The Arf Family GTPase Arl4A Complexes with ELMO Proteins to Promote Actin Cytoskeleton Remodeling and Reveals a Versatile Ras-binding Domain in the ELMO Proteins Family

• Published in: The Journal of biological chemistry Vol. 286; no. 45; pp. 38969 - 38979
• Main Authors: Patel, Manishha, Chiang, Tsai-Chen, Tran, Viviane, Lee, Fang-Jen S., Côté, Jean-François
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 11.11.2011; American Society for Biochemistry and Molecular Biology
• Subjects: Adaptor Proteins, Signal Transducing - genetics; Adaptor Proteins, Signal Transducing - metabolism; ADP-Ribosylation Factors - genetics; ADP-Ribosylation Factors - metabolism; Arl4A GTPase; Cell Biology; Cell Membrane - genetics; Cell Membrane - metabolism; Cytoskeletal Reorganization; Cytoskeleton; DOCK180; ELMO; Guanine Nucleotide Exchange Factor (GEF); HEK293 Cells; HeLa Cells; Humans; Protein Binding - physiology; Protein Structure, Tertiary; Protein Transport - physiology; Protein-Protein Interactions; Rac; rac GTP-Binding Proteins - genetics; rac GTP-Binding Proteins - metabolism; Ras-binding Domain; rho-Associated Kinases - genetics; rho-Associated Kinases - metabolism; Signal Transduction - physiology; Small GTPases; Stress Fibers - genetics; Stress Fibers - metabolism; Guanine Nucleotide Exchange Factor (GEF); Rac; Small GTPases; Ras-binding Domain; Cytoskeleton; ELMO; Arl4A GTPase; Protein-Protein Interactions; Cytoskeletal Reorganization; DOCK180
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.274191

The prototypical DOCK protein, DOCK180, is an evolutionarily conserved Rac regulator and is indispensable during processes such as cell migration and myoblast fusion. The biological activity of DOCK180 is tightly linked to its binding partner ELMO. We previously reported that autoinhibited ELMO proteins regulate signaling from this pathway. One mechanism to activate the ELMO-DOCK180 complex appears to be the recruitment of this complex to the membrane via the Ras-binding domain (RBD) of ELMO. In the present study, we aimed to identify novel ELMO-interacting proteins to further define the molecular events capable of controlling ELMO recruitment to the membrane. To do so, we performed two independent interaction screens: one specifically interrogated an active GTPase library while the other probed a brain cDNA library. Both methods converged on Arl4A, an Arf-related GTPase, as a specific ELMO interactor. Biochemically, Arl4A is constitutively GTP-loaded, and our binding assays confirm that both wild-type and constitutively active forms of the GTPase associate with ELMO. Mechanistically, we report that Arl4A binds the ELMO RBD and acts as a membrane localization signal for ELMO. In addition, we report that membrane targeting of ELMO via Arl4A promotes cytoskeletal reorganization including membrane ruffling and stress fiber disassembly via an ELMO-DOCK1800-Rac signaling pathway. We conclude that ELMO is capable of interacting with GTPases from Rho and Arf families, leading to the conclusion that ELMO contains a versatile RBD. Furthermore, via binding of an Arf family GTPase, the ELMO-DOCK180 is uniquely positioned at the membrane to activate Rac signaling and remodel the actin cytoskeleton. Background: ELMO complexes with DOCK180 and contributes to Rac signaling. Results: Arl4A binds ELMO and is a membrane localization signal that triggers DOCK180-Rac-dependent actin cytoskeleton remodeling. Conclusion: ELMO, via its versatile Ras-binding domain, binds its effector Arl4A, and this novel interaction facilitates Rac signaling. Significance: This is the first demonstration of a Ras-binding domain that binds Arf or Rho family GTPases.