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A more recent version of this article appeared on October 1, 2007
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Submitted on December 19, 2006
Revised on June 27, 2007
Accepted on July 6, 2007


*Department of Pathology, National Institute of Infectious Diseases, Shinjuku, Tokyo 162-8640, Japan;
Nippi Research Institute of Biomatrix, Toride, Ibaraki 302-0017, Japan;
Japan Institute of Leather Research, Adachi, Tokyo 120-8601, Japan
Monitoring Editor: Sean Munro
p180 was originally reported as a ribosome-binding protein on the rough endoplasmic reticulum membrane, although its precise role in animal cells has not yet been elucidated. Here, we characterized a new function of human p180 as a microtubule-binding and modulating protein. Overexpression of p180 in mammalian cells induced an elongated morphology and enhanced acetylated microtubules. Consistently, electron microscopic analysis clearly revealed microtubule bundles in p180-overexpressing cells. Targeted depletion of endogenous p180 by siRNAs led to aberrant patterns of microtubules and endoplasmic reticulum in mammalian cells, suggesting a specific interaction between p180 and microtubules. In vitro sedimentation assays using recombinant polypeptides revealed that p180 bound to microtubules directly and possessed a novel microtubule-binding domain (designated MTB-1). MTB-1 consists of a predicted coiled-coil region and repeat domain, and strongly promoted bundle formation both in vitro and in vivo when expressed alone. Overexpression of p180 induced acetylated microtubules in cultured cells in an MTB-1-dependent manner. Thus, our data suggest that p180 mediates interactions between the endoplasmic reticulum and microtubules mainly through the novel microtubule-binding and bundling domain MTB-1.