Shear Stress Regulates Tumor Cell Mechanics and Actomyosin-Dependent Survival and Chemoresistance

Metastasis is the main cause of cancer death,and tumor cells mainly disseminate to the distal organs through the blood circulation,in which they experience considerable levels of fluid shear stress.CTCs are heterogeneous with diverse subpopulations of distinct genotypes and phenotypes and the frequency of CTCs is correlated with poor prognosis and overall survival in cancer patients.Less than 0.01%of them may eventually generate metastatic tumors in secondary sites,indicating the inefficiency of metastasis.Nevertheless,metastasis accounts for over 90%of cancer-related deaths,suggesting that a subpopulation of CTCs are able to survive the metastatic process and form metastases.To target metastasis,it is thus essential to understand the roles of various factors during dissemination in the survival and functions of CTCs.However,the effects of hemodynamic shear stress on biophysical properties and functions of CTCs in suspension are not fully understood.This study was to investigate the effect of hemodynamic shear stress on the survival and anti-chemotherapy ability of suspended circulating tumor cells during metastasis,and the effect of actomyosin activity on this regulation.In this study,we developed a circulatory system to generate physiologic levels of hemodynamic shear stress,which mimicked certain important aspects of the CTC microenvironment in blood circulation.The survival of tumor cells in suspension,as a model for real CTCs,under different shear stress and circulation duration was examined.We found that the majority of breast tumor cells s in suspension can be eliminated by hemodynamic shear stress.The surviving cells exhibit unique biophysical properties,including significantly retarded cell adhesion,mesenchymal-like cell morphology,and reduced F-actin expression and cellular stiffness.Cancer stem cells which has been reported in other papers have lower stiffness compared with conventional tumor cells showed significantly higher survival in blood flow.Importantly,low actomyosin activity promotes the survival of CTCs in blood shear flow while high actomyosin activity inhibits tumor cells surviving shear stress treatment.These findings might be explained by the up-and down-regulation of the anti-apoptosis genes.Soft surviving tumor cells held survival advantages in shear flow and higher resistance to chemotherapy.Metastasis is closely linked with chemoresistance.However,the underlying mechanisms have not been fully understood,in particular,the roles of hemodynamic shear stress and actomyosin-dependent cell mechanics in drug resistance of CTCs remain unclear.Inhibiting actomyosin activity in suspended tumor cells enhanced chemoresistance,while activating actomyosin suppressed this ability.These findings might be associated with the corresponding changes in multidrug resistance related genes.Our study unveils the regulatory roles of actomyosin in the survival and drug resistance of circulating tumor cells in hemodynamic shear flow,which imply the importance of fluid shear stress and actomyosin activity in tumor metastasis.Our findings reveal a new mechanism by which circulating tumor cells are able to survive hemodynamic shear stress and chemotherapy and may offer a new potential strategy to target circulating tumor cells in shear flow and combat chemoresistance through actomyosin.