Yeast Endocytic Adaptor AP‐2 Binds the Stress Sensor Mid2 and Functions in Polarized Cell Responses

Abstract

The AP-2 complex is a heterotetrameric endocytic cargo-binding adaptor that facilitates uptake of membrane proteins during mammalian clathrin-mediated endocytosis. While budding yeast has clear homologues of all four AP-2 subunits which form a complex and localize to endocytic sites in vivo, the function of yeast AP-2 has remained enigmatic. Here, we demonstrate that AP-2 is required for hyphal growth in Candida albicans and polarized cell responses in Saccharomyces cerevisiae. Deletion of APM4, the cargo-binding mu subunit of AP-2, causes defects in pseudohyphal growth, generation of a mating projection and the cell wall damage response. In an apm4 null mutant, the cell wall stress sensor Mid2 is unable to relocalize to the tip of a mating projection following pheromone addition, or to the mother bud neck in response to cell wall damage. A direct binding interaction between Mid2 and the mu homology domain of Apm4 further supports a model in which AP-2 binds Mid2 to facilitate its internalization and relocalization in response to specific signals. Thus, Mid2 is the first cargo for AP-2 identified in yeast. We propose that endocytic recycling of Mid2 and other components is required for polarized cell responses ensuring cell wall deposition and is tightly monitored during cell growth.

New Regulators of Clathrin-Mediated Endocytosis Identified in Saccharomyces cerevisiae by Systematic Quantitative Fluorescence Microscopy

“…Thus, a majority of the known endocytic machinery proteins were located high in this ranking (Table S1 and Table S2). Interestingly, all four subunits of the AP-2 complex scored a colocalizing PCC, consistent with recent findings that AP-2 does in fact play a role in yeast CME (Carroll et al 2009;Chapa-Y-Lazo et al 2014). The lower range of the 197 colocalizing proteins was enriched in proteins spanning a variety of functions and containing predicted or known transmembrane domains.…”

Vacuolar H+-ATPase Protects Saccharomyces cerevisiae Cells against Ethanol-Induced Oxidative and Cell Wall Stresses

“…The structural components and networks of the yeast cell wall are thereby remodeled in order to maintain cell wall integrity and function (45). Endocytosis and recycling of cell wall sensors from endosomes back to the plasma membrane have been shown to play an important role in regulation of the cell wall integrity pathway (46)(47)(48). Similar to the mislocalization of plasma membrane H ϩ -ATPase Pma1p in the vma mutants (16), the deletion of VMA genes has recently been reported to result in mislocalization of Wsc1p from the plasma membrane to the vacuole (49), suggesting a role for V-ATPase in the maintenance of yeast cell wall integrity through the endocytic recycling of Wsc1p.…”

FgAP‐2 complex is essential for pathogenicity and polarised growth and regulates the apical localisation of membrane lipid flippases inFusarium graminearum

“…In addition, Apm4, the mu subunit of the yeast AP‐2, interacts with Pkc1, a cell wall integrity‐associated protein (Chapa & Ayscough, ). AP‐2 binds the stress sensor Mid2 on the plasma membrane to function in polarised cell responses in yeast (Chapa‐y‐Lazo, Allwood, Smaczynska‐de Rooij, Snape, & Ayscough, ). However, very little is known about the role of AP‐2 complex in filamentous fungi.…”