs alter cell proliferation. We selected one of the lncRNAs that increased cell proliferation, KILR, for follow-up functional studies. KILR pull-down followed by mass spectrometry was used to identify binding proteins. Knockdown and overexpression studies were performed to assess the mechanism by which KILR regulates proliferation. RESULTS: We show that KILR functions as a tumor suppressor, safeguarding breast cells against uncontrolled proliferation. The half-life of KILR is significantly reduced by the risk haplotype, revealing an alternative mechanism by which variants alter cancer risk. Mechanistically, KILR sequesters RPA1, a subunit of the RPA complex required for DNA replication and repair. Reduced KILR expression promotes breast cancer cell proliferation by increasing the available pool of RPA1 and speed of DNA replication. Conversely, KILR overexpression promotes apoptosis in breast cancer cells, but not normal breast cells. CONCLUSIONS: Our results confirm lncRNAs as mediators of breast cancer risk, emphasize the need to annotate noncoding transcripts in relevant cell types when investigating GWAS variants and provide a scalable platform for mapping phenotypes associated with lncRNAs.

Inwardly rectifying potassium channels mediate polymyxin-induced nephrotoxicity.

Polymyxin antibiotics are often used as a last-line defense to treat life-threatening Gram-negative pathogens. However, polymyxin-induced kidney toxicity is a dose-limiting factor of paramount importance and can lead to suboptimal treatment. To elucidate the mechanism and develop effective strategies to overcome polymyxin toxicity, we employed a whole-genome CRISPR screen in human kidney tubular HK-2 cells and identified 86 significant genes that upon knock-out rescued polymyxin-induced toxicity. Specifically, we discovered that knockout of the inwardly rectifying potassium channels Kir4.2 and Kir5.1 (encoded by KCNJ15 and KCNJ16, respectively) rescued polymyxin-induced toxicity in HK-2 cells. Furthermore, we found that polymyxins induced cell depolarization via Kir4.2 and Kir5.1 and a significant cellular uptake of polymyxins was evident. All-atom molecular dynamics simulations revealed that polymyxin B1 spontaneously bound to Kir4.2, thereby increasing opening of the channel, resulting in a potassium influx, and changes of the membrane potential. Consistent with these findings, small molecule inhibitors (BaCl2 and VU0134992) of Kir potassium channels reduced polymyxin-induced toxicity in cell culture and mouse explant kidney tissue. Our findings provide critical mechanistic information that will help attenuate polymyxin-induced nephrotoxicity in patients and facilitate the design of novel, safer polymyxins.

GeNets: a unified web platform for network-based genomic analyses.

Functional genomics networks are widely used to identify unexpected pathway relationships in large genomic datasets. However, it is challenging to compare the signal-to-noise ratios of different networks and to identify the optimal network with which to interpret a particular genetic dataset. We present GeNets, a platform in which users can train a machine-learning model (Quack) to carry out these comparisons and execute, store, and share analyses of genetic and RNA-sequencing datasets.

Loss of ATRX, genome instability, and an altered DNA damage response are hallmarks of the alternative lengthening of telomeres pathway.

The Alternative Lengthening of Telomeres (ALT) pathway is a telomerase-independent pathway for telomere maintenance that is active in a significant subset of human cancers and in vitro immortalized cell lines. ALT is thought to involve templated extension of telomeres through homologous recombination, but the genetic or epigenetic changes that unleash ALT are not known. Recently, mutations in the ATRX/DAXX chromatin remodeling complex and histone H3.3 were found to correlate with features of ALT in pancreatic neuroendocrine cancers, pediatric glioblastomas, and other tumors of the central nervous system, suggesting that these mutations might contribute to the activation of the ALT pathway in these cancers. We have taken a comprehensive approach to deciphering ALT by applying genomic, molecular biological, and cell biological approaches to a panel of 22 ALT cell lines, including cell lines derived in vitro. Here we show that loss of ATRX protein and mutations in the ATRX gene are hallmarks of ALT-immortalized cell lines. In addition, ALT is associated with extensive genome rearrangements, marked micronucleation, defects in the G2/M checkpoint, and altered double-strand break (DSB) repair. These attributes will facilitate the diagnosis and treatment of ALT positive human cancers.

Systematic loss-of-function screens identify pathway-specific functional circular RNAs.

Circular RNA (circRNA) is covalently closed, single-stranded RNA produced by back-splicing. A few circRNAs have been implicated as functional; however, we lack understanding of pathways that are regulated by circRNAs. Here we generated a pooled short-hairpin RNA library targeting the back-splice junction of 3,354 human circRNAs that are expressed at different levels (ranging from low to high) in humans. We used this library for loss-of-function proliferation screens in a panel of 18 cancer cell lines from four tissue types harbouring mutations leading to constitutive activity of defined pathways. Both context-specific and non-specific circRNAs were identified. Some circRNAs were found to directly regulate their precursor, whereas some have a function unrelated to their precursor. We validated these observations with a secondary screen and uncovered a role for circRERE(4-10) and circHUWE1(22,23), two cell-essential circRNAs, circSMAD2(2-6), a WNT pathway regulator, and circMTO1(2,RI,3), a regulator of MAPK signalling. Our work sheds light on pathways regulated by circRNAs and provides a catalogue of circRNAs with a measurable function.

Pattern of retinoblastoma pathway inactivation dictates response to CDK4/6 inhibition in GBM.

Glioblastoma multiforme (GBM) is a fatal primary brain tumor harboring myriad genetic and epigenetic alterations. The recent multidimensional analysis of the GBM genome has provided a more complete view of the landscape of such alterations and their linked pathways. This effort has demonstrated that certain pathways are universally altered, but that the specific genetic events altered within each pathway can vary for each particular patient's tumor. With this atlas of genetic and epigenetic events, it now becomes feasible to assess how the patterns of mutations in a pathway influence response to drugs that are targeting such pathways. This issue is particularly important for GBM because, in contrast to other tumor types, molecularly targeted therapies have failed to alter overall survival substantially. Here, we combined functional genetic screens and comprehensive genomic analyses to identify CDK6 as a GBM oncogene that is required for proliferation and viability in a subset of GBM cell lines and tumors. Using an available small molecule targeting cyclin-dependent kinases (CDKs) 4 and 6, we sought to determine if the specific pattern of retinoblastoma pathway inactivation dictated the response to CDK4/6 inhibitor therapy. We showed that codeletion of CDKN2A and CDKN2C serves as a strong predictor of sensitivity to a selective inhibitor of CDK4/6. Thus, genome-informed drug sensitivity studies identify a subset of GBMs likely to respond to CDK4/6 inhibition. More generally, these observations demonstrate that the integration of genomic, functional and pharmacologic data can be exploited to inform the development of targeted therapy directed against specific cancer pathways.

Technological Convergence: Highlighting the Power of CRISPR Single-Cell Perturbation Toolkit for Functional Interrogation of Enhancers.

Higher eukaryotic enhancers, as a major class of regulatory elements, play a crucial role in the regulation of gene expression. Over the last decade, the development of sequencing technologies has flooded researchers with transcriptome-phenotype data alongside emerging candidate regulatory elements. Since most methods can only provide hints about enhancer function, there have been attempts to develop experimental and computational approaches that can bridge the gap in the causal relationship between regulatory regions and phenotypes. The coupling of two state-of-the-art technologies, also referred to as crisprQTL, has emerged as a promising high-throughput toolkit for addressing this question. This review provides an overview of the importance of studying enhancers, the core molecular foundation of crisprQTL, and recent studies utilizing crisprQTL to interrogate enhancer-phenotype correlations. Additionally, we discuss computational methods currently employed for crisprQTL data analysis. We conclude by pointing out common challenges, making recommendations, and looking at future prospects, with the aim of providing researchers with an overview of crisprQTL as an important toolkit for studying enhancers.

Heritable methylation marks associated with prostate cancer risk.

DNA methylation marks that are inherited from parents to offspring are known to play a role in cancer risk and could explain part of the familial risk for cancer. We therefore conducted a genome-wide search for heritable methylation marks associated with prostate cancer risk. Peripheral blood DNA methylation was measured for 133 of the 469 members of 25 multiple-case prostate cancer families, using the EPIC array. We used these families to systematically search the genome for methylation marks with Mendelian patterns of inheritance, then we tested the 1,000 most heritable marks for association with prostate cancer risk. After correcting for multiple testing, 41 heritable methylation marks were associated with prostate cancer risk. Separate analyses, based on 869 incident cases and 869 controls from a prospective cohort study, showed that 9 of these marks near the metastable epiallele VTRNA2-1 were also nominally associated with aggressive prostate cancer risk in the population.

Pediatric glioma histone H3.3 K27M/G34R mutations drive abnormalities in PML nuclear bodies.

BACKGROUND: Point mutations in histone variant H3.3 (H3.3K27M, H3.3G34R) and the H3.3-specific ATRX/DAXX chaperone complex are frequent events in pediatric gliomas. These H3.3 point mutations affect many chromatin modifications but the exact oncogenic mechanisms are currently unclear. Histone H3.3 is known to localize to nuclear compartments known as promyelocytic leukemia (PML) nuclear bodies, which are frequently mutated and confirmed as oncogenic drivers in acute promyelocytic leukemia. RESULTS: We find that the pediatric glioma-associated H3.3 point mutations disrupt the formation of PML nuclear bodies and this prevents differentiation down glial lineages. Similar to leukemias driven by PML mutations, H3.3-mutated glioma cells are sensitive to drugs that target PML bodies. We also find that point mutations in IDH1/2-which are common events in adult gliomas and myeloid leukemias-also disrupt the formation of PML bodies. CONCLUSIONS: We identify PML as a contributor to oncogenesis in a subset of gliomas and show that targeting PML bodies is effective in treating these H3.3-mutated pediatric gliomas.

CRISPR screens identify gene targets at breast cancer risk loci.

BACKGROUND: Genome-wide association studies (GWAS) have identified > 200 loci associated with breast cancer risk. The majority of candidate causal variants are in non-coding regions and likely modulate cancer risk by regulating gene expression. However, pinpointing the exact target of the association, and identifying the phenotype it mediates, is a major challenge in the interpretation and translation of GWAS. RESULTS: Here, we show that pooled CRISPR screens are highly effective at identifying GWAS target genes and defining the cancer phenotypes they mediate. Following CRISPR mediated gene activation or suppression, we measure proliferation in 2D, 3D, and in immune-deficient mice, as well as the effect on DNA repair. We perform 60 CRISPR screens and identify 20 genes predicted with high confidence to be GWAS targets that promote cancer by driving proliferation or modulating the DNA damage response in breast cells. We validate the regulation of a subset of these genes by breast cancer risk variants. CONCLUSIONS: We demonstrate that phenotypic CRISPR screens can accurately pinpoint the gene target of a risk locus. In addition to defining gene targets of risk loci associated with increased breast cancer risk, we provide a platform for identifying gene targets and phenotypes mediated by risk variants.

Immortalised Cas9-expressing Cell lines for Gene interrogation.

The ability of modifying the genome of multiple species, precisely and without or minimal off-targeted effects, have opened numerous opportunities for the biotechnology industry. In this chapter, we describe an easy to establish, robust, and practical pipeline that can be used to generate immortalized cell lines, from different tissues, to capture cell linage context and validate the tools required for genome editing and genetic modification. This pipeline serves as a reference for similar approaches for gene interrogation in other species.

CRISPRi enables isoform-specific loss-of-function screens and identification of gastric cancer-specific isoform dependencies.

INTRODUCTION: Genes contain multiple promoters that can drive the expression of various transcript isoforms. Although transcript isoforms from the same gene could have diverse and non-overlapping functions, current loss-of-function methodologies are not able to differentiate between isoform-specific phenotypes. RESULTS: Here, we show that CRISPR interference (CRISPRi) can be adopted for targeting specific promoters within a gene, enabling isoform-specific loss-of-function genetic screens. We use this strategy to test functional dependencies of 820 transcript isoforms that are gained in gastric cancer (GC). We identify a subset of GC-gained transcript isoform dependencies, and of these, we validate CIT kinase as a novel GC dependency. We further show that some genes express isoforms with opposite functions. Specifically, we find that the tumour suppressor ZFHX3 expresses an isoform that has a paradoxical oncogenic role that correlates with poor patient outcome. CONCLUSIONS: Our work finds isoform-specific phenotypes that would not be identified using current loss-of-function approaches that are not designed to target specific transcript isoforms.

Integration of HIV-1 DNA is regulated by interplay between viral rev and cellular LEDGF/p75 proteins.

The present work describes a novel interaction between the human immunodeficiency virus type 1 (HIV-1) Rev protein and the cellular lens epithelium-derived growth factor p75 (LEDGF/p75) protein in vitro and in virus-infected cells. Here we show, for the first time, that formation of an Rev-LEDGF/p75 complex is a crucial step in regulating viral cDNA integration. Coimmunoprecipitation experiments at various times after virus infection revealed that, first, an integrase enzyme (IN)-LEDGF/p75 complex is formed, which is then replaced by a Rev-LEDGF/p75 and Rev-IN complexes. This was supported by in vitro experiments showing that Rev promotes dissociation of the IN-LEDGF/p75 complex. Combination of the viral IN and the cellular LEDGF/p75 is required for proper integration of the viral cDNA into the host chromosomal DNA. Our findings demonstrate that integration of HIV-1 cDNA is regulated by an interplay between viral Rev and the host-cell LEDGF/p75 proteins.

Engineered Plant-Based Nanocellulose Hydrogel for Small Intestinal Organoid Growth.

Organoids are three-dimensional self-renewing and organizing clusters of cells that recapitulate the behavior and functionality of developed organs. Referred to as "organs in a dish," organoids are invaluable biological models for disease modeling or drug screening. Currently, organoid culture commonly relies on an expensive and undefined tumor-derived reconstituted basal membrane which hinders its application in high-throughput screening, regenerative medicine, and diagnostics. Here, we introduce a novel engineered plant-based nanocellulose hydrogel is introduced as a well-defined and low-cost matrix that supports organoid growth. Gels containing 0.1% nanocellulose fibers (99.9% water) are ionically crosslinked and present mechanical properties similar to the standard animal-based matrix. The regulation of the osmotic pressure is performed by a salt-free strategy, offering conditions for cell survival and proliferation. Cellulose nanofibers are functionalized with fibronectin-derived adhesive sites to provide the required microenvironment for small intestinal organoid growth and budding. Comparative transcriptomic profiling reveals a good correlation with transcriptome-wide gene expression pattern between organoids cultured in both materials, while differences are observed in stem cells-specific marker genes. These hydrogels are tunable and can be combined with laminin-1 and supplemented with insulin-like growth factor (IGF-1) to optimize the culture conditions. Nanocellulose hydrogel emerges as a promising matrix for the growth of organoids.

Chromatin interactome mapping at 139 independent breast cancer risk signals.

BACKGROUND: Genome-wide association studies have identified 196 high confidence independent signals associated with breast cancer susceptibility. Variants within these signals frequently fall in distal regulatory DNA elements that control gene expression. RESULTS: We designed a Capture Hi-C array to enrich for chromatin interactions between the credible causal variants and target genes in six human mammary epithelial and breast cancer cell lines. We show that interacting regions are enriched for open chromatin, histone marks for active enhancers, and transcription factors relevant to breast biology. We exploit this comprehensive resource to identify candidate target genes at 139 independent breast cancer risk signals and explore the functional mechanism underlying altered risk at the 12q24 risk region. CONCLUSIONS: Our results demonstrate the power of combining genetics, computational genomics, and molecular studies to rationalize the identification of key variants and candidate target genes at breast cancer GWAS signals.

Inhibition of HIV-1 integrase nuclear import and replication by a peptide bearing integrase putative nuclear localization signal.

BACKGROUND: The integrase (IN) of human immunodeficiency virus type 1 (HIV-1) has been implicated in different steps during viral replication, including nuclear import of the viral pre-integration complex. The exact mechanisms underlying the nuclear import of IN and especially the question of whether it bears a functional nuclear localization signal (NLS) remain controversial. RESULTS: Here, we studied the nuclear import pathway of IN by using multiple in vivo and in vitro systems. Nuclear import was not observed in an importin alpha temperature-sensitive yeast mutant, indicating an importin alpha-mediated process. Direct interaction between the full-length IN and importin alpha was demonstrated in vivo using bimolecular fluorescence complementation assay (BiFC). Nuclear import studies in yeast cells, with permeabilized mammalian cells, or microinjected cultured mammalian cells strongly suggest that the IN bears a NLS domain located between residues 161 and 173. A peptide bearing this sequence -NLS-IN peptide- inhibited nuclear accumulation of IN in transfected cell-cycle arrested cells. Integration of viral cDNA as well as HIV-1 replication in viral cell-cycle arrested infected cells were blocked by the NLS-IN peptide. CONCLUSION: Our present findings support the view that nuclear import of IN occurs via the importin alpha pathway and is promoted by a specific NLS domain. This import could be blocked by NLS-IN peptide, resulting in inhibition of viral infection, confirming the view that nuclear import of the viral pre-integration complex is mediated by viral IN.