dictyNews
Electronic Edition
Volume 44, number 28
October 5, 2018
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Abstracts
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Fam49/CYRI interacts with Rac1 and locally suppresses protrusions.
Fort L, Batista JM, Thomason PA, Spence HJ, Whitelaw JA, Tweedy L,
Greaves J, Martin KJ, Anderson KI, Brown P, Lilla S, Neilson MP,
Tafelmeyer P, Zanivan S, Ismail S, Bryant DM, Tomkinson NCO,
Chamberlain LH, Mastick GS, Insall RH, Machesky LM.
Nature Cell Biol https://www.nature.com/articles/s41556-018-0198-9
Actin-based protrusions are reinforced through positive feedback, but
it is unclear what restricts their size, or limits positive signals when they
retract or split. We identify an evolutionarily conserved regulator of actin-
based protrusion: CYRI (CYFIP-related Rac interactor) also known as
Fam49 (family of unknown function 49). CYRI binds activated Rac1 via
a domain of unknown function (DUF1394) shared with CYFIP, defining
DUF1394 as a Rac1-binding module. CYRI-depleted cells have broad
lamellipodia enriched in Scar/WAVE, but reduced protrusion-retraction
dynamics. Pseudopods induced by optogenetic Rac1 activation in
CYRI-depleted cells are larger and longer lived. Conversely, CYRI
overexpression suppresses recruitment of active Scar/WAVE to the cell
edge, resulting in short-lived, unproductive protrusions. CYRI thus
focuses protrusion signals and regulates pseudopod complexity by
inhibiting Scar/WAVE-induced actin polymerization. It thus behaves like
a 'local inhibitor' as predicted in widely accepted mathematical models,
but not previously identified in cells. CYRI therefore regulates chemotaxis,
cell migration and epithelial polarization by controlling the polarity and
plasticity of protrusions.
submitted by: Robert Insall [[log in to unmask]]
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Distinct interaction sites of Rac GTPase with WAVE regulatory complex
have non-redundant functions in vivo
Matthias Schaks, Shashi Singh, Frieda Kage, Thomas Klünemann,
Anika Steffen, Wulf Blankenfeldt, Theresia E. Stradal, Robert Insall,
and Klemens Rottner
Current Biology, in press
Cell migration often involves the formation of sheet-like lamellipodia,
generated by actin filament branching through Arp2/3 complex. In
these structures, the latter is activated by WAVE regulatory complex
(WRC) downstream of small GTPases of the Rac family [2]. Recent
structural studies defined two independent Rac1 binding sites on WRC
within the Sra-1/PIR121 subunit of the pentameric WRC, but the
functions of these sites in vivo has remained unknown.
Here we used CRISPR/Cas9-mediated gene disruption of Sra-1 and
its paralogue PIR121 in murine B16-F1 cells combined with Sra-1 mutant
rescue to dissect the mechanism of WRC activation and the relative
relevance of the two distinct Rac binding sites on Sra-1 in vivo. We
found that the low-affinity site positioned adjacent to the binding region
of WAVE-WCA mediating actin- and Arp2/3 complex binding (A site) is
the main site for allosteric activation of WRC. In contrast, the recently
discovered more distantly positioned D site is dispensable for WRC
activation but required for optimal lamellipodium morphology and function.
These results were confirmed in evolutionarily distant Dictyostelium
amoeba. Moreover, the D site-specific phenotype was recapitulated in
previously employed Rac1 mutants deduced to abolish this interaction.
Finally, disruption of both Rac interaction sites did not abolish
lamellipodium formation entirely given that WRC was constitutively active.
Our data establish that the physical interaction between Rac and WRC is
obligatory for allosteric activation of the latter, in particular through the A
site, but not essential for WRC recruitment to and accumulation in the
lamellipodium.
submitted by: Robert Insall [[log in to unmask]]
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[End dictyNews, volume 44, number 28]
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