The CARMA3-Bcl10-MALT1 Signalosome Promotes Angiotensin II-dependent Vascular Inflammation and Atherogenesis

The CARMA1, Bcl10, and MALT1 proteins together constitute a signaling complex (CBM signalosome) that mediates antigen-dependent activation of NF-κB in lymphocytes, thereby representing a cornerstone of the adaptive immune response. Although CARMA1 is restricted to cells of the immune system, the analogous CARMA3 protein has a much wider expression pattern. Emerging evidence suggests that CARMA3 can substitute for CARMA1 in non-immune cells to assemble a CARMA3-Bcl10-MALT1 signalosome and mediate G protein-coupled receptor activation of NF-κB. Here we show that one G protein-coupled receptor, the type 1 receptor for angiotensin II, utilizes this mechanism for activation of NF-κB in endothelial and vascular smooth muscle cells, thereby inducing pro-inflammatory signals within the vasculature, a key factor in atherogenesis. Further, we demonstrate that Bcl10-deficient mice are protected from developing angiotensin-dependent atherosclerosis and aortic aneurysms. By uncovering a novel vascular role for the CBM signalosome, these findings illustrate that CBM-dependent signaling has functions outside the realm of adaptive immunity and impacts pathobiology more broadly than previously known.     

HCN-Encoded Pacemaker Channels: From Physiology and Biophysics to Bioengineering

The depolarizing membrane ionic current I _h (also known as I _f, “f” for funny), encoded by the hyperpolarization-activated cyclic-nucleotide-modulated (HCN1-4) channel gene family, was first discovered in the heart over 25 years ago. Later, I _h was also found in neurons, retina, and taste buds. HCN channels structurally resemble voltage-gated K⁺ (Kv) channels but the molecular features underlying their opposite gating behaviors (activation by hyperpolarization rather than depolarization) and non-selective permeation profiles (≥25 times less selective for K⁺ than Kv channels) remain largely unknown. Although I _h has been functionally linked to biological processes from the autonomous beating of the heart to pain transmission, the underlying mechanistic actions remain largely inferential and, indeed, somewhat controversial due to the slow kinetics and negative operating voltage range relative to those of the bioelectrical events involved (e.g., cardiac pacing). This article reviews the current state of our knowledge in the structure-function properties of HCN channels in the context of their physiological functions and potential HCN-based therapies via bioengineering.     

Melatonin and lipid uptake by murine fibroblasts: clinical implications

The current study was undertaken to uncover the role of melatonin in lipid metabolism in the murine fibroblasts. The results show melatonin in vitro enhances lipid accumulation and lipid droplet formation in this cell line. Using oil red O staining, it was found that when oleic acid was present in the culture media, melatonin at doses of 0.1-2mM, significantly increased the lipid concentrations in the cells. However, low levels of melatonin, with or without oleic acid, did not influence lipid metabolism in the cultured fibroblasts. When a non-specific melatonin receptor antagonist, luzindole 10 microM was co-incubated with 1mM melatonin, the stimulatory effects of melatonin on lipid accumulation in these cells was significantly reduced. It appears that the effects of melatonin on lipid metabolism in murine fibroblasts is mediated by melatonin membrane receptors.     

Multiple determinants influence root colonization and induction of induced systemic resistance by Pseudomonas chlororaphis O6

Colonization of the roots of tobacco by Pseudomonas chlororaphis O6 induces systemic resistance to the soft-rot pathogen, Erwinia carotovora ssp. carotovara SCC1. A screen of the transposon mutants of P. chlororaphis O6 showed mutants with about a fivefold reduction in ability to induce systemic resistance to the soft-rot disease. These mutations disrupted genes involved in diverse functions: a methyl-accepting chemotaxis protein, biosynthesis of purines, phospholipase C, transport of branched-chain amino acids and an ABC transporter. Additional mutations were detected in the intergenic spacer regions between genes encoding a GGDEF protein and fumarate dehydratase, and in genes of unknown function. The mutants in the ABC transporters did not display reduced root colonization. However, the other mutants had up to 100-fold reduced colonization levels. Generally the production of metabolites important for interactions in the rhizosphere, phenazines and siderophores, was not altered by the mutations. A reduced induction of systemic resistance by a purine biosynthesis mutant with a disrupted purM gene correlated with poor growth rate, lesser production of phenazines and siderophore and low levels of root colonization. These studies showed that multiple determinants are involved in the induction of systemic resistance, with there being a requirement for strong root colonization.     

Structure of a novel phosphotyrosine-binding domain in Hakai that targets E-cadherin

Phosphotyrosine-binding domains, typified by the SH2 (Src homology 2) and PTB domains, are critical upstream components of signal transduction pathways. The E3 ubiquitin ligase Hakai targets tyrosine-phosphorylated E-cadherin via an uncharacterized domain. In this study, the crystal structure of Hakai (amino acids 106-206) revealed that it forms an atypical, zinc-coordinated homodimer by utilizing residues from the phosphotyrosine-binding domain of two Hakai monomers. Hakai dimerization allows the formation of a phosphotyrosine-binding pocket that recognizes specific phosphorylated tyrosines and flanking acidic amino acids of Src substrates, such as E-cadherin, cortactin and DOK1. NMR and mutational analysis identified the Hakai residues required for target binding within the binding pocket, now named the HYB domain. ZNF645 also possesses a HYB domain but demonstrates different target specificities. The HYB domain is structurally different from other phosphotyrosine-binding domains and is a potential drug target due to its novel structural features.