br Conflicts of interest br Acknowledgements br Introduction

Conflicts of interest
Acknowledgements
Introduction Atherosclerosis is the number one cause of death in the United States and among the leading causes of morbidity and mortality globally [1]. Inflammation is critical in all stages of atherosclerosis from the formation of a plaque in the vessel wall to its eventual rupture resulting in coronary ischemia, stroke, or peripheral arterial occlusion [[2], [3], [4], [5]]. Therapies that lower circulating low-density lipoprotein (LDL) levels form the cornerstone of atherosclerosis treatment. However, as tamoxifen citrate has been increasingly implicated in the pathogenesis of atherosclerosis, a new genus of anti-inflammatory therapies has emerged that may provide additional therapeutic benefit beyond LDL reduction [2]. One such anti-inflammatory agent is Canakinumab, a monoclonal antibody that targets interleukin-1β. In a recent clinical trial patients already treated with LDL lowering agents experienced a 15% reduction in recurrent cardiovascular events without any change in circulating LDL levels when administered Canakinumab rather than placebo, providing proof-of-concept and validation of targeted anti-inflammatory therapies for atherosclerosis [6,7]. Because agents like Canakinumab work independent of LDL levels they have the potential to add a new dimension to the treatment of atherosclerosis beyond LDL reduction. These developments underscore the critical need for further investigation of the modulators of the inflammatory response in atherosclerosis and how they can be targeted by novel anti-inflammatory agents [7]. A key inciting event in atherosclerosis is the deposition of circulating low-density lipoprotein (LDL) in the subendothelial space of major arteries. In the subendothelium, native LDL is no longer protected by circulating antioxidants and is oxidatively modified to oxidized LDL (OxLDL) [5]. OxLDL is no longer recognized by the LDL receptor but rather by scavenger receptors such as CD36 on the surface of the macrophage [5]. Once ligated by OxLDL, CD36 recruits Toll-like receptors (TLR) 4 and 6 and activates an intracellular signaling cascade that requires adapter proteins including tumor necrosis factor receptor associated factors (TRAFs) [8,9]. This signaling cascade phosphorylates and activates the p65 subunit of NF-κB resulting in secretion of pro-inflammatory mediators that perpetuate the inflammatory response and establish the atherosclerotic lesion in the vessel wall [8]. Hence, surface receptor activation coupled to signal transduction through key intermediates that stimulate the cytokine response is critical in mediating actions of modified LDL. It has been shown that the protein stability of TLRs and signaling intermediates such as TRAF proteins are important in controlling pro-inflammatory responses [10]. Ubiquitination controls the lifespan of the majority of proteins and involves a hierarchical, exquisite system. Ubiquitination involves the stepwise transfer of ubiquitin from an E1 ubiquitin-activating enzyme to an E2 ubiquitin-conjugating enzyme, and finally to an E3 ubiquitin ligase complex [11]. In the final step of the reaction, the E3 ubiquitin ligase transfers ubiquitin chains to the substrate to facilitate degradation by the 26S proteasome or sorting to the endosome-lysosome pathway. Two E1 enzymes, almost 40 E2 enzymes, and >1000 E3 enzymes have been identified in mammalian cells [12]. The Skp-Cullin-F-box (SCF) superfamily represents the largest group of E3 ligases that mediate critical roles in cell biology, including tumorigenesis and inflammation. Within the SCF apparatus is a receptor module, termed F-box protein that binds substrates. We previously identified and characterized the molecular behavior of F-box protein FBXO3, that targets another F-box subunit, FBXL2, that in turn controls the stability of TRAF proteins [10]. Therefore, inhibition of FBXO3 increases FBXL2 which decreases levels of TRAF proteins to limit inflammation. TRAF proteins also link cell-surface receptors such as CD36 to NF-κB which appears to be controlled, in part, by the SCFFBXO3 E3 ligase [10]. FBXO3 is a particularly attractive drug target in atherosclerosis because a small molecule inhibitor of FBXO3 is effective in preclinical studies [10].