Complex-dependent histone acetyltransferase activity of KAT8 determines its role in transcription and cellular homeostasis.

Acetylation of lysine 16 on histone H4 (H4K16ac) is catalyzed by histone acetyltransferase KAT8 and can prevent chromatin compaction in vitro. Although extensively studied in Drosophila, the functions of H4K16ac and two KAT8-containing protein complexes (NSL and MSL) are not well understood in mammals. Here, we demonstrate a surprising complex-dependent activity of KAT8: it catalyzes H4K5ac and H4K8ac as part of the NSL complex, whereas it catalyzes the bulk of H4K16ac as part of the MSL complex. Furthermore, we show that MSL complex proteins and H4K16ac are not required for cell proliferation and chromatin accessibility, whereas the NSL complex is essential for cell survival, as it stimulates transcription initiation at the promoters of housekeeping genes. In summary, we show that KAT8 switches catalytic activity and function depending on its associated proteins and that, when in the NSL complex, it catalyzes H4K5ac and H4K8ac required for the expression of essential genes.

Serum-based measurements of stromal activation through ADAM12 associate with poor prognosis in colorectal cancer.

BACKGROUND: Recently it has been recognized that stromal markers could be used as a clinically relevant biomarker for therapy response and prognosis. Here, we report on a serum marker for stromal activation, A Disintegrin and Metalloprotease 12 (ADAM12) in colorectal cancer (CRC). METHODS: Using gene expression databases we investigated ADAM12 expression in CRC and delineated the source of ADAM12 expression. The clinical value of ADAM12 was retrospectively assessed in the CAIRO2 trial in metastatic CRC with 235 patients (31% of total cohort), and an independent rectal cancer cohort (n = 20). RESULTS: ADAM12 is expressed by activated CRC associated fibroblasts. In the CAIRO2 trial cohort, ADAM12 serum levels were prognostic (ADAM12 low versus ADAM12 high; median OS 25.3 vs. 17.1 months, HR 1.48 [95% CI 1.11-1.96], P = 0.007). The prognostic potential was specifically high for metastatic rectal cancer (HR 1.78 [95% CI 1.06-3.00], P = 0.030) and mesenchymal subtype tumors (HR 2.12 [95% CI 1.25-3.60], P = 0.004). ADAM12 also showed potential for predicting recurrence in an exploratory analysis of non-metastatic rectal cancers. CONCLUSIONS: Here we describe a non-invasive marker for activated stroma in CRC which associates with poor outcome, especially for primary cancers located in the rectum.

Dabigatran potentiates gemcitabine-induced growth inhibition of pancreatic cancer in mice.

Pancreatic cancer is one of the most lethal solid malignancies with little treatment options. We have recently shown that expression of protease activated receptor (PAR)-1 in the tumor microenvironment drives progression and induces chemoresistance of pancreatic cancer. As thrombin is the prototypical PAR-1 agonist, here we addressed the effect of the direct thrombin inhibitor dabigatran on pancreatic cancer growth and drug resistance in an orthotropic pancreatic cancer model. We show that dabigatran treatment did not affect primary tumor growth whereas it significantly increased tumor dissemination throughout the peritoneal cavity. Increased dissemination was accompanied by intratumoral bleeding and increased numbers of aberrant and/or collapsed blood vessels in the primary tumors. In combination with gemcitabine, dabigatran treatment limited primary tumor growth, did not induce bleeding complications and prevented tumor cell dissemination. Dabigatran was however not as efficient as genetic ablation of PAR-1 in our previous study suggesting that thrombin is not the main PAR-1 agonist in the setting of pancreatic cancer. Overall, we show that dabigatran potentiates gemcitabine-induced growth inhibition of pancreatic cancer but does not affect primary tumor growth when used as a monotherapy.

Blocking Hedgehog release from pancreatic cancer cells increases paracrine signaling potency.

Members of the Hedgehog (Hh) family of morphogens play crucial roles in development but are also involved in the progression of certain types of cancer. Despite being synthesized as hydrophobic dually lipid-modified molecules, and thus being strongly membrane-associated, Hh ligands are able to spread through tissues and act on target cells several cell diameters away. Various mechanisms that mediate Hh release have been discussed in recent years; however, little is known about dispersion of this ligand from cancer cells. Using co-culture models in conjunction with a newly developed reporter system, we were able to show that different members of the ADAM family of metalloproteinases strongly contribute to the release of endogenous bioactive Hh from pancreatic cancer cells, but that this solubilization decreases the potency of cancer cells to signal to adjacent stromal cells in direct co-culture models. These findings imply that under certain conditions, cancer-cell-tethered Hh molecules are the more potent signaling activators and that retaining Hh on the surface of cancer cells can unexpectedly increase the effective signaling range of this ligand, depending on tissue context.

Establishment of patient-derived xenograft models and cell lines for malignancies of the upper gastrointestinal tract.

BACKGROUND: The upper gastrointestinal tract is home to some of most notorious cancers like esophagogastric and pancreatic cancer. Several factors contribute to the lethality of these tumors, but one that stands out for both tumor types is the strong inter- as well as intratumor heterogeneity. Unfortunately, genetic tumor models do not match this heterogeneity, and for esophageal cancer no adequate genetic models exist. To allow for an improved understanding of these diseases, tissue banks with sufficient amount of samples to cover the extent of diversity of human cancers are required. Additionally, xenograft models that faithfully mimic and span the breadth of human disease are essential to perform meaningful functional experiments. METHODS: We describe here the establishment of a tissue biobank, patient derived xenografts (PDXs) and cell line models of esophagogastric and pancreatic cancer patients. Biopsy material was grafted into immunocompromised mice and PDXs were used to establish primary cell cultures to perform functional studies. Expression of Hedgehog ligands in patient tumor and matching PDX was assessed by immunohistochemical staining, and quantitative real-time PCR as well as flow cytometry was used for cultured cells. Cocultures with Hedgehog reporter cells were performed to study paracrine signaling potency. Furthermore, SHH expression was modulated in primary cultures using lentiviral mediated knockdown. RESULTS: We have established a panel of 29 PDXs from esophagogastric and pancreatic cancers, and demonstrate that these PDXs mirror several of the (immuno)histological and biochemical characteristics of the original tumors. Derived cell lines can be genetically manipulated and used to further study tumor biology and signaling capacity. In addition, we demonstrate an active (paracrine) Hedgehog signaling mode by both tumor types, the magnitude of which has not been compared directly in previous studies. CONCLUSIONS: Our established PDXs and their matching primary cell lines retain important characteristics seen in the original tumors, and this should enable future studies to address the responses of these tumors to different treatment modalities, but also help in gaining mechanistic insight in how some tumors respond to certain regimens and others do not.

TAK1 inhibition leads to RIPK1-dependent apoptosis in immune-activated cancers.

Poor survival and lack of treatment response in glioblastoma (GBM) is attributed to the persistence of glioma stem cells (GSCs). To identify novel therapeutic approaches, we performed CRISPR/Cas9 knockout screens and discovered TGFß activated kinase (TAK1) as a selective survival factor in a significant fraction of GSCs. Loss of TAK1 kinase activity results in RIPK1-dependent apoptosis via Caspase-8/FADD complex activation, dependent on autocrine TNFα ligand production and constitutive TNFR signaling. We identify a transcriptional signature associated with immune activation and the mesenchymal GBM subtype to be a characteristic of cancer cells sensitive to TAK1 perturbation and employ this signature to accurately predict sensitivity to the TAK1 kinase inhibitor HS-276. In addition, exposure to pro-inflammatory cytokines IFNγ and TNFα can sensitize resistant GSCs to TAK1 inhibition. Our findings reveal dependency on TAK1 kinase activity as a novel vulnerability in immune-activated cancers, including mesenchymal GBMs that can be exploited therapeutically.

Generation of locus-specific degradable tag knock-ins in mouse and human cell lines.

Protein degradation technologies represent a powerful functional genomics tool, allowing fast and controllable target protein depletion. Establishing these systems requires a knock-in of the degradation tag into both endogenous target gene alleles. Here, we provide a step-by-step protocol for the efficient generation of biallelic degradation tag knock-ins in mouse and human cell lines using CRISPR-Cas9. We use knockin of an endogenous Kansl3 degradation tag in mouse embryonic stem (ES) cells as an example but provide modifications for application in other cell types. For complete details on the use and execution of this protocol, please refer to Radzisheuskaya et al. (2021).

Unsupervised class discovery in pancreatic ductal adenocarcinoma reveals cell-intrinsic mesenchymal features and high concordance between existing classification systems.

Pancreatic ductal adenocarcinoma (PDAC) has the worst prognosis of all common cancers. However, divergent outcomes exist between patients, suggesting distinct underlying tumor biology. Here, we delineated this heterogeneity, compared interconnectivity between classification systems, and experimentally addressed the tumor biology that drives poor outcome. RNA-sequencing of 90 resected specimens and unsupervised classification revealed four subgroups associated with distinct outcomes. The worst-prognosis subtype was characterized by mesenchymal gene signatures. Comparative (network) analysis showed high interconnectivity with previously identified classification schemes and high robustness of the mesenchymal subtype. From species-specific transcript analysis of matching patient-derived xenografts we constructed dedicated classifiers for experimental models. Detailed assessments of tumor growth in subtyped experimental models revealed that a highly invasive growth pattern of mesenchymal subtype tumor cells is responsible for its poor outcome. Concluding, by developing a classification system tailored to experimental models, we have uncovered subtype-specific biology that should be further explored to improve treatment of a group of PDAC patients that currently has little therapeutic benefit from surgical treatment.

Patched-2 functions to limit Patched-1 deficient skin cancer growth.

PURPOSE: Basal cell carcinoma (BCC) is one of the most common skin cancers, and is typically driven by an aberrantly activated Hedgehog (Hh) pathway. The Hh pathway is regulated by interactions between the Patched-1 (Ptch1) and Smoothened (Smo) receptors. Smo is an activating receptor and is subject to inhibition by Ptch1. Following ligand binding to Ptch1, its inhibitory action is relieved and pathway activation occurs. This receptor interaction is pivotal to restraining uncontrolled cellular growth. Both receptors have been found to be frequently mutated in BCCs. Ptch2 is a Ptch1 paralog that exhibits overlapping functions in both normal development and tissue homeostasis. As yet, its contribution to cancer growth is poorly defined. Here we set out to assess how Ptch2 inhibits BCC growth. METHODS: We used several in vitro readouts for transcriptional and chemotactic Hh signaling in BCC-derived ASZ001 cells, and a novel xenograft model to assess in vivo BCC tumor growth. Gene editing by TALEN was used to untangle the different Ptch2-dependent responses to its ligand sonic hedgehog (Shh). RESULTS: We first defined the signaling competence of Ptch2 in Ptch1-deficient ASZ001 cells in vitro, and found that Ptch2 ligand binding drives their migration rather than eliciting a transcriptional response. We found that subsequent targeting of Ptch2 abrogated the chemotaxic effect. Next, we tested the contribution of Ptch2 to in vivo tumor growth using a xenograft model and found that reduced Ptch function results in increased tumor growth, but that selective pressure appatently acts against complete Ptch2 ablation. CONCLUSIONS: We conclude that like Ptch1, Ptch2 exerts a tumor-suppressive function in BCC cells, and that after targeting of both paralogs, ligand-independent activation of the Hh pathway contributes to tumor growth.

Accurate H3K27 methylation can be established de novo by SUZ12-directed PRC2.

Polycomb repressive complex 2 (PRC2) catalyzes methylation on lysine 27 of histone H3 (H3K27) and is required for maintaining transcriptional patterns and cellular identity, but the specification and maintenance of genomic PRC2 binding and H3K27 methylation patterns remain incompletely understood. Epigenetic mechanisms have been proposed, wherein pre-existing H3K27 methylation directs recruitment and regulates the catalytic activity of PRC2 to support its own maintenance. Here we investigate whether such mechanisms are required for specifying H3K27 methylation patterns in mouse embryonic stem cells (mESCs). Through re-expression of PRC2 subunits in PRC2-knockout cells that have lost all H3K27 methylation, we demonstrate that methylation patterns can be accurately established de novo. We find that regional methylation kinetics correlate with original methylation patterns even in their absence, and specification of the genomic PRC2 binding pattern is retained and specifically dependent on the PRC2 core subunit SUZ12. Thus, the H3K27 methylation patterns in mESCs are not dependent on self-autonomous epigenetic inheritance.

Stromal SPOCK1 supports invasive pancreatic cancer growth.

Pancreatic ductal adenocarcinoma (PDAC) is marked by an abundant stromal deposition. This stroma is suspected to harbor both tumor-promoting and tumor-suppressing properties. This is underscored by the disappointing results of stroma targeting in clinical studies. Given the complexity of tumor-stroma interaction in PDAC, there is a need to identify the stromal proteins that are predominantly tumor-promoting. One possible candidate is SPOCK1 that we previously identified in a screening effort in PDAC. We extensively mined PDAC gene expression datasets, and used species-specific transcript analysis in mixed-species models for PDAC to study the patterns and driver mechanisms of SPOCK1 expression in PDAC. Advanced organotypic coculture models with primary patient-derived tumor cells were used to further characterize the function of this protein. We found SPOCK1 expression to be predominantly stromal. Expression of SPOCK1 was associated with poor disease outcome. Coculture and ligand stimulation experiments revealed that SPOCK1 is expressed in response to tumor cell-derived transforming growth factor-beta. Functional assessment in cocultures demonstrated that SPOCK1 strongly affects the composition of the extracellular collagen matrix and by doing so, enables invasive tumor cell growth in PDAC. By defining the expression pattern and functional properties of SPOCK1 in pancreatic cancer, we have identified a stromal mediator of extracellular matrix remodeling that indirectly affects the aggressive behavior of PDAC cells. The recognition that stromal proteins actively contribute to the protumorigenic remodeling of the tumor microenvironment should aid the design of future clinical studies to target specific stromal targets.

ADAM10-mediated release of heregulin confers resistance to trastuzumab by activating HER3.

Receptor tyrosine kinases of the HER-family are involved in the development and progression of multiple epithelial tumors, and have consequently become widely used targets for new anti-cancer therapies. Trastuzumab, an antibody against HER2, has shown potent growth inhibitory effects on HER2 overexpressing tumors, including gastro-esophageal cancer, however, resistance to this therapy is inevitable. Unfortunately, a paucity of data on the cellular mechanisms of resistance to targeted therapeutic agents exists in esophageal adenocarcinoma. Using primary established HER2-overexpressing cultures and patient-derived xenograft models, we now reveal a novel resistance mechanism to trastuzumab in esophageal cancer: In response to trastuzumab, both HER3 and the metalloprotease ADAM10 are simultaneously upregulated. The proteolytic activity of the latter then releases the HER3 ligand heregulin from the cell surface to activate HER3 and confer resistance to trastuzumab by inducing compensatory growth factor receptor signaling. Blocking either HER3 or ADAM10 effectively reverts the acquired resistance to trastuzumab. Our data thus provide strategies to inhibit this signaling and circumvent resistance to trastuzumab.

Assessment of the stromal contribution to Sonic Hedgehog-dependent pancreatic adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal malignancies. It is typically detected at an advanced stage, at which the therapeutic options are very limited. One remarkable feature of PDAC that contributes to its resilience to treatment is the extreme stromal activation seen in these tumors. Often, the vast majority of tumor bulk consists of non-tumor cells that together provide a tumor-promoting environment. One of the signals that maintains and activates the stroma is the developmental protein Sonic Hedgehog (SHH). As the disease progresses, tumor cells produce increasing amounts of SHH, which activates the surrounding stroma to aid in tumor progression. To better understand this response and identify targets for inhibition, we aimed to elucidate the proteins that mediate the SHH-driven stromal response in PDAC. For this a novel mixed-species coculture model was set up in which the cancer cells are human, and the stroma is modeled by mouse fibroblasts. In conjunction with next-generation sequencing we were able to use the sequence difference between these species to genetically distinguish between the epithelial and stromal responses to SHH. The stromal SHH-dependent genes from this analysis were validated and their relevance for human disease was subsequently determined in two independent patient cohorts. In non-microdissected tissue from PDAC patients, in which a large amount of stroma is present, the targets were confirmed to associate with tumor stroma versus normal pancreatic tissue. Patient survival analysis and immunohistochemistry identified CDA, EDIL3, ITGB4, PLAUR and SPOCK1 as SHH-dependent stromal factors that are associated with poor prognosis in PDAC patients. Summarizing, the presented data provide insight into the role of the activated stroma in PDAC, and how SHH acts to mediate this response. In addition, the study has yielded several candidates that are interesting therapeutic targets for a disease for which treatment options are still inadequate.

Hedgehog-stimulated chemotaxis is mediated by smoothened located outside the primary cilium.

Regulation of the Hedgehog (Hh) pathway relies on an interaction of two receptors. In the absence of Hh, Patched1 (Ptch1) inhibits the pathway. Binding of the ligand Hh to Ptch1 stimulates the localization of the activating receptor Smoothened (Smo) to the primary cilium, which is required for the transcriptional Hh response. Hh can also induce chemotaxis through a nontranscriptional pathway. We assessed the effects of defective ciliary localization of Smo on its subcellular trafficking and ability to mediate chemotactic signaling. Cells expressing mutants of Smo that could not localize to the primary cilium or cells lacking the primary cilium showed altered intracellular trafficking of Smo and, in response to Hh or Smo agonists, decreased transcriptional signaling and enhanced chemotactic responsiveness. Thus, the ciliary localization machinery appears to transport Smo to subcellular sites where it can mediate transcriptional signaling and away from locations where it can mediate chemotactic signaling. The subcellular localization of Smo is thus a crucial determinant of its signaling characteristics and implies the existence of a pool of Smo dedicated to chemotaxis.

Hedgehog-EGFR cooperation response genes determine the oncogenic phenotype of basal cell carcinoma and tumour-initiating pancreatic cancer cells.

Inhibition of Hedgehog (HH)/GLI signalling in cancer is a promising therapeutic approach. Interactions between HH/GLI and other oncogenic pathways affect the strength and tumourigenicity of HH/GLI. Cooperation of HH/GLI with epidermal growth factor receptor (EGFR) signalling promotes transformation and cancer cell proliferation in vitro. However, the in vivo relevance of HH-EGFR signal integration and the critical downstream mediators are largely undefined. In this report we show that genetic and pharmacologic inhibition of EGFR signalling reduces tumour growth in mouse models of HH/GLI driven basal cell carcinoma (BCC). We describe HH-EGFR cooperation response genes including SOX2, SOX9, JUN, CXCR4 and FGF19 that are synergistically activated by HH-EGFR signal integration and required for in vivo growth of BCC cells and tumour-initiating pancreatic cancer cells. The data validate EGFR signalling as drug target in HH/GLI driven cancers and shed light on the molecular processes controlled by HH-EGFR signal cooperation, providing new therapeutic strategies based on combined targeting of HH-EGFR signalling and selected downstream target genes.