TEDS Site Phosphorylation of the Yeast Myosins I Is Required for Ligand-induced but Not for Constitutive Endocytosis of the G Protein-coupled Receptor Ste2p

Abstract

The yeast myosins I Myo3p and Myo5p have well established functions in the polarization of the actin cytoskeleton and in the endocytic uptake of the G protein-coupled receptor Ste2p. A number of results suggest that phosphorylation of the conserved TEDS serine of the myosin I motor head by the Cdc42p activated p21-activated kinases Ste20p and Cla4p is required for the organization of the actin cytoskeleton. However, the role of this signaling cascade in the endocytic uptake has not been investigated. Interestingly, we find that Myo5p TEDS site phosphorylation is not required for slow, constitutive endocytosis of Ste2p, but it is essential for rapid, ligand-induced internalization of the receptor. Our results strongly suggest that a kinase activates the myosins I to sustain fast endocytic uptake. Surprisingly, however, despite the fact that only p21-activated kinases are known to phosphorylate the conserved TEDS site, we find that these kinases are not essential for ligand-induced internalization of Ste2p. Our observations indicate that a different signaling cascade, involving the yeast homologues of the mammalian PDK1 (3-phosphoinositide-dependent-protein kinase-1), Phk1p and Pkh2p, and serum and glucocorticoid-induced kinase, Ypk1p and Ypk2p, activate Myo3p and Myo5p for their endocytic function.Myosins I constitute a well characterized and ubiquitous group of unconventional myosins, which participate in a variety of cellular processes, including endocytosis, phagocytosis, cell motility, secretion, and cell polarity (1, 2). As other myosins, myosins I bear an N-terminal actin-activated ATPase, which can translocate actin filaments in vitro (3). A short positively charged tail that binds acidic phospholipids and targets the myosin to the appropriate cellular membranes follows the conserved motor domain (1, 2, 4, 5). The fungal and the protozoal myosins I bear an additional C-terminal extension that participates in the activation of Arp2/3-dependent actin polymerization (6 -10). In the yeast Saccharomyces cerevisiae, two highly homologous genes encode myosins I: MYO3 and MYO5. Deletion of either gene does not result in any obvious phenotype, whereas, depending on the strain background, a double knock-out is lethal or very sick, suggesting functional redundancy (11,12). Genetic analysis indicates that the yeast myosins I participate in the polarization of the actin cytoskeleton and in endocytosis. Cortical actin patches, which concentrate in the daughter cells in wild type budding yeast, partially redistribute to mother cells in a double myo3⌬ myo5⌬ null mutant generated in a permissive strain background (11, 12). Besides, Myo3p and Myo5p have a well established function in the ligand-induced internalization of the ␣-factor pheromone receptor Ste2p. Ste2p is a G protein-coupled receptor that triggers the mating response in the presence of ␣-factor (13). Binding of the pheromone to its receptor accelerates its internalization and degradation rate as part of a pheromone desensitization program (14). Temperature-sens...

Target of Rapamycin Complex 2 Signals to Downstream Effector Yeast Protein Kinase 2 (Ypk2) through Adheres-Voraciously-to-Target-of-Rapamycin-2 Protein 1 (Avo1) in Saccharomyces cerevisiae

“…To date, Ypk2 substrates or downstream effectors involved in regulating actin organization and/or cell wall integrity have remained elusive. One interesting candidate is a yeast type I myosin protein Myo5, which can be phosphorylated by Ypk2 in vitro (42) and has been implicated in regulating the actin assembly (43). Further investigation is required to see whether Ypk2 334 -677 can phosphorylate Myo5 or to uncover other Ypk2 downstream effectors and examine their interactions with Ypk2 334 -677 .…”

Function and regulation of Saccharomyces cerevisiae myosins-I in endocytic budding

“…Phosphorylation of the TEDS site is essential for ligandinduced Ste2 internalization [38]. However, Cdc42 and the PAKs are dispensable, suggesting that other signalling cascades can control TEDS site phosphorylation [38]. Consistently, it was demonstrated that the yeast SGK (serum and glucocorticoid-induced kinase) homologue Ypk2 interacts with Myo5 and can phosphorylate its TEDS site [38].…”

“…However, even though the TEDS site phosphorylation is required for endocytic uptake [6,38], the role of the Cdc42/PAK signalling cascade in endocytosis is far from being understood. Phosphorylation of the TEDS site is essential for ligandinduced Ste2 internalization [38]. However, Cdc42 and the PAKs are dispensable, suggesting that other signalling cascades can control TEDS site phosphorylation [38].…”

“…Numerous results demonstrate that the yeast myosins-I are also targets of the Cdc42-activated PAKs controlling actin assembly and polarization in yeast [21]. However, even though the TEDS site phosphorylation is required for endocytic uptake [6,38], the role of the Cdc42/PAK signalling cascade in endocytosis is far from being understood. Phosphorylation of the TEDS site is essential for ligandinduced Ste2 internalization [38].…”

Myosin VI altered at threonine 406 stabilizes actin filaments in vivo

“…Phosphorylation at this site, also known as the TEDS rule site [Bement and Mooseker, 1995] is required to activate ATPase activity and functional motility in ameboid class I myosin [Wu et al, 1997;Novak and Titus, 1998;Yamashita and May, 1998;Grosshans et al, 2006]. We theorized that phosphorylation at the equivalent site in myosin VI, threonine 406 (T406), could serve as the motor-to-tether signal.…”