siRNA-directed inhibition of HIV-1 infection

RNA interference silences gene expression through short interfering 21 23-mer double-strand RNA segments that guide mRNA degradation in a sequence-specific fashion. Here we report that siRNAs inhibit virus production by targeting the mRNAs for either the HIV-1 cellular receptor CD4, the viral structural Gag protein or green fluorescence protein substituted for the Nef regulatory protein. siRNAs effectively inhibit pre- and/or post-integration infection events in the HIV-1 life cycle. Thus, siRNAs may have potential for therapeutic intervention in HIV-1 and other viral infections.     

The p47 GTPase Lrg-47 (Irgm1) links host defense and hematopoietic stem cell proliferation

Hematopoietic stem cells (HSCs) are self-renewing bone marrow cells that give rise to all blood lineages and retain a remarkable capacity to proliferate in response to insult. Although some controls on HSC activation are known, little is understood about how this process is linked to natural signals. We report that the interferon-inducible GTPase Lrg-47 (Irgm1), previously shown to play a critical role in host defense, inhibits baseline HSC proliferation and is required for a normal HSC response to chemical and infectious stimuli. Overproliferating Lrg-47(-/-) HSCs are severely impaired in functional repopulation assays, and when challenged with hematopoietic ablation by 5-fluorouracil or infection with Mycobacterium avium, Lrg-47(-/-) mice fail to achieve the expected expansion response in stem and progenitor cell populations. Our results establish a link between the response to infection and HSC activation and demonstrate a novel function for a member of the p47 GTPase family.     

Terrequinone A biosynthesis through L-tryptophan oxidation, dimerization and bisprenylation

The antitumor fungal metabolite terrequinone A, identified in extracts of Aspergillus sp., is biosynthesized by the five-gene cluster tdiA-tdiE. In this work, we have overproduced all five proteins (TdiA-TdiE) in the bacterial host Escherichia coli, fully reconstituting the biosynthesis of terrequinone A. This pathway involves aminotransferase activity, head-to-tail dimerization and bisprenylation of the scaffold to yield the benzoquinone natural product. We have established that TdiD is a pyridoxal-5'-phosphate-dependent L-tryptophan aminotransferase that generates indolepyruvate for an unusual nonoxidative coupling by the tridomain nonribosomal peptide synthetase TdiA. TdiC, an NADH-dependent quinone reductase, generates the nucleophilic hydroquinone for two distinct rounds of prenylation by the single prenyltransferase TdiB. TdiE is required to shunt the benzoquinone away from an off-pathway monoprenylated species by an as yet unknown mechanism. Overall, we have biochemically characterized the complete biosynthetic pathway to terrequinone A, highlighting the nonoxidative dimerization pathway and the unique asymmetric prenylation involved in its maturation.     

Quorum-sensing regulation in rhizobia and its role in symbiotic interactions with legumes

Legume-nodulating bacteria (rhizobia) usually produce N-acyl homoserine lactones, which regulate the induction of gene expression in a quorum-sensing (or population-density)-dependent manner. There is significant diversity in the types of quorum-sensing regulatory systems that are present in different rhizobia and no two independent isolates worked on in detail have the same complement of quorum-sensing genes. The genes regulated by quorum sensing appear to be rather diverse and many are associated with adaptive aspects of physiology that are probably important in the rhizosphere. It is evident that some aspects of rhizobial physiology related to the interaction between rhizobia and legumes are influenced by quorum sensing. However, it also appears that the legumes play an active role, both in terms of interfering with the rhizobial quorum-sensing systems and responding to the signalling molecules made by the bacteria. In this article, we review the diversity of quorum-sensing regulation in rhizobia and the potential role of legumes in influencing and responding to this signalling system.     

Synthesis and identification of novel oxa-steroids as progesterone receptor antagonists

A novel series of oxa-steroids 6 derived from (8S, 13S, 14R)-7-oxa-estra-4,9-diene-3,17-dione 1 have been synthesized and identified as potent and selective progesterone receptor antagonists. These novel oxa-steroids showed similar potency to mifepristone. Preliminary SAR study resulted in the most potent 17-phenylethynyl oxa-steroid 6i wih an IC(50) of 1.4nM. In contrast to the equipotent mifepristone toward the progesterone receptor (PR) and glucocorticoid receptor (GR), compound 6i had over 200-fold selectivity for PR over GR.