The clinical introduction of the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib, which targets B-cell antigen-receptor (BCR)-controlled integrin-mediated retention of malignant B cells in their growth-supportive lymphoid organ microenvironment, provided a major breakthrough in lymphoma and leukemia treatment. Unfortunately, a significant subset of patients is intrinsically resistant or acquires resistance against ibrutinib. Here, to discover novel therapeutic targets, we present an unbiased loss-of-adhesion CRISPR-Cas9 knockout screening method to identify proteins involved in BCR-controlled integrin-mediated adhesion. Illustrating the validity of our approach, several kinases with an established role in BCR-controlled adhesion, including BTK and PI3K, both targets for clinically applied inhibitors, are among the top hits of our screen. We anticipate that pharmacological inhibitors of the identified targets, e.g. PAK2 and PTK2B/PYK2, may have great clinical potential as therapy for lymphoma and leukemia patients. Furthermore, this screening platform is highly flexible and can be easily adapted to identify cell adhesion-regulatory proteins and signaling pathways for other stimuli, adhesion molecules, and cell types.

Murine atherosclerosis models are key for investigation of atherosclerosis pathophysiology and drug development. However, they do not feature spontaneous atherothrombosis as a final stage of atherosclerosis. Transgenic mice expressing both the human mutant apolipoprotein E form APOE*3-Leiden and human cholesteryl ester transfer protein (CETP), i.e. APOE*3-Leiden.CETP mice, feature a moderate hyperlipoproteinemia and atherosclerosis phenotype. In contrast to apolipoprotein E deficient (Apoe-/-) mice, APOE*3-Leiden.CETP mice respond well to lipid-lowering and anti-atherosclerotic drugs. The aim of the study was to investigate whether silencing of anticoagulant Protein C (Proc) allows APOE*3-Leiden.CETP mice to feature thrombosis as a final stage of atherosclerosis. Female APOE*3-Leiden.CETP mice were fed a Western-type diet to induce advanced atherosclerosis, followed by an injection with a small interfering RNA targeting Proc (siProc). Presence of atherosclerosis and atherothrombosis was determined by histologic analysis of the aortic root. Atherosclerosis severity in the aortic root area of APOE*3-Leiden.CETP mice varied from type "0" (no lesions) to type "V" lesions (advanced and complex lesions). Atherothrombosis following siProc injection was observed for 4 out of 21 APOE*3-Leiden.CETP mice (19% incidence). The atherothrombosis presented as large, organized, fibrin- and leukocyte-rich thrombi on top of advanced (type "V") atherosclerotic plaques in the aortic root. This atherothrombosis was comparable in appearance and incidence as previously reported for Apoe-/- mice with a more severe atherosclerosis (19% incidence). APOE*3-Leiden.CETP mice with modest hyperlipidemia and atherosclerosis can develop atherothrombosis upon transient Proc-silencing. This further extends the use of these mice as a test model for lipid-lowering and anti-atherosclerotic drugs.

Cancer enhances the risk of venous thromboembolism, but a hypercoagulant microenvironment also promotes cancer progression. Although anticoagulants have been suggested as a potential anticancer treatment, clinical studies on the effect of such modalities on cancer progression have not yet been successful for unknown reasons. In normal physiology, complex formation between the subendothelial-expressed tissue factor (TF) and the blood-borne liver-derived factor VII (FVII) results in induction of the extrinsic coagulation cascade and intracellular signaling via protease-activated receptors (PARs). In cancer, TF is overexpressed and linked to poor prognosis. Here, we report that increased levels of FVII are also observed in breast cancer specimens and are associated with tumor progression and metastasis to the liver. In breast cancer cell lines, tumor-expressed FVII drives changes reminiscent of epithelial-to-mesenchymal transition (EMT), tumor cell invasion, and expression of the prometastatic genes, SNAI2 and SOX9. In vivo, tumor-expressed FVII enhanced tumor growth and liver metastasis. Surprisingly, liver-derived FVII appeared to inhibit metastasis. Finally, tumor-expressed FVII-induced prometastatic gene expression independent of TF but required a functional endothelial protein C receptor, whereas recombinant activated FVII acting via the canonical TF:PAR2 pathway inhibited prometastatic gene expression. Here, we propose that tumor-expressed FVII and liver-derived FVII have opposing effects on EMT and metastasis.

Silencing of anticoagulant protein C using RNA interference (siProc) evokes low incident but spontaneous atherothrombosis in the aortic root of apolipoprotein E-deficient (Apoe-/-) mice. The aims of the current study were (1) to analyze if plaque characteristics or circulating factors could be linked to atherothrombosis susceptibility, (2) to increase the incidence of atherothrombosis by transiently increasing blood pressure, and (3) to direct atherothrombosis to an additional predefined vascular site by applying a semi-constrictive collar around the carotid artery. siProc-driven spontaneous atherothrombosis in the aortic root of Apoe-/- mice was reproduced and occurred at an incidence of 23% (9 out of 39 mice), while the incidence of collar-induced atherothrombosis in the carotid artery was 2.6% (1 out of 39 mice). Treatment with phenylephrine, to transiently increase blood pressure, did not increase atherothrombosis in the aortic root of the Apoe-/- mice nor in the carotid arteries with collars. Plaques in the aortic root with an associated thrombus were lower in collagen and macrophage content, and mice with atherothrombosis had significantly more circulating platelets. Plasma protein C, white blood cell counts, total cholesterol, fibrinogen, serum amyloid A, and IL-6 were not different amongst siProc treated mice with or without thrombosis. Remarkably, our data revealed that thrombus formation preferably occurred on plaques in the right coronary sinus of the aortic root. In conclusion, there is a predilection of low protein C-induced spontaneous atherothrombosis in Apoe-/- mice for the right coronary sinus, a process that is associated with an increase in platelets and plaques lower in collagen and macrophage content.

Obesity is associated with a hypercoagulable state and increased risk for thrombotic cardiovascular events.

The anti-apoptotic protein myeloid cell leukemia 1 (Mcl-1) plays an important role in survival and differentiation of leukocytes, more specifically of neutrophils. Here, we investigated the impact of myeloid Mcl-1 deletion in atherosclerosis. Western type diet fed LDL receptor-deficient mice were transplanted with either wild-type (WT) or LysMCre Mcl-1fl/fl (Mcl-1-/-) bone marrow. Mcl-1 myeloid deletion resulted in enhanced apoptosis and lipid accumulation in atherosclerotic plaques. In vitro, Mcl-1 deficient macrophages also showed increased lipid accumulation, resulting in increased sensitivity to lipid-induced cell death. However, plaque size, necrotic core and macrophage content were similar in Mcl-1-/- compared to WT mice, most likely due to decreased circulating and plaque-residing neutrophils. Interestingly, Mcl-1-/- peritoneal foam cells formed up to 45% more multinucleated giant cells (MGCs) in vitro compared to WT, which concurred with an increased MGC presence in atherosclerotic lesions of Mcl-1-/- mice. Moreover, analysis of human unstable atherosclerotic lesions also revealed a significant inverse correlation between MGC lesion content and Mcl-1 gene expression, coinciding with the mouse data. Taken together, these findings suggest that myeloid Mcl-1 deletion leads to a more apoptotic, lipid and MGC-enriched phenotype. These potentially pro-atherogenic effects are however counteracted by neutropenia in circulation and plaque.

Single nucleotide polymorphisms (SNPs) in a 4q35.2 locus that harbors the coagulation factor XI (F11), prekallikrein (KLKB1), and a cytochrome P450 family member (CYP4V2) genes are associated with deep venous thrombosis (DVT). These SNPs exert their effect on DVT by modifying the circulating levels of FXI. However, SNPs associated with DVT were not necessarily all in F11, but also in KLKB1 and CYP4V2. Here, we searched for evidence for common regulatory elements within the 4q35.2 locus, outside the F11 gene, that might control FXI plasma levels and/or DVT risk. To this end, we investigated the regulation of the orthologous mouse gene cluster under several metabolic conditions that impact mouse hepatic F11 transcription. In livers of mice in which HNF4α, a key transcription factor controlling F11, was ablated, or reduced by siRNA, a strong decrease in hepatic F11 transcript levels was observed that correlated with Cyp4v3 (mouse orthologue of CYP4V2), but not by Klkb1 levels. Estrogens induced hepatic F11 and Cyp4v3, but not Klkb1 transcript levels, whereas thyroid hormone strongly induced hepatic F11 transcript levels, and reduced Cyp4v3, leaving Klkb1 levels unaffected. Mice fed a high-fat diet also had elevated F11 transcription, markedly paralleled by an induction of Klkb1 and Cyp4v3 expression. We conclude that within the mouse F11, Klkb1, Cyp4v3 gene cluster, F11 and Cyp4v3 frequently display striking parallel transcriptional responses suggesting the presence of shared regulatory elements.

Hepatocyte nuclear factor 4α (HNF4α) and CCAAT/enhancer-binding protein α (C/EBPα) are important for the transcriptional control of coagulation factors. To determine in vivo the direct role of HNF4α and C/EBPα in control of genes encoding coagulation factors, a synthetic small interfering (si)RNA approach was used that enabled strong reduction of mouse hepatic HNF4α and C/EBPα under conditions that minimized target-related secondary effects. For both HNF4α and C/EBPα, intravenous injection of specific synthetic siRNAs (siHNF4α and siC/EBPα) resulted in more than 75% reduction in their liver transcript and protein levels 2 days post-injection. For siHNF4α, this coincided with marked and significantly reduced transcript levels of the coagulation genes Hrg, Proz, Serpina5, F11, F12, F13b, Serpinf2, F5, and F9 (in order of magnitude of effect) as compared to levels in control siRNA injected animals. Significant decreases in HNF4α target gene mRNA levels were also observed at 5 days post-siRNA injection, despite a limited level of HNF4α knockdown at this time point. Compared to HNF4α, C/EBPα knockdown had a modest impact on genes encoding coagulation factors. A strong reduction in C/EBPα transcript and protein levels resulted in significantly affected transcript levels of the control genes Pck1 and Fasn and a modest downregulation for coagulation genes Fba, Fbg and F5. F5 and F11 were the sole coagulation genes that were significantly affected upon prolonged (5 day) C/EBPα knockdown. We conclude that in the mouse, HNF4α has a direct and essential regulatory role for multiple hepatic coagulation genes, while a role for C/EBPα is more restricted. In addition, this study demonstrates that synthetic siRNA provides a simple and fast means for determining liver transcription factor involvement in vivo.

Patients with advanced colorectal cancer (CRC) still depend on chemotherapy regimens that are associated with significant limitations, including resistance and toxicity. The contribution of tyrosine kinase inhibitors (TKIs) to the prolongation of survival in these patients is limited, hampering clinical implementation. It is suggested that an optimal combination of appropriate TKIs can outperform treatment strategies that contain chemotherapy. We have previously identified a strongly synergistic drug combination (SDC), consisting of axitinib, erlotinib, and dasatinib that is active in renal cell carcinoma cells. In this study, we investigated the activity of this SDC in different CRC cell lines (SW620, HT29, and DLD-1) in more detail. SDC treatment significantly and synergistically decreased cell metabolic activity and induced apoptosis. The translation of the in-vitro-based results to in vivo conditions revealed significant CRC tumor growth inhibition, as evaluated in the chicken chorioallantoic membrane (CAM) model. Phosphoproteomics analysis of the tested cell lines revealed expression profiles that explained the observed activity. In conclusion, we demonstrate promising activity of an optimized mixture of axitinib, erlotinib, and dasatinib in CRC cells, and suggest further translational development of this drug mixture.

BCL-2 family proteins are frequently aberrantly expressed in mantle cell lymphoma (MCL). Recently, the BCL-2-specific inhibitor venetoclax has been approved by the US Food and Drug Administration for chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML). In MCL, venetoclax has shown promising efficacy in early clinical trials; however, a significant subset of patients is resistant. By conducting a kinome-centered CRISPR-Cas9 knockout sensitizer screen, we identified casein kinase 2 (CK2) as a major regulator of venetoclax resistance in MCL. Interestingly, CK2 is over-expressed in MCL and high CK2 expression is associated with poor patient survival. Targeting of CK2, either by inducible short hairpin RNA (shRNA)-mediated knockdown of CK2 or by the CK2-inhibitor silmitasertib, did not affect cell viability by itself, but strongly synergized with venetoclax in both MCL cell lines and primary samples, also if combined with ibrutinib. Furthermore, targeting of CK2 reduced MCL-1 levels, which involved impaired MCL-1 translation by inhibition of eIF4F complex assembly, without affecting BCL-2 and BCL-XL expression. Combined, this results in enhanced BCL-2 dependence and, consequently, venetoclax sensitization. In cocultures, targeting of CK2 overcame stroma-mediated venetoclax resistance of MCL cells. Taken together, our findings indicate that targeting of CK2 sensitizes MCL cells to venetoclax through downregulation of MCL-1. These novel insights provide a strong rationale for combining venetoclax with CK2 inhibition as therapeutic strategy for MCL patients.

Proapoptotic Bcl-2 family member Bim is particularly relevant for deletion of autoreactive and activated T and B cells, implicating Bim in autoimmunity. As atherosclerosis is a chronic inflammatory process with features of autoimmune disease, we investigated the impact of hematopoietic Bim deficiency on plaque formation and parameters of plaque stability. Bim -/- or wild type bone marrow transplanted ldlr -/- mice were fed a Western type diet (WTD) for 5 or 10 weeks, after which they were immunophenotyped and atherosclerotic lesions were analyzed. Bim -/- transplanted mice displayed splenomegaly and overt lymphocytosis. CD4+ and CD8+ T cells were more activated (increased CD69 and CD71 expression, increased interferon gamma production). B cells were elevated by 147%, with a shift towards the pro-atherogenic IgG-producing B2 cell phenotype, resulting in a doubling of anti-oxLDL IgG1 antibody titers in serum of bim -/- mice. Bim -/- mice displayed massive intraplaque accumulation of Ig complexes and of lesional T cells, although this did not translate in changes in plaque size or stability features (apoptotic cell and macrophage content). The surprising lack in plaque phenotype despite the profound pro-atherogenic immune effects may be attributable to the sharp reduction of serum cholesterol levels in WTD fed bim -/- mice.

Genome wide association studies (GWAS) identified SLC44A2 as a novel susceptibility gene for venous thrombosis (VT) and previous work established that SLC44A2 contributed to clot formation upon vascular injury.

An imbalance in von Willebrand factor (VWF) may either lead to bleeding (von Willebrand disease, VWD) or thrombosis. Both disorders have shortcomings in the currently available treatments. VWF itself could be a potential therapeutic target because of its role in both bleeding and thrombosis. Inhibiting VWF gene expression through allele-selective silencing of VWF with small interfering RNAs (siRNAs) could be a personalized approach to specifically inhibit mutant VWF in VWD or to normalize increased VWF levels in thrombotic disorders without complete VWF knockdown. Therefore, we investigated a method to allele-selectively silence the VWF gene in mice as a therapeutic strategy. Fourteen candidate siRNAs targeting murine Vwf of either the C57BL/6J (B6) or the 129S1/SvImJ (129S) strain were tested in vitro in cells expressing B6- and 129S-Vwf for inhibitory effect and allele-selective potential. Together with a nonselective siVwf, 2 lead candidate siRNAs, siVwf.B6 and siVwf.129S, were further tested in vivo in B6 and 129S mice. Efficient endothelial siRNA delivery was achieved by siRNA encapsulation into 7C1 oligomeric lipid nanoparticles. Treatment with the nonselective siVwf resulted in dose-dependent inhibition of up to 80% of both lung messenger RNA and plasma VWF protein in both mouse strains. In contrast, the allele-selective siVwf.B6 and siVwf.129S were shown to be effective in and selective solely for their corresponding mouse strain. To conclude, we showed efficient endothelial delivery of siRNAs that are highly effective in allele-selective inhibition of Vwf in mice, which constitutes an in vivo proof of principle of allele-selective VWF silencing as a therapeutic approach.