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Cytoskeletal keratin glycosylation protects epithelial tissue from injury

Nature Cell Biology volume 12, pages 876–885 (2010)Cite this article

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Abstract

Keratins 8 and 18 (K8 and K18) are heteropolymeric intermediate filament phosphoglycoproteins of simple-type epithelia. Mutations in K8 and K18 predispose the affected individual to liver disease as they protect hepatocytes from apoptosis. K18 undergoes dynamic O-linked N-acetylglucosamine glycosylation at Ser 30, 31 and 49. We investigated the function of K18 glycosylation by generating mice that overexpress human K18 S30/31/49A substitution mutants that cannot be glycosylated (K18–Gly−), and compared the susceptibility of these mice to injury with wild-type and other keratin-mutant mice. K18–Gly− mice are more susceptible to liver and pancreatic injury and apoptosis induced by streptozotocin or to liver injury by combined N-acetyl-D-glucosaminidase inhibition and Fas administration. The enhanced apoptosis in the livers of mice that express K18–Gly− involves the inactivation of Akt1 and protein kinase Cθ as a result of their site-specific hypophosphorylation. Akt1 binds to K8, which probably contributes to the reciprocal hyperglycosylation and hypophosphorylation of Akt1 that occurs on K18 hypoglycosylation, and leads to decreased Akt1 kinase activity. Therefore, K18 glycosylation provides a unique protective role in epithelial injury by promoting the phosphorylation and activation of cell-survival kinases.

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Figure 1: Expression of K18–Gly− predisposes transgenic mice to STZ-induced injury.
Figure 2: Comparison of the STZ-induced tissue injury in wild-type K18- versus K18–Gly−-expressing mice.
Figure 3: Immunostaining microscopy of pancreata from wild-type K18 and K18–Gly−-expressing mice, and biochemical assessment of apoptosis in liver and pancreas tissues.
Figure 4: Expression of the K18–Gly− mutant predisposes transgenic mice to PUGNAc/Fas-induced injury.
Figure 5: Expression of the K18–Gly− mutation alters protein kinase phosphorylation and promotes apoptosis in response to STZ treatment.
Figure 6: Expression of K18–Gly− inhibits Akt1 Thr 308 phosphorylation and decreases Hsp70, which is acccompanied by enhanced apoptosis in response to PUGNAc/Fas treatment.
Figure 7: K8/K18 and Akt1 association is independent of PUGNAc/Fas treatment and Akt1 associates with keratin 8.
Figure 8: Model of K8 association with Akt1 and the effect of K18 glycosylation on reciprocal Akt1 phosphorylation and glycosylation.

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Acknowledgements

We are grateful to R. Oshima (The Sanford-Burnham Medical Research Institute) and T. Magin (University of Leipzig) for making the mice that express wild-type K18 and the K18-null available to us, Y. Chen-Tsai and the Stanford University Transgenic Facility for helping generate the transgenic mice, E. Resurreccion for assistance with immune staining and P. Chu for assistance with hematoxylin and eosin staining. This work was supported by NIH grant DK47918 and the Department of Veterans Affairs (M.B.O.), NIH Digestive Disease Center grant DK56339 to Stanford University, NIH Michigan Gastrointestinal Peptide Research Center grant DK34933 and WCU project (R31-2008-000-10086-0) from the Korean Ministry of Education, Science and Technology to N. -O.K.

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Authors and Affiliations

  1. Department of Molecular & Integrative Physiology, University of Michigan Medical School, 7744 Medical Science II, 1301 East Catherine Street, Ann Arbor, 48109-5622, MI, USA

    Nam-On Ku & M. Bishr Omary

  2. Department of Biomedical Sciences, Graduate School, Yonsei University, 120-749, Seoul, Korea

    Nam-On Ku

  3. Department of Biosciences, Åbo Akademi University, Tykistökatu 6A, FI 20521, Turku, Finland

    Diana M. Toivola

  4. Department of Internal Medicine I, University Medical Center Ulm, Albert-Einstein-Allee 23, D-89081, Ulm, Germany

    Pavel Strnad

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Contributions

N.-O.K. and M.B.O. conceived and designed the study. N.-O.K., D.M.T. and P.S. performed the experiments and analysed the data. N.-O.K., D.M.T., P.S. and M.B.O. interpreted the data. N.-O.K. and M.B.O. wrote the manuscript with comments from D.M.T. and P.S.

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Correspondence to Nam-On Ku or M. Bishr Omary.

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Ku, NO., Toivola, D., Strnad, P. et al. Cytoskeletal keratin glycosylation protects epithelial tissue from injury. Nat Cell Biol 12, 876–885 (2010). https://doi.org/10.1038/ncb2091

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