The multidomain protein Trio binds the LAR transmembrane tyrosine phosphatase, contains a protein kinase domain, and has separate rac-specific and rho-specific guanine nucleotide exchange factor domains.

Abstract

The ras-like GTP binding proteins cdc42, rac, and rho regulate diverse cellular processes including cell growth and actin remodeling associated with changes in cell morphology, growth, adhesion, and motility (1-4). In fibroblasts, cdc42 regulates actin polymerization and focal complexes necessary for filopodia formation, rac mediates actin polymerization and focal complex assembly within lamellipodia and membrane ruffles, and rho induces actin stress fiber and focal adhesion (FA) complex formation (5). A hierarchical relationship exists among cdc42, rac, and rho, whereby cdc42 regulates rac activity and rac regulates rho activity, suggesting that these proteins may orchestrate the spatial and temporal changes in the actin cytoskeleton necessary for cell movement (5, 6). cdc42 and rac also regulate activation of the c-Jun N-terminal kinase/stressactivated kinase via a mitogen-activated protein (MAP) kinase pathway (7-9), and rac and rho are essential for ras transformation (10, 11). cdc42, rho, and rac all appear to stimulate c-fos transcription (12), as well as cell cycle progression through GI and subsequent DNA synthesis (9). The activation state of ras-like GTP binding proteins is positively regulated by guanine nucleotide exchange factors (GEFs) that promote the exchange of GDP for GTP, and negatively by GTPase activating proteins (2). A number of putative GEFs for rho-like GTPases have been identified by sequence comparison (2), and several of these demonstrate GEF activity in vitro. The dbl and ost oncogene products have cdc42 and rho GEF activity (13-15); the lbc oncogene product has rho GEF activity (16); the invasion-inducing Tiaml gene product has cdc42, rho, and rac GEF activity (17); and the yeast CDC24 gene product has cdc42 GEF activity (18). LAR is a broadly expressed transmembrane protein tyrosine phosphatase (PTPase) comprised of a cell adhesion-like extracellular region and two intracellular PTPase domains (19)(20)(21)(22). A role for LAR in regulating cell-matrix interactions was proposed, as LAR colocalizes with a coiled-coil protein, termed LAR interacting protein 1 (LIP.1) at the ends of FAs (23), and LAR expression was observed at regions of association between cells and basement membrane in various tissues (19). To identify putative substrates and other proteins involved in LAR-mediated signal transduction, we screened for proteins that bind the LAR PTPase domains using the interaction-trap assay and coimmunoprecipitation studies. A protein thus isolated is a novel multidomain GEF we have named Trio because it contains three enzyme domains: two GEF domains, one of which has racl GEF activity and the other has rhoA GEF activity, and a serine/threonine kinase (PSK) domain. In addition, Trio contains four N-terminal spectrinlike domains, two pleckstrin-like domains, and an Ig-like domain. Because proteins with cdc42, rac, or rho GEF activity are generally involved in regulating cytoskeletal organization (1), it is likely that Trio in conjunction with LAR plays a key role in coordinating the ...

Significance of nerve growth factor overexpression and its autocrine loop in oesophageal squamous cell carcinoma

“…It is known to be involved in the NGF pathway (Estrach et al, 2002), and activates RhoA with its GEF2 domain (Debant et al, 1996;Bateman and Van Vactor, 2001). Further investigation is necessary to unveil the involvement of Rho-GEF Trio in NGF pathway of OESCC cells.…”

Distinct expression patterns and transforming properties of multiple isoforms of Ost, an exchange factor for RhoA and Cdc42

“…Spectrin is a SH3-domain containing protein which provides structural support to the plasma membrane by linking speci®c integral membrane proteins to the cytoskeleton through the binding of actin ®laments (Viel and Branton, 1996). Interestingly, the EN domain of Ost was most similar to the N terminal regions of Trio and Kalirin/p-CIP10, two proteins which bind to integral membrane proteins and also contain spectrin-like repeat sequences (Alam et al, 1996;Debant et al, 1996). Moreover, ectopic overexpression of isoforms containing the EN and/or N domains resulted in di erences in the localization of Ost within the cytoplasm (unpublished observations), suggesting that these domains, possibly together with the SH3 domain, may alter the ability of the protein to interact with cytoplasmic targets.…”

Small Rho GTPase-mediated actin dynamics at endothelial adherens junctions

“…22 Trio displays 2 GEF domains of distinct specificity, enabling activation of multiple Rho GTPases: Rac1, RhoG and RhoA. 23,24 Our findings suggest that by activating Rac1 at junctions, Trio promotes the formation of cortical actin bundles adjacent to the junction, which is concomitant with the stabilization of cell-cell junctions and supports endothelial barrier function. Of note, the role of Rac1 in endothelial cell-cell adhesion seems contradictory in some occasions, as Rac1 has also been described to be involved in regulation of loss of VEcadherin-based cell-cell contacts.…”

“…In addition, Trio encodes an N-terminal putative lipid-transfer SEC14 domain, 9 spectrin-repeats, 2 SH3-domains, an Ig-like domain and a C-terminal serine/threonine kinase domain. [94][95][96][97][98][99][100][101] The presence of these numerous domains indicates that Trio may function as an integrator of multiple signaling pathways. Trio is unique in that it can activate Rac1, RhoG and RhoA with its 2 separate GEF units.…”