Essential roles of KIF4 and its binding partner PRC1 in organized central spindle midzone formation

Abstract

A number of proteins accumulate in the anaphase spindle midzone, but the interaction and precise role of these proteins in midzone organization remain obscure. Here, we found that the microtubule-bundling protein PRC1 bound separately to the three motor proteins, KIF4, MKLP1 and CENP-E, but not to the chromosomal passenger proteins. In KIF4-deficient cells, the central spindle was disorganized, and all midzone-associated proteins including PRC1 failed to concentrate at the midline, instead being dispersed along the loosened microtubule bundles of the central spindle. This suggests that KIF4 is essential for the organization of central spindles and for midzone formation. In PRC1-deficient cells, no midzone was formed, KIF4 and CENP-E did not localize to the disconnected half-spindle, and MKLP1 and chromosomal passenger proteins localized to discrete subdomains near microtubule plus ends in the half-spindle. Thus, PRC1 is required for interaction of the two half-spindles and for localization of KIF4 and CENP-E. These results suggest that KIF4 and its binding partner PRC1 play essential roles in the organization of central spindles and midzone formation.

PRC1 associates with the hsp70i promoter and interacts with HSF2 during mitosis

“…Previous data indicated that PRC1 does not bind to microtubules during metaphase due to cell cycle-dependent phosphorylation [1,2]. Consistent with our hypothesis that the HSF2/PRC1 interaction is not dependent on microtubule dynamics, our immunofluorescence analysis of untreated cells indicates that HSF2 does not co-localize with α-tubulin during mitosis and that HSF2 and PRC1 localize together at prometaphase and metaphase but not in the later stages of mitosis when PRC1 is localized at the spindle midzone [1,2,4]. As mentioned above, previous studies in our laboratory indicated that HSF2 is present at the hsp70i promoter during mitosis to mediate bookmarking of the hsp70i gene [12].…”

“…Supporting the hypothesis of a functional complex involving HSF2 and PRC1 is the finding that CAP-G, the subunit of the condensin complex that HSF2 binds to during bookmarking of the hsp70i promoter [12], also interacts with Kif4 [20], a kinesin-4 family member that has been shown to interact with and translocate PRC1 along the mitotic spindle [4,5,20]. The interaction between Kif4 and PRC1 is regulated by phosphorylation of PRC1 [4,5].…”

“…The interaction between Kif4 and PRC1 is regulated by phosphorylation of PRC1 [4,5]. Early in mitosis both PRC1 and Kif4 are present at the mitotic spindle, when PRC1 is phosphorylated, but these two proteins do not interact at that time [5].…”

“…Email: kdsarge@uky.edu. b Current address: University of Dayton, Department of Biology, Dayton, OH, 45469. chromokinesin Kif4 and PRC1, regulated by the Cdk phosphorylation state of PRC1, occurs at the metaphase-to-anaphase transition and is responsible for translocating PRC1 along the spindle, allowing PRC1 to bundle interdigitating microtubules (MTs) and form the spindle midzone [4,5]. PRC1 also interacts with the motor proteins MKLP-1 and CENP-E in late mitosis [4].…”

Prime movers: the mechanochemistry of mitotic kinesins

“…The clustering and crosslinking activities of centralspindlin enable it to assemble cooperatively and maintain the central spindle array of antiparallel microtubules 157,158 . KIF4 (kinesin-4 family) is recruited to the central spindle via its interaction with PRC1, a cross-linker that stabilizes antiparallel microtubule overlaps 159 . In addition to their function in pre-anaphase, KIF4 motors also have a key role in controlling the size of the central spindle through regulation of microtubule dynamics 160,161 KIF4 recruitment to the central spindle is controlled by the phosphorylation of its C-terminal tail by a KIF20A (kinesin-6)-dependent pool of the Aurora B mitotic kinase 162 .…”