RacGAP1 is a Cdc42 GAP,36and it is therefore possible that IQGAP1-mediated recruitment of RacGAP1 may also modulate Cdc42 activity. integrin engagement. Furthermore, following literature-curated searches and recent mass spectrometric analysis of IQGAP1-binding partners, we report that IQGAP1 recruits other small GTPases, including RhoC, Rac2, M-Ras, RhoQ, Rab10, and Rab5, small GTPase regulators, including Tiam1, RacGAP1, srGAP2 and HERC1, and small GTPase effectors, including PAK6, N-WASP, several sub-units of the Arp2/3 complex and the formin mDia1. Therefore, we propose that IQGAP1 acts as a small GTPase scaffolding platform within the small GTPase network, and recruits and/or regulates small GTPases, small GTPase regulators and effectors to orchestrate cell behavior. Finally, to identify other putative key regulators of small GTPase crosstalk, we have assembled a small GTPase network using protein-protein interaction databases. Keywords:small GTPase crosstalk, IQGAP1, Ras GTPases, small GTPase network, signal transduction The small GTP-binding proteins (GTPases) act as molecular switches to control virtually every cellular process, including cell proliferation (Ras family), membrane trafficking (Arf and Rab families), cytoskeletal dynamics (Rho family) and nuclear transport (Ran family).1Together, these GTPases orchestrate multiple physiological processes, including embryogenesis, polarity, adhesion, migration, and cell fate. Dysregulated GTPase activity has been implicated in a variety of human pathologies including cancer development, progression and dissemination, inflammation, vascular diseases, mental retardation, and infection.1-3 Small GTPases cycle between an active GTP-bound form and an inactive GDP-bound form. The GTPase activation-state dictates function through recruitment of different binding partners Senicapoc (ICA-17043) (including downstream effectors and GTPase regulators). The cycling of small GTPases between active and inactive states is tightly controlled by GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs).4-6Classically, small GTPases are thought to be activated by transmembrane receptors such as integrins or growth factor receptors, in response to environmental cues.1,2,4Accumulating evidence suggests that GTPases can also be regulated by other GTPase family members, share common GTPase regulators, and converge on the same signaling pathway.7-10This interplay between small GTPases is crucial for the regulation of complex physiological processes, such as directional cell migration, that require the integration of multiple signaling cues at specific times and places.11Indeed, directional cell migration is achieved by Rabbit Polyclonal to RNF138 spatial and temporal coordination of multiple small GTPases that regulate actin cytoskeleton dynamics, membrane protrusion and the delivery and activation of receptors, Senicapoc (ICA-17043) including integrins, at new cell-matrix adhesion sites.12,13It is now well established that the small GTPases Rac1 and RhoA, through opposing roles and antagonistic activities, are required for directional cell migration. The balance between Rac1/RhoA Senicapoc (ICA-17043) defines actin cytoskeleton structure, cell-matrix adhesion stability and Senicapoc (ICA-17043) membrane protrusion dynamics and consequently dictates the mode of invasive cell migration.9,14,15Other examples of known crosstalk between small GTPases include interplay between the small GTPases Cdc42 and Rac1, Rac1 and RhoG, Rac1 and Arf6,16-18Arf6 and several Rabs (Rab11, Rab7, Rab8),19-21and connections between Rab GTPases, Ras, and Rac1.22Recent mass spectrometric analysis of Rac1-binding partners identified over 25 regulators of GTPase activity including specific modulators of Rac1 and several modulators of RhoA, Ras, Rap1 and Arf5, thereby revealing putative novel crosstalk Senicapoc (ICA-17043) between these GTPases.23Thus, the basic mechanisms of single GTPase regulation within cells are fairly well understood and crosstalk between small GTPase pairs are getting to be elucidated. Nevertheless, how signaling from multiple GTPases (3 or even more) is normally coordinated to mediate complicated processes, such as for example directional cell migration, continues to be unknown. Chances are that such coordination is normally attained by the life of specialized proteins hubs that integrate and decipher multiple signaling occasions resulting in the spatial and temporal legislation of multiple little GTPase actions. We among others possess discovered IQ-motif-containing GTPase-activating proteins 1 (IQGAP1), a scaffolding proteins mixed up in legislation of microtubule and actin company, cell migration and cell proliferation, as an integral regulator of multiple little GTPases and little GTPase features (Fig. 1).15,23-25Supporting a job for IQGAP1 regulating little GTPase features, Gene Ontology analysis of IQGAP1-binding proteins, discovered by mass spectrometry,23revealed an enrichment of proteins involved with Small GTPase-mediated sign transduction (Fig. 1). The diverse roles of IQGAP1 may be dictated simply by IQGAP1 subcellular localization and IQGAP1-binding partners. IQGAP1.