The transient receptor potential vanilloid 4 (TRPV4) channel is a mechanosensor in endothelial cells (EC) that regulates cyclic strain-induced reorientation and flow mediated nitric oxide production. We have recently demonstrated that TRPV4 expression is reduced in tumor EC and tumors grown in TRPV4KO mice exhibited enhanced growth and immature leaky vessels. However, the mechanism by which TRPV4 regulates tumor vascular integrity and metastasis is not known. Here, we demonstrate that VE-cadherin expression at the cell-cell contacts is significantly reduced in TRPV4-deficient tumor EC and TRPV4KO EC. In vivo angiogenesis assays with Matrigel of varying stiffness (700-900 Pa) revealed a significant stiffness-dependent reduction in VE-cadherin positive vessels in Matrigel plugs from TRPV4KO mice compared with WT mice, despite an increase in vessel growth. Further, syngeneic Lewis Lung Carcinoma (LLC) tumor experiments demonstrated a significant decrease in VE-cadherin positive vessels in TRPV4KO tumors compared with WT. Functionally, enhanced tumor cell metastasis to the lung was observed in TRPV4KO mice. Our findings demonstrate that TRPV4 channels regulate tumor vessel integrity by maintaining VE-cadherin expression at cell-cell contacts and identifies TRPV4 as a novel target for metastasis.

VEGF signaling via VEGF receptor-2 (VEGFR2) is a major regulator of endothelial cell (EC) functions, including angiogenesis. Although most studies of angiogenesis focus on soluble VEGF signaling, mechanical signaling also plays a critical role. Here, we examined the consequence of disruption of mechanical signaling on soluble signaling pathways. Specifically, we observed that small interfering RNA (siRNA) knockdown of a mechanosensitive ion channel, transient receptor potential vanilloid 4 (TRPV4), significantly reduced perinuclear (Golgi) VEGFR2 in human ECs with a concomitant increase in phosphorylation at Y1175 and membrane translocation. TRPV4 knockout (KO) ECs exhibited increased plasma membrane localization of phospho-VEGFR2 compared with normal ECs. The knockdown also increased phospho-VEGFR2 in whole cell lysates and membrane fractions compared with control siRNA-treated cells. siRNA knockdown of TRPV4 enhanced nuclear localization of mechanosensitive transcription factors, yes-associated protein/transcriptional coactivator with PDZ-binding motif via rho kinase, which were shown to increase VEGFR2 trafficking to the plasma membrane. Furthermore, TRPV4 deletion/knockdown enhanced VEGF-mediated migration in vitro and increased expression of VEGFR2 in vivo in the vasculature of TRPV4 KO tumors compared with wild-type tumors. Our results thus show that TRPV4 channels regulate VEGFR2 trafficking and activation to identify novel cross-talk between mechanical (TRPV4) and soluble (VEGF) signaling that controls EC migration and angiogenesis.-Kanugula, A. K., Adapala, R. K., Midha, P., Cappelli, H. C., Meszaros, J. G., Paruchuri, S., Chilian, W. M., Thodeti, C. K., Novel non-canonical regulation of soluble VEGF/VEGFR2 signaling by mechanosensitive ion channel TRPV4.

VEGF and VEGFR2 signaling is the major regulator of endothelial functions such as proliferation, migration, and angiogenesis. While many studies on the modulation of angiogenesis focus on targeting VEGF signaling, mechanical forces also play critical role. We have recently shown that the mechanosensitive ion channel transient receptor potential vanilloid 4 (TRPV4) negatively regulates angiogenesis via modulation of Rho/Rho kinase‐dependent endothelial mechanosensing. Nevertheless, it is not known if a cross‐talk exists between TRPV4 and VEGF signaling. To explore this nexus, we silenced TRPV4 in endothelial cells (EC) and measured VEGFR2 expression, localization, and phosphorylation. Immunofluorescence analysis revealed significant localization of total‐VEGFR2 around the perinuclear (Golgi) compartment in control EC. Small interfering RNA (siRNA) knockdown of TRPV4 significantly decreased perinuclear localization of VEGFR2. Interestingly, we found increased phosphorylation of VEGFR2 at Y1175 and its localization to the plasma membrane in TRPV4 knocked‐down cells. We also found increased plasma membrane localization of phospho‐VEGFR2 Y1175 in TRPV4 null EC. Western blot analysis further revealed a significant increase in phospho‐VEGFR2 at Y1175 in whole cell lysates and membrane fractions of TRPV4 knocked‐down cells compared to control siRNA‐treated cells. Finally, TRPV4 deletion/knockdown also increased VEGF‐mediated migration with localization of phospho‐VEGFR2 at the leading edge of migrating EC. Taken together, our results suggest that TRPV4 channels regulate VEGFR2 localization and activation to identify novel cross‐talk between mechanical (TRPV4) and soluble (VEGF) signaling in EC.Support or Funding InformationThis work was supported by National Institutes of Health (NIH) R01HL119705 and National Cancer Institute (NCI) R15CA202847This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.