Raf-1 activation disrupts its binding to keratins during cell stress

• Type of Material: Article
• Authors: Haian Fu, Emory University; Nam-On Ku, Stanford University; M Bishr Omary, Stanford University
• Language: English
• Date: 2004-08-16
• Publisher: Rockefeller University Press
• Publication Version: Final Published Version
• Copyright Statement: © 2004, The Rockefeller University Press
• Final Published Version (URL): http://dx.doi.org/10.1083/jcb.200402051
• Title of Journal or Parent Work: Journal of Cell Biology
• ISSN: 0021-9525
• Volume: 166
• Issue: 4
• Start Page: 479
• End Page: 485
• Grant/Funding Information: This work was supported by National Institutes of Health (NIH) grants DK52951 and VA Merit (to M.B. Omary), and NIH GM53165 (to H. Fu). N.-O. Ku is supported, in part, by a Veterans Administration Research Enhancement Award Program and an NIH Digestive Disease Center grant DK56339 pilot award.
• Keywords: PROGRESSION; KINASE; cell stress; INTERMEDIATE-FILAMENTS; CRYSTAL-STRUCTURE; 14-3-3 PROTEINS; Raf-1 kinase; Science & Technology; Cell Biology; COFACTOR; ASSOCIATE; intermediate filaments; 14-3-3 proteins; Life Sciences & Biomedicine; PHOSPHORYLATION; DISEASE; keratins; CELL BIOLOGY; APOPTOSIS
• Research Categories: Biology, Cell; Biology, Molecular

Abstract

Keratins 8 and 18 (K8/18) heteropolymers may regulate cell signaling via the known K18 association with 14-3-3 proteins and 14-3-3 association with Raf-1 kinase. We characterized Raf-keratin-14-3-3 associations and show that Raf associates directly with K8, independent of Raf kinase activity or Ras-Raf interaction, and that K18 is a Raf physiologic substrate. Raf activation during oxidative and toxin exposure in cultured cells and animals disrupt keratin-Raf association in a phosphorylation-dependent manner. Mutational analysis showed that 14-3-3 residues that are essential for Raf binding also regulate 14-3-3-keratin association. Similarly, Raf phosphorylation sites that are important for binding to 14-3-3 are also essential for Raf binding to K8/18. Therefore, keratins may modulate some aspects of Raf signaling under basal conditions via sequestration by K8, akin to Raf-14-3-3 binding. Keratin-bound Raf kinase is released upon Raf hyperphosphorylation and activation during oxidative and other stresses.