Frizzled-5: a high affinity receptor for secreted frizzled-related protein-2 activation of nuclear factor of activated T-cells c3 signaling to promote angiogenesis

The emerging understanding of Frizzled receptors

The Wnt signaling pathway is a huge network governing development and homeostasis, dysregulation of which is associated with a myriad of human diseases. The Frizzled receptor (FZD) family comprises receptors for Wnt ligands, which indispensably mediate Wnt signaling jointly with a variety of co-receptors. Studies of FZDs have revealed that 10 FZD subtypes play diverse roles in physiological processes. At the same time, dysregulation of FZDs is also responsible for various diseases, in particular human cancers. Enormous attention has been paid to the molecular understanding and targeted therapy of FZDs in the past decade. In this review, we summarize the latest research on FZD structure, function, regulation and targeted therapy, providing a basis for guiding future research in this field.

Frizzled receptors (FZDs) in Wnt signaling: potential therapeutic targets for human cancers

Frizzled receptors (FZDs) are key contributors intrinsic to the Wnt signaling pathway, activation of FZDs triggering the Wnt signaling cascade is frequently observed in human tumors and intimately associated with an aggressive carcinoma phenotype. It has been shown that the abnormal expression of FZD receptors contributes to the manifestation of malignant characteristics in human tumors such as enhanced cell proliferation, metastasis, chemotherapy resistance as well as the acquisition of cancer stemness. Given the essential roles of FZD receptors in the Wnt signaling in human tumors, this review aims to consolidate the prevailing knowledge on the specific status of FZD receptors (FZD1-10) and elucidate their respective functions in tumor progression. Furthermore, we delineate the structural basis for binding of FZD and its co-receptors to Wnt, and provide a better theoretical foundation for subsequent studies on related mechanisms. Finally, we describe the existing biological classes of small molecule-based FZD inhibitors in detail in the hope that they can provide useful assistance for design and development of novel drug candidates targeted FZDs.

Secreted frizzled-related protein 2 ameliorates diabetic cardiomyopathy by activating mitophagy

OBJECTIVES

Secreted frizzled-related protein 2 (SFRP2), a novel adipokine that used to be considered an inhibitor of the canonical Wnt pathway, may play a protective role in metabolic disorders. However, its effect on diabetic cardiomyopathy was still unclear. Accumulating evidence indicates that mitophagy can protect cardiac function in the diabetic heart. The present study aimed to explore the roles of SFRP2 on diabetic cardiomyopathy, focusing on the effects and mechanisms for regulating mitophagy.

METHODS

Wild-type H9c2 cells, Sfrp2 overexpression and knockdown H9c2 cells were exposed to a glucolipotoxic milieu. Reactive oxygen species (ROS) production, cell viability, apoptosis, mitophagy and lysosomal activity were detected. The interaction of SFRP2 with frizzled 5 (FZD5), and its effect on expression and intracellular localization of transcription factor EB (TFEB) and β-catenin were also explored. Diabetic rats and Sfrp2 overexpression diabetic rats were constructed to further document the findings from the in vitro study.

RESULTS

The expression of SFRP2 was low and mitophagy was inhibited in H9c2 cells in a glucolipotoxic milieu. Sfrp2 overexpression activated mitophagy and reduced H9c2 cells injury, whereas Sfrp2 deficiency inhibited mitophagy and worsened this injury. Consistent with the in vitro findings, Sfrp2 overexpression ameliorated the impairment in cardiac function of diabetic rats by activating mitophagy. Sfrp2 overexpression upregulated the expression of calcineurin and TFEB, but did not affect β-catenin in vitro and in vivo. The calcineurin inhibitor tacrolimus can inhibit mitophagy and worsen cell injury in Sfrp2 overexpression H9c2 cells. Furthermore, we found that FZD5 is required for the SFRP2-induced activation of the calcineurin/TFEB pathway and interacts with SFRP2 in H9c2 cells. Transfection with small interfering RNA targeting FZD5 opposed the effects of Sfrp2 overexpression on mitophagy and cell survival in a glucolipotoxic environment.

CONCLUSIONS

SFRP2 can protect the diabetic heart by interacting with FZD5 and activating the calcineurin/TFEB pathway to upregulate mitophagy in H9c2 cells.

A fibroblast-dependent TGFβ1/sFRP2 noncanonical Wnt signaling axis underlies epithelial metaplasia in idiopathic pulmonary fibrosis

Reciprocal interactions between alveolar fibroblasts and epithelial cells are crucial for lung homeostasis, injury repair, and fibrogenesis, but underlying mechanisms remain unclear. To investigate this, we administered the fibroblast-selective TGFβ1 signaling inhibitor, epigallocatechin gallate (EGCG), to Interstitial Lung Disease (ILD) patients undergoing diagnostic lung biopsy and conducted single-cell RNA sequencing on spare tissue. Unexposed biopsy samples showed higher fibroblast TGFβ1 signaling compared to non-disease donor or end-stage ILD tissues. In vivo, EGCG significantly downregulated TGFβ1 signaling and several pro-inflammatory and stress pathways in biopsy samples. Notably, EGCG reduced fibroblast secreted Frizzle-like Receptor Protein 2 (sFRP2), an unrecognized TGFβ1 fibroblast target gene induced near type II alveolar epithelial cells (AEC2s). In human AEC2-fibroblast coculture organoids, sFRP2 was essential for AEC2 trans-differentiation to basal cells. Precision cut lung slices (PCLS) from normal donors demonstrated that TGFβ1 promoted KRT17 expression and AEC2 morphological change, while sFRP2 was necessary for KRT5 expression in AEC2-derived basaloid cells. Wnt-receptor Frizzled 5 (Fzd5) expression and downstream calcineurin-related signaling in AEC2s were required for sFRP2-induced KRT5 expression. These findings highlight stage-specific TGFβ1 signaling in ILD, the therapeutic potential of EGCG in reducing IPF-related transcriptional changes, and identify the TGFβ1-non-canonical Wnt pathway crosstalk via sFRP2 as a novel mechanism for dysfunctional epithelial signaling in Idiopathic Pulmonary Fibrosis/ILD.

Secreted frizzled related-protein 2 is prognostic for human pancreatic cancer patient survival and is associated with fibrosis

Pancreatic adenocarcinoma (PDAC) is one of the deadliest cancers, with five-year survival rates of 9%. We hypothesized that secreted frizzled-related protein 2 (SFRP2) may influence stromal growth in pancreatic cancer, since it increases fibrosis and collagen production in non-neoplastic pathologies. We assessed SFRP2 value as a biomarker and assessed its function in PDAC. SFRP2 gene expression in patients with PDAC was analyzed using TCGA data. Disease free survival (DFS) was analyzed using Kaplan Meier test. The effect of KRAS inhibition on SFRP2 expression in PDAC cells was assessed. The associations of stromal content with SFPR2 mRNA and protein with fibrosis were analyzed. The role of SFRP2 in mesenchymal transformation was assessed by western blot in fibroblasts. Of all cancers in TCGA, SFRP2 levels were highest in PDAC, and higher in PDAC than normal tissues (n= 234, p= 0.0003). High SFRP2 levels correlated with decreased DFS (p= 0.0097). KRAS inhibition reduced SFRP2 levels. Spearman correlation was 0.81 between stromal RNA and SFRP2 in human PDAC, and 0.75 between fibrosis and SFRP2 levels in PDAC tumors. SFRP2-treated fibroblasts displayed mesenchymal characteristics. SFRP2 is prognostic for PDAC survival, regulated by KRAS, and associated with PDAC fibrosis.

CircNPM1 strengthens Adriamycin resistance in acute myeloid leukemia by mediating the miR-345-5p/FZD5 pathway

Acute myeloid leukemia (AML) is an aggressive hematological malignancy with poor long-term outcomes. Numerous studies claim that circular RNAs (circRNAs) are important regulators in AML progression. This study intended to explore the role of circNPM1 in AML development and drug chemoresistance. The expression of circNPM1 and miR-345-5p was detected by quantitative real-time polymerase chain reaction (qRT-PCR). Cellular activities, including cell growth, apoptosis, cell cycle, migration and invasion, were monitored using colony formation assay, flow cytometry assay and transwell assay, respectively. The relationship between miR-345-5p and circNPM1 or Frizzled-5 (FZD5) was predicted by the bioinformatics tool starBase and validated by dual-luciferase reporter assay or RNA immunoprecipitation (RIP) assay. CircNPM1 was abundantly expressed in serum samples from AML patients and AML cell lines. CircNPM1 silence or miR-345-5p restoration repressed colony formation, cell migration and invasion, contributed to cell apoptosis and cell cycle arrest, and weakened Adriamycin (ADM) resistance of AML cells. MiR-345-5p was a target of circNPM1 and was downregulated in AML serum and cells. MiR-345-5p deficiency reversed the effects of circNPM1 silence. Further, FZD5 was targeted by miR-345-5p, and circNPM1 regulated FZD5 expression by adsorbing miR-345-5p. FZD5 overexpression could block the function of miR-345-5p restoration. CircNPM1 might be a vital regulator for ADM chemoresistance in AML cells, which partly depended on the role of the miR-345-5p/FZD5 axis. Our study presents the view that circNPM1 degradation may be a key strategy in AML resistance therapy.

Mitophagy in Diabetic Cardiomyopathy: Roles and Mechanisms

Cardiovascular disease is the leading complication of diabetes mellitus (DM), and diabetic cardiomyopathy (DCM) is a major cause of mortality in diabetic patients. Multiple pathophysiologic mechanisms, including myocardial insulin resistance, oxidative stress and inflammation, are involved in the development of DCM. Recent studies have shown that mitochondrial dysfunction makes a substantial contribution to the development of DCM. Mitophagy is a type of autophagy that takes place in dysfunctional mitochondria, and it plays a key role in mitochondrial quality control. Although the precise molecular mechanisms of mitophagy in DCM have yet to be fully clarified, recent findings imply that mitophagy improves cardiac function in the diabetic heart. However, excessive mitophagy may exacerbate myocardial damage in patients with DCM. In this review, we aim to provide a comprehensive overview of mitochondrial quality control and the dual roles of mitophagy in DCM. We also propose that a balance between mitochondrial biogenesis and mitophagy is essential for the maintenance of cellular metabolism in the diabetic heart.

Overcoming PD-1 Inhibitor Resistance with a Monoclonal Antibody to Secreted Frizzled-Related Protein 2 in Metastatic Osteosarcoma

Secreted frizzled-related protein 2 (SFRP2) promotes the migration/invasion of metastatic osteosarcoma (OS) cells and tube formation by endothelial cells. However, its function on T-cells is unknown. We hypothesized that blocking SFRP2 with a humanized monoclonal antibody (hSFRP2 mAb) can restore immunity by reducing CD38 and PD-1 levels, ultimately overcoming resistance to PD-1 inhibitors. Treating two metastatic murine OS cell lines in vivo, RF420 and RF577, with hSFRP2 mAb alone led to a significant reduction in the number of lung metastases, compared to IgG1 control treatment. While PD-1 mAb alone had minimal effect, hSFRP2 mAb combination with PD-1 mAb had an additive antimetastatic effect. This effect was accompanied by lower SFRP2 levels in serum, lower CD38 levels in tumor-infiltrating lymphocytes and T-cells, and lower PD-1 levels in T-cells. In vitro data confirmed that SFRP2 promotes NFATc3, CD38 and PD-1 expression in T-cells, while hSFRP2 mAb treatment counteracts these effects and increases NAD⁺ levels. hSFRP2 mAb treatment further rescued the suppression of T-cell proliferation by tumor cells in a co-culture model. Finally, hSFRP2 mAb induced apoptosis in RF420 and RF577 OS cells but not in T-cells. Thus, hSFRP2 mAb therapy could potentially overcome PD-1 inhibitor resistance in metastatic osteosarcoma.

Wnt Signaling in the Tumor Microenvironment

Dysregulated Wnt signaling plays a central role in initiation, progression, and metastasis in many types of human cancers. Cancer development and resistance to conventional cancer therapies are highly associated with the tumor microenvironment (TME), which is composed of numerous stable non-cancer cells, including immune cells, extracellular matrix (ECM), fibroblasts, endothelial cells (ECs), and stromal cells. Recently, increasing evidence suggests that the relationship between Wnt signaling and the TME promotes the proliferation and maintenance of tumor cells, including leukemia. Here, we review the Wnt pathway, the role of Wnt signaling in different components of the TME, and therapeutic strategies for targeting Wnt signaling.

Secreted frizzled-related protein 2: a key player in noncanonical Wnt signaling and tumor angiogenesis

Secreted frizzled-related proteins (SFRP) are glycoproteins containing a so-called frizzled-like cysteine-rich domain. This domain enables them to bind to Wnt ligands or frizzled (FzD) receptors, making potent regulators of Wnt signaling. As Wnt signaling is often altered in cancer, it is not surprising that Wnt regulators such as SFRP proteins are often differentially expressed in the tumor microenvironment, both in a metastatic and non-metastatic setting. Indeed, SFRP2 is shown to be specifically upregulated in the tumor vasculature of several types of cancer. Several studies investigated the functional role of SFRP2 in the tumor vasculature, showing that SFRP2 binds to FzD receptors on the surface of tumor endothelial cells. This activates downstream Wnt signaling and which is, thereby, stimulating angiogenesis. Interestingly, not the well-known canonical Wnt signaling pathway, but the noncanonical Wnt/Ca²⁺ pathway seems to be a key player in this event. In tumor models, the pro-angiogenic effect of SFRP2 could be counteracted by antibodies targeting SFRP2, without the occurrence of toxicity. Since tumor angiogenesis is an important process in tumorigenesis and metastasis formation, specific tumor endothelial markers such as SFRP2 show great promise as targets for anti-cancer therapies. This review discusses the role of SFRP2 in noncanonical Wnt signaling and tumor angiogenesis, and highlights its potential as anti-angiogenic therapeutic target in cancer.

Multiple Roles of sFRP2 in Cardiac Development and Cardiovascular Disease

The Wnt signaling pathway plays important roles in organ development and disease processes. Secreted frizzled-related protein 2 (sFRP2), a vital molecule of Wnt signaling, can regulate cardiac development and cardiovascular disease. Recent studies have suggested that sFRP2 is not only an antagonist of the canonical Wnt signaling pathway, but also has a more complex relationship in myocardial fibrosis, angiogenesis, cardiac hypertrophy and cardiac regeneration. Here, we review the role of sFRP2 and Wnt signaling in cardiac development and cardiovascular disease.

Suramin protects hepatocytes from LPS-induced apoptosis by regulating mitochondrial stress and inactivating the JNK-Mst1 signaling pathway

An uncontrolled inflammatory response has been implicated in the progression of acute liver failure through poorly understood mechanisms. The aim of our study was to investigate whether suramin attenuates inflammation-mediated hepatocyte apoptosis by modulating mitochondrial homeostasis. Primary hepatocytes were isolated from mice and treated with LPS in vitro in the presence or absence of suramin. Western blotting, immunofluorescence staining, and ELISAs were used to evaluate the mitochondrial stress. The LPS treatment caused hepatocyte death via apoptosis. Interestingly, suramin supplementation attenuated LPS-mediated hepatocyte death by reducing Mst1 expression; the overexpression of Mst1 abolished the anti-apoptotic effects of suramin on LPS-treated hepatocytes. At the molecular level, suramin treatment repressed mitochondrial oxidative stress, sustained mitochondrial dynamics and blocked the caspase-9-mediated mitochondrial apoptosis pathway; these effects of suramin were achieved by reversing Mst1 expression. Furthermore, our study found that suramin modulated Mst1 expression via the JNK signaling pathway. Activation of JNK prevented the suramin-mediated Mst1 downregulation and concomitantly increased hepatocyte apoptosis and mitochondrial dysfunction. Taken together, our results confirmed the anti-apoptotic and anti-inflammatory effects of suramin on LPS-challenged hepatocytes. Suramin sustained hepatocyte viability and attenuated mitochondrial stress via repressing the JNK-Mst1 signaling pathway.

Upregulation of FZD5 in Eosinophilic Chronic Rhinosinusitis with Nasal Polyps by Epigenetic Modification

Eosinophilic chronic rhinosinusitis with nasal polyps (CRSwNP) is one of the most challenging problems in clinical rhinology. FZD5 is a receptor for Wnt5A, and its complex with Wnt5A contributes to activating inflammation and tissue modification. Nasal polyps and eosinophil/non-eosinophil counts are reported to be directly correlated. This study investigated the expression and distribution of FZD5, and the role of eosinophil infiltration and FZD5 in eosinophilic CRSwNP pathogenesis. The prognostic role of eosinophil levels was evaluated in seven patients with CRSwNP. Fifteen patients with CRS were classified based on the percentage of eosinophils in nasal polyp tissue. Methylated genes were detected using methyl-CpG-binding domain sequencing, and qRT-PCR and immunohistochemistry were used to detect FZD5 expression in nasal polyp tissue samples. The results showed that mRNA expression of FZD5 was upregulated in nasal polyps. FZD5 expression was significantly higher in nasal polyp samples from patients with eosinophilic CRSwNP than in those from patients with non-eosinophilic CRSwNP, as indicated by immunohistochemistry. Furthermore, inflammatory cytokine levels were higher in eosinophilic CRSwNP-derived epithelial cells than in normal tissues. In conclusion, FZD5 expression in nasal mucosal epithelial cells is correlated with inflammatory cells and might play a role in the pathogenesis of eosinophilic CRSwNP.

LATS2 overexpression attenuates the therapeutic resistance of liver cancer HepG2 cells to sorafenib-mediated death via inhibiting the AMPK-Mfn2 signaling pathway

Background

Effective therapy for hepatocellular carcinoma (HCC) is currently an imperative issue, and sorafenib is a first-line drug for the treatment of HCC. However, the clinical benefit of sorafenib is often impaired by drug resistance. Accordingly, the present study was conducted to investigate the molecular mechanisms involving sorafenib resistance, with a focus on large tumor suppressor 2 (LATS2) and mitophagy.

Methods

HepG2 liver cancer cells were treated with sorafenib and infected with adenovirus-loaded LATS2 (Ad-LATS2). Cell death, proliferation and migration were measured via western blotting analysis, immunofluorescence and qPCR. Mitochondrial function and mitophagy were determined via western blotting and immunofluorescence.

Results

Our data indicated that LATS2 expression was repressed by sorafenib treatment, and overexpression of LATS2 could further enhance sorafenib-mediated apoptosis in HepG2 liver cancer cells. At the molecular level, mitochondrial stress was triggered by sorafenib treatment, as evidenced by decreased mitochondrial membrane potential, increased mitochondrial ROS production, more cyc-c release into the nucleus, and elevated mitochondrial pro-apoptotic proteins. However, in response to mitochondrial damage, mitophagy was activated by sorafenib treatment, whereas LATS2 overexpression effectively inhibited mitophagy activity and thus augmented sorafenib-mediated mitochondrial stress. Subsequently, we also demonstrated that the AMPK–MFN2 signaling pathway was involved in mitophagy regulation after exposure to sorafenib treatment and/or LATS2 overexpression. Inhibition of the AMPK pathway interrupted mitophagy and thus enhanced the antitumor property of sorafenib, similar to the results obtained via overexpression of LATS2.

Conclusions

Altogether, our findings revealed the importance of the LATS2/AMPK/MFN2/mitophagy axis in understanding sorafenib resistance mechanisms, with a potential application to increase the sensitivity response of sorafenib in the treatment of liver cancer.

Yap-Hippo promotes A549 lung cancer cell death via modulating MIEF1-related mitochondrial stress and activating JNK pathway

Although the role of Yes-associated protein (Yap) has been described in the progression of lung cancer, the downstream effector of the Yap-Hippo pathway has not been identified. Accordingly, the aim of our study is to explore whether Yap modulates the activity of lung cancer by controlling mitochondrial elongation factor 1 (MIEF1)-related mitochondrial stress in a manner dependent on the JNK pathway. Cell viability was determined via MTT, LDH release and immunofluorescence assays. ATP production, the mitochondrial membrane potential, and caspase-9 activity were investigated to assess mitochondrial function. siRNA transfection and pathway blockers were used to observe the roles of MIEF1 and JNK in Yap-modulated cell viability in lung cancer cells in vitro. Yap deletion reduced cell viability in A549 and H358 lung cancer cells. At the molecular level, Yap deletion promoted mitochondrial dysfunction, as evidenced by the decreased mitochondrial potential, increased mitochondrial oxidative stress, augmented mitochondrial pro-apoptotic factor leakage and elevated caspase-9 activity. In addition, we found that Yap modulated mitochondrial stress via MIEF1 and that loss of MIEF1 abolished the regulatory actions of Yap on mitochondrial stress and cell viability. Besides, we provided evidence to support the necessary role of JNK in Yap-mediated MIEF1 upregulation. Inhibition of JNK abolished the promotive effect of Yap deletion on MIEF1 activation. Taken together, our results identified the JNK-MIEF1 pathway and mitochondrial stress as downstream effectors of Yap in lung cancer. This finding suggests a novel approach for the treatment of lung cancer in clinical practice.

Sepsis-related myocardial injury is associated with Mst1 upregulation, mitochondrial dysfunction and the Drp1/F-actin signaling pathway

LPS-induced septic cardiomyopathy has been found to be connected with mitochondrial stress through unknown mechanisms. Mitochondrial fission is an early event in mitochondrial dysfunction. The aim of our study was to determine the role and regulatory mechanism of mitochondrial fission in the progression of LPS-induced septic cardiomyopathy, with a particular focus on Mst1 and F-actin. Our data demonstrated that Mst1 expression was rapidly upregulated in LPS-treated hearts and that increased Mst1 promoted cardiomyocyte death by inducing mitochondrial stress. Mechanistically, elevated expression of Mst1 upregulated Drp1, and the latter initiated mitochondrial fission. Excessive mitochondrial fission caused mitochondrial oxidative injury, mitochondrial membrane potential reduction, mitochondrial proapoptotic element translocation into the cytoplasm/nucleus, mitochondrial energy dysfunction and mitochondrial apoptosis activation. Inhibition of mitochondrial fission sustained mitochondrial function and favored cardiomyocyte survival. Furthermore, we identified F-actin degradation as an apparent downstream event of mitochondrial fission activation in the context of LPS-induced septic cardiomyopathy. Stabilization of F-actin attenuated fission-mediated cardiomyocyte death. Altogether, our results define the Mst1/Drp1/mitochondrial fission/F-actin axis as a new signaling pathway that mediates LPS-related septic cardiomyopathy by inducing mitochondrial stress and cardiomyocyte death. Therefore, Mst1 expression, mitochondrial fission modification and F-actin stabilization may serve as potential therapeutic targets for sepsis-related myocardial injury.

Mst1 facilitates hyperglycemia-induced retinal pigmented epithelial cell apoptosis by evoking mitochondrial stress and activating the Smad2 signaling pathway

Hyperglycemia induces retinal pigmented epithelial cell apoptosis and mitochondrial stress via poorly understood mechanisms. The goal of our current study is to explore whether mammalian sterile 20-like kinase 1 (Mst1) is involved in the pathogenesis of hyperglycemia-mediated retinal pigmented epithelial cell apoptosis by triggering mitochondrial abnormalities and activating the Smad2 signaling pathway. Retinal pigmented epithelial ARPE-19 cells were presented with a high-glucose challenge in vitro. Cell viability and apoptosis were measured via western blotting, ELISAs, and immunofluorescence assays. Mitochondrial function was detected via JC-1 staining, mitochondrial ROS flow cytometry, western blotting, and ELISAs. Loss- and gain-of-function assays were performed via cell transfection and transduction with Mst1 siRNA and Smad2 adenovirus, respectively. The results indicated that hyperglycemia treatment upregulated the levels of Mst1, an effect that was accompanied by an increase in ARPE-19 cell apoptosis. Loss of Mst1 attenuated hyperglycemia-induced cell apoptosis, and this effect seemed to be associated with mitochondrial protection. In response to hyperglycemia stimulus, mitochondrial stress was noted in ARPE-19 cells, including mitochondrial ROS overproduction, mitochondrial respiratory metabolism dysfunction, mitochondrial fission/fusion imbalance, and mitochondrial apoptosis activation. Further, we provided evidence to support the crucial role played by Smad2 in promoting Mst1-mediated cell apoptosis and mitochondrial stress. Overexpression of Smad2 abrogated the beneficial effects of Mst1 deletion on ARPE-19 cell viability and mitochondrial protection. Altogether, our results identified Mst1 as a novel mediator controlling the fate of retinal pigmented epithelial cells and mitochondrial homeostasis via the Smad2 signaling pathway. Based on this finding, strategies to repress Mst1 upregulation and block Smad2 activation are vital to alleviate hyperglycemia-mediated retinal pigmented epithelial cell damage.

Anti-PD1 'SHR-1210' aberrantly targets pro-angiogenic receptors and this polyspecificity can be ablated by paratope refinement

Monoclonal anti-programmed cell death 1 (PD1) antibodies are successful cancer therapeutics, but it is not well understood why individual antibodies should have idiosyncratic side-effects. As the humanized antibody SHR-1210 causes capillary hemangioma in patients, a unique toxicity amongst anti-PD1 antibodies, we performed human receptor proteome screening to identify nonspecific interactions that might drive angiogenesis. This screen identified that SHR-1210 mediated aberrant, but highly selective, low affinity binding to human receptors such as vascular endothelial growth factor receptor 2 (VEGFR2), frizzled class receptor 5 and UL16 binding protein 2 (ULBP2). SHR-1210 was found to be a potent agonist of human VEGFR2, which may thereby drive hemangioma development via vascular endothelial cell activation. The v-domains of SHR-1210's progenitor murine monoclonal antibody 'Mab005' also exhibited off-target binding and agonism of VEGFR2, proving that the polyspecificity was mediated by the original mouse complementarity-determining regions (CDRs), and had survived the humanization process. Molecular remodelling of SHR-1210 by combinatorial CDR mutagenesis led to deimmunization, normalization of binding affinity to human and cynomolgus PD1, and increased potency in PD1/PD-L1 blockade. Importantly, CDR optimization also ablated all off-target binding, rendering the resulting antibodies fully PD1-specific. As the majority of changes to the paratope were found in the light chain CDRs, the germlining of this domain drove the ablation of off-target binding. The combination of receptor proteome screening and optimization of the antibody binding interface therefore succeeded in generating novel, higher-potency, specificity-enhanced therapeutic IgGs from a single, clinically sub-optimal progenitor. This study showed that highly-specific off-target binding events might be an under-appreciated phenomenon in therapeutic antibody development, but that these unwanted properties can be fully ameliorated by paratope refinement.

Endothelial loss of Fzd5 stimulates PKC/Ets1-mediated transcription of Angpt2 and Flt1

Aims

Formation of a functional vascular system is essential and its formation is a highly regulated process initiated during embryogenesis, which continues to play important roles throughout life in both health and disease. In previous studies, Fzd5 was shown to be critically involved in this process and here we investigated the molecular mechanism by which endothelial loss of this receptor attenuates angiogenesis.

Methods and results

Using short interference RNA-mediated loss-of-function assays, the function and mechanism of signaling via Fzd5 was studied in human endothelial cells (ECs). Our findings indicate that Fzd5 signaling promotes neovessel formation in vitro in a collagen matrix-based 3D co-culture of primary vascular cells. Silencing of Fzd5 reduced EC proliferation, as a result of G₀/G₁ cell cycle arrest, and decreased cell migration. Furthermore, Fzd5 knockdown resulted in enhanced expression of the factors Angpt2 and Flt1, which are mainly known for their destabilizing effects on the vasculature. In Fzd5-silenced ECs, Angpt2 and Flt1 upregulation was induced by enhanced PKC signaling, without the involvement of canonical Wnt signaling, non-canonical Wnt/Ca²⁺-mediated activation of NFAT, and non-canonical Wnt/PCP-mediated activation of JNK. We demonstrated that PKC-induced transcription of Angpt2 and Flt1 involved the transcription factor Ets1.

Conclusions

The current study demonstrates a pro-angiogenic role of Fzd5, which was shown to be involved in endothelial tubule formation, cell cycle progression and migration, and partly does so by repression of PKC/Ets1-mediated transcription of Flt1 and Angpt2.

Electronic supplementary material

The online version of this article (10.1007/s10456-018-9625-6) contains supplementary material, which is available to authorized users.