Abstract 1916: Actomyosin-YAP/TAZ signaling regulates the viability and chemoresistance of circulating tumor cells in hemodynamic shear stress
Authors: Tan Youhua , Xin Ying , Li Keming 
Published: August 2019

Abstract
Background: Tumor cells metastasize to distant organs mainly through hematogenous dissemination, where they experience considerable levels of shear stress. However, the influence of hemodynamic shear stress on the biophysical properties of circulating tumor cells (CTCs) remains elusive. The mechanisms underlying the survival of a subpopulation of CTCs in fluid shear flow and chemoresistance are unclear.
Methods: A circulatory microfluidic system was developed to mimic blood circulation in vitro. The survival of suspended breast tumor cells in fluid shear flow and tumor cells after chemotherapy was tested by MTS assay. The expressions of the related genes and proteins were measured by qPCR and western blotting. The biophysical properties of surviving tumor cells were examined by various methods.
Results: The majority of suspended breast CTCs could be eliminated by fluid shear stress and the survival rate depended on the magnitudes of shear stress and circulation duration. As the driving force for metastasis, cancer stem cells held survival advantages in shear flow. Higher fluid shear stress facilitated more nuclear translocation of YAP/TAZ in suspended tumor cells and induced lower cell survival. Inhibiting the entry of YAP/TAZ into the nucleus enhanced cell survival in shear flow. Further, suppressing actomyosin attenuated YAP/TAZ activity, which promoted the survival of suspended tumor cells in shear flow. In contrast, activating actomyosin enhanced the nuclear translocation of YAP/TAZ, which suppressed the survival of CTCs and cancer stem cells. Mechanistically, the nuclear YAP/TAZ interacted with p73, which then initiated the transcription of pro-apoptosis genes (including BAX) and promoted cell apoptosis.
Compared to untreated cells, tumor cells surviving shear stress exhibited unique biophysical properties: the adhesion of surviving tumor cells was significantly retarded; these cells exhibited elongated morphology, enhanced spreading, and up-regulated genes related to epithelial-mesenchymal transition; surviving tumor cells showed reduced F-actin expression and stiffness. Soft surviving tumor cells held survival advantages in shear flow and higher resistance to chemotherapy. Inhibiting actomyosin activity and YAP/TAZ in untreated cells enhanced chemoresistance, while activating actomyosin and YAP/TAZ in surviving tumor cells suppressed this ability, which may be associated with the corresponding changes in the expressions of the genes related to multidrug resistance.
Conclusion: This study unveils the regulatory roles of actomyosin-YAP/TAZ signaling in the survival and drug resistance of CTCs in hemodynamic shear flow, which suggest the importance of fluid shear stress and actomyosin-YAP/TAZ activity in tumor metastasis.
Note: This abstract was not presented at the meeting.
Citation Format: Youhua Tan, Ying Xin, Keming Li. Actomyosin-YAP/TAZ signaling regulates the viability and chemoresistance of circulating tumor cells in hemodynamic shear stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1916.