Regulated gene expression and progeny production are essential for persistent and chronic infection by human pathogens, such as hepatitis B virus (HBV), which affects >400 million people worldwide and is a major cause of liver disease. In this study, we provide the first direct evidence that a liver‐specific microRNA, miR‐122, binds to a highly conserved HBV pregenomic RNA sequence via base‐pairing interactions and inhibits HBV gene expression and replication. The miR‐122 target sequence is located at the coding region of the mRNA for the viral polymerase and the 3' untranslated region of the mRNA for the core protein. In cultured cells, HBV gene expression and replication reduces with increased expression of miR‐122, and the expression of miR‐122 decreases in the presence of HBV infection and replication. Furthermore, analyses of clinical samples demonstrated an inverse linear correlation in vivo between the miR‐122 level and the viral loads in the peripheral blood mononuclear cells of HBV‐positive patients. Our results suggest that miR‐122 may down‐regulate HBV replication by binding to the viral target sequence, contributing to the persistent/chronic infection of HBV, and that HBV‐induced modulation of miR‐122 expression may represent a mechanism to facilitate viral pathogenesis.—Chen, Y., Shen, A., Rider, P. J., Yu, Y., Wu, K., Mu, Y., Hao, Q, Liu, Y., Gong, H., Zhu, Y., Liu, F., Wu, J. A liver‐specific microRNA binds to a highly conserved RNA sequence of hepatitis B virus and negatively regulates viral gene expression and replication. FASEB J. 25, 4511–4521 (2011). www.fasebj.org

Ligand receptor interactions instruct axon guidance during development. How dendrites are guided to specific targets is less understood. The C. elegans PVD sensory neuron innervates muscle-skin interface with its elaborate dendritic branches. Here, we found that LECT-2, the ortholog of leukocyte cell-derived chemotaxin-2 (LECT2), is secreted from the muscles and required for muscle innervation by PVD. Mosaic analyses showed that LECT-2 acted locally to guide the growth of terminal branches. Ectopic expression of LECT-2 from seam cells is sufficient to redirect the PVD dendrites onto seam cells. LECT-2 functions in a multi-protein receptor-ligand complex that also contains two transmembrane ligands on the skin, SAX-7/L1CAM and MNR-1, and the neuronal transmembrane receptor DMA-1. LECT-2 greatly enhances the binding between SAX-7, MNR-1 and DMA-1. The activation of DMA-1 strictly requires all three ligands, which establishes a combinatorial code to precisely target and pattern dendritic arbors.

Human cytomegalovirus (HCMV) is the largest human herpesvirus and its virion contains many viral encoded proteins found in the capsid, tegument, and envelope. In this study, we carried out a yeast two-hybrid (YTH) analysis to study potential binary interactions among 56 HCMV-encoded virion proteins. We have tested more than 3,500 pairwise combinations for binary interactions in the YTH analysis, and identified 79 potential interactions that involve 37 proteins. Forty five of the 79 interactions were also identified in human cells expressing the viral proteins by co-immunoprecipitation (co-IP) experiments. To our knowledge, 58 of the 79 interactions revealed by YTH analysis, including those 24 that were also identified in co-IP experiments, have not been reported before. Novel potential interactions were found between viral capsid proteins and tegument proteins, between tegument proteins, between tegument proteins and envelope proteins, and between envelope proteins. Furthermore, both the YTH and co-IP experiments have identified 9, 7, and 5 interactions that were involved with UL25, UL24, and UL89, respectively, suggesting that these “hub” proteins may function as the organizing centers for connecting multiple virion proteins in the mature virion and for recruiting other virion proteins during virion maturation and assembly. Our study provides a framework to study potential interactions between HCMV proteins and investigate the roles of protein-protein interactions in HCMV virion formation or maturation process.

Cardiac β-adrenergic receptor (βAR) signalling is susceptible to heterologous desensitization by different neurohormonal stimuli in clinical conditions associated with heart failure. We aim to examine the underlying mechanism of cross talk between βARs and a set of G-protein coupled receptors (GPCRs) activated by hormones/agonists. Rat ventricular cardiomyocytes were used to determine heterologous phosphorylation of βARs under a series of GPCR agonists. Activation of G_s-coupled dopamine receptor, adenosine receptor, relaxin receptor and prostaglandin E2 receptor, and G_q-coupled α₁ adrenergic receptor and angiotensin II type 1 receptor promotes phosphorylation of β₁AR and β₂AR at putative protein kinase A (PKA) phosphorylation sites; but activation of G_i-coupled α₂ adrenergic receptor and activation of protease-activated receptor does not. The GPCR agonists that promote β₂AR phosphorylation effectively inhibit βAR agonist isoproterenol-induced PKA phosphorylation of phospholamban and contractile function in ventricular cardiomyocytes. Heterologous GPCR stimuli have minimal to small effect on isoproterenol-induced β₂AR activation and G-protein coupling for cyclic adenosine monophosphate (cAMP) production. However, these GPCR stimuli significantly promote phosphorylation of phosphodiesterase 4D (PDE4D), and recruit PDE4D to the phosphorylated β₂AR in a β-arrestin 2 dependent manner without promoting β₂AR endocytosis. The increased binding between β₂AR and PDE4D effectively hydrolyzes cAMP signal generated by subsequent stimulation with isoproterenol. Mutation of PKA phosphorylation sites in β₂AR, inhibition of PDE4, or genetic ablation of PDE4D or β-arrestin 2 abolishes this heterologous inhibitory effect. Ablation of β-arrestin 2 or PDE4D gene also rescues β-adrenergic stimuli-induced myocyte contractile function. These data reveal essential roles of β-arrestin 2 and PDE4D in a common mechanism for heterologous desensitization of cardiac βARs under hormonal stimulation, which is associated with impaired cardiac function during the development of pathophysiological conditions.