TY - JOUR T1 - Cell-substrate adhesion drives Scar/WAVE activation and phosphorylation, which controls pseudopod lifetime JF - bioRxiv DO - 10.1101/732768 SP - 732768 AU - Shashi Prakash Singh AU - Peter A. Thomason AU - Sergio Lilla AU - Matthias Schaks AU - Qing Tang AU - Bruce L. Goode AU - Laura M. Machesky AU - Klemens Rottner AU - Robert H. Insall Y1 - 2019/01/01 UR - http://biorxiv.org/content/early/2019/08/12/732768.abstract N2 - The Scar/WAVE complex is the principal catalyst of pseudopod and lamellipod formation. Here we show that Scar/WAVE’s proline-rich domain is polyphosphorylated after the complex is activated. Treatments that stop activation block phosphorylation in both Dictyostelium and mammalian cells. This implies that phosphorylation modulates pseudopods after they have been formed, rather than controlling whether a protrusion is initiated. Unexpectedly, activation-dependent phosphorylation is not promoted by chemotactic signalling, or by signal-dependent kinases such as ERKs, but is greatly stimulated by cell:substrate adhesion. Scar/WAVE that has been mutated to be either unphosphorylatable or phosphomimetic is activated normally, and rescues the phenotype of scar− cells, demonstrating that phosphorylation is dispensible for activation and actin regulation. However, pseudopods and patches of Scar/WAVE complex recruitment last substantially longer in unphosphorylatable mutants, altering cell polarisation and the efficiency of migration. We conclude that pseudopod engagement with substratum is more important than extracellular signals at regulating Scar/WAVE’s activity, and that phosphorylation acts as a timer, restricting pseudopod lifetime by promoting Scar/WAVE turnover. ER -