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First published online July 1, 2009
In this issue |
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Protein kinase C (PKC) family members are post-translationally regulated in an unusual way – they become dephosphorylated (and thereby inactivated) as a consequence of their own kinase activity. Once inactive, PKCs are ubiquitylated and degraded, or are rescued through their association with Hsp70-family chaperones and subsequent rephosphorylation. Now, on page 2491, Pedro Salas and colleagues investigate an atypical PKC isoform (PKC
) and demonstrate a role for the intermediate-filament (IF) protein keratin in restoring its activity. The authors first show that a pool of functional PKC colocalises with IFs in the apical domain in a carcinoma cell line, and that PKC, Hsp70 and filamentous keratin form a ternary complex in vitro. In an in vitro assay, they report, the rephosphorylation of PKC requires keratins and Hsp70; moreover, active (T555-phosphorylated) PKC is depleted in keratin-null mice. Hsp70 and PKC are mislocalised in mice overexpressing keratin 8. On the basis of these and other data, the authors conclude that Hsp70 and filamentous keratins are both required for the rescue of active PKC. Their work provides evidence that keratins have roles beyond that of structural support, and highlights the emerging role of IFs as scaffolds for signalling molecules.
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