Keratin 8 phosphorylation by p38 kinase regulates cellular keratin filament reorganization: modulation by a keratin 1-like disease causing mutation.

Abstract

Keratin 8 (K8) serine 73 occurs within a relatively conserved type II keratin motif ((68)NQSLLSPL) and becomes phosphorylated in cultured cells and organs during mitosis, cell stress, and apoptosis. Here we show that Ser-73 is exclusively phosphorylated in vitro by p38 mitogen-activated protein kinase. In cells, Ser-73 phosphorylation occurs in association with p38 kinase activation and is inhibited by SB203580 but not by PD98059. Transfection of K8 Ser-73 --> Ala or K8 Ser-73 --> Asp with K18 generates normal-appearing filaments. In contrast, exposure to okadaic acid results in keratin filament destabilization in cells expressing wild-type or Ser-73 --> Asp K8, whereas Ser-73 --> Ala K8-expressing cells maintain relatively stable filaments. p38 kinase associates with K8/18 immunoprecipitates and binds selectively with K8 using an in vitro overlay assay. Given that K1 Leu-160 --> Pro ((157)NQSLLQPL --> (157)NQSPLQPL) leads to epidermolytic hyperkeratosis, we tested and showed that the analogous K8 Leu-71 --> Pro leads to K8 hyperphosphorylation by p38 kinase in vitro and in transfected cells, likely due to Ser-70 neo-phosphorylation, in association with significant keratin filament collapse upon cell exposure to okadaic acid. Hence, K8 Ser-73 is a physiologic phosphorylation site for p38 kinase, and its phosphorylation plays an important role in keratin filament reorganization. The Ser-73 --> Ala-associated filament reorganization defect is rescued by a Ser-73 --> Asp mutation. Also, disease-causing keratin mutations can modulate keratin phosphorylation and organization, which may affect disease pathogenesis.

• Authors: Nam-On Ku, Salman Azhar, M Bishr Omary
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 277 Issue 13 Pg. 10775-82 (Mar 29 2002) ISSN: 0021-9258 [Print] United States
• PMID: 11788583 (Publication Type: Journal Article, Research Support, U.S. Gov't, Non-P.H.S., Research Support, U.S. Gov't, P.H.S.)

Chemical References

• KRT8 protein, human
• Keratin-8
• Keratins
• Mitogen-Activated Protein Kinases
• p38 Mitogen-Activated Protein Kinases

Topics

• Amino Acid Sequence
• Amino Acid Substitution
• Cell Line
• Humans
• Keratin-8
• Keratins (chemistry, metabolism)
• Mitogen-Activated Protein Kinases (metabolism)
• Mutation
• Peptide Mapping
• Phosphorylation
• Transfection
• p38 Mitogen-Activated Protein Kinases