Phosphorylation of the Cdc42 Exchange Factor Cdc24 by the PAK-like Kinase Cla4 May Regulate Polarized Growth in Yeast

Abstract

Rho-type GTPases control many cytoskeletal rearrangements, but their regulation remains poorly understood. Here, we show that in S. cerevisiae, activation of the CDK Cdc28-Cln2 at bud emergence triggers relocalization of Cdc24, the GEF for Cdc42, from the nucleus to the polarization site, where it is stably maintained by binding to the adaptor Bem1. Locally activated Cdc42 then polarizes the cytoskeleton in a manner dependent on its effectors Bni1 and the PAK-like kinase Cla4. In addition, Cla4 induces phosphorylation of Cdc24, leading to its dissociation from Bem1 at bud tips, thereby ending polarized bud growth in vivo. Our results thus suggest a dynamic temporal and spatial regulation of the Cdc42 module: Cdc28-Cln triggers actin polarization by activating Cdc42, which in turn restricts its own activation via a negative feedback loop acting on its GEF Cdc24.

A PtdInsP3- and Rho GTPase-mediated positive feedback loop regulates neutrophil polarity

“…The second ingredient of this self-organizing pattern formation system 22 is that signals from the activator generate a more long-range inhibitor of signalling. Good candidates for this inhibitory function in eukaryotic chemotaxis include negative regulators of PtdInsP 3 accumulation, such as the lipid phosphatases PTEN (phosphatase and tensin homologue deleted on chromosome ten) 23,24 and SHIP (SH2-containing inositol phosphatase) 25 , and negative regulators of Rho GTPase activation (for example, a recently identified negative feedback loop in Saccharomyces cerevisiae, in which Cdc42 induces phosphorylation and inactivation of its own guanine nucleotide exchange factor 26 ). In addition to chemotaxis 22 , pattern formation systems that are consistent with this general model (though not necessarily the same components) include hydra regeneration and retinotectal mapping.…”

A novel interplay between GEFs orchestrates Cdc42 activity during cell polarity and cytokinesis

“…Surprisingly, we report that active Cdc42 is not sufficient to recruit Scd1 in the absence of Gef1. While it has been proposed that Cdc42 establishes positive feedback through the formation of the ternary complex consisting of the Cdc42 effector PAK (p21-activated kinases) and its associated scaffold protein (Scd2 or Bem1) (Butty et al, 2002;Kozubowski et al, 2008), studies in S. pombe and S. cerevisiae suggest that Pak1 kinase activity antagonizes either the Cdc42 scaffold or the GEF, rather than establishing a positive feedback (Das et al, 2012;Gulli et al, 2000;Kuo et al, 2014;Rapali et al, 2017). In support of this antagonistic role of Pak1, we find that more Scd1 accumulates at cell ends and at the division site in the pak1 switch-off mutant.…”

Yeast and fungal morphogenesis from an evolutionary perspective

“…Ste20 and Cla4 have been shown to phosphorylate and activate type I myosins Myo3 and Myo5 [98], which in turn have a role in the internalization step of endocytosis via actin patches [99,100]. Cla4 is also the major kinase that phosphorylates the GEF Cdc24, although the exact role for this phosphorylation is still controversial [74,101]. Cla4 plays a critical role in the assembly of the septin ring at the bud neck [102].…”