TORC2-Gad8-dependent myosin phosphorylation modulates regulation by calcium

Abstract

Cells respond to changes in their environment through signaling networks that modulate cytoskeleton and membrane organization to coordinate cell-cycle progression, polarized cell growth and multicellular development. Here, we define a novel regulatory mechanism by which the motor activity and function of the fission yeast type one myosin, Myo1, is modulated by TORC2-signalling-dependent phosphorylation. Phosphorylation of the conserved serine at position 742 (S742) within the neck region changes both the conformation of the neck region and the interactions between Myo1 and its associating calmodulin light chains. S742 phosphorylation thereby couples the calcium and TOR signaling networks that are involved in the modulation of myosin-1 dynamics to co-ordinate actin polymerization and membrane reorganization at sites of endocytosis and polarised cell growth in response to environmental and cell-cycle cues.

Acetylation stabilises calmodulin‐regulated calcium signalling

“…As the genes encoding for each fusion protein are expressed from the endogenous cam1 + promoter at its chromosomal locus, this is likely to reflect differences in functionality. Here, we confirm that Cam1 binding to Myo1 impacts localisation of the motor to membrane at sites of endocytosis, affecting distribution and duration of the subsequent endocytic events [11]. Both unmodified and acetylated Cam1 bound to the two Myo1 IQ motifs (comparable amplitudes and 2 rates consistent with cooperative binding to the 2 IQ motifs – Fig.…”

“…Calmodulin light chains bind to IQ motifs in the neck region of myosins, regulating their function [29]. The fission yeast Class I myosin, Myo1 contains an IQ motif neck region which binds Cam1 [10,11]. We previously described a recombinant Myo1IQ 12 -FRET protein consisting of a donor CyPet fluorophore and an acceptor YPet fluorophore separated by a linker region of the two Myo1 IQ motifs [11].…”

“…The fission yeast Class I myosin, Myo1 contains an IQ motif neck region which binds Cam1 [10,11]. We previously described a recombinant Myo1IQ 12 -FRET protein consisting of a donor CyPet fluorophore and an acceptor YPet fluorophore separated by a linker region of the two Myo1 IQ motifs [11]. Unbound IQ motifs have a flexible, collapsed conformation which allows FRET between the two fluorophores.…”

“…In contrast, Cam2 is not only a non-Ca 2+ binding CaM homologue, but is also non-essential to the viability of the cell, playing subtle roles in modulating polarised growth in response to changes in the cellular environment [11,12]. Each CaM associates with the neck region of the class I myosin, Myo1 [10,11,13], stiffening the lever arm to regulate Myo1 dynamics during endocytosis [11].…”

mTORC2 coordinates the leading and trailing edge cytoskeletal programs during neutrophil migration

“…Biochemical studies in neutrophils have shown that mTORC2 kinase effector PKC regulates RhoA and myosin activity in neutrophils (Liu et al, 2014(Liu et al, , 2010. In fission yeast, TORC2 kinase activity also stimulates myosin activation (Baker et al, 2019) Our results show that the kinase-independent roles of Rictor/mTORC2 inhibit Rac activity in the front, while the kinase roles of mTORC2 stimulate contractility at the back allowing the two divergent downstream arms of mTORC2 to execute opposing effects on the front and back polarity programs. We next explore the consequence of this regulatory circuit for front-back polarity coordination during motility.…”