Phosphorylation-dependent regulation of the F-BAR protein Hof1 during cytokinesis

Abstract

Spatial and timely coordination of cytokinesis is crucial for the maintenance of organelle inheritance and genome integrity. The mitotic exit network (MEN) pathway controls both the timely initiation of mitotic exit and cytokinesis in budding yeast. Here we identified the conserved F-BAR protein Hof1 as a substrate of the MEN kinase complex Dbf2-Mob1 during cytokinesis. We show that polo-like kinase Cdc5 first phosphorylates Hof1 to allow subsequent phosphorylation by Dbf2-Mob1. This releases Hof1 from the septin ring and facilitates Hof1 binding to the medial actomyosin ring (AMR), where Hof1 promotes AMR contraction and membrane ingression. Domain structure analysis established that the central, unstructured, region of Hof1, named the ring localization sequence (RLS), is sufficient to mediate Hof1's binding to the medial ring in a cell cycle-dependent manner. Genetic and functional data support a model in which Dbf2-Mob1 regulates Hof1 by inducing domain rearrangements, leading to the exposure of the Hof1 RLS domain during telophase.

Mechanisms of cytokinesis in budding yeast

“…First, the MEN could control AMR constriction by controlling septin hourglass splitting [Cid et al, 2001;Lippincott et al, 2001]. However, in the MEN mutants forced to exit mitosis by overexpression of the CDK1 inhibitor Sic1, the septin hourglass is split into two cortical rings but AMR constriction still cannot occur [Meitinger et al, 2010;Meitinger et al, 2011], suggesting that the MEN controls AMR constriction independently of septin hourglass splitting. Second, the MEN could control AMR constriction by controlling PS formation.…”

Hippo signalling in the G2/M cell cycle phase: Lessons learned from the yeast MEN and SIN pathways

“…In particular, the regulation of budding yeast Hof1p appears to be conserved between SIN and MEN. Fission yeast Cdc15p is one of two functional homologues of Hof1p [51][52][53], which is the only established target of budding yeast Mob1p/ Dbf2p in cytokinesis [37]. Furthermore, Cdc15p is phosphorylated on a conserved RXXS motif that can be targeted by Mob1p/Sid2p [53].…”

“…Nevertheless, recent evidence suggests that MEN signalling components have more direct roles in orchestrating the process of cytokinesis. On one hand, Dbf2p and Mob1p have been found at the actin-myosin ring (AMR) structure that is essential for abscission [35][36][37][38], and Cdc15p, Dbf2p and Mob1p are required for AMR contraction [39,40]. Moreover, current evidence suggests that the MEN components Dbf2p and Mob1p can regulate the cytokinetic components Chs2p, Hof1p, and Inn1p (summarised in [33,41]).…”

Microcompartments within the yeast plasma membrane

“…The proline-rich region of Inn1 binds to the SH3 domain of the transient actomyosin component Hof1, an F-BAR protein, which appears at the septin ring already early during cell cycle (Nishihama et al , 2009 ). In the late anaphase, Hof1 is phosphorylated by the components of the mitotic exit network (MEN; specifically by the Dbf2-Mob1 heterotrimer), which triggers its release from the septin filaments and a shift to the AMR, where it promotes ring contraction and membrane ingression (Meitinger et al , 2011 ). Besides, with Hof1, Inn1 also interacts with Cyk3, which might have a role in a cytokinesis pathway that is triggered by Iqg1 independently from the AMR (Ko et al , 2007 ;Jendretzki et al , 2009 ).…”

“…They orchestrate cell division and act as a signaling platform for cytokinesis Vrabioiu and Mitchison , 2006 ;McMurray and Thorner , 2009a ;Roncero and Sanchez , 2010 AMR (Myo1, Mlc1, Act1) AMR assembles during early mitosis Myo1; type II myosin of the AMR; Mcl1, type V myosin, light chain of Myo1; Act1, forming filamentous actin Vallen et al , 2000 Iqg1 ( = Cyk1) Ring-like structure at the bud neck Essential for actomyosin formation but has also a cytokinetic function that is independent from the AMR; interacts with Myo1 independently of septins Epp and Chant , 1997 ;Ko et al , 2007 Cyk3 Ring-like structure at the bud neck Recruits Inn1 to the bud neck; when overexpressed, Inn1 recruitment is AMR independent Jendretzki et al , 2009 ;Meitinger et al , 2010 Inn1 Localizes to the bud neck during late mitosis Required for plasma membrane ingression concomitant with AMR constriction; binds to Hof1 and Cyk3 Jendretzki et al , 2009 ;Meitinger et al , 2010 Hof1 Bud neck at anaphase; initially forms a double ring that fuses after AMR constriction Binds to the formin Bnr1 and triggers AMR constriction; then, it relocates to the septin filaments Vallen et al , 2000 ;Meitinger et al , 2011 Formins (Bni1, Bnr1) Bni1 localizes at the bud tip during bud growth and later at the bud neck; Bnr1 stably associates with septins at the bud neck Promote actin polymerization in a Rho1 dependent manner.…”