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A keratin cytoskeletal protein regulates protein synthesis and epithelial cell growth

Abstract

Cell growth, an increase in mass and size, is a highly regulated cellular event. The Akt/mTOR (mammalian target of rapamycin) signalling pathway has a central role in the control of protein synthesis and thus the growth of cells, tissues and organisms1. A striking example of a physiological context requiring rapid cell growth is tissue repair in response to injury2. Here we show that keratin 17, an intermediate filament protein rapidly induced in wounded stratified epithelia3, regulates cell growth through binding to the adaptor protein 14-3-3σ. Mouse skin keratinocytes lacking keratin 17 (ref. 4) show depressed protein translation and are of smaller size, correlating with decreased Akt/mTOR signalling activity. Other signalling kinases have normal activity, pointing to the specificity of this defect. Two amino acid residues located in the amino-terminal head domain of keratin 17 are required for the serum-dependent relocalization of 14-3-3σ from the nucleus to the cytoplasm, and for the concomitant stimulation of mTOR activity and cell growth. These findings reveal a new and unexpected role for the intermediate filament cytoskeleton in influencing cell growth and size by regulating protein synthesis.

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Figure 1: K17 -/- keratinocytes are smaller than wild-type cells in the embryonic ectoderm and in primary cultures.
Figure 2: Depressed protein translation and Akt/mTOR activity in K17 -/- keratinocytes.
Figure 3: Changes in subcellular localization of 14-3-3 proteins in K17 -/- keratinocytes.
Figure 4: Role of K17 in retaining 14-3-3 in the cytoplasm and promoting protein translation and cell growth.

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Acknowledgements

We thank members of the Coulombe laboratory for support, B. Vogelstein for providing 14-3-3σ antibody and cDNA, T. Yoshimori for providing anti-LC3 antibody, and C. Parent, S. Craig, J. Lorsch, D. Ginty, S. H. Cha, S. Kim, C. S. Lee and C. Moon for advice. This work was supported by a grant from the National Institute of Arthritis, Musculoskeletal and Skin Diseases (NIAMS) to P.A.C.

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Correspondence to Pierre A. Coulombe.

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Supplementary information

Supplementary Figure Legends

This file contains text to accompany the below Supplementary Figures. (DOC 32 kb)

Supplementary Figure 1

Complement to analyses of K17 null keratinocytes. (JPG 427 kb)

Supplementary Figure 2

Additional analyses of Akt/mTOR pathway in K17 null keratinocytes (JPG 517 kb)

Supplementary Figure 3

Identification of 14-3-3σ as a keratin 17-binding protein. (JPG 1491 kb)

Supplementary Figure 4

Further analysis of the significance of the K17/14-3-3σ interaction for regulation of protein synthesis and growth in skin keratinocytes. (JPG 386 kb)

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Kim, S., Wong, P. & Coulombe, P. A keratin cytoskeletal protein regulates protein synthesis and epithelial cell growth. Nature 441, 362–365 (2006). https://doi.org/10.1038/nature04659

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