Mechanisms regulating targeting of recycling endosomes to the cleavage furrow during cytokinesis

Abstract

Recently, recycling endosomes have emerged as a key components required for the successful completion of cytokinesis. Furthermore, FIP3 (family of Rab11-interacting protein 3), a Rab11 GTPase-binding protein, has been implicated in targeting the recycling endosomes to the midbody of dividing cells. Previously, we have shown that FIP3/Rab11-containing endosomes associate with centrosomes until anaphase, at which time they translocate to the cleavage furrow. At telophase, FIP3/Rab11-containing endosomes move from the furrow into the midbody, and this step is required for abscission. While several other proteins were implicated in regulating FIP3 targeting to the cleavage furrow, the mechanisms regulating the dynamics of FIP3-containing endosomes during mitosis have not been defined. To identify the factors regulating FIP3 targeting to the furrow, we used a combination of siRNA (small interfering RNA) screens and proteomic analysis to identify Cyk-4/MgcRacGAP (GTPase-activating protein) and kinesin I as FIP3-binding proteins. Furthermore, kinesin I mediates the transport of FIP3-containing endosomes to the cleavage furrow. Once in the furrow, FIP3 binds to Cyk-4 as part of centralspindlin complex and accumulates at the midbody. Finally, we demonstrated that ECT2 regulates FIP3 association with the centralspindlin complex. Thus we propose that kinesin I, in concert with centralspindlin complex, plays a role in temporal and spatial regulation of endosome transport to the cleavage furrow during cytokinesis.

Figure 1. Schematic representation of the FIP protein family

Class I FIP proteins include FIP1, 2 and 5, whereas class II FIP proteins include FIP3 and 4. Both classes contain the highly conserved 20-amino-acid Rab11-binding domain. BD, binding domain.

Figure 2. Schematic representation of protein-protein interactions that mediate targeting of recycling endosomes to the midbody

Proteins localized to the recycling endosomes, such as VAMP8, RalA and the complex ARF6-FIP3-Rab11, interact with snapin and the exocyst complex, which causes targeting of the endosomes to the midbody during cytokinesis.