Functional classification of drugs by properties of their pairwise interactions

Multidrug treatments are increasingly important in medicine and for probing biological systems. Although many studies have focused on interactions between specific drugs, little is known about the system properties of a full drug interaction network. Like their genetic counterparts, two drugs may have no interaction, or they may interact synergistically or antagonistically to increase or suppress their individual effects. Here we use a sensitive bioluminescence technique to provide quantitative measurements of pairwise interactions among 21 antibiotics that affect growth rate in Escherichia coli. We find that the drug interaction network possesses a special property: it can be separated into classes of drugs such that any two classes interact either purely synergistically or purely antagonistically. These classes correspond directly to the cellular functions affected by the drugs. This network approach provides a new conceptual framework for understanding the functional mechanisms of drugs and their cellular targets and can be applied in systems intractable to mutant screening, biochemistry or microscopy.     

Let-7b is a novel regulator of hepatitis C virus replication

The non-coding microRNA (miRNA) is involved in the regulation of hepatitis C virus (HCV) infection and offers an alternative target for developing anti-HCV agent. In this study, we aim to identify novel cellular miRNAs that directly target the HCV genome with anti-HCV therapeutic potential. Bioinformatic analyses were performed to unveil liver-abundant miRNAs with predicted target sequences on HCV genome. Various cell-based systems confirmed that let-7b plays a negative role in HCV expression. In particular, let-7b suppressed HCV replicon activity and down-regulated HCV accumulation leading to reduced infectivity of HCVcc. Mutational analysis identified let-7b binding sites at the coding sequences of NS5B and 5'-UTR of HCV genome that were conserved among various HCV genotypes. We further demonstrated that the underlying mechanism for let-7b-mediated suppression of HCV RNA accumulation was not dependent on inhibition of HCV translation. Let-7b and IFNα-2a also elicited a synergistic inhibitory effect on HCV infection. Together, let-7b represents a novel cellular miRNA that targets the HCV genome and elicits anti-HCV activity. This study thereby sheds new insight into understanding the role of host miRNAs in HCV pathogenesis and to developing a potential anti-HCV therapeutic strategy.     

Local generation of glia is a major astrocyte source in postnatal cortex

Glial cells constitute nearly 50% of the cells in the human brain. Astrocytes, which make up the largest glial population, are crucial to the regulation of synaptic connectivity during postnatal development. Because defects in astrocyte generation are associated with severe neurological disorders such as brain tumours, it is important to understand how astrocytes are produced. Astrocytes reportedly arise from two sources: radial glia in the ventricular zone and progenitors in the subventricular zone, with the contribution from each region shifting with time. During the first three weeks of postnatal development, the glial cell population, which contains predominantly astrocytes, expands 6-8-fold in the rodent brain. Little is known about the mechanisms underlying this expansion. Here we show that a major source of glia in the postnatal cortex in mice is the local proliferation of differentiated astrocytes. Unlike glial progenitors in the subventricular zone, differentiated astrocytes undergo symmetric division, and their progeny integrate functionally into the existing glial network as mature astrocytes that form endfeet with blood vessels, couple electrically to neighbouring astrocytes, and take up glutamate after neuronal activity.     

Structure prediction for the down state of a potassium channel voltage sensor

Voltage-gated potassium (Kv) channels, essential for regulating potassium uptake and cell volume in plants and electrical excitability in animals, switch between conducting and non-conducting states as a result of conformational changes in the four voltage-sensing domains (VSDs) that surround the channel pore. This process, known as gating, is initiated by a cluster of positively charged residues on the fourth transmembrane segment (S4) of each VSD, which drives the VSD into a 'down state' at negative voltages and an 'up state' at more positive voltages. The crystal structure of Kv1.2 probably corresponds to the up state, but the local environment of S4 in the down state and its motion in voltage gating remains unresolved. Here we employed several conditional lethal/second-site suppressor yeast screens to determine the transmembrane packing of the VSD in the down state. This screen relies on the ability of KAT1, a eukaryotic Kv channel, to conduct potassium when its VSDs are in the down state, thereby rescuing potassium-transport-deficient yeast. Starting with KAT1 channels bearing conditional lethal mutations, we identified second-site suppressor mutations throughout the VSD that recover yeast growth. We then constructed a down state model of the channel using six pairs of interacting residues as structural constraints and verified this model by engineering suppressor mutations on the basis of spatial considerations. A comparison of this down state model with the up state Kv1.2 structure suggests that the VSDs undergo large rearrangements during gating, whereas the S4 segment remains positioned between the central pore and the remainder of the VSD in both states.     

Object replication and CORBA fault-tolerant object service

CORBA (Common Object Request Broker Architecture) provides 16 Common Object Services for distributed application development, but none of them are fault-tolerance related services. In this paper, we propose a replicated object based Fault-Tolerant Object Service (FTOS) for CORBA environment. Two fault-tolerant mechanisms are provided in FTOS including dynamic voting mechanism and object replication mechanism. The dynamic voting mechanism uses majority-voting strategy to ensure object state consistency in failure situations. The object replication mechanism can help system administrators to replicate and start-up objects easily. Our implementation provides a library according to the style of COSS. With this library, programmers can develop distributed applications with fault-tolerance capability very easily.     

Cleavage of active peptides by a lung enzyme

Zusammenfassung Ein Enzym (Angiotensin I «converting enzyme» oder Kininase II; DH) wurde aus Schweinelungen isoliert und gereinigt. DH splatet Dipeptide vom Carboxyterminus der Peptidsubstrate mit Einschluss von Bradykinin, Angiotensin I, B-Kette von Insulin und¹⁴C-DNS-Gly-Gly-Gly. Zu den besten Inhibitoren des Enzyms gehören zwei kürzlich synthetisierte Peptide sowie Glutathion und Insulin. Die Experimente deuten auf ein einziges Enzym hin, das alle erwähnten Substrate hydrolysiert.

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Supported in part by grants No. HE 08764 and No. 5T01 HE 05859 from N.I.H., U.S.P.H.S. and by the O.N.R. No. N00014-68-A-0496 and No. N00014-69-A-0385.

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During the tenure of a fellowship of the Oklahoma Heart Association.

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Acknowledgements. MissDeborah Downs assisted us in some of the experiments. HHL was donated by Dr.D. Cushman of the Squibb Institute.     

The sensitivity to plasmin digestion of human IgG proteins of different heavy chain subclasses

Summary Normal IgG and purified IgG proteins of all 4 subclasses were digested with plasmin. As expected, IgG₃ proteins were highly susceptible to degradation. Usually, activation with streptokinase resulted in faster and more accentuated degradation, but normal IgG was more intensely degraded by nonactivated plasmin. The presence of plasmin activators in IgG preparations might account for this observation.This is publication no. 125 from the Department of Basic and Clinical Immunology and Microbiology, Medical University of South Carolina.Acknowledgments. The authors with to express their gratitude to Mr Charles L. Smith for excellent editorial assistance and to Mrs Louise B. Just for photographic work. Research supported in part by ACS Grant IM-161.