IQGAP1IQ and IQGAP1WW each partially rescuedSalmonellainvasion to 54.67.6% and 57.512.5% (meanS.E.M., n=3,p<0.05), respectively, Eglumegad of that seen in control MEFs (Fig. is usually usurped bySalmonellato invade fibroblasts and suggest that IQGAP1 may be a potential therapeutic target forSalmonellapathogenesis. == Introduction == Eglumegad Salmonella typhimuriumis a highly virulent, gram-negative pathogen that causes severe systemic disease, including gastroenteritis and typhoid fever in humans [1,2]. During contamination,Salmonellausurps host cell signaling pathways, particularly those that regulate the actin cytoskeleton [3,4].Salmonellais equipped with a type three secretion system (T3SS) that injects host cells with several bacterial proteins [5]. These include SopE and SopE2, which mimic the function of guanine nucleotide exchange factors (GEFs) and activate the Rho GTPases Rac1 and Cdc42 by stimulating the exchange of GDP for GTP [6,7]. Rabbit Polyclonal to Cytochrome P450 17A1 Active Rac1 and Cdc42 induce the activation of the neuronal Wiskott Aldrich Syndrome protein (N-WASP), the WASP family member 2 (WAVE2) and the actin-related protein (Arp2/3) complex, which triggers actin polymerization and membrane ruffling [810]. The generation of membrane ruffles substantially facilitates bacterial invasion into host cells [3,4]. After entry,Salmonellainactivates Rac1 and Cdc42 using SptP, a GTPase activating protein (GAP) that helps restore the host cells initial cytoskeletal architecture [3]. While it is generally accepted that Rho GTPases participate inSalmonellainvasion, the exact functions of Rac1 and Cdc42 duringSalmonellauptake are unclear. For example, Chenet al.[11] reported decreasedSalmonellainvasion into COS-1 cells expressing a dominant negative Cdc42 construct, suggesting that Cdc42 is the pivotal GTPase manipulated during host cell invasion. However, the same group showed thatSalmonellainvasion into COS-2 fibroblasts and intestinal Henle 407 cells was abrogated following siRNA-mediated knockdown of Rac1, but not Cdc42, indicating that Rac1 is the more important small GTPase forSalmonellaentry [12]. Another group observed that siRNA-mediated knockdown of Rac1 and Cdc42 had no significant effect onSalmonellainvasion into human foreskin fibroblasts [13]. While some of the discrepant data have been ascribed to differences among cell types, these studies indicate that this mechanisms underlying Rac1 and Cdc42 function inSalmonellapathogenesis are incompletely comprehended. The mitogen activated protein kinase (MAPK) pathway relays extracellular signals to various intracellular targets, including the actin cytoskeleton [1416]. The most extensively studied module of the MAPK pathway is the MAPK kinase/extracellular-regulated kinase (MEK/ERK) cascade. In this cascade, extracellular stimuli induce activation of the small GTPase Ras, which activates B-Raf. B-Raf then phosphorylates and activates MEK, resulting in phosphorylation of ERK [16]. The MEK/ERK Eglumegad pathway regulates cell adhesion and motility, processes that are governed by changes in the actin cytoskeleton [14]. Importantly,Salmonellastimulates MAPK activation in host cells [1719] and treatment of cells with the MEK inhibitor PD98059 reducesSalmonellauptake [13,19]. These findings suggest thatSalmonellamay also target the actin cytoskeleton via the MAPK cascade to achieve infection, although the precise mechanism by which this occurs is usually unknown. IQGAP1 is usually a ubiquitously expressed 189-kDa protein that is a pivotal element of cytoskeletal architecture and function [20,21]. IQGAP1 crosslinks actin filaments [22,23] and influences actin assembly both by virtue of its association with actin, N-WASP and the Arp 2/3 complex [24] and by modulating the active state of Rac1 and Cdc42 [25,26]. Despite its name, IQGAP1 is not a GAP, but preferentially binds to activated Rac1 and Cdc42, stabilizing the GTPases in their active forms [26,27]. In addition, IQGAP1 binds to numerous other proteins, including actin, calmodulin and growth factor receptors [28]. It has become apparent that IQGAP1 functions as a Eglumegad scaffold, integrating diverse signaling pathways [28]. For example, IQGAP1 binds to and regulates the activation of B-Raf [29], MEK [30] and ERK [31], thereby facilitating MAPK signaling. A recently uncovered role for.