Open AccessMicrotubule assembly by the Apc protein is regulated by importin-β—RanGTP
Author(s) -
Dina Dikovskaya,
Zhuoyu Li,
Ian P. Newton,
Iain F. Davidson,
James R. A. Hutchins,
Petr Kaláb,
Paul R. Clarke,
Inke Näthke
Publication year - 2010
Publication title -
journal of cell science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.384
H-Index - 278
eISSN - 1477-9137
pISSN - 0021-9533
DOI - 10.1242/jcs.060806
Subject(s) - importin , biology , xenopus , ran , microbiology and biotechnology , microtubule , nuclear transport , adenomatous polyposis coli , mitosis , tubulin , cell nucleus , biochemistry , genetics , gene , cytoplasm , colorectal cancer , cancer
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-β as a binding partner of Apc that regulates its effect on MTs. Apc binds importin-β in vitro and in Xenopus egg extracts, and RanGTP inhibits this interaction. The armadillo-like repeat domain of importin-β binds to the middle of Apc, where it can compete with β-catenin. In addition, two independent sites in the C terminus of Apc bind the N-terminal region of importin-β. Binding to importin-β 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-β. Thus, importin-β binds to Apc and negatively regulates the MT-assembly and spindle-promoting activity of Apc in a Ran-regulatable manner.