Serotonin Receptor Agonist 5-Nonyloxytryptamine Alters the Kinetics of Reovirus Cell Entry.

UNLABELLED: Mammalian orthoreoviruses (reoviruses) are nonenveloped double-stranded RNA viruses that infect most mammalian species, including humans. Reovirus binds to cell surface glycans, junctional adhesion molecule A (JAM-A), and the Nogo-1 receptor (depending on the cell type) and enters cells by receptor-mediated endocytosis. Within the endocytic compartment, reovirus undergoes stepwise disassembly, which is followed by release of the transcriptionally active viral core into the cytoplasm. In a small-molecule screen to identify host mediators of reovirus infection, we found that treatment of cells with 5-nonyloxytryptamine (5-NT), a prototype serotonin receptor agonist, diminished reovirus cytotoxicity. 5-NT also blocked reovirus infection. In contrast, treatment of cells with methiothepin mesylate, a serotonin antagonist, enhanced infection by reovirus. 5-NT did not alter cell surface expression of JAM-A or attachment of reovirus to cells. However, 5-NT altered the distribution of early endosomes with a concomitant impairment of reovirus transit to late endosomes and a delay in reovirus disassembly. Consistent with an inhibition of viral disassembly, 5-NT treatment did not alter infection by in vitro-generated infectious subvirion particles, which bind to JAM-A but bypass a requirement for proteolytic uncoating in endosomes to infect cells. We also found that treatment of cells with 5-NT decreased the infectivity of alphavirus chikungunya virus and coronavirus mouse hepatitis virus. These data suggest that serotonin receptor signaling influences cellular activities that regulate entry of diverse virus families and provides a new, potentially broad-spectrum target for antiviral drug development. IMPORTANCE: Identification of well-characterized small molecules that modulate viral infection can accelerate development of antiviral therapeutics while also providing new tools to increase our understanding of the cellular processes that underlie virus-mediated cell injury. We conducted a small-molecule screen to identify compounds capable of inhibiting cytotoxicity caused by reovirus, a prototype double-stranded RNA virus. We found that 5-nonyloxytryptamine (5-NT) impairs reovirus infection by altering viral transport during cell entry. Remarkably, 5-NT also inhibits infection by an alphavirus and a coronavirus. The antiviral properties of 5-NT suggest that serotonin receptor signaling is an important regulator of infection by diverse virus families and illuminate a potential new drug target.

An expressed retrogene of the master embryonic stem cell gene POU5F1 is associated with prostate cancer susceptibility.

Genetic association studies of prostate and other cancers have identified a major risk locus at chromosome 8q24. Several independent risk variants at this locus alter transcriptional regulatory elements, but an affected gene and mechanism for cancer predisposition have remained elusive. The retrogene POU5F1B within the locus has a preserved open reading frame encoding a homolog of the master embryonic stem cell transcription factor Oct4. We find that 8q24 risk alleles are expression quantitative trait loci correlated with reduced expression of POU5F1B in prostate tissue and that predicted deleterious POU5F1B missense variants are also associated with risk of transformation. POU5F1 is known to be self-regulated by the encoded Oct4 transcription factor. We further observe that POU5F1 expression is directly correlated with POU5F1B expression. Our results suggest that a pathway critical to self-renewal of embryonic stem cells may also have a role in the origin of cancer.

Reovirus cell entry requires functional microtubules.

UNLABELLED: Mammalian reovirus binds to cell-surface glycans and junctional adhesion molecule A and enters cells by receptor-mediated endocytosis in a process dependent on ß1 integrin. Within the endocytic compartment, reovirus undergoes stepwise disassembly, allowing release of the transcriptionally active viral core into the cytoplasm. To identify cellular mediators of reovirus infectivity, we screened a library of small-molecule inhibitors for the capacity to block virus-induced cytotoxicity. In this screen, reovirus-induced cell killing was dampened by several compounds known to impair microtubule dynamics. Microtubule inhibitors were assessed for blockade of various stages of the reovirus life cycle. While these drugs did not alter reovirus cell attachment or internalization, microtubule inhibitors diminished viral disassembly kinetics with a concomitant decrease in infectivity. Reovirus virions colocalize with microtubules and microtubule motor dynein 1 during cell entry, and depolymerization of microtubules results in intracellular aggregation of viral particles. These data indicate that functional microtubules are required for proper sorting of reovirus virions following internalization and point to a new drug target for pathogens that use the endocytic pathway to invade host cells. IMPORTANCE: Screening libraries of well-characterized drugs for antiviral activity enables the rapid characterization of host processes required for viral infectivity and provides new therapeutic applications for established pharmaceuticals. Our finding that microtubule-inhibiting drugs impair reovirus infection identifies a new cell-based antiviral target.

A high-throughput fluorescence polarization anisotropy assay for the 70N domain of replication protein A.

Replication protein A (RPA) interacts with multiple checkpoint proteins and promotes signaling through the ATR kinase, a key regulator of checkpoint pathways in the mammalian response to DNA damage. In cancer cells, increased DNA repair activity contributes to resistance to chemotherapy. Therefore, small molecules that block binding of checkpoint proteins to RPA may inhibit the DNA damage response and, thus, sensitize cancer cells to DNA-damaging agents. Here we report on the development of a homogeneous, high-throughput fluorescence polarization assay for identifying compounds that block the critical protein-protein interaction site in the basic cleft of the 70N domain of RPA (RPA70N). A fluorescein isothiocyanate (FITC)-labeled peptide derived from the ATR cofactor, ATRIP, was used as a probe in the binding assay. The ability of the assay to accurately detect relevant ligands was confirmed using peptides derived from ATRIP, RAD9, MRE11, and p53. The assay was validated for use in high-throughput screening using the Spectrum collection of 2000 compounds. The FPA assay was performed with a Z' factor of ≥ 0.76 in a 384-well format and identified several compounds capable of inhibiting the RPA70N binding interface.