YAP1 Inhibition in Vascular Endothelial Cells Is Associated with Enhanced Release of lncRNA MALAT1-Containing Exosomes and Increased Hepatocarcinoma Invasion and Metastasis

Background: Liver cancer is one of the most common gastrointestinal malignancies. Anti-angiogenesis therapies have recently demonstrated promise in the treatment of liver cancer and other malignancies, although early treatment benefits may be accompanied by metastasis over time. Additional and more effective anti-angiogenic treatment modalities are therefore needed. We previously found that YAP1 expression is increased in hepatocellular carcinoma, particularly around tumor-associated blood vessels, suggesting a role in angiogenesis. The YAP1 inhibitor verteporfin (VP) is presently in anti-angiogenic clinical trials for the treatment of various cancers. Further elucidating the role of YAP1 in tumor angiogenesis may offer novel therapeutic targets. Methods and Results: We depleted YAP1 from vascular endothelial cells effectively reduces proliferation and tube formation, validating its utility as an anti-angiogenesis target. We also show that YAP1 depletion or inhibition in vascular endothelial cells leads to increased release of exosomes containing the lncRNA MALAT1 into the tumor microenvironment. Direct exosomal transfer of MALAT1 to hepatic cells leads to increased hepatic cell invasion and migration via activation of ERK1/2 signaling. Depletion of endothelial MALAT1 or inhibition of hepatocyte ERK1/2 signaling can suppress VP treatment-associated hepatocyte invasion and migration. Furthermore, we find that MALAT1 expression in patients with hepatocellular carcinoma is associated with decreased disease-free survival and increased lymph node metastasis. Conclusions: These observations may explain the occurrence of distant tumor metastasis with YAP1-associated anti-angiogenic therapy over time, and provide insight into new pathways and treatment paradigms that may be targeted to increase the long-term success of anti-angiogenic therapies. Funding Statement: This work was supported by grants from National Natural Science Foundation of China (No.81472302/No.81572425/No.81871983/No.81572831). Declaration of Interests: The authors declare no conflicts of interest. Ethics Approval Statement: The Institutional Review Board of the Fourth Affiliated Hospital of China Medical University approved the use of human tissue samples for this project. All patients gave their informed written consent for the use of clinical specimens for research.