Fission yeast Pak1 phosphorylates anillin-like Mid1 for spatial control of cytokinesis

Abstract

Magliozzi et al. show that fission yeast cell polarity kinase Pak1 regulates cytokinesis. Through a phosphoproteomic screen and subsequent mutant analysis, their work uncovers direct targets and mechanisms for Pak1 activity during cell division. AbstractProtein kinases direct polarized growth by regulating the cytoskeleton in time and space, and could play similar roles in cell division. We found that the Cdc42-activated polarity kinase Pak1 colocalizes with the assembling contractile actomyosin ring (CAR) and remains at the division site during septation. Mutations in pak1 led to defects in CAR assembly and genetic interactions with cytokinesis mutants. Through a phosphoproteomic screen, we identified novel Pak1 substrates that function in polarized growth and cytokinesis. For cytokinesis, we found that Pak1 regulates the localization of its substrates Mid1 and Cdc15 to the CAR. Mechanistically, Pak1 phosphorylates the Mid1 N-terminus to promote its association with cortical nodes that act as CAR precursors. Defects in Pak1-Mid1 signaling lead to misplaced and defective division planes, but these phenotypes can be rescued by synthetic tethering of Mid1 to cortical nodes. Our work defines a new signaling mechanism driven by a cell polarity kinase that promotes CAR assembly in the correct time and place.

The Multiple Functions of Rho GTPases in Fission Yeasts

“…The NDR/LATS kinase Orb6 phosphorylates Gef1 and promotes its binding to 14-3-3 protein Rad24, which displaces Gef1 from the cortex, to reduce polarized activation of Cdc42 [61,70]. On the other hand, a recent phosphoproteomic study has identified Scd1 as one of the p21-activated serine/threonine kinase Pak1 targets involved in polarized growth [89]. Scd1 phosphorylation by Pak1 is important for the regulation of its nuclear shuttling [89].…”

“…On the other hand, a recent phosphoproteomic study has identified Scd1 as one of the p21-activated serine/threonine kinase Pak1 targets involved in polarized growth [89]. Scd1 phosphorylation by Pak1 is important for the regulation of its nuclear shuttling [89]. In S. cerevisiae, it has already been described that the inhibitory phosphorylation of Cdc24 by PAKs is important in the negative feedback regulation of Cdc42 activity [143,148].…”

“…Other kinases beyond Pom1 are also involved in modulating Rga4 localization. Recent data have shown that the Cdc42 effector Pak1, unlike Pom1, directly phosphorylates Rga4 [89]. In the absence of Pom1 and Pak1, Rga4 becomes enriched at both cell tips, indicating that both polarity kinases collaborate as tip exclusion factors and that cells require active repulsion of this GAP at cell ends to sustain polarized growth [89].…”

“…Recent data have shown that the Cdc42 effector Pak1, unlike Pom1, directly phosphorylates Rga4 [89]. In the absence of Pom1 and Pak1, Rga4 becomes enriched at both cell tips, indicating that both polarity kinases collaborate as tip exclusion factors and that cells require active repulsion of this GAP at cell ends to sustain polarized growth [89]. Orb6 might also be involved in Rga4 phosphorylation to modulate Cdc42 activation, thus controlling cell dimensions and growth symmetry [61,121].…”

“…Such phosphorylation may serve to slow node dynamics by reducing force production by Myo2, which permits sufficient time to allow chromosome segregation to occur before cytokinesis [87]. Pak1 also phosphorylates and regulates the localization to the CAR of other cytokinetic proteins like the contractile ring anillin-related protein Mid1, F-BAR protein Cdc15, and Cyk3 (Figure 4A) [89,92]. In budding yeast, PAK kinases have not been involved in the phosphorylation of Cdc15 ortholog Hof1, which depends primarily on cell cycle kinases [216].…”