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ErbB4 is a member of the ErbB receptor tyrosine kinase family. It has both pro- and anti-oncogenic activities in tumors. Vasculogenic mimicry (VM), a phenomenon in which cancer cells form capillary-like structures without endothelial cells, has been recognized to be a cause of malignant phenotypes in some solid tumors. Here, we used an in vitro VM formation assay, and demonstrated that ErbB4 negatively regulated VM formation in human breast cancer cells. By using CRISPR/Cas9-mediated gene knockout, we verified that the depletion of endogenous ErbB4 improved the VM formation capability. Although treatment with neuregulin 1 (NRG1), a ligand of ErbB4, induced the phosphorylation of ErbB4 and promoted VM formation in a dose-dependent manner, it did not induce such activities in kinase-dead K751M ErbB4-overexpressing cells. Moreover, we examined the effect of the missense mutation E872K of ErbB4, which has been reported in multiple tumors, on VM formation, and found that the mutation enhanced the basal phosphorylation level and ErbB4-mediated VM formation in the absence of NRG1 stimulation. Whereas NRG1 stimulated VM formation, excessive activation of ErbB4 induced a negative effect. In E872K ErbB4-overexpressing cells, but not in wild-type ErbB4-overexpressing cells, the number of VM tubes was significantly decreased by low-dose treatment with the ErbB inhibitor afatinib. Taken together, our findings demonstrated the significance of ErbB4-mediated VM formation, and suggested the possibility of ErbB4 mutations as effective targets in breast cancer.

Melanoma is a type of skin cancer that derives from melanocytes; this tumor is highly metastatic and causes poor clinical outcomes in patients. Vasculogenic mimicry (VM), a vascular-like network that is formed by tumor cells instead of endothelial cells, promotes the growth and metastasis of tumors by providing tumors with oxygen- and nutrient-containing blood. VM correlates with a poor prognosis in patients with melanoma, but the melanoma-specific mechanisms of VM are unknown. The present study revealed that treatment with the melanogenesis stimulators 3-isobutyl 1-methylxanthine (IBMX) and α-melanocyte-stimulating hormone (α-MSH) significantly inhibited VM in MNT-1 human pigmented melanoma cells. Tyrosinase (TYR), an essential enzyme in melanin production, was upregulated on treatment with α-MSH and IBMX, prompting an examination of the association between TYR and VM. A TYR inhibitor, arbutin, promoted VM in melanoma cells. Furthermore, CRISPR/Cas9-mediated knockout (KO) of TYR increased VM by melanoma cells. Notably, even in non-pigmented melanoma cells, TYR attenuated VM. Although re-expression of wild-type TYR suppressed VM in TYR-KO cells, T373K TYR, a frequently detected mutation in individuals with albinism, failed to inhibit VM. Overall, these results demonstrated that TYR negatively regulates VM, providing novel insights into the antioncogenic function of TYR in melanomas.

Vasculogenic mimicry (VM) is the formation of a blood supply system that confers aggressive and metastatic properties to tumors and correlates with a poor prognosis in cancer patients. Thus, the inhibition of VM is considered an effective approach for cancer treatment, although such a mechanism remains poorly described. In the present study, we examined methionine aminopeptidase‑2 (MetAP2), a key factor of angiogenesis, and demonstrated that it is pivotal for VM, using pharmacological and genetic approaches. Fumagillin and TNP‑470, angiogenesis inhibitors that target MetAP2, significantly suppressed VM in various human cancer cell lines. We established MetAP2‑knockout (KO) human fibrosarcoma HT1080 cells using the CRISPR/Cas9 system and found that VM was attenuated in these cells. Furthermore, re‑expression of wild‑type MetAP2 restored VM in the MetAP2‑KO HT1080 cells, but the substitution of D251, a conserved amino acid in MetAP2, failed to rescue the VM. Collectively, our results demonstrate that MetAP2 is critical for VM in human cancer cells and suggest fumagillin and TNP‑470 as potent VM‑suppressing agents.

CCN1 is a secreted protein and belongs to the CCN family of matricellular proteins. CCN1 binds to various cell surface receptors; thus, CCN1 has important functions in cell proliferation, migration and angiogenesis through a variety of signaling pathways. We have reported that CCN1 is O-fucosylated and that this O-fucosylation regulates the secretion of CCN1 into the extracellular region. In this study, we detected collagen-like glycosylation and hydroxylation at Lys203 of recombinant CCN1 by mass spectrometry. We then examined the role of collagen-like glycosylation in the functions of CCN1. As a result, we found that a deficiency in collagen-like glycosylation decreased the secretion of CCN1 using wild-type CCN1- and collagen-like glycosylation-defective mutant CCN1-overexpressing cell lines. Further, knockout of lysyl hydroxylase3, a multifunctional protein with hydroxylase and glucosyltransferase activities, impaired the secretion and glycosylation level of recombinant CCN1. Previous studies reported that collagen glycosylation of Lys residues mediated by lysyl hydroxylase3 is glucosyl-galactosyl-hydroxylation, presuming that this collagen-like glycosylation detected at Lys203 of recombinant CCN1 in this study might be glucosyl-galactosyl-hydroxylation. Taken together, our results demonstrate the novel function of the collagen-like glycosylation of CCN1 and suggest that lysyl hydroxylase3-mediated glycosylation is important for CCN1 secretion.

Vasculogenic mimicry (VM) formation by cancer cells is known to play a crucial role in tumor progression, but its detailed mechanism is unclear. In the present study, we focused on integrin β1 (ITGB1) and assessed the role of ITGB1 in VM formation. We used in vitro methods to seed cancer cells on Matrigel to evaluate the capability of VM formation. We carried out ITGB1 gene deletion using the CRISPR/Cas9 system, and these ITGB1-knockout cells did not show a VM-like network formation. Further, reintroduction of ITGB1 rescued VM-like network formation in ITGB1-knockout cells. In conclusion, ITGB1 is a critical factor in VM of human cancer cells, and inhibition of ITGB1 may be a novel therapeutic approach for malignant cancer.

Tumor metastasis is caused by multiple processes, such as epithelial-mesenchymal transition, lymph node metastasis, and angiogenesis. In recent years, vasculogenic mimicry (VM) is focused on the association with tumor malignancy. VM is a unique phenomenon, a blood vessel-like network structure formed only by cancer cells without vascular endothelial cells, and is observed in extracellular matrix (ECM) rich region. Although previous studies suggested that VM plays a crucial role in tumor metastasis, a detailed mechanism of VM formation has not been fully understood. Latest studies indicate that cell surface proteins such as integrins and cadherins contribute to VM formation. In this study, we focused on transmembrane cell surface receptor, integrin β1. Integrin β1 is an important factor for interactions between cell-cell and cell-ECM, and mediates several cell signalings. Therefore, we investigated the importance of integrin β1 in VM formation. We assessed VM formation capability as network structure formed by cancer cells on matrigel. Since previous studies revealed that Ca2+ regulates integrin activities, we treated with EGTA and CaCl2 to assess whether Ca2+ is necessary for VM formation. We performed integrin β1 gene knockout (KO) by using CRISPR/Cas9 system in human fibrosarcoma HT1080 cells, and assessed VM formation capability of the KO cells. In addition, we established integrin β1-rescued HT1080 cells by reintroduction of Cas9-resistant integrin β1-expressing vector to integrin β1-KO HT1080 cells to confirm the importance of integrin β1 in VM formation. Furthermore, we also established integrin β1-KO human breast cancer MDA-MB-231 cells to verify that integrin β1 is necessary for VM formation in other human cancer cell lines. As a result, chelation of Ca2+ by treatment with EGTA inhibited network formation in HT1080 cells, and cotreatment with CaCl2 rescued this effect, suggesting that integrins might be important for VM formation. In integrin β1-KO HT1080 cells, which is confirmed the completely knockout of integrin β1 by Western blot, network formation was abrogated. Additionally, integrin β1-rescued HT1080 cells exhibited network formation as well as parental HT1080 cells. These results suggested that integrin β1 is a critical factor in VM formation. Furthermore, integrin β1-KO MDA-MB-231 cells also did not form network structure, suggesting that integrin β1 plays a crucial role in VM formation in general human cancer cell lines. Taken together, our study provides new knowledge of the association between VM and integrin β1, and inhibition of integrin β1 may be a novel therapeutic approach for metastatic cancer. Citation Format: Ryota Kawahara, Yuki Niwa, Siro Simizu. Integrin β1 plays a crucial role in vasculogenic mimicry formation [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B204.