Spatial and temporal control of cofilin activity is required for directional sensing during chemotaxis.
BACKGROUND
Previous work has led to the hypothesis that cofilin severing, as regulated by PLC, is involved in chemotactic sensing. We have tested this hypothesis by investigating whether activation of endogenous cofilin is spatially and temporally linked to sensing an EGF point source in carcinoma cells.


RESULTS
We demonstrate that inhibition of endogenous cofilin activity with either siRNA or overexpression of LIMK suppresses directional sensing in carcinoma cells. LIMK siRNA knockdown, which suppresses cofilin phosphorylation, and microinjection of S3C cofilin, a cofilin mutant that is constitutively active and not phosphorylated by LIMK, also inhibits directional sensing and chemotaxis. These results indicate that phosphorylation of cofilin by LIMK, in addition to cofilin activity, is required for chemotaxis. Cofilin activity concentrates rapidly at the newly formed leading edge facing the gradient, whereas cofilin phosphorylation increases throughout the cell. Quantification of these results indicates that the amplification of asymmetric actin polymerization required for protrusion toward the EGF gradient occurs at the level of cofilin but not at the level of PLC activation by EGFR.


CONCLUSIONS
These results indicate that local activation of cofilin by PLC and its global inactivation by LIMK phosphorylation combine to generate the local asymmetry of actin polymerization required for chemotaxis.
Mouneimne
Ghassan
G
Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA. ghassan_mouneimne@hms.harvard.edu
DesMarais
Vera
V
Sidani
Mazen
M
Scemes
Eliana
E
Wang
Weigang
W
Song
Xiaoyan
X
Eddy
Robert
R
Condeelis
John
J
D008841:Actin Cytoskeleton / Q000378:metabolism; D051339:Actin Depolymerizing Factors / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology*; D002630:Chemotactic Factors / Q000378:metabolism; D002633:Chemotaxis / Q000187:drug effects / Q000502:physiology*; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology; D054461:Lim Kinases; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D010738:Type C Phospholipases / Q000378:metabolism
D051339:Actin Depolymerizing Factors; D002630:Chemotactic Factors; D034741:RNA, Small Interfering; D004815:Epidermal Growth Factor; D011494:Protein Kinases; D054461:Lim Kinases; C515894:Limk1 protein, rat; D010738:Type C Phospholipases