Tumor suppressor CYLD: negative regulation of NF-κB signaling and more

CYLD is a protein with tumor suppressor properties which was originally discovered associated with cylindromatosis, an inherited cancer exclusively affecting the folicullo-sebaceous-apocrine unit of the epidermis. CYLD exhibits deubiquitinating activity and acts as a negative regulator of NF-κB and JNK signaling through its interaction with NEMO and TRAF2. Recent data suggest that this is unlikely to be its unique function in vivo. CYLD has also been shown to control other seemingly disparate cellular processes, such as proximal T cell receptor signaling, TrkA endocytosis and mitosis. In each case, this enzyme appears to act by regulating a specific type of polyubiquitination, K63 polyubiquitination, that does not result in recognition and degradation of proteins by the proteasome but instead controls their activity through diverse mechanisms. Received 6 October 2007; received after revision 2 November 2007; accepted 23 November 2007     

Human papillomavirus 16 E5 up-regulates the expression of vascular endothelial growth factor through the activation of epidermal growth factor receptor, MEK/ ERK1,2 and PI3K/Akt

The E5 oncoprotein of human papillomavirus (HPV) 16 plays an important role in early cervical carcinogenesis. Vascular endothelial growth factor (VEGF) plays a central role in switching on the angiogenic phenotype during early cervical carcinogenesis. However, the relationship between E5 and VEGF has not previously been examined. To clarify the regulatory role of E5 in VEGF expression, we transferred the E5 gene into various cell types. E5 increased VEGF expression. The addition of epidermal growth factor receptor (EGFR) inhibitor significantly suppressed VEGF expression, demonstrating that E5 stimulates VEGF expression through the activation of EGFR. E5-mediated EGFR activation was accompanied by phosphorylation of Akt and ERK1/2, which are also involved in VEGF expression. Furthermore, the mRNA stability of VEGF was not affected by E5, but VEGF promoter activity could be modulated by inhibitors of the EGFR, MEK-ERK1/2 and PI3K/Akt pathways in E5-expressing cells. Collectively, these novel results suggest that HPV 16 E5 increases VEGF expression by activating EGFR, MEK/ERK1/2 and PI3K/Akt. Received 23 November 2005; received after revision 10 January 2006; accepted 9 February 2006     

Molecular mimicry in neurological disease: what is the evidence?

Autoimmune diseases are a leading cause of disability and are increasing in incidence in industrialized countries. How people develop autoimmune diseases is not completely understood, but is related to an interaction between genetic background, environmental agents, autoantigens and the immune response. Molecular mimicry continues to be an important hypothesis that explains how an infection with an environmental agent results in autoimmune disease of the nervous system and other target organs. Although molecular mimicry has yet to be unequivocally proven, in the past several years there has been a sharpening of its definition with better experimental data implicating it as a cause of neurological disease in humans. Received 9 July 2007; received after revision 15 November 2007; accepted 27 November 2007     

RNA-splicing endonuclease structure and function

The RNA-splicing endonuclease is an evolutionarily conserved enzyme responsible for the excision of introns from nuclear transfer RNA (tRNA) and all archaeal RNAs. Since its first identification from yeast in the late 1970s, significant progress has been made toward understanding the biochemical mechanisms of this enzyme. Four families of the splicing endonucleases possessing the same active sites and overall architecture but with different subunit compositions have been identified. Two related consensus structures of the precursor RNA splice sites and the critical elements required for intron excision have been established. More recently, a glimpse was obtained of the structural mechanism by which the endonuclease recognizes the consensus RNA structures and cleaves at the splice sites. This review summarizes these findings and discusses their implications in the evolution of intron removal processes. Received 24 August 2007; received after revision 24 November 2007; accepted 27 November 2007     

The innate immunity of the central nervous system in chronic pain: The role of Toll-like receptors

Toll-like receptors (TLRs) are a family of pattern recognition receptors that mediate innate immune responses to stimuli from pathogens or endogenous signals. Under various pathological conditions, the central nervous system (CNS) mounts a well-organized innate immune response, in which glial cells, in particular microglia, are activated. Further, the innate immune system has emerged as a promising target for therapeutic control of development and persistence of chronic pain. Especially, microglial cells respond to peripheral and central infection, injury, and other stressor signals arriving at the CNS and initiate a CNS immune activation that might contribute to chronic pain facilitation. In the orchestration of this limited immune reaction, TLRs on microglia appear to be most relevant in triggering and tailoring microglial activation, which might be a driving force of chronic pain. New therapeutic approaches targeting the CNS innate immune system may achieve the essential pharmacological control of chronic pain. Received 21 November 2006; received after revision 8 January 2007; accepted 7 February 2007     

The roles of poly(ADP-ribose)-metabolizing enzymes in alkylation-induced cell death

Poly(ADP-ribose) (PAR) has been identified as a DNA damage-inducible cell death signal upstream of apoptosis-inducing factor (AIF). PAR causes the translocation of AIF from mitochondria to the nucleus and triggers cell death. In living cells, PAR molecules are subject to dynamic changes pending on internal and external stress factors. Using RNA interference (RNAi), we determined the roles of poly(ADP-ribose) polymerases-1 and -2 (PARP-1, PARP-2) and poly(ADP-ribose) glycohydrolase (PARG), the key enzymes configuring PAR molecules, in cell death induced by an alkylating agent. We found that PARP-1, but not PARP-2 and PARG, contributed to alkylation-induced cell death. Likewise, AIF translocation was only affected by PARP-1. PARP-1 seems to play a major role configuring PAR as a death signal involving AIF translocation regardless of the death pathway involved. Received 7 November 2007; received after revision 19 December 2007; accepted 21 December 2007 O. Cohausz, C. Blenn: These two authors contributed equally to this work.     

Interaction of aging-associated signaling cascades: Inhibition of NF-κB signaling by longevity factors FoxOs and SIRT1

Research on aging in model organisms has revealed different molecular mechanisms involved in the regulation of the lifespan. Studies on Saccharomyces cerevisiae have highlighted the role of the Sir2 family of genes, human Sirtuin homologs, as the longevity factors. In Caenorhabditis elegans, the daf-16 gene, a mammalian homolog of FoxO genes, was shown to function as a longevity gene. A wide array of studies has provided evidence for a role of the activation of innate immunity during aging process in mammals. This process has been called inflamm-aging. The master regulator of innate immunity is the NF-κB system. In this review, we focus on the several interactions of aging-associated signaling cascades regulated either by Sirtuins and FoxOs or NF-κB signaling pathways. We provide evidence that signaling via the longevity factors of FoxOs and SIRT1 can inhibit NF-κB signaling and simultaneously protect against inflamm-aging process. Received 4 October 2007; received after revision 7 November 2007; accepted 9 November 2007     

Serglycin – Structure and biology

Serglycin is a proteoglycan found in hematopoietic cells and endothelial cells. It has important functions related to formation of several types of storage granules. In connective tissue mast cells the covalently attached glycosaminoglycan is heparin, whereas mucosal mast cells and activated macrophages contain oversulfated chondroitin sulfate (type E). In mast cells, serglycin interact with histamine, chymase, tryptase and carboxypeptidase, in neutrophils with elastase, in cytotoxic T cells with granzyme B, in endothelial cells with tissue-type plasminogen activator and in macrophages with tumor necrosis factor-α. Serglycin is important for the retention of key inflammatory mediators inside storage granules and secretory vesicles. Serglycin can further modulate the activities of partner molecules in different ways after secretion from activated immune cells, through protection, transport, activation and interactions with substrates or target cells. Serglycin is a proteoglycan with important roles in inflammatory reactions. Received 2 October 2007; received after revision 7 November 2007; accepted 12 November 2007     

Role of serotonin in the hepato-gastroIntestinal tract: an old molecule for new perspectives

Beside its role as a neurotransmitter in the central nervous system, serotonin appears to be a central physiologic mediator of many gastrointestinal (GI) functions and a mediator of the brain-gut connection. By acting directly and via modulation of the enteric nervous system, serotonin has numerous effects on the GI tract. The main gut disturbances in which serotonin is involved are acute chemotherapy-induced nausea and vomiting, carcinoid syndrome and irritable bowel syndrome. Serotonin also has mitogenic properties. Platelet-derived serotonin is involved in liver regeneration after partial hepatectomy. In diseased liver, serotonin may play a crucial role in the progression of hepatic fibrosis and the pathogenesis of steatohepatitis. Better understanding of the role of the serotonin receptor subtypes and serotonin mechanisms of action in the liver and gut may open new therapeutic strategies in hepato-gastrointestinal diseases. Received 15 August 2007; received after revision 1 November 2007; accepted 5 November 2007     

The cytotoxicity of eosinophil cationic protein/ribonuclease 3 on eukaryotic cell lines takes place through its aggregation on the cell membrane

Human eosinophil cationic protein (ECP)/ ribonuclease 3 (RNase 3) is a protein secreted from the secondary granules of activated eosinophils. Specific properties of ECP contribute to its cytotoxic activities associated with defense mechanisms. In this work the ECP cytotoxic activity on eukaryotic cell lines is analyzed. The ECP effects begin with its binding and aggregation to the cell surface, altering the cell membrane permeability and modifying the cell ionic equilibrium. No internalization of the protein is observed. These signals induce cell-specific morphological and biochemical changes such as chromatin condensation, reversion of membrane asymmetry, reactive oxygen species production and activation of caspase-3-like activity and, eventually, cell death. However, the ribonuclease activity component of ECP is not involved in this process as no RNA degradation is observed. In summary, the cytotoxic effect of ECP is attained through a mechanism different from that of other cytotoxic RNases and may be related with the ECP accumulation associated with the inflammatory processes, in which eosinophils are present. Received 26 October 2007; accepted 23 November 2007     

Role of heregulin in human cancer

Heregulin (HRG) is a soluble secreted growth factor, which, upon binding and activation of ErbB3 and ErbB4 transmembrane receptor tyrosine kinases, is involved in cell proliferation, invasion, survival and differentiation of normal and malignant tissues. The HRG gene family consists of four members: HRG-1, HRG-2, HRG-3 and HRG-4, of which a multitude of different isoforms are synthesized by alternative exon splicing, showing various tissue distribution and biological activities. Disruption of the physiological balance between HRG ligands and their ErbB receptors is implicated in the formation of a variety of human cancers. The general mechanisms involved in HRG-induced tumorigenesis is discussed. Received 8 March 2007; received after revision 6 May 2007; accepted 9 May 2007     

Does the urokinase receptor exist in a latent form?

Multiple cellular functions of urokinase and its receptor are associated with the receptor’s capability to interact with a number of ligands at the molecular level. The presence of urokinase is generally needed for the urokinase receptor to acquire this capability. Recent X-ray studies of the structure of the urokinase receptor in complex with either its ligand or peptide inhibitors demonstrate the flexibility of the domain organization of the receptor, suggesting that unliganded urokinase receptor may exist in a latent form that has a conformation different from its ligand-binding form. Received 22 November 2006; received after revision 8 January 2007; accepted 7 February 2007     

Aspirin: recent developments

Aspirin exerts anti-thrombotic action by acetylating and inactivating cyclooxygenase-1, preventing the production of thromboxane A ₂ in platelets. Through this inhibition of platelet function, aspirin is considered as a preventative of ischemic diseases such as coronary and cerebral infarction. However, many studies have revealed that aspirin has other beneficial actions in addition to its anti-platelet activity. For example, aspirin may confer some benefit against colorectal cancer. Here, we discuss the involvement of inflammation in atherosclerosis and how aspirin exerts its beneficial actions in atherosclerotic diseases and cancer. Received 30 September 2007; received after revision 31 October 2007; accepted 6 November 2007     

Effects of ulapualide A and synthetic macrolide analogues on actin dynamics and gene regulation

Several marine macrolide toxins act as potent and specific actin-severing molecules. Recent elucidation of their stereochemistries and modes of interaction with actin has allowed the syntheses of bioactive analogues. Here we used synthetic analogues in a structure-function analysis of ulapualide A, a trisoxazole-based macrolide. Ulapualide A harboured potent actin-depolymerising activity both in cells and in vitro. Its synthetic diastereoisomer was three orders of magnitude less active than the natural toxin and synthetic macrolide fragments lacked actin-capping/ severing activity altogether. Modulation of serum response factor (SRF)-dependent gene expression, as described for other actin-binding toxins, was also examined. Specific changes in response to ulapualide A were not observed, primarily due to its profound effects on cytoskeletal integrity and cell adhesion. Several synthetic fragments of ulapualide A also had no effect on SRF-dependent gene expression. However, inhibition was observed with a molecule corresponding to the extended aliphatic side chain of halichondramide, a structurally related macrolide. These findings indicate that side-chain derivatives of trisoxazole-based macrolides may serve to uncouple gene-regulatory events from actin dynamics. E. Vincent and J. Saxton: These two authors contributed equally Received 27 September 2006; received after revision 30 November 2006; accepted 8 January 2007     

Biology-inspired synthesis of compound libraries

Biologically active small molecules represent the basis for chemical biology applications in which small molecules are used as chemical tools to probe biological processes. In this report, we review two approaches to design and synthesize compound libraries for biological screenings, i.e., diversity-oriented synthesis (DOS) and biology-oriented synthesis (BIOS). Received 23 October 2007; received after revision 26 November 2007; accepted 28 November 2007     

Extended and bent conformations of the mannose receptor family

In mammals, the mannose receptor family consists of four members, Endo180, DEC-205, phospholipase A₂ receptor and the mannose receptor. The extracellular domains of all these receptors contain a similar arrangement of domains in which an Nterminal cysteine-rich domain is followed by a single fibronectin type II domain and eight or ten C-type lectin-like domains. This review focuses on the threedimensional structure of the receptors in the mannose receptor family and its functional implication. Recent research has revealed that several members of this family can exist in at least two configurations: an extended conformation with the N-terminal cysteinerich domain pointing outwards from the cell membrane and a bent conformation where the N-terminal domains fold back to interact with C-type lectin-like domains at the middle of the structure. Conformational transitions between these two states seem to regulate the interaction of these receptors with ligands and their oligomerization. Received 25 October 2007; received after revision 23 November 2007; accepted 7 December 2007     

Genetic factors for human obesity

Obesity is a multifactorial and heterogeneous condition that results from alterations of various genes, each having a partial and additive effect. The inheritance pattern of obesity is thus complex, and environmental factors play an important role in promoting or delaying its development. The identification of susceptibility genes and genetic variants for obesity requires various methodological approaches. Obesity is classified into three main categories on the basis of genetic etiology: monogenic, syndromic, and polygenic obesity. Here we review monogenic and syndromic obesity. We also review the linkage analysis studies followed by the candidate gene approaches and genome-wide association studies. Identification of the underlying genetic causes of obesity will likely provide a basis both for the development of new therapeutic agents and for the personalized prevention of this condition. Received 2 October 2007; received after revision 15 November 2007; accepted 19 November 2007     

TRAIL induces proliferation of human glioma cells by c-FLIPL-mediated activation of ERK1/2

TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis in TRAIL-sensitive human malignant glioma cells. We show for the first time that TRAIL stimulates cell growth in TRAIL-resistant glioma cells. TRAIL-induced cell growth in resistant cells occurred through increased cell cycle progression as determined by flow cytometry and Western blot analysis of retinoblastoma protein phosphorylation. Western blot analysis of TRAIL-treated resistant cells revealed phosphorylation of ERK1/2 proteins and in vitro kinase analysis confirmed the activation of the ERK1/2 kinases. Inhibition of MEK1 eliminated both TRAIL-induced ERK1/2 activation and cell proliferation. In addition, siRNA inhibition of c-FLIP expression eliminates TRAIL-induced ERK1/2 activation and proliferation. Furthermore, overexpression of c-FLIP_L potentiates TRAIL-induced ERK1/2 activation and proliferation of resistant glioma cells. Our results have shown for the first time that TRAIL-induced ERK1/2 activation and proliferation of TRAIL-resistant human glioma cells is dependent upon the expression of the long form of the caspase-8 inhibitor c-FLIP_L. Received 2 November 2007; received after revision 14 December 2007; accepted 21 December 2007     

Darier’s disease: a calcium-signaling perspective

Ca²⁺ influx evoked across the plasma membrane upon internal store depletion is essential for a myriad of cellular functions including gene expression, cell proliferation, differentiation and even apoptosis. Darier’s disease (DD), an autosomal dominant inherited disorder of the skin, arising due to mutations in the isoform 2 of the sarco (endo) plasmic reticulum Ca²⁺ ATPase (SERCA2), exemplifies an anomaly of Ca²⁺ signaling disturbances. Owing to loss of function mutations in SERCA2, keratinocytes in DD patients have a reduced pool of endoplasmic reticulum (ER) Ca²⁺. Importantly, the status of ER Ca²⁺ is critical for the activation of a class of plasma membrane Ca²⁺ channels referred to as store operated Ca²⁺ channels (SOCs). The widely expressed transient receptor potential (TRP) family of channels is proposed to be SOCs. In this review we discuss DD from the viewpoint of Ca²⁺ signaling and present a potential role for TRPC1 in the disease pathogenesis. Received 30 August 2007; received after revision 17 October 2007; accepted 6 November 2007     

Xanthorhodopsin: Proton pump with a carotenoid antenna

Retinal proteins function as photoreceptors and ion pumps. Xanthorhodopsin of Salinibacter ruber is a recent addition to this diverse family. Its novel and distinctive feature is a second chromophore, a carotenoid, which serves as light-harvesting antenna. Here we discuss the properties of this carotenoid/retinal complex most relevant to its function (such as the specific binding site controlled by the retinal) and its relationship to other retinal proteins (bacteriorhodopsin, archaerhodopsin, proteorhodopsin and retinal photoreceptors of archaea and eukaryotes). Antenna addition to a retinal protein has not been observed among the archaea and emerged in bacteria apparently in response to environmental conditions where light-harvesting becomes a limiting factor in retinal protein functioning. Received 2 April 2007; received after revision 14 May 2007; accepted 16 May 2007