The dynamics of receptor recognition by human rhinoviruses

Heterocyclic pharmacochemistry of new rhinovirus antiviral agents: A combined computational and experimental study

Rhinovirus (RV), member of the Enterovirus genus, is known to be involved in more than half of the common colds. Through advances in molecular biology, rhinoviruses have also been associated with exacerbations of chronic pulmonary diseases (e.g. asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis). In the current investigation, we develop a novel series of 4,5-dimethoxybenzyl derivatives that potently inhibits rhinovirus replication. Compound (S)-7f blocks RV-B14 replication with an EC₅₀ value of 0.25 μM and shows a low toxicity in HeLa cells (CC₅₀ > 271 μM). Enantioseparation followed by an absolute configuration determination by a Mosher's method revealed the interest of enantiopure compounds. Molecular docking studies permitted the identification of key biological interactions within the drug-binding pocket and an in silico drug-like study revealed a good potential for the development of these derivatives.

Virus-receptor interactions and receptor-mediated virus entry into host cells

The virus particles described in previous chapters are vehicles that transmit the viral genome and the infection from cell to cell. To initiate the infective cycle, the viral genome must therefore translocate from the viral particle to the cytoplasm. Via distinct proteins or motifs in their outermost shell, the particles attach initially to specific molecules on the host cell surface. These virus receptors thus mediate penetration of the viral genome inside the cell, where the intracellular infective cycle starts. The presence of these receptors on the cell surface is a principal determinant of virus host tropism. Viruses can use diverse types of molecules to attach to and enter into cells. In addition, virus-receptor recognition can evolve over the course of an infection, and virus variants with distinct receptor-binding specificities and tropism can appear. The identification of virus receptors and the characterization of virus-receptor interactions have been major research goals in virology for the last two decades. In this chapter, we will describe, from a structural perspective, several virus-receptor interactions and the active role of receptor molecules in virus entry.

Intercellular adhesion molecule 1: recent findings and new concepts involved in mammalian spermatogenesis

Spermatogenesis, the process of spermatozoa production, is regulated by several endocrine factors, including testosterone, follicle stimulating hormone, luteinizing hormone and estradiol 17β. For spermatogenesis to reach completion, developing germ cells must traverse the seminiferous epithelium while remaining transiently attached to Sertoli cells. If germ cell adhesion were to be compromised for a period of time longer than usual, germ cells would slough from the seminiferous epithelium and infertility would result. Presently, Sertoli-germ cell adhesion is known to be mediated largely by classical and desmosomal cadherins. More recent studies, however, have begun to expand long-standing concepts and to examine the roles of other proteins such as intercellular adhesion molecules. In this review, we focus on the biology of intercellular adhesion molecules in the mammalian testis, hoping that this information is useful in the design of future studies.

Uncoating of human rhinoviruses

Human rhinoviruses (HRVs) are a major cause of the common cold. The more than one hundred serotypes, divided into species HRV-A and HRV-B, either bind intercellular adhesion molecule 1 (major group viruses) or members of the low-density lipoprotein receptor (minor group viruses) for cell entry. Some major group HRVs can also access the host cell via heparan sulphate proteoglycans. The cell attachment protein(s) of the recently discovered phylogenetic clade HRV-C is unknown. The respective receptors direct virus uptake via clathrin-dependent or independent endocytosis or via macropinocytosis. Triggered by ICAM-1 and/or the low pH environment in endosomes the virions undergo conformational alterations giving rise to hydrophobic subviral particles. These are handed over from the receptors to the endosomal membrane. According to the current view, the RNA genome is released through an opening at one of the fivefold axes of the icosahedral capsid and crosses the membrane through a pore presumably formed by viral proteins. Alternatively, the membrane may be ruptured allowing subviral particles and RNA to enter the cytosol. Whether a channel is formed or the membrane is disrupted most probably depends on the respective HRV receptor.

Modulation of the immune system by human rhinoviruses

Human rhinoviruses (HRV) are the major cause of the common cold, one of the most frequent infectious diseases in humans. Though HRV infections of the upper respiratory tract are usually rather harmless, there is increasing evidence that HRV sets the stage for more dangerous pathogens, elicits asthmatic exacerbations, severe diseases in the lower respiratory tract and even autoimmunity. The pathogenic mechanisms of HRV infections leading to such complications are still poorly understood. It is a common strategy of pathogens to manipulate our immune system in order to evade an efficient immune response. A major characteristic of HRV is a high degree of species specificity. Thus, analyzing the potential immune evasion mechanisms used by HRV will be helpful for a better understanding of the pathogenesis of the common cold and may contribute to a better understanding of the human immune system as well. In this review we want to illuminate what is known about potential immune escape mechanisms used by HRV and discuss how such disturbances might lead to a suppressed and dysregulated immune competence in man.

Engagement of ICAM-1 by major group rhinoviruses activates the LFA-1/ICAM-3 cell adhesion pathway in mononuclear phagocytes

Cell-cell interactions are critical at key points of immune responses and are mediated by a complex array of adhesion receptors. One of the most important adhesion molecules on leukocytes is intercellular adhesion molecule 1 (ICAM-1, CD54). Here we demonstrate that engagement of ICAM-1 with human major group rhinoviruses (HRV) enhances adhesiveness and homotypic aggregation of human monocytes and monocyte-derived dendritic cells (DC). Cluster formation upon engagement of ICAM-1 with HRV14 represents an active process. It is temperature and energy dependent, requires divalent cations, an intact cytoskeleton and protein de novo synthesis. Homotypic interaction between monocytes induced by HRV14 can be inhibited with blocking mAbs against LFA-1 (CD11a/CD18) and ICAM-3 (CD50) as well as with a mAb against the first immunoglobulin (Ig)-domain of PECAM-1 (CD31). Induction of enhanced cytoadhesiveness by HRV14 was not accompanied with an upregulation of LFA-1, ICAM-3 or PECAM-1 expression. Binding studies with recombinant PECAM-1 proteins indicated, however, that monocyte clustering upon engagement of ICAM-1 with HRV was accompanied with increased homophilic PECAM-1 interactions. Taken together the results of our study demonstrate that signalling via ICAM-1 induces adhesiveness of mononuclear phagocytes, which critically involves PECAM-1 and is mediated via LFA-1/ICAM-3.

Rhinovirus-stabilizing activity of artificial VLDL-receptor variants defines a new mechanism for virus neutralization by soluble receptors

Members of the low-density lipoprotein receptor family possess various numbers of ligand binding repeats that non-equally contribute to binding of minor group human rhinoviruses. Using an artificial concatemer of five copies of repeat 3 of the human very-low density lipoprotein receptor, we demonstrate protection of HRV2 against low-pH mediated uncoating and inhibition of penetration of an RNA-specific fluorescent dye into the intact virion. This indicates that the recombinant receptor inhibits viral breathing and irreversible conformational modifications of the capsid that precede RNA release, providing a new mechanism for rhinovirus neutralization by soluble receptor molecules.

Human Rhinoviruses Inhibit the Accessory Function of Dendritic Cells by Inducing Sialoadhesin and B7-H1 Expression

Dendritic cells (DC) are professional APCs with an unmatched ability to interact with and activate T cells. There is accumulating evidence that DC not only efficiently stimulate T cell activation but also regulate T cell responses. However, little is known about cell surface structures on DC involved in the regulation of T cell responses. We demonstrate that human rhinoviruses (HRV) can efficiently inhibit the accessory function of DC through induction of inhibitory cell surface receptors. We observed that treatment of DC with HRV14 (R-DC), a member of the major group HRV family, diminished their T cell stimulatory capacity and induced a promiscuous and deep anergic state in cocultured T cells despite high levels of MHC molecules as well as costimulatory molecules, e.g., B7-1 (CD80) and B7-2 (CD86), and independent of inhibitory soluble factors such as IL-10. In contrast, expression of inhibitory B7-H1 molecules was up-regulated and R-DC de novo expressed sialoadhesin (Sn). Most importantly, blocking of B7-H1 and Sn on R-DC with specific mAbs against both receptors reverted the inhibitory phenotype. Thus, inhibitory signals delivered from R-DC to T cells via B7-H1 and Sn were critical for the induction of anergy. These observations suggest that an altered accessory molecule repertoire on DC upon interaction with HRV down-modulates adaptive immune responses during the viral infection.