A role for Ral GTPase-activating protein subunit β in mitotic regulation

Ral proteins are small GTPases that play critical roles in normal physiology and in oncogenesis. There is little information on the GTPase-activating proteins (GAPs) that downregulate their activity. Here, we provide evidence that the noncatalytic β subunit of RalGAPα_1/2β complexes is involved in mitotic control. RalGAPβ localizes to the Golgi and nucleus during interphase, and relocalizes to the mitotic spindle and cytokinetic intercellular bridge during mitosis. Depletion of RalGAPβ causes chromosome misalignment and decreases the amount of mitotic cyclin B1, disturbing the metaphase-to-anaphase transition. Overexpression of RalGAPβ interferes with cell division, leading to binucleation and multinucleation, and cell death. We propose that RalGAPβ plays an essential role in the sequential progression of mitosis by controlling the spatial and temporal activation of Ral GTPases in the spindle assembly checkpoint (SAC) and cytokinesis. Deregulation of RalGAPβ might cause genomic instability, leading to human carcinogenesis. Structured digital abstract RalGAP beta physically interacts with Tubulin beta5, tubulin alpha, Hsp70, EF1a, RalGAP alpha 2, DDX15 and RalGAP alpha 1 by tandem affinity purification (View interaction) RalGAP beta and GM130 colocalize by fluorescence microscopy (View interaction) The RalGAPα_1/2β heterodimers that inactivate the small GTPases RalA and RalB remain poorly characterized. We identify a role for the noncatalytic RalGAPβ subunit as a regulator of mitotic spindle assembly and cytokinesis. Depletion of RalGAPβ causes chromosome misalignment and disturbs the metaphase-to-anaphase transition. Overexpression of RalGAPβ interferes with cell division. RalGAPβ deregulation might be a cause of genomic instability.