Chih-Tai Leu

HIV-1 protease specificity of peptide cleavage is sufficient for processing of gag and pol polyproteins.

The mature proteins of retroviruses originate as a result of proteolytic cleavages of polyprotein precursors. Retroviruses encode proteases responsible for several of these processing events, making them potential antiviral drug targets. A 99-amino acid HIV-1 protease, produced by chemical synthesis or by expression in bacteria, is shown here to hydrolyze peptides corresponding to all of the known cleavage sites in the HIV-1 gag and pol polyproteins. It does not hydrolyze peptides corresponding to an env cleavage site or a distantly related retroviral gag cleavage site.

A Regulatory Circuit Mediating Convergence between Nurr1 Transcriptional Regulation and Wnt Signaling

ABSTRACT The orphan nuclear receptor Nurr1 is essential for the development and maintenance of midbrain dopaminergic neurons, the cells that degenerate during Parkinsons disease, by promoting the transcription of genes involved in dopaminergic neurotransmission. Since Nurr1 lacks a classical ligand-binding pocket, it is not clear which factors regulate its activity and how these factors are affected during disease pathogenesis. Since Wnt signaling via β-catenin promotes the differentiation of Nurr1+ dopaminergic precursors in vitro, we tested for functional interactions between these systems. We found that β-catenin and Nurr1 functionally interact at multiple levels. In the absence of β-catenin, Nurr1 is associated with Lef-1 in corepressor complexes. β-Catenin binds Nurr1 and disrupts these corepressor complexes, leading to coactivator recruitment and induction of Wnt- and Nurr1-responsive genes. We then identified KCNIP4/calsenilin-like protein as being responsive to concurrent activation by Nurr1 and β-catenin. Since KCNIP4 interacts with presenilins, the Alzheimers disease-associated proteins that promote β-catenin degradation, we tested the possibility that KCNIP4 induction regulates β-catenin signaling. KCNIP4 induction limited β-catenin activity in a presenilin-dependent manner, thereby serving as a negative feedback loop; furthermore, Nurr1 inhibition of β-catenin activity was absent in PS1−/− cells or in the presence of small interfering RNAs specific to KCNIP4. These data describe regulatory convergence between Nurr1 and β-catenin, providing a mechanism by which Nurr1 could be regulated by Wnt signaling.

Discovery of the Selective Androgen Receptor Modulator MK-0773 Using a Rational Development Strategy Based on Differential Transcriptional Requirements for Androgenic Anabolism Versus Reproductive Physiology

Selective androgen receptor modulators (SARMs) are androgen receptor (AR) ligands that induce anabolism while having reduced effects in reproductive tissues. In various experimental contexts SARMs fully activate, partially activate, or even antagonize the AR, but how these complex activities translate into tissue selectivity is not known. Here, we probed receptor function using >1000 synthetic AR ligands. These compounds produced a spectrum of activities in each assay ranging from 0 to 100% of maximal response. By testing different classes of compounds in ovariectomized rats, we established that ligands that transactivated a model promoter 40–80% of an agonist, recruited the coactivator GRIP-1 <15%, and stabilized the N-/C-terminal interdomain interaction <7% induced bone formation with reduced effects in the uterus and in sebaceous glands. Using these criteria, multiple SARMs were synthesized including MK-0773, a 4-aza-steroid that exhibited tissue selectivity in humans. Thus, AR activated to moderate levels due to reduced cofactor recruitment, and N-/C-terminal interactions produce a fully anabolic response, whereas more complete receptor activation is required for reproductive effects. This bimodal activation provides a molecular basis for the development of SARMs.

Design, synthesis, and biological evaluation of 16-substituted 4-azasteroids as tissue-selective androgen receptor modulators (SARMs).

A novel series of 16-substituted-4-azasteroids has been identified as potential tissue-selective androgen receptor modulators. These ligands display potent hAR binding and agonist activity, low virilizing potential, and good pharmacokinetic profiles in dogs. On the basis of its in vitro profile, 21 was evaluated in the OVX and ORX rat models and exhibited an osteoanabolic, tissue-selective profile.

Interaction of Mutant Forms of the HIV-1 Protease with Substrate and Inhibitors

The protease of HIV-1 is considered to be a prime target for the treatment of AIDS with small molecular weight inhibitors. 1,2,3 Many groups have now demonstrated that compounds designed as potent inhibitors of the enzyme in vitro are effective inhibitors of viral polyprotein processing and viral spread in cultured cells.4–7 Continued effort to discover new potent inhibitors with suitable properties for use in humans is thus justified.

Retraction for Kitagawa et al., A Regulatory Circuit Mediating Convergence between Nurr1 Transcriptional Regulation and Wnt Signaling

Hirochika Kitagawa, William J. Ray, Helmut Glantschnig, Pascale V. Nantermet, Yuanjiang Yu, Chih-Tai Leu, Shun-ichi Harada, Shigeaki Kato, Leonard P. Freedman Department of Molecular Endocrinology, Merck Research Laboratories, West Point, Pennsylvania, USA; Institute of Molecular and Cellular Biosciences, University of Tokyo, Bunkyo-ku, Tokyo, Japan; ERATO, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan