Microtubule assembly by the Apc protein is regulated by importin-beta--RanGTP.
Mutations in the tumour suppressor Adenomatous polyposis coli (Apc) initiate most sporadic colorectal cancers. Apc is implicated in regulating microtubule (MT) dynamics in interphase and mitosis. However, little is known about the underlying mechanism or regulation of this Apc function. We identified importin-beta as a binding partner of Apc that regulates its effect on MTs. Apc binds importin-beta in vitro and in Xenopus egg extracts, and RanGTP inhibits this interaction. The armadillo-like repeat domain of importin-beta binds to the middle of Apc, where it can compete with beta-catenin. In addition, two independent sites in the C terminus of Apc bind the N-terminal region of importin-beta. Binding to importin-beta reduces the ability of Apc to assemble and bundle MTs in vitro and to promote assembly of microtubule asters in Xenopus egg extracts, but does not affect the binding of Apc to MTs or to EB1. Depletion of Apc decreases the formation of cold-stable spindles in Xenopus egg extracts. Importantly, the ability of purified Apc to rescue this phenotype was reduced when it was constitutively bound to importin-beta. Thus, importin-beta binds to Apc and negatively regulates the MT-assembly and spindle-promoting activity of Apc in a Ran-regulatable manner.
Division of Cell and Developmental Biology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK. d.dikovskaya@dundee.ac.uk
Dina
D
Dikovskaya
Zhuoyu
Z
Li
Ian P
IP
Newton
Iain
I
Davidson
James R A
JR
Hutchins
Petr
P
Kalab
Paul R
PR
Clarke
Inke S
IS
Näthke
D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites / Q000235:genetics / Q000502:physiology; D047468:Immunoprecipitation; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D014981:Xenopus; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism; D028961:beta Karyopherins / Q000378:metabolism*; D020931:ran GTP-Binding Protein / Q000378:metabolism*
D025601:Adenomatous Polyposis Coli Protein; C405804:EB1 microtubule binding proteins; D008869:Microtubule-Associated Proteins; D029867:Xenopus Proteins; D051176:beta Catenin; D028961:beta Karyopherins; D020931:ran GTP-Binding Protein