Evidence for Rho protein regulation of renal tubular epithelial cell function

Rho proteins are small guanine 5'-triphosphate (GTP)-binding proteins felt to be important regulators of several aspects of cell function, including the organization of the actin cytoskeleton. The effects of Rho proteins on the regulation of renal tubular epithelial cell function are not known.

Selected bacterial toxins that inhibit Rho protein function were used to examine the effect of Rho in cultured renal tubular epithelial cells.

Clostridium difficile toxin A significantly and dose dependently inhibited LLC-PK(1) cell (3)H-thymidine uptake and healing of small wounds made in confluent monolayers, and it induced apoptosis. A second Clostridium difficile toxin (toxin B) that acted via a different receptor also impaired LLC-PK(1) thymidine uptake and wound healing, and it induced apoptosis. A third bacterial toxin, C3 toxin from Clostridium botulinum, also impaired LLC-PK(1) thymidine uptake and stimulated apoptosis in LLC-PK(1) cells. Since Rho inhibition disrupted organization of the actin cytoskeleton, we examined the effects of another agent that disrupted the actin cytoskeleton (cytochalasin D) and found significant dose-dependent effects that impaired LLC-PK1 thymidine uptake and wound healing and that induced apoptosis. The effects of toxin A and cytochalasin D to induce apoptosis were not associated with significant changes in expression of Bcl-2, BAD, or BAK proteins and were significantly attenuated by a pancaspase inhibitor.

Our results suggest that Rho proteins are important endogenous regulators of several aspects of renal tubular epithelial cell function, including proliferation, migration, and apoptosis. Further studies are needed to clarify the cellular mechanisms of Rho regulation of renal epithelial cell function.