RhoA-mediated potential regulation of blood-tumor barrier permeability by bradykinin

The purpose of this work is to investigate the potential for the small G protein RhoA to play a role in bradykinin (BK)-induced actin cytoskeleton rearrangement, tight junction (TJ) protein disassembly, and an increase in blood-tumor barrier (BTB) permeability in rat brain microvascular endothelial cells (RBMECs). Our study used primary RBMECs as an in vitro BTB model and a RhoA inhibitor (C(3) exoenzyme) to establish whether RhoA played a role in the process of TJ disassembly, stress fiber formation, and increasing BTB permeability by BK. Data from the HRP flux and TEER assays revealed that BTB permeability was increased by BK induction. C(3) exoenzyme could partially inhibit endothelial leakage and restored normal TEER values in RBMECs. An obvious shift in occludin distribution from insoluble to soluble fractions was observed as assessed by Western blot, which was prevented by C(3) exoenzyme. In addition, C(3) exoenzyme inhibited BK-induced relocation of occludin from cellular borders into the cytoplasm, as well as stress fiber formation in RBMECs. A time-dependent increase in RhoA activity by BK administration was observed, which was inhibited by C(3) exoenzyme. RhoA activation is important for BK-induced increase in BTB permeability and appears to involve the ability for RhoA to mediate occludin disassembly and stress fiber formation.