CK1α protects WAVE from degradation to regulate cell shape and motility in the immune response

Abstract

The WAVE regulatory complex (WRC) is the major Arp2/3 activator, promoting lamellipodial protrusions in migrating cells. The WRC is basally inactive but can be activated by Rac1 and phospholipids, and phosphorylation. However, the in vivo relevance of phosphorylation of WAVE remains largely unknown. Here, we identified the kinase CK1α as a novel regulator of WAVE controlling cell shape and cell motility in Drosophila macrophages. CK1α binds and phosphorylates WAVE in vitro. Phosphorylation of WAVE by CK1α appears not to be required for activation but rather regulates its stability. Pharmacologic inhibition of CK1α promotes ubiquitin-dependent degradation of WAVE. Consistently, loss of ck1α but not ck2 function phenocopies WAVE depletion. Phosphorylation-deficient mutations in the CK1α consensus sequences within the VCA domain of WAVE can neither rescue mutant lethality nor lamellipodia defects. By contrast, phosphomimetic mutations rescue all cellular and developmental defects. Finally, RNAi-mediated suppression of 26S proteasome or E3 ligase complexes substantially rescues lamellipodia defects in CK1α depleted macrophages. Thus, we conclude that the basal phosphorylation of WAVE by CK1α protects it from premature ubiquitin-dependent degradation, thus promoting WAVE function in vivo.

PPP2R1A regulates migration persistence through the NHSL1-containing WAVE Shell Complex

“…Freeing WAVE from the WRC that maintains it inactive 6,7 would be another way to expose its Arp2/3-activating WCA motif. WAVE proteins were reported to be degraded by proteasomes upon cell activation and ubiquitylated on a specific lysine residue in their WHD 56,57 . But these reports do not demonstrate that this is a free form of WAVE that is degraded after activation.…”

PPP2R1A Regulates Migration Persistence through the WAVE Shell Complex

“…It is difficult to anticipate the mechanism by which WAVE would disengage from the WRC. WAVE proteins were reported to be degraded by proteasomes upon cell activation and ubiquitylated on a specific lysine residue in their WHD 50,51 . But these reports do not demonstrate that this is a free form of WAVE that is degraded after activation.…”

The Scar/WAVE complex drives normal actin protrusions without the Arp2/3 complex, but proline-rich domains are required

“…For this reason the manipulation of the lifetime of the active WRC is extremely important, as has been shown in simpler systems like WASP 42 . The inactive WRC is stable, but on activation it is subjected to exceptionally rapid proteolysis 43 . The WRC deleted of its VCA domain is deprived of its normal autoinhibition.…”