Ji Young Hyun

A Small Molecule Inhibitor of ATPase Activity of HSP70 Induces Apoptosis and Has Antitumor Activities

The heat shock protein HSP70 plays antiapoptotic and oncogenic roles, and thus its inhibition has been recognized as a potential avenue for anticancer therapy. Here we describe the small molecule, apoptozole (Az), which inhibits the ATPase activity of HSP70 by binding to its ATPase domain and, as a result, induces an array of apoptotic phenotypes in cancer cells. Affinity chromatography provides evidence that Az binds HSP70 but not other types of heat shock proteins including HSP40, HSP60, and HSP90. We also demonstrate that Az induces cancer cell death via caspase-dependent apoptosis by disrupting the interaction of HSP70 with APAF-1. Animal studies indicate that Az treatment retards tumor growth in a xenograft mouse model without affecting mouse viability. These studies suggest that Az will aid the development of new cancer therapies and serve as a chemical probe to gain a better understanding of the diverse functions of HSP70.

Screening of Pre-miRNA-155 Binding Peptides for Apoptosis Inducing Activity Using Peptide Microarrays

MicroRNA-155, one of the most potent miRNAs that suppress apoptosis in human cancer, is overexpressed in numerous cancers, and it displays oncogenic activity. Peptide microarrays, constructed by immobilizing 185 peptides containing the C-terminal hydrazide onto epoxide-derivatized glass slides, were employed to evaluate peptide binding properties of pre-miRNA-155 and to identify its binding peptides. Two peptides, which were identified based on the results of peptide microarray and in vitro Dicer inhibition studies, were found to inhibit generation of mature miRNA-155 catalyzed by Dicer and to enhance expression of miRNA-155 target genes in cells. In addition, the results of cell experiments indicate that peptide inhibitors promote apoptotic cell death via a caspase-dependent pathway. Finally, observations made in NMR and molecular modeling studies suggest that a peptide inhibitor preferentially binds to the upper bulge and apical stem-loop region of pre-miRNA-155, thereby suppressing Dicer-mediated miRNA-155 processing.

Suppression of Sin3A activity promotes differentiation of pluripotent cells into functional neurons

Sin3 is a transcriptional corepressor for REST silencing machinery that represses multiple neuronal genes in non-neuronal cells. However, functions of Sin3 (Sin3A and Sin3B) in suppression of neuronal phenotypes are not well characterized. Herein we show that Sin3A knockdown impedes the repressive activity of REST and enhances differentiation of pluripotent P19 cells into electrophysiologically active neurons without inducing astrogenesis. It is also found that silencing Sin3B induces neurogenesis of P19 cells with a lower efficiency than Sin3A knockdown. The results suggest that Sin3A has a more profound effect on REST repressive machinery for silencing neuronal genes in P19 cells than Sin3B. Furthermore, we show that a peptide inhibitor of Sin3A-REST interactions promotes differentiation of P19 cells into functional neurons. Observations made in studies using genetic deletion and a synthetic inhibitor suggests that Sin3A plays an important role in the repression of neuronal genes by the REST regulatory mechanism.

The Glycan Microarray Story from Construction to Applications

Not only are glycan-mediated binding processes in cells and organisms essential for a wide range of physiological processes, but they are also implicated in various pathological processes. As a result, elucidation of glycan-associated biomolecular interactions and their consequences is of great importance in basic biological research and biomedical applications. In 2002, we and others were the first to utilize glycan microarrays in efforts aimed at the rapid analysis of glycan-associated recognition events. Because they contain a number of glycans immobilized in a dense and orderly manner on a solid surface, glycan microarrays enable multiple parallel analyses of glycan-protein binding events while utilizing only small amounts of glycan samples. Therefore, this microarray technology has become a leading edge tool in studies aimed at elucidating roles played by glycans and glycan binding proteins in biological systems. In this Account, we summarize our efforts on the construction of glycan microarrays and their applications in studies of glycan-associated interactions. Immobilization strategies of functionalized and unmodified glycans on derivatized glass surfaces are described. Although others have developed immobilization techniques, our efforts have focused on improving the efficiencies and operational simplicity of microarray construction. The microarray-based technology has been most extensively used for rapid analysis of the glycan binding properties of proteins. In addition, glycan microarrays have been employed to determine glycan-protein interactions quantitatively, detect pathogens, and rapidly assess substrate specificities of carbohydrate-processing enzymes. More recently, the microarrays have been employed to identify functional glycans that elicit cell surface lectin-mediated cellular responses. Owing to these efforts, it is now possible to use glycan microarrays to expand the understanding of roles played by glycans and glycan binding proteins in biological systems.

Carbohydrate Analogue Microarrays for Identification of Lectin-Selective Ligands

Fifty‐five mono‐ and disaccharide analogues were prepared and used for the construction of microarrays to uncover lectin‐selective ligands. The microarray study showed that two disaccharide analogues, 28′ and 44′, selectively bind to Solanum tuberosum lectin (STL) and wheat germ agglutinin (WGA), respectively. Cell studies indicated that 28′ and 44′ selectively block the binding of STL and WGA to mammalian cells, unlike the natural ligand LacNAc, which suppresses binding of both STL and WGA to cells.

Carbohydrate Microarrays Containing Glycosylated Fluorescent Probes for Assessment of Glycosidase Activities

Carbohydrate microarrays, containing glycosylated fluorescent probes, have been constructed using N-hydroxysuccinimide (NHS) ester-conjugated BSA modified surfaces. When the carbohydrate moieties were cleaved from the fluorescent probes in the conjugates by glycosidases, the fluorescence signals of the probes were enhanced. In this study, we have applied these microarrays to profile glycosidase activities and have employed them to determine IC50 values of glycosidase inhibitors.