Citron kinase-dependent F-actin maintenance at midbody secondary ingression sites mediates abscission

Abstract

Abscission is the final step of cytokinesis whereby the intercellular bridge (ICB) linking the two daughter cells is cut. The ICB contains a structure called the midbody, required for the recruitment and organization of the abscission machinery. Final midbody severing is mediated by formation of secondary midbody ingression sites, where the ESCRT III component CHMP4B is recruited to mediate membrane fusion. It is presently unknown how cytoskeletal elements cooperate with CHMP4B to mediate abscission. Here, we show that F-actin is associated with midbody secondary sites and is necessary for abscission. F-actin localization at secondary sites depends on the activity of RhoA and on the abscission regulator citron kinase (CITK). CITK depletion accelerates loss of F-actin proteins at the midbody and subsequent cytokinesis defects are reversed by restoring actin polymerization. Conversely, midbody hyperstabilization produced by overexpression of CITK and ANLN is reversed by actin depolymerization. CITK is required for localization of F-actin and ANLN at the abscission sites, as well as for CHMP4B recruitment. These results indicate that control of actin dynamics downstream of CITK prepares the abscission site for the final cut.

Inactivation of Citron Kinase Inhibits Medulloblastoma Progression by Inducing Apoptosis and Cell Senescence

“…During mitosis, it is first localized to the nucleus (27), it is enriched at spindle poles before anaphase (28), it is concentrated at cleavage furrow and midbody from anaphase to cytokinesis (25). CITK is a specific regulator of abscission at the end of cytokinesis (25,(29)(30)(31)(32). In addition, it regulates mitotic spindle orientation (33) and it is involved in genomic stability independently of its role in cytokinesis (34).…”

CITK Loss Inhibits Growth of Group 3 and Group 4 Medulloblastoma Cells and Sensitizes Them to DNA-Damaging Agents

“…In order to silence CITK expression, previously published CITK double-stranded RNAs (siCITK1 and siCITK2) and nontargeting siRNA were used (Dharmacon, Lafayette, CO, USA) [31,58]. Cells were placed on six-well plates and were transfected, using 6.25 µL of the required siRNA (20 µmol/L), together with 1.5 µL of Lipofectamine 2000 (Invitrogen, Carlsbad, CA, USA) according to the manufacturer's instructions.…”

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

“…45,46 To determine whether rearrangement of the actin cytoskeleton affects ciliary localization of CHMP4B, we treated RPE1 cells with cyto D and measured the intensity of CHMP4B immunofluorescence. 45,46 To determine whether rearrangement of the actin cytoskeleton affects ciliary localization of CHMP4B, we treated RPE1 cells with cyto D and measured the intensity of CHMP4B immunofluorescence.…”

“…During cytokinesis, disassembly of filamentous actin (F-actin) is required for the localization of CHMP4B to the abscission site. 45,46 To determine whether rearrangement of the actin cytoskeleton affects ciliary localization of CHMP4B, we treated RPE1 cells with cyto D and measured the intensity of CHMP4B immunofluorescence. Cyto D treatment promoted cilium elongation as previously reported ( Figure 7B).…”