DENND2B activates Rab35 at the intercellular bridge regulating cytokinetic abscission and tetraploidy

Cytokinesis is the final stage of cell division. Successful cytokinesis requires membrane trafficking pathways regulated by Rabs, molecular switches activated by guanine nucleotide exchange factors (GEFs). Late in cytokinesis, an intercellular cytokinetic bridge (ICB) connecting the two daughter cells undergoes abscission, which requires depolymerization of actin. Rab35 recruits MICAL1 to oxidate and depolymerize actin filaments. We report that DENND2B, a protein previously implicated in cancer, mental retardation and multiple congenital disorders functions as a GEF for Rab35 and recruits and activates the GTPase at the ICB. Unexpectedly, the N-terminal region of DENND2B interacts with an active mutant of Rab35, suggesting that DENND2B is both a Rab35 GEF and effector. Knockdown of DENND2B delays abscission resulting in increased multinucleated cells and over-accumulation of F-actin at the ICB. F-actin accumulation leads to formation of a chromatin bridge, a process known to activate the NoCut/abscission checkpoint, and DENND2B knockdown actives Aurora B kinase, a hallmark of checkpoint activation. This study identifies DENND2B as a crucial player in cytokinetic abscission and provides insight into the multisystem disorder associated with DENND2B mutation.

细胞分裂的最终阶段为细胞质分裂。细胞质分裂的成功依赖于由Rab蛋白调控的膜转运途径以及由鸟苷酸交换因子（GEFs）激活的分子开关。在细胞质分裂的晚期，连接两个子细胞的细胞间细胞质分裂桥（ICB）发生断裂，这需要肌动蛋白的解聚。Rab35通过募集MICAL1氧化和解聚肌动蛋白丝。本研究报告指出，DENND2B蛋白，一种先前与癌症、智力障碍和多种先天性紊乱相关的蛋白，作为Rab35的GEF，并募集和激活位于ICB处的GTP酶。令人意外的是，DENND2B的N端区域与Rab35的一个活性突变体相互作用，表明DENND2B既是Rab35的GEF，也是效应器。DENND2B的敲低延迟了断裂过程，导致多核细胞增多和ICB处F-肌动蛋白的过度积累。F-肌动蛋白的积累导致染色质桥的形成，这一过程已知可激活NoCut/断裂检查点，并且DENND2B的敲低激活了Aurora B激酶，这是检查点激活的标志。本研究将DENND2B鉴定为细胞质分裂断裂的关键参与者，并揭示了与DENND2B突变相关的多系统紊乱。