Revealing PAK2's Function in the Cell Division through MKLP1's Interactome.

Cell division-related proteins are essential for the normal development and differentiation of cells and may be related to the occurrence of cancer and the drug resistance mechanism of cancer cells. The mitotic kinesin-like protein 1 (MKLP1) is a kinesin protein that has been involved in the assembly of the midzone/midbody during mitosis and cytokinesis. In this study, we found that the tail domain of MKLP1 exhibited an autoinhibitory effect on its motor activity. Overexpression of the tail domain in HEK293 cells blocked cytokinesis and caused bi-/multinucleation. It is possible that protein binding to the MKLP1 tail relieves this autoinhibition and induces the motility of MKLP1. We used the GST pull-down assay followed by the LC-MS/MS analysis and identified 54 MKLP1 tail domain-specific binding proteins. Further, we confirmed the MS result by coimmunoprecipitation and FRET that a serine/threonine kinase, p21-activated kinase 2 (PAK2), binding to MKLP1. Endogenous PAK2 expression was found to be identical to that of MKLP1 in HEK293 cells during cytokinesis. Finally, functional studies indicated that when PAK2 expression was downregulated by siRNA, MKLP1 underwent a change in its localization away from the midbody, and cell cytokinesis was subsequently impeded. This study presents a novel regulatory mechanism that PAK2 promotes the activation of MKLP1 and contributes to complete cell cytokinesis.