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First published online February 23, 2005
doi: 10.1242/10.1242/jcs.01667

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Identification of trichoplein, a novel keratin filament-binding protein

Miwako Nishizawa^1,*, Ichiro Izawa^1,*, Akihito Inoko^1,*, Yuko Hayashi¹, Koh-ichi Nagata¹, Tomoya Yokoyama^1,2, Jiro Usukura³ and Masaki Inagaki^1,

¹ Division of Biochemistry, Aichi Cancer Center Research Institute, 1-1 Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan
² Department of Dermatology, Mie University Faculty of Medicine, 2-174 Edobashi, Tsu 514-8507, Japan
³ Department of Anatomy and Cell Biology, Nagoya University School of Medicine, 65 Tsurumai, Showa-ku, Nagoya 466-8550, Japan

Author for correspondence (e-mail: minagaki{at}aichi-cc.jp)

Accepted 29 November 2004

Keratins 8 and 18 (K8/18) are major components of the intermediate filaments (IFs) of simple epithelia. We report here the identification of a novel protein termed trichoplein. This protein shows a low degree of sequence similarity to trichohyalin, plectin and myosin heavy chain, and is a K8/18-binding protein. Among interactions between trichoplein and various IF proteins that we tested using two-hybrid methods, trichoplein interacted significantly with K16 and K18, and to some extent with K5, K6a, K8 and K14. In in vitro co-sedimentation assays, trichoplein directly binds to K8/18, but not with vimentin, desmin, actin filaments or microtubules. An antibody raised against trichoplein specifically recognized a polypeptide with a relative molecular mass of 61 kDa in cell lysates. Trichoplein was immunoprecipitated using this antibody in a complex with K8/18 and immunostaining revealed that trichoplein colocalized with K8/18 filaments in HeLa cells. In polarized Caco-2 cells, trichoplein colocalized not only with K8/18 filaments in the apical region but also with desmoplakin, a constituent of desmosomes. In the absorptive cells of the small intestine, trichoplein colocalized with K8/18 filaments at the apical cortical region, and was also concentrated at desmosomes. Taken together, these results suggest that trichoplein is a keratin-binding protein that may be involved in the organization of the apical network of keratin filaments and desmosomes in simple epithelial cells.

Key words: Intermediate filament, Keratin, Plectin, Trichohyalin, Trichoplein

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