WHIMP links the actin nucleation machinery to Src-family kinase signaling during protrusion and motility

Abstract

17Cell motility is governed by cooperation between the Arp2/3 complex and nucleation factors 18 from the Wiskott-Aldrich Syndrome Protein (WASP) family, which together assemble actin 19 filament networks to drive membrane protrusion. Here we identify WHIMP (WAVE Homology In 20Membrane Protrusions) as a new member of the WASP family. The Whimp gene is encoded on 21 the X-chromosome of multiple animals, including mice. Murine WHIMP promotes Arp2/3-22 dependent actin assembly, but is less potent than other nucleation factors. Nevertheless, 23 WHIMP-mediated Arp2/3 activation enhances both plasma membrane ruffling and wound 24 healing migration, whereas WHIMP depletion impairs protrusion and slows motility. WHIMP 25 expression also increases Src-family kinase activity, and WHIMP-induced ruffles contain the 26 additional nucleation factors WAVE1, WAVE2, and N-WASP, but not JMY or WASH. Perturbing 27 the function of Src-family kinases, WAVE proteins, or Arp2/3 complex inhibits WHIMP-driven 28 ruffling. These results suggest that WHIMP-mediated actin assembly plays a direct role in 29 membrane protrusion, but also results in feedback control of tyrosine kinase signaling to 30 modulate the activation of multiple WASP-family proteins. 31 32 33 3 AUTHOR SUMMARY 34The actin cytoskeleton is a collection of protein polymers that assemble and disassemble within 35 cells at specific times and locations. Sophisticated cytoskeletal regulators called nucleation 36 factors ensure that actin polymerizes when and where it is needed, and most nucleation factors 37 are members of the Wiskott-Aldrich Syndrome Protein (WASP) family. Several of the 8 known 38WASP-family proteins function in cell motility, but how the different factors collaborate with one 39 another is not well understood. In this study, we identified WHIMP, a new WASP-family 40 member which is encoded on the X chromosome of a variety of animals. In mouse cells, 41 WHIMP enhances cell motility by assembling actin filaments that push the cell membrane 42 forward. Unexpectedly, WHIMP also activates tyrosine kinase enzymes, proteins that stimulate 43 multiple WASP-family members during motility. Our results open new avenues of research into 44 how nucleation factors cooperate during movement and how the molecular activities that 45 underlie motility differ in distinct cell types and organisms. 46 47 48 the recruitment and activation of a 7-subunit macromolecule named the Arp2/3 complex [2], 52 which acts in concert with binding partners called nucleation-promoting factors [3]. Many such 53 factors are members of the Wiskott-Aldrich Syndrome Protein (WASP) family, and are integral in 54 activating the complex at different cellular locations [4]. Most WASP-family proteins promote 55 actin assembly during membrane protrusion and cell motility [5], but how the different factors 56 collaborate during these processes is not well understood. 57 WASP-family members are defined by the presence of a WH2-Connector-Acidic (WCA) 58 domain in which one or more WH2 motifs bind actin monome...

Short linear motif candidates in the cell entry system used by SARS-CoV-2 and their potential therapeutic implications

“…The ACE2 YASID sequence has a weak Ala at pY + 1, neutral Ser at pY + 2, and strong Ile and Asp at pY + 3/+4, making this a plausible motif for binding SFKs. Because all human cells have at least one SFK, and they are involved in regulating endocytosis and actin filament formation (113)(114)(115), their SH2 domains are plausible candidates for binding the ACE2 tail. For example, Abl kinases have specialized cytoskeletal remodeling capacity mediated through their actin binding and actin bundling domains (113), while SRC enhances receptor endocytosis and focal adhesion (FA) remodeling through the phosphorylation of Eps8 and dynamin2 (115).…”