Polo-like kinase 1 regulates RhoA during cytokinesis exit in human cells

Objective: Both RhoA (Rho1) and polo-like kinase 1 (Plk1) are implicated in the regulation of cytokinesis, a cellular process that marks the division of cytoplasm of a parent cell into daughter cells after nuclear division. Cytokinesis failure is often accompanied by the generation of cells with an unstable tetraploid content, which predisposes it to chromosomal-instability and oncogenic transformation. Several studies using lower eukaryotic systems demonstrate that RhoA and Plk1 are essential for mitotic progression and cytokinesis. Materials and methods: Physical and functional interactions between RhoA and Plk-1 were analyzed using subcellular localization of RhoA and Plk1 in HeLa cells by immunofluorescence and co-precipitation techniques, followed by Western blotting in RboA transfected cells. Results: Plk1 localizes to kinetochores as well as to spindle poles during prophase and metaphase; it translocates to the midbody during telophase. RhoA is also enriched at the midbody region during telophase and colocalizes with Plk1. Recombinant RhoA, expressed as a GFP fusion protein, is enriched in the nucleus of HeLa and U2OS cells. Ectopically expressed GFP-RhoA does not cause significant cell death, although there exist a group of cells that appear to exhibit a delay in mitotic exit or in impaired cytokinesis. Conclusion: Co-immunoprecipitation reveals that RhoA and Plk1 physically interact and that their interaction appears to be enhanced during mitosis. Given the role of RhoA and Plk1 in cytokinesis, our findings suggest that regulated activation of RhoA is important for cytokinesis and that Plk1 may alter activation of RboA during mitotic cytokinesis.