The Role And Mechanism Of Hippo/YAP Pathway In Angiogenesis

Angiogenesis is a complex process governed by the interaction of several signaling pathways such as vascular endothelial growth factor（VEGF）and interleukin-6（IL-6）that have a crucial effect on the regulation of endothelial cells（ECs）proliferation and migration.Emerging evidence supports that as a transcription coactivator yes-associated protein（YAP）plays an important role in regulating the angiogenic activity of ECs.However,the underlying mechanism of Hippo/YAP pathway in angiogenesis has not been fully elucidated.The aim of our study is to investigate the role of YAP in VEGF-mediated angiogenesis in ECs and find the possible partner transcription factor and relation between Hippo/YAP pathway and the other pathways involved in regulation of angiogenesis.In ECs,VEGF reduced YAP phosphorylation and subsequently increased its nuclear accumulation in time-and dose-dependent manners.Silencing YAP by Small interfering RNA blocked VEGF-induced proliferation,migration and tube formation of ECs.Meanwhile,overexpression of YAP in ECs of mice increased retinal and tumor angiogenesis.Because YAP lacks a DNA-binding domain,its angiogenic function is driven by its association with other transcriptional factors.To search for the transcriptional activators that might interact with YAP in ECs,we preformed immunoprecipitation and mass spectrometry analysis.Fortunately,STAT3 was identified as a target partner transcription factor of YAP in ECs.The predicted 3D structure of the STAT3/YAP complex suggested that a peptide of the YAP SH3binding domain could interact with STAT3 at amino acids 656-687.Moreover,structural modeling predicted that the binding of YAP could mask the nuclear export signal of STAT3.Indeed,Western blot and immunoprecipitation assays revealed that binding of YAP to STAT3 prolonged interleukin-6–induced STAT3 nuclear accumulation by blocking chromosomal maintenance 1-mediated STAT3 nuclear export without affecting its phosphorylation.STAT3-induced angiopoietin-2（ANG2）expression was enhanced by YAP overexpression in ECs.Finally,a selective STAT3inhibitor or Ang2 blockage greatly attenuated retinal angiogenesis in EC-YAP^Tg mice.We conclude that YAP binding may detain STAT3 in the nucleus to enhance the latter’s transcriptional activity and promote angiogenesis via its transcriptional regulation of Ang2.In conclusion,our observations provide a new mechanism for the role of YAP in angiogenesis.The connection between VEGF-induced YAP activation and the STAT3/ANG2 pathway revealed by this study has several important implications.Blood vessels that transport blood throughout the entire body play pivotal roles in maintaining homeostasis under physiological conditions.Once dysregulated,the formation of new blood vessels contributes to numerous malignant,ischemic,inflammatory,infectious and immune disorders.Our results may generate brand new molecular insights into these processes and new clinical therapeutic opportunities for related diseases.