Differential role for VPS4 isoforms in cytokinetic abscission confers a regulatory function for monomeric VPS4A and VTA1 in mammalian cells
Mutations in the human AAA-ATPase VPS4 isoform, VPS4A, cause severe Neurodevelopmental defects and Congenital Dyserythropoietic Anemia (CDA). VPS4 is a crucial component of the ESCRT system, which drives membrane remodeling in numerous cellular processes, including receptor degradation, cell division, and neural pruning. Notably, while most organisms encode for a single VPS4 gene, human cells have two VPS4 paralogs, namely VPS4A and VPS4B, but the functional differences between these paralogs is mostly unknown. Here, we set out to investigate the role of the human VPS4 paralogs in cytokinetic abscission using a series of knockout cell lines. We found that VPS4A and VPS4B hold both overlapping and distinct roles in abscission. VPS4A depletion resulted in a severe abscission delay, which was fully rescued by VPS4A expression but only partially rescued by VPS4B overexpression. Unexpectedly, expressing a monomeric-locked VPS4A mutant also partially rescued the abscission delay in VPS4A KO cells and bound the abscission checkpoint proteins CHMP4C and ANCHR. Depletion of VTA1, a co-factor of VPS4, disrupted VPS4A- ANCHR interactions and accelerated abscission, indicating a role for VTA1 in the abscission checkpoint. Our findings reveal a dual role for VPS4A in abscission, one that is canonical and can be compensated by VPS4B, and another that is regulatory and is mediated by its monomeric form. These observations provide a potential mechanistic explanation for the neurodevelopmental defects and other related disorders reported in VPS4A-mutated patients with a fully functional VPS4B paralog.