CPAP/CENPJ is essential for the stability and function of ESCRT-pathway associated AAA+ ATPase VPS4B

Function of CENPJ/CPAP is essential for centriole duplication and cilia biogenesis, disruption of which can lead to microcephaly and Seckel syndrome. Recently, we showed that CPAP is an integral Endosomal Sorting Complexes Required for Transport (ESCRT)-0-like protein that recruits ESCRT-I protein TSG101 to early endosome (EE) and it positively regulates multi-vesicular body (MVB) formation. Sequential recruitment of the ESCRT protein complexes and AAA+ ATPase VPS4B to EE facilitates MVB biogenesis. VPS4B is critical for ESCRT-III disassembly/recycling and contributes to membrane fission in several cellular processes. Here, we report that CPAP is critical for the protein stability and EE localization of VPS4B, and this function is independent from its role as an ESCRT-0 protein. Other well-recognized VPS4B-dependent cellular processes such as cytokinesis, extracellular vesicle production, and retroviral budding are also compromised under CPAP deficiency. We found that CPAP overexpression leads to cellular accumulation and CPAP deficiency causes proteasomal degradation of VPS4B. We also found that VPS4B interacts with the C-terminal CC4 domain of CPAP, which is considered as its centriole localization domain, and this interaction prevents the proteasome degradation of VPS4B. Notably, the EE localization of VPS4B can be attributed to microcephaly-associated C-terminal TCP domain of CPAP. Overall, these observations provide evidence that CPAP is critical for VPS4B and its ESCRT-associated function and suggest that distinct pools of CPAP may be involved in its ESCRT-0 and VPS4B stabilization roles. This study also provides clues to potential mechanisms underlying the clinical phenotypes of CPAP deficiency.