ESCRT subunit CHMP4B localizes to primary cilia and is required for the structural integrity of the ciliary membrane

Abstract

Proteins specialized in the detection, generation, or stabilization of membrane curvature play important roles in establishing various morphologies of cells and cellular organelles. Primary cilia are cellular organelles that protrude from the cell surface using a microtubule-based cytoskeleton called the axoneme as a structural support.It is unclear whether the integrity of the high curvature of the ciliary membrane depends on membrane curvature-related proteins. Charged Multivesicular Body Protein 4B (CHMP4B), a subunit of the endosomal sorting complexes required for transport (ESCRT), can stabilize membrane curvature. Here we show that CHMP4B is involved in the assembly and maintenance of primary cilia. CHMP4B was localized to primary cilia in mammalian cells. Knockdown of CHMP4B interfered with cilium assembly and also caused fragmentation of preexisting cilia. By contrast, cilium formation was unaffected by the interruption of the ESCRT-dependent endocytic degradation pathway. Morpholino (MO)-mediated CHMP4B depletion in zebrafish embryos induced characteristic phenotypes of ciliary defects such as curved body axis, hydrocephalus, otolith malformation, and kidney cyst. Our study reveals a new role for the multifunctional protein CHMP4B as a key factor in maintaining the structural integrity of primary cilia. K E Y W O R D Sciliopathy phenotype, endosomal sorting complex, membrane curvature 1332 | JUNG et al.

Midbody Remnant Inheritance Is Regulated by the ESCRT Subunit CHMP4C

“…There are conflicting results about the requirement of ESCRT proteins for primary ciliogenesis in cells such as NIH 3T3 cells that, unlike MDCK cells, use the intracellular route of ciliogenesis. Primary cilium formation appears to be independent of ESCRT proteins in one of the studies (Ott et al, 2018) but not in the other (Jung et al, 2020). We cannot discount the contribution of indirect effects, because the ESCRT-III machinery participates in numerous cellular functions, but, despite this, we propose that a functional consequence of the loss of the connection caused by CHMP4C silencing is the impairment of primary ciliogenesis in MDCK cells and that, therefore, the connection is required for the alternative route of primary ciliogenesis.…”

A Model for Primary Cilium Biogenesis by Polarized Epithelial Cells: Role of the Midbody Remnant and Associated Specialized Membranes

“…Under these conditions, ∼30% of NIH-3T3 cells have a large vesicle at the distal end of their mother centriole, suggesting that the VPS4 impedes the progress of the process of ciliogenesis beyond this stage (Ott et al, 2018). The ESCRT-III components CHMP2A and CHMP4A are at the base and along the cilium, respectively, of RPE1 and IMCD3 cells (Jung et al, 2020). CHMP4B depletion reduces the number of ciliated cells, indicating that CHMP4B is necessary for proper primary cilium formation (Jung et al, 2020).…”

“…The ESCRT-III components CHMP2A and CHMP4A are at the base and along the cilium, respectively, of RPE1 and IMCD3 cells (Jung et al, 2020). CHMP4B depletion reduces the number of ciliated cells, indicating that CHMP4B is necessary for proper primary cilium formation (Jung et al, 2020). Thus, it is clear that ESCRT and ESCRT-associated proteins may have multiple roles that could affect ciliogenesis.…”

Tracking extracellular vesicle (EV) cargo as a platform for studying EVomics, signaling, and targeting in vivo

“…For the full list of the identified ESCRT-associated machinery and its human orthologs see Table S2. Role of the ESCRT machinery in ciliary EV biogenesis is suggested by studies in zebrafish [20,21] and Chlamydomonas [22,23], but remains largely unexplored.…”