Regulated Membrane Localization of Tiam1, Mediated by the NH2-Terminal Pleckstrin Homology Domain, Is Required for Rac-Dependent Membrane Ruffling and C-Jun NH2-Terminal Kinase Activation

• Published in: The Journal of cell biology Vol. 137; no. 2; pp. 387 - 398
• Main Authors: Michiels, Frits, Stam, Jord C., Hordijk, Peter L., van der Kammen, Rob A., Stalle, Lisette Ruuls-Van, Feltkamp, Constance A., Collard, John G.
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 21.04.1997; The Rockefeller University Press
• Subjects: 3T3 Cells; Actins; Animals; Blood Proteins - genetics; Calcium-Calmodulin-Dependent Protein Kinases - metabolism; Cell lines; Cell Membrane - chemistry; Cell membranes; Cells; Cellular biology; COS Cells; Cytoplasm; Drosophila Proteins; Enzyme Activation; Genes; GTP-Binding Proteins - physiology; Guanine Nucleotide Exchange Factors; Insect Proteins - genetics; JNK Mitogen-Activated Protein Kinases; Mice; Mitogen-Activated Protein Kinases; NIH 3T3 cells; P branes; Phenotypes; Phosphoproteins; Proteins - analysis; Proteins - genetics; Proto-Oncogene Proteins pp60(c-src) - genetics; rac GTP-Binding Proteins; Recombinant Fusion Proteins; Ruffles; Sequence Deletion; Sequence Homology, Amino Acid; Signal Transduction - physiology; T-Lymphoma Invasion and Metastasis-inducing Protein 1; Tumor Suppressor Proteins
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.137.2.387

Rho-like GTPases, including Cdc42, Rac, and Rho, regulate signaling pathways that control actin cytoskeletal structures and transcriptional activation. The Tiam1 gene encodes an activator of Rac1, and similarly to constitutively activated (V12)Rac1, overexpression of Tiam1 in fibroblasts induces the formation of membrane ruffles. Tiam1 contains a Dbl homology (DH) domain and adjacent pleckstrin homology (PH) domain, hallmarks for activators of Rho-like GTPases. Unique for Tiam1 are an additional PH domain and a Discs-large homology region in the NH2-terminal part of the protein. Here we show that both in fibroblasts and COS cells, membrane localization of Tiam1 is required for the induction of membrane ruffling. A detailed mutational analysis, in combination with confocal laser scanning microscopy and immunoelectron microscopy, demonstrates that the NH2-terminal PH domain of Tiam1, but not the DH-adjacent PH domain, is essential for membrane association. This NH2-terminal PH domain of Tiam1 can be functionally replaced by the myristoylated membrane localization domain of c-Src, indicating that the primary function of this PH domain is to localize the protein at the membrane. After serum starvation, both membrane association of Tiam1 and ruffling can be induced by serum, suggesting that receptor stimulation induces membrane translocation of Tiam1. Similar to V12Rac1, Tiam1 stimulates the activity of the c-Jun NH2-terminal kinase (JNK). This Rac-dependent stimulation of JNK also requires membrane association of Tiam1. We conclude that the regulated membrane localization of Tiam1 through its NH2-terminal PH domain determines the activation of distinct Rac-mediated signaling pathways.