title: Binding and inhibition of the ternary complex factor Elk-4/Sap1 by the adapter protein Dok-4.
abstract: 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.
authors.affiliation: Department of Medicine, Division of Nephrology, McGill University Health Centre, Montreal, QC, Canada.
authors.forename: Erika
authors.initials: E
authors.lastname: Hooker
authors.affiliation: Department of Medicine, Division of Nephrology, McGill University Health Centre, Montreal, QC, Canada.
authors.forename: Cindy
authors.initials: C
authors.lastname: Baldwin
authors.affiliation: Department of Medicine, Division of Nephrology, McGill University Health Centre, Montreal, QC, Canada.
authors.forename: Victoria
authors.initials: V
authors.lastname: Roodman
authors.affiliation: Department of Medicine, Division of Nephrology, McGill University Health Centre, Montreal, QC, Canada.
authors.forename: Anupam
authors.initials: A
authors.lastname: Batra
authors.affiliation: Department of Medicine, Division of Nephrology, McGill University Health Centre, Montreal, QC, Canada.
authors.forename: Naajia Nur
authors.initials: NN
authors.lastname: Isa
authors.affiliation: Department of Medicine, Division of Nephrology, McGill University Health Centre, Montreal, QC, Canada.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Takano
authors.affiliation: Department of Medicine, Division of Nephrology, McGill University Health Centre, Montreal, QC, Canada serge.lemay@mcgill.ca.
authors.forename: Serge
authors.initials: S
authors.lastname: Lemay
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000235:genetics; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D049109:Cell Proliferation / Q000235:genetics; D004285:Dogs; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D061985:Madin Darby Canine Kidney Cells; D051379:Mice; D018613:Microscopy, Confocal; D049790:Nuclear Export Signals / Q000235:genetics*; D019913:Nuclear Localization Signals / Q000235:genetics*; D011485:Protein Binding; D034622:RNA Interference; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D050808:ets-Domain Protein Elk-4 / Q000235:genetics* / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C432911:Dok4 protein, mouse; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D050808:ets-Domain Protein Elk-4
keywords: adaptor proteins; protein–protein interactions; proteolysis; transcription factors