Targeted wild-type and jerker espins reveal a novel, WH2-domain-dependent way to make actin bundles in cells.
The espin actin-bundling proteins, which are the target of deafness mutations, are present in the parallel actin bundles of stereocilia and microvilli and appear to increase their steady-state length. Here, we report a new activity of the espins, one that depends on their enigmatic WH2 domain: the ability to assemble a large actin bundle when targeted to a specific subcellular location. This activity was observed for wild-type espins targeted to the centrosome in transfected neuronal cells and for jerker espins targeted to the nucleolus in a wide variety of transfected cells as a result of the frameshifted peptide introduced into the espin C-terminus by the jerker deafness mutation. This activity, which appears specific to espins, requires two espin F-actin-binding sites and the actin-monomer-binding activity of the espin WH2 domain, but can be mimicked by adding a WH2 domain to an unrelated actin-bundling protein, villin. Espins do not activate the Arp2/3 complex in vitro, and bundle assembly is not indicative of in-vitro nucleation activity. Our results suggest a novel way to build actin bundles at specific sites in cells.
Department of Cell and Molecular Biology, Feinberg School of Medicine, and Institute for Neuroscience, Northwestern University, Chicago, IL 60611, USA.
Patricia A
PA
Loomis
Alexander E
AE
Kelly
Lili
L
Zheng
Benjarat
B
Changyaleket
Gabriella
G
Sekerková
Enrico
E
Mugnaini
Adriana
A
Ferreira
R Dyche
RD
Mullins
James R
JR
Bartles
D051376:Actin-Related Protein 2-3 Complex / Q000502:physiology; D000199:Actins / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D002466:Cell Nucleolus / Q000378:metabolism; D002503:Centromere / Q000378:metabolism*; D018374:LLC-PK1 Cells; D008840:Microfilament Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D016716:PC12 Cells; D020033:Protein Isoforms / Q000235:genetics*; D051381:Rats; D013552:Swine; D014162:Transfection
D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; C493274:ESPN protein, human; D008840:Microfilament Proteins; D020033:Protein Isoforms