SNAIL1 employs ß-Catenin-LEF1 complexes to control colorectal cancer cell invasion and proliferation.

The transcription factor SNAIL1 is a master regulator of epithelial-to-mesenchymal transition (EMT), a process entailing massive gene expression changes. To better understand SNAIL1-induced transcriptional reprogramming we performed time-resolved transcriptome analysis upon conditional SNAIL1 expression in colorectal cancer cells. Gene set variation analyses indicated that SNAIL1 strongly affected features related to cell cycle and Wnt/ß-Catenin signalling. This correlated with upregulation of LEF1, a nuclear binding partner of ß-Catenin. Likewise, transcriptomes of cell lines and colorectal cancers, including poor-prognosis mesenchymal tumours, exhibit positively correlated SNAI1 and LEF1 expression, and elevated LEF1 levels parallel increased patient mortality. To delineate the functional contribution of LEF1 to SNAIL1-induced EMT, we used the CRISPR/Cas9 system to knock-out LEF1 in colorectal cancer cells, and to engineer cells that express LEF1 mutants unable to interact with ß-Catenin. Both complete LEF1-deficiency and prevention of the ß-Catenin-LEF1 interaction impaired the ability of SNAIL1 to elicit expression of an alternative set of Wnt/ß-catenin targets, and to promote cancer cell invasion. Conversely, overexpression of wildtype, but not of mutant LEF1, stimulated alternative Wnt/ß-Catenin target gene expression, and caused cell-cycle arrest. Moreover, like SNAIL1, LEF1 retarded tumour growth in xenotransplantations. Thus, LEF1 phenocopies SNAIL1 with respect to several critical aspects of EMT. Indeed, comparative transcriptomics suggested that 35% of SNAIL1-induced transcriptional changes are attributable to LEF1. However, LEF1 did not autonomously induce EMT. Rather, LEF1 appears to be a strictly ß-Catenin-dependent downstream effector of SNAIL1. Apparently, SNAIL1 employs ß-Catenin-LEF1 complexes to redirect Wnt/ß-Catenin pathway activity towards pro-invasive and anti-proliferative gene expression.

MicroRNA-100 Suppresses Chronic Vascular Inflammation by Stimulation of Endothelial Autophagy.

RATIONALE: The interaction of circulating cells within the vascular wall is a critical event in chronic inflammatory processes, such as atherosclerosis, but the control of the vascular inflammatory state is still largely unclear. OBJECTIVE: This study was undertaken to characterize the function of the endothelial-enriched microRNA miR-100 during vascular inflammation and atherogenesis. METHODS AND RESULTS: Based on a transcriptome analysis of endothelial cells after miR-100 overexpression, we identified miR-100 as a potent suppressor of endothelial adhesion molecule expression, resulting in attenuated leukocyte-endothelial interaction in vitro and in vivo as shown by flow cytometry and intravital imaging. Mechanistically, miR-100 directly repressed several components of mammalian target of rapamycin complex 1-signaling, including mammalian target of rapamycin and raptor, which resulted in a stimulation of endothelial autophagy and attenuated nuclear factor κB signaling in vitro and in vivo. In a low-density lipoprotein receptor-deficient atherosclerotic mouse model, pharmacological inhibition of miR-100 resulted in enhanced plaque lesion formation and a higher macrophage content of the plaque, whereas a systemic miR-100 replacement therapy had protective effects and attenuated atherogenesis, resulting in a decrease of plaque area by 45%. Finally, analysis of miR-100 expression in >70 samples obtained during carotid endarterectomy revealed that local miR-100 expression was inversely correlated with inflammatory cell content in patients. CONCLUSIONS: In summary, we describe an anti-inflammatory function of miR-100 in the vascular response to injury and inflammation and identify an important novel modulator of mammalian target of rapamycin signaling and autophagy in the vascular system. Our findings of miR-100 as a potential protective anti-athero-miR suggest that the therapeutic replacement of this microRNA could be a potential strategy for the treatment of chronic inflammatory diseases, such as atherosclerosis, in the future.

Metadherin exon 11 skipping variant enhances metastatic spread of ovarian cancer.

Metastatic ovarian cancer has a dismal prognosis and current chemotherapeutic approaches have very limited success. Metadherin (MTDH) is expressed in human ovarian cancer tissue and its expression inversely correlates with patients overall survival. Consistent with these studies, we observed MTDH expression in tissue specimens of FIGO Stage III ovarian carcinomas (72/83 cases). However, we also observed this in normal human ovarian epithelial (OE) cells, which raised the question of whether MTDH-variants with functional differences exist. We identified a novel MTDH exon 11 skipping variant (MTDHdel) which was seen at higher levels in ovarian cancer compared to benign OE cells. We analyzed MTDH-binding partner interactions and found that 12 members of the small ribosomal subunit and several mRNA binding proteins bound stronger to MTDHdel than to wildtype MTDH which indicates differential effects on gene translation. Knockdown of MTDH in ovarian cancer cells reduced the amount of distant metastases and improved the survival of ovarian cancer-bearing mice. Selective overexpression of the MTDHdel enhanced murine and human ovarian cancer progression and caused a malignant phenotype in originally benign human OE cells. MTDHdel was detectable in microdissected ovarian cancer cells of some human tissue specimens of ovarian carcinomas. In summary, we have identified a novel MTDH exon 11 skipping variant that shows enhanced binding to small ribosomal subunit members and that caused reduced overall survival of ovarian cancer bearing mice. Based on the findings in the murine system and in human tissues, MTDHdel must be considered a major promalignant factor for ovarian cancer.

Kinase Insert Domain Receptor Q472H Pathogenic Germline Variant Impacts Melanoma Tumor Growth and Patient Treatment Outcomes.

BACKGROUND: We previously reported a higher incidence of a pathogenic germline variant in the kinase insert domain receptor (KDR) in melanoma patients compared to the general population. Here, we dissect the impact of this genotype on melanoma tumor growth kinetics, tumor phenotype, and response to treatment with immune checkpoint inhibitors (ICIs) or targeted therapy. METHODS: The KDR genotype was determined and the associations between the KDR Q472H variant (KDR-Var), angiogenesis, tumor immunophenotype, and response to MAPK inhibition or ICI treatment were examined. Melanoma B16 cell lines were transfected with KDR-Var or KDR wild type (KDR-WT), and the differences in tumor kinetics were evaluated. We also examined the impact of KDR-Var on the response of melanoma cells to a combination of VEGFR inhibition with MAPKi. RESULTS: We identified the KDR-Var genotype in 81/489 (37%) patients, and it was associated with a more angiogenic (p = 0.003) and immune-suppressive tumor phenotype. KDR-Var was also associated with decreased PFS to MAPKi (p = 0.022) and a trend with worse PFS to anti-PD1 therapy (p = 0.06). KDR-Var B16 murine models had increased average tumor volume (p = 0.0027) and decreased CD45 tumor-infiltrating lymphocytes (p = 0.0282). The anti-VEGFR treatment Lenvatinib reduced the tumor size of KDR-Var murine tumors (p = 0.0159), and KDR-Var cells showed synergistic cytotoxicity to the combination of dabrafenib and lenvatinib. CONCLUSIONS: Our data demonstrate a role of germline KDR-Var in modulating melanoma behavior, including response to treatment. Our data also suggest that anti-angiogenic therapy might be beneficial in patients harboring this genotype, which needs to be tested in clinical trials.

miR-146a Controls Immune Response in the Melanoma Microenvironment.

MicroRNAs (miR) are small noncoding RNAs that regulate gene expression, posttranscription, and manipulate immune responses in different types of cancers. In this study, we identify miR-146a as a negative regulator of immune activation, comparable to immune-checkpoint molecules. miR-146a levels were increased in melanoma microenvironmental tissue, and miR-146a-/- mice survived longer and developed less metastases in comparison with wild-type melanoma-bearing mice. T cells isolated from miR-146a-/- mice revealed higher expression levels of the miR-146a target gene Stat1 and the Stat1-regulated cytokine IFNγ. Neutralization of IFNγ in miR-146a-/- mice decreased survival and increased melanoma metastasis patterns to those of wild-type mice. In vitro, IFNγ reduced melanoma cell migration, cell-cycle activity, and basal metabolic rate. Conversely, IFNγ also increased PD-L1 levels on the melanoma cells, which may counterbalance some of the beneficial effects increasing immune escape in vivo. Combined treatment with a miR-146a antagomiR and anti-PD-1 resulted in improved survival over isotype control or anti-PD-1 treatment alone. In summary, these data show that miR-146a plays a central role within the STAT1/IFNγ axis in the melanoma microenvironment, affecting melanoma migration, proliferation, and mitochondrial fitness as well as PD-L1 levels. Additionally, combined inhibition of PD-1 and miR-146a could be a novel strategy to enhance antitumor immune response elicited by checkpoint therapy. SIGNIFICANCE: These findings identify a microRNA-based mechanism by which melanoma cells escape the immune system, providing a new therapeutic strategy to improve the current management of patients with melanoma.

GPCR-specific autoantibody signatures are associated with physiological and pathological immune homeostasis.

Autoantibodies have been associated with autoimmune diseases. However, studies have identified autoantibodies in healthy donors (HD) who do not develop autoimmune disorders. Here we provide evidence of a network of immunoglobulin G (IgG) autoantibodies targeting G protein-coupled receptors (GPCR) in HD compared to patients with systemic sclerosis, Alzheimer's disease, and ovarian cancer. Sex, age and pathological conditions affect autoantibody correlation and hierarchical clustering signatures, yet many of the correlations are shared across all groups, indicating alterations to homeostasis. Furthermore, we identify relationships between autoantibodies targeting structurally and functionally related molecules, such as vascular, neuronal or chemokine receptors. Finally, autoantibodies targeting the endothelin receptor type A (EDNRA) exhibit chemotactic activity, as demonstrated by neutrophil migration toward HD-IgG in an EDNRA-dependent manner and in the direction of IgG from EDNRA-immunized mice. Our data characterizing the in vivo signatures of anti-GPCR autoantibodies thus suggest that they are a physiological part of the immune system.

Loss of LSR affects epithelial barrier integrity and tumor xenograft growth of CaCo-2 cells.

The lipolysis-stimulated lipoprotein receptor (LSR) is a lipoprotein receptor, serves as host receptor for clostridial iota-like toxins and is involved in the formation of tricellular contacts. Of particular interest is the role of LSR in progression of various cancers. Here we aimed to study the tumor growth of LSR-deficient colon carcinoma-derived cell lines HCT116 and CaCo-2 in a mouse xenograft model. Whereas knockout of LSR had no effect on tumor growth of HCT116 cells, we observed that CaCo-2 LSR knockout tumors grew to a smaller size than their wild-type counterparts. Histological analysis revealed increased apoptotic and necrotic cell death in a tumor originating from LSR-deficient CaCo-2 cells. LSR-deficient CaCo-2 cells exhibited increased cell proliferation in vitro and an altered epithelial morphology with impaired targeting of tricellulin to tricellular contacts. In addition, loss of LSR reduced the transepithelial electrical resistance of CaCo-2 cell monolayers and increased permeability for small molecules. Moreover, LSR-deficient CaCo-2 cells formed larger cysts in 3D culture than their wild-type counterparts. Our study provides evidence that LSR affects epithelial morphology and barrier formation in CaCo-2 cells and examines for the first time the effects of LSR deficiency on the tumor growth properties of colon carcinoma-derived cell lines.

The Atypical Kinase RIOK1 Promotes Tumor Growth and Invasive Behavior.

Despite being overexpressed in different tumor entities, RIO kinases are hardly characterized in mammalian cells. We investigated the role of these atypical kinases in different cancer cells. Using isogenic colon-, breast- and lung cancer cell lines, we demonstrate that knockdown of RIOK1, but not of RIOK2 or RIOK3, strongly impairs proliferation and invasiveness in conventional and 3D culture systems. Interestingly, these effects were mainly observed in RAS mutant cancer cells. In contrast, growth of RAS wildtype Caco-2 and Bcr-Abl-driven K562 cells is not affected by RIOK1 knockdown, suggesting a specific requirement for RIOK1 in the context of oncogenic RAS signaling. Furthermore, we show that RIOK1 activates NF-κB signaling and promotes cell cycle progression. Using proteomics, we identified the pro-invasive proteins Metadherin and Stathmin1 to be regulated by RIOK1. Additionally, we demonstrate that RIOK1 promotes lung colonization in vivo and that RIOK1 is overexpressed in different subtypes of human lung- and breast cancer. Altogether, our data suggest RIOK1 as a potential therapeutic target, especially in RAS-driven cancers.

Biglycan expression in the melanoma microenvironment promotes invasiveness via increased tissue stiffness inducing integrin-ß1 expression.

Novel targeted and immunotherapeutic approaches have revolutionized the treatment of metastatic melanoma. A better understanding of the melanoma-microenvironment, in particular the interaction of cells with extracellular matrix molecules, may help to further improve these new therapeutic strategies.We observed that the extracellular matrix molecule biglycan (Bgn) was expressed in certain human melanoma cells and primary fibroblasts when evaluated by microarray-based gene expression analysis. Bgn expression in the melanoma tissues correlated with low overall-survival and low progression-free-survival in patients. To understand the functional role of Bgn we used gene-targeted mice lacking functional Bgn. Here we observed that melanoma growth, metastasis-formation and tumor-related death were reduced in Bgn-/- mice compared to Bgn+/+ mice. In vitro invasion of melanoma cells into organotypic-matrices derived from Bgn-/- fibroblasts was reduced compared to melanoma invasion into Bgn-proficient matrices. Tissue stiffness as determined by atomic-force-microscopy was reduced in Bgn-/- matrices. Isolation of melanoma cells and fibroblasts from the stiffer Bgn+/+ matrices revealed an increase in integrin-ß1 expression compared to the Bgn-/- fibroblast matrices. Overexpression of integrin-ß1 in B16-melanoma cells abolished the survival benefit seen in Bgn-/- mice. Consistent with the studies performed in mice, the abundance of Bgn-expression in human melanoma samples positively correlated with the expression of integrin-ß1, which is in agreement with results from the organotypic invasion-assay and the in vivo mouse studies.This study describes a novel role for Bgn-related tissue stiffness in the melanoma-microenvironment via regulation of integrin-ß1 expression by melanoma cells in both mice and humans.

Pregnancy Specific ß-1 Glycoprotein 1 is Expressed in Pancreatic Ductal Adenocarcinoma and its Subcellular Localization Correlates with Overall Survival.

Proteins of the pregnancy specific ß-1 glycoprotein (PSG) family are renowned for their elevated expression during pregnancy. Only few reports have investigated their expression in adenocarcinomas. We studied the expression of PSG1 in pancreatic adenocarcinoma (PDAC). In a cohort of 104 patient samples, immunohistochemical analysis determined PSG1 expression in every specimen. PSG1 was found at apical and cytoplasmic localization or solely at cytoplasmic localization, with the latter case being correlated to shortened median survival (25 vs 11 months, logrank p-value < 0.001). At the same time, enzyme linked immunosorbent assay (ELISA) did not detect elevated PSG1 levels in the plasma of PDAC patients as opposed to the plasma of healthy, non-pregnant control individuals. We also probed the impact of PSG1 expression in a murine tumor model system, using subcutaneous injection of Colo-26 cells into immunocompetent BALB/c mice. Here, tumor growth was not affected by the expression of human PSG1. Our study reaffirms interest into the tumor-contextual biology of PSG proteins.

B-Raf inhibitors induce epithelial differentiation in BRAF-mutant colorectal cancer cells.

BRAF mutations are associated with aggressive, less-differentiated and therapy-resistant colorectal carcinoma. However, the underlying mechanisms for these correlations remain unknown. To understand how oncogenic B-Raf contributes to carcinogenesis, in particular to aspects other than cellular proliferation and survival, we generated three isogenic human colorectal carcinoma cell line models in which we can dynamically modulate the expression of the B-Raf(V600E) oncoprotein. Doxycyclin-inducible knockdown of endogenous B-Raf(V600E) decreases cellular motility and invasion in conventional and three-dimensional (3D) culture, whereas it promotes cell-cell contacts and induces various hallmarks of differentiated epithelia. Importantly, all these effects are recapitulated by B-Raf (PLX4720, vemurafenib, and dabrafenib) or MEK inhibitors (trametinib). Surprisingly, loss of B-Raf(V600E) in HT29 xenografts does not only stall tumor growth, but also induces glandular structures with marked expression of CDX2, a tumor-suppressor and master transcription factor of intestinal differentiation. By performing the first transcriptome profiles of PLX4720-treated 3D cultures of HT29 and Colo-205 cells, we identify several upregulated genes linked to epithelial differentiation and effector functions, such as claudin-1, a Cdx-2 target gene encoding a critical tight junction component. Thereby, we provide a mechanism for the clinically observed correlation between mutant BRAF and the loss of Cdx-2 and claudin-1. PLX4720 also suppressed several metastasis-associated transcripts that have not been implicated as targets, effectors or potential biomarkers of oncogenic B-Raf signaling so far. Together, we identify a novel facet of clinically applied B-Raf or MEK inhibitors by showing that they promote cellular adhesion and differentiation of colorectal carcinoma cells.

BRAF inhibitor-associated ERK activation drives development of chronic lymphocytic leukemia.

Patients with BRAFV600E/K-driven melanoma respond to the BRAF inhibitor vemurafenib due to subsequent deactivation of the proliferative RAS/RAF/MEK/ERK pathway. In BRAF WT cells and those with mutations that activate or result in high levels of the BRAF activator RAS, BRAF inhibition can lead to ERK activation, resulting in tumorigenic transformation. We describe a patient with malignant melanoma who developed chronic lymphocytic leukemia (CLL) in the absence of RAS mutations during vemurafenib treatment. BRAF inhibition promoted patient CLL proliferation in culture and in murine xenografts and activated MEK/ERK in primary CLL cells from additional patients. BRAF inhibitor-driven ERK activity and CLL proliferation required B cell antigen receptor (BCR) activation, as inhibition of the BCR-proximal spleen tyrosine kinase (SYK) reversed ERK hyperactivation and proliferation of CLL cells from multiple patients, while inhibition of the BCR-distal Bruton tyrosine kinase had no effect. Additionally, the RAS-GTP/RAS ratio in primary CLL cells exposed to vemurafenib was reduced upon SYK inhibition. BRAF inhibition increased mortality and CLL expansion in mice harboring CLL xenografts; however, SYK or MEK inhibition prevented CLL proliferation and increased animal survival. Together, these results suggest that BRAF inhibitors promote B cell malignancies in the absence of obvious mutations in RAS or other receptor tyrosine kinases and provide a rationale for combined BRAF/MEK or BRAF/SYK inhibition.