Introduction: Interstitial fluid flow plays important role in delivering anticancer agents to tumor tissue. Recent studies suggested that anti-angiogenic or vasculature disrupting agents may enhance the therapeutic effect of radiotherapy by regulating tumor blood flow and interstitial fluid pressure. Although the importance of interstitial fluid flow in modulating tumor microenvironment has been studied, the molecular mechanisms of shear flow on tumor cell survival and sensitivity to therapeutic agents have not been much explored. We would like to investigate the interaction of shear stress with irradiation on tumor cells. Materials and methods: Human T84 and SW480 colon adenocarcinoma cells were used in this study. Cells were seeded onto glass slides pre-coated with fibronectin, and then subjected to 0-12 dyne/cm2 laminar shear stress in parallel plate flow chamber (PPFC) system for 0-24 hours. Cells were then exposed to 0-8Gy irradiation (IR) by a RS2000 X-ray irradiator. MTT and clonogenic assays were used to study cell survival. Tumor cell cycle and apoptosis were evaluated by flow cytometry and Western blot. Candidate signal molecules were measured by real time PCR and immunoblots with or without pretreatment with cyclohexamide or MG132. Results: MTT and clonogenic assays revealed a synergistic effect of 24 hour- shear stress and IR on tumor cytotoxicity. Shear stress downregulates FAK, phosphor-FAK, AKT and phosphor-AKT expression but not ILK and GSK3B through integrin β1. Decreased protein expression was mainly through proteosomal degradation but not transcriptional suppression. By enhancing G2/M phase cell accumulation, shear stress increases tumor apoptosis after IR. The above phenomenon was not observed in IR pretreated with 3 hour-shear stress. Conclusion: The above observation suggests that shear stress may enhance colon cancer cell radiation sensitivity by inducing G2/M arrest, and FAK protein degradation via integrin β1 signaling pathway.
