The samples were separated on SDS-PAGE in 8% Tris-glycine pre-cast gels (Invitrogen) and then transferred to nitrocellulose membranes. shown to be efficient inhibitors ofE. coli- and LPS-induced IL-8 secretion as well as JNK1/2 activation/phosphorylation in CD36-overexpressing cells. These results indicate that CD36 functions as a phagocytic receptor for a variety of bacteria and mediates signaling induced by Gram-negative bacteria and LPS via a JNK-mediated signaling pathway in a TLR2/4-impartial manner. Keywords:CD36, lipopolysaccharide, bacteria, phagocytosis, signal transduction == Introduction == Scavenger receptor CD36 is an 88-kDa transmembrane glycoprotein and a member of the class B scavenger receptor family. CD36 is found in macrophages, microglia, microvascular endothelium, cardiac and skeletal muscle, adipocytes and platelets (1). As a pattern recognition receptor, CD36 binds a diverse set of ligands, including oxidized low-density lipoprotein (oxLDL)3, anionic phospholipids (2), long-chain fatty acids, thrombospondin-1, fibrillar -amyloid, and the membrane of cells undergoing apoptosis (1,3,4). CD36 has been Rabbit Polyclonal to TK (phospho-Ser13) implicated in a wide variety of normal and pathologic biological functions, including angiogenesis, atherosclerosis, phagocytosis, inflammation, lipid metabolism and removal of apoptotic cells (1,3). Recent findings provide evidence for the essential role of type B scavenger receptors in the innate immune response of the mammalian host to exogenous pathogens, in particular, to bacteria and LY 344864 hydrochloride their inflammatory compounds. Philipset al. (5) exhibited that two members of the CD36 family, namely human Cla-1 and Cla-2 (orthologs of rodent SR-BI and SR-BII), mediate the uptake ofMycobacterium fortuituminto non-phagocytic cells, while the transfection of cells with the murine CD36 results in intracellular uptake ofEscherichia coli (E. coli)and, to a lesser extentStaphylococcus aureus (S. aureus). Other findings by Stuartet al. (6) indicated that CD36 is LY 344864 hydrochloride predominantly involved in phagocytosis and cytokine production in response to the Gram-positiveS. aureusand its cell component lipoteichoic acid (LTA), and only to a lesser extent to the Gram-negativeE. coliand its cell wall component, lipopolysaccharides (LPS). There is considerable evidence for an important role of Toll-like receptors (TLRs) as sensors for a variety of microbial pathogens (79). Toll-like receptor 4 (TLR4) is considered to be the primary signaling receptor for Gram-negative bacteria and their surface cell wall component LPS. Membrane protein CD14 (mCD14) recruits LPS to TLR4, thereby facilitating signal transduction (10). Despite this widely accepted concept, it has been acknowledged that, at least in mCD14-unfavorable cells such as like endothelial and epithelial cells, the scavenger receptor pathway could be implicated in LPS uptake and clearance (1113). Furthermore, results of recent studies have exhibited that scavenger receptor CD36 is an essential co-receptor involved in recognition of LTA and certain diacylglycerides, leading to activation of TLR2/6 (14). By analogy with mCD14, some authors have proposed that CD36 functions as an accessory protein, required to present bacterial ligands to the TLR-mediated signaling pathways (6,15). The C-terminal domain name of CD36 was shown to be a requirement for LY 344864 hydrochloride the internalization ofS. aureusand LTA as well as for the activation of TLR2/6 signaling. It has been also reported that CD36 plays a role as a TLR-independent signaling receptor, initiating a down-stream cascade upon ligand binding. CD36 receptor was found to be actually associated with three LY 344864 hydrochloride members (Fyn, Yes and Lyn proteins) of the Src family of protein tyrosine kinases (PTKs), known to be upstream GTPases involved in MAP.