Tropomyosin Promotes Lamellipodial Persistence by Collaborating with Arp2/3 at the Leading Edge.
At the leading edge of migrating cells, protrusion of the lamellipodium is driven by Arp2/3-mediated polymerization of actin filaments [1]. This dense, branched actin network is promoted and stabilized by cortactin [2, 3]. In order to drive filament turnover, Arp2/3 networks are remodeled by proteins such as GMF, which blocks the actin-Arp2/3 interaction [4, 5], and coronin 1B, which acts by directing SSH1L to the lamellipodium where it activates the actin-severing protein cofilin [6, 7]. It has been shown in vitro that cofilin-mediated severing of Arp2/3 actin networks results in the generation of new pointed ends to which the actin-stabilizing protein tropomyosin (Tpm) can bind [8]. The presence of Tpm in lamellipodia, however, is disputed in the literature [9-19]. Here, we report that the Tpm isoforms 1.8/9 are enriched in the lamellipodium of fibroblasts as detected with a novel isoform-specific monoclonal antibody. RNAi-mediated silencing of Tpm1.8/9 led to an increase of Arp2/3 accumulation at the cell periphery and a decrease in the persistence of lamellipodia and cell motility, a phenotype consistent with cortactin- and coronin 1B-deficient cells [2, 7]. In the absence of coronin 1B or cofilin, Tpm1.8/9 protein levels are reduced while, conversely, inhibition of Arp2/3 with CK666 leads to an increase in Tpm1.8/9 protein. These findings establish a novel regulatory mechanism within the lamellipodium whereby Tpm collaborates with Arp2/3 to promote lamellipodial-based cell migration.
Oncology Research Unit, School of Medical Sciences, UNSW Australia, Sydney, NSW 2052, Australia.
Simon
S
Brayford
Oncology Research Unit, School of Medical Sciences, UNSW Australia, Sydney, NSW 2052, Australia.
Nicole S
NS
Bryce
Oncology Research Unit, School of Medical Sciences, UNSW Australia, Sydney, NSW 2052, Australia.
Galina
G
Schevzov
Department of Cell and Developmental Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA.
Elizabeth M
EM
Haynes
Department of Cell and Developmental Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA.
James E
JE
Bear
Cellular and Genetic Medicine Unit, School of Medical Sciences, UNSW Australia, Sydney, NSW 2052, Australia.
Edna C
EC
Hardeman
Oncology Research Unit, School of Medical Sciences, UNSW Australia, Sydney, NSW 2052, Australia. Electronic address: p.gunning@unsw.edu.au.
Peter W
PW
Gunning
D008841:Actin Cytoskeleton / Q000378:metabolism*; D051376:Actin-Related Protein 2-3 Complex / Q000235:genetics* / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D058105:Polymerization; D020033:Protein Isoforms; D011554:Pseudopodia / Q000235:genetics* / Q000378:metabolism; D014335:Tropomyosin / Q000235:genetics* / Q000378:metabolism
D051376:Actin-Related Protein 2-3 Complex; D020033:Protein Isoforms; C490775:TPM1 protein, human; D014335:Tropomyosin