Evidence for Rho protein regulation of renal tubular epithelial cell function

Background Rho proteins are small guanine 5'-triphosphate (GTP)-binding pro teins felt to be important regulators of several aspects of cell function, including the organization of the actin cytoskeleton. The effects of Rho pr oteins on the regulation of renal tubular epithelial cell function are not known. Methods. Selected bacterial toxins that inhibit Rho protein function were u sed to examine the effect of Rho in cultured renal tubular epithelial cells . Results. Clostridium difficile toxin A significantly and dose dependently i nhibited LLC-PK1 cell H-3-thymidine uptake and healing of small wounds made in confluent monolayers, and it induced apoptosis. A second Clostridium di fficile toxin (toxin B) that acted via a different receptor also impaired L LC-PK1 thymidine uptake and wound healing, and it induced apoptosis. A thir d bacterial toxin, C3 toxin from Clostridium botulinum, also impaired LLC-P K1 thymidine uptake and stimulated apoptosis in LLC-PK1 cells. Since Rho in hibition disrupted organization of the actin cytoskeleton, we examined the effects of another agent that disrupted the actin cytoskeleton (cytochalasi n D) and found significant dose-dependent effects that impaired LLC-PK1, th ymidine uptake and wound healing and that induced apoptosis. The effects of toxin A and cytochalasin D to induce apoptosis were not associated with si gnificant changes in expression of Bcl-2, BAD, or BAK proteins and were sig nificantly attenuated by a pancaspase inhibitor. Conclusions. Our results suggest that Rho proteins are important endogenous regulators of several aspects lar epithelial cell function, including prol iferation, migration, and apoptosis. Further studies are needed to clarify the cellular mechanisms of Rho regulation of renal epithelial cell function .