The adapter protein Dok-4 (downstream of kinase-4) has been reported as both an activator and inhibitor of Erk and Elk-1, but lack of knowledge about the identity of its partner molecules has precluded any mechanistic insight into these seemingly conflicting properties. We report that Dok-4 interacts with the transactivation domain of Elk-4 through an atypical phosphotyrosine-binding domain-mediated interaction. Dok-4 possesses a nuclear export signal and can relocalize Elk-4 from nucleus to cytosol, whereas Elk-4 possesses two nuclear localization signals that restrict interaction with Dok-4. The Elk-4 protein, unlike Elk-1, is highly unstable in the presence of Dok-4, through both an interaction-dependent mechanism and a pleckstrin homology domain-dependent but interaction-independent mechanism. This is reversed by proteasome inhibition, depletion of endogenous Dok-4 or lysine-to-arginine mutation of putative Elk-4 ubiquitination sites. Finally, Elk-4 transactivation is potently inhibited by Dok-4 overexpression but enhanced by Dok-4 knockdown in MDCK renal tubular cells, which correlates with increased basal and EGF-induced expression of Egr-1, Fos and cylcinD1 mRNA, and cell proliferation despite reduced Erk activation. Thus, Dok-4 can target Elk-4 activity through multiple mechanisms, including binding of the transactivation domain, nuclear exclusion and protein destabilization, without a requirement for inhibition of Erk.
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Cover Image
Cover Image
3D reconstructions of 4 individual Escherichia coli cells that have been serially sectioned and immunolabelled to unambiguously identify a membrane protein of interest (TatA, position marked by spheres). The reconstructions illustrate a linear clustering of TatA protein in the inner membrane of E. coli – a previously uncharacterised distribution for this protein. For more information, please see article by Sarah M. Smith et al, pages 1495–1508. Image provided by Sarah M. Smith.
Binding and inhibition of the ternary complex factor Elk-4/Sap1 by the adapter protein Dok-4
Erika Hooker, Cindy Baldwin, Victoria Roodman, Anupam Batra, Naajia Nur Isa, Tomoko Takano, Serge Lemay; Binding and inhibition of the ternary complex factor Elk-4/Sap1 by the adapter protein Dok-4. Biochem J 1 May 2017; 474 (9): 1509–1528. doi: https://doi.org/10.1042/BCJ20160832
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