Small molecules discovered in a pathway screen target the Rho pathway in cytokinesis

We report the discovery of small molecules that target the Rho pathway, which is a central regulator of cytokinesis-the final step in cell division. We have developed a way of targeting a small molecule screen toward a specific pathway, which should be widely applicable to the investigation of any signaling pathway. In a chemical genetic variant of a classical modifier screen, we used RNA interference (RNAi) to sensitize cells and identified small molecules that suppressed or enhanced the RNAi phenotype. We discovered promising candidate molecules, which we named Rhodblock 1-8, and we identified the target of Rhodblock 6 as Rho kinase. Several Rhodblocks inhibited one function of the Rho pathway in cells: the correct localization of phosphorylated myosin light chain during cytokinesis. Rhodblocks differentially perturb Rho pathway proteins in cells and can be used to dissect the mechanism of the Rho pathway during cytokinesis.