Protein kinase Gin4 negatively regulates flippase function and controls plasma membrane asymmetry

Abstract

In yeast, the protein kinase Gin4 locally controls plasma membrane lipid asymmetry, which is necessary for optimal cytokinesis.

Septin-Associated Protein Kinases in the Yeast Saccharomyces cerevisiae

“…Syp1 is a highly phosphorylated protein (Albuquerque et al, 2008; Soulard et al, 2010; Swaney et al, 2013). In this regard, it is interesting that eight of the phospho-sites detected in Syp1 fit the -T/S-P- consensus for the protein kinase Cdk1/Cdc28 that is the major cell cycle driver (Verma et al, 1997; Mok et al, 2010) and five of them fit the consensus sequence (-R-x-x-S/T-) determined for the bud neck-localized protein kinase Gin4 (Mok et al, 2010; Roelants et al, 2015). However, Syp1 also localizes prominently to cortical puncta and functions as an endocytic adaptor that is involved in cargo selection and negative regulation of Las17 (yeast WASp)-Arp2/3 complex activity (Boettner et al, 2009; Reider et al, 2009) during the early stages of endocytic patch formation (Stimpson et al, 2009).…”

“…It has been reported that localization of septins, Hsl7 and Elm1 all depend upon local membrane curvature (Bridges et al, 2016; Kang et al, 2016); it is possible, therefore, that these factors serve as sensors of cell geometry, thereby integrating this input into the timing of the decision of when to allow passage through G2-M. Although Gin4 and Kcc4 have been implicated in septin collar assembly (Longtine et al, 1998) and in the Swe1 degradation pathway (Barral et al, 1999), more recent evidence indicates that these enzymes likely exert their effects more indirectly by modulating the plasma membrane lipid distribution (Roelants et al, 2015) (see further below). Indeed, like Hsl1, Gin4 and Kcc4 also possess phosphatidylserine-binding C-terminal KA-1 domains that are required for their function in vivo (Moravcevic et al, 2010).…”

“…At sites of polarized growth, the protein kinase Fpk1 (and its paralog Fpk2) phosphorylate and stimulate two PM-localized flippases (Dnf1 and Dnf2), which translocate phosphatidylethanolamine (PtdEth) and phosphatidylserine from the outer to the inner leaflet of the PM (Nakano et al, 2008; Roelants et al, 2010). However, at the bud neck, septin-anchored protein kinase Gin4 phosphorylates and inhibits Fpk1 (and Fpk2) function (Roelants et al, 2015). Thus, flipping of aminoglycerophospholipids is prevented in a highly localized manner.…”

“…Thus, flipping of aminoglycerophospholipids is prevented in a highly localized manner. Preventing flipping of aminoglycerophospholipids in this way contributes to enhancing the efficiency of cell division because alterations that compromise flippase function suppress the inviabiity phenotype of a variety of mutations ( hof1, inn1, cyk3 , and myo1 , the type II myosin of the AMR) known to cause defects in cytokinesis (Roelants et al, 2015). Moreover, Gin4 is released from the septin collar just before it splits and the AMR contracts, whereas the bulk of Fpk1 remains (Roelants et al, 2015), presumably fine-tuning the timing of transbilayer lipid flipping necessary for the completion of PM scission and cell separation.…”

“…Preventing flipping of aminoglycerophospholipids in this way contributes to enhancing the efficiency of cell division because alterations that compromise flippase function suppress the inviabiity phenotype of a variety of mutations ( hof1, inn1, cyk3 , and myo1 , the type II myosin of the AMR) known to cause defects in cytokinesis (Roelants et al, 2015). Moreover, Gin4 is released from the septin collar just before it splits and the AMR contracts, whereas the bulk of Fpk1 remains (Roelants et al, 2015), presumably fine-tuning the timing of transbilayer lipid flipping necessary for the completion of PM scission and cell separation. The mechanisms responsible for the cell cycle-coupled ejection of Gin4 and the recruitment of Fpk1 are not known, although Gin4 is phosphorylated and activated in a cell cycle-dependent manner at the G2-M transition, apparently by Clb2-Cdc28 (Altman and Kellogg, 1997) and, conversely, the septins are required for the mitosis-specific activation of Gin4 (Carroll et al, 1998).…”