Department of Biochemistry and Cell Biology, The Geisel School of Medicine at Dartmouth, Hanover, NH.
Norris Cotton Cancer Center, The Geisel School of Medicine at Dartmouth, Lebanon, NH.
J Cell Biol. 2020 Aug 3;219(8). doi: 10.1083/jcb.201908017.
Protein kinases direct polarized growth by regulating the cytoskeleton in time and space and could play similar roles in cell division. We found that the Cdc42-activated polarity kinase Pak1 colocalizes with the assembling contractile actomyosin ring (CAR) and remains at the division site during septation. Mutations in pak1 led to defects in CAR assembly and genetic interactions with cytokinesis mutants. Through a phosphoproteomic screen, we identified novel Pak1 substrates that function in polarized growth and cytokinesis. For cytokinesis, we found that Pak1 regulates the localization of its substrates Mid1 and Cdc15 to the CAR. Mechanistically, Pak1 phosphorylates the Mid1 N-terminus to promote its association with cortical nodes that act as CAR precursors. Defects in Pak1-Mid1 signaling lead to misplaced and defective division planes, but these phenotypes can be rescued by synthetic tethering of Mid1 to cortical nodes. Our work defines a new signaling mechanism driven by a cell polarity kinase that promotes CAR assembly in the correct time and place.
蛋白激酶通过在时间和空间上调节细胞骨架来指导极化生长，并且在细胞分裂中可能发挥类似的作用。我们发现，Cdc42 激活的极性激酶 Pak1 与正在组装的收缩性肌动球蛋白环（CAR）共定位，并在分隔过程中留在分裂位点。pak1 的突变导致 CAR 组装缺陷，并与胞质分裂突变体发生遗传相互作用。通过磷酸化蛋白质组学筛选，我们鉴定了新的 Pak1 底物，这些底物在极化生长和胞质分裂中发挥作用。对于胞质分裂，我们发现 Pak1 调节其底物 Mid1 和 Cdc15 到 CAR 的定位。在机制上，Pak1 磷酸化 Mid1 N 端以促进其与作为 CAR 前体的皮质节点的结合。Pak1-Mid1 信号通路的缺陷导致分裂平面错位和缺陷，但通过将 Mid1 与皮质节点的人工连接可以挽救这些表型。我们的工作定义了一个新的信号机制，该机制由细胞极性激酶驱动，可在正确的时间和位置促进 CAR 组装。
