Jong-Won Oh

New Thermophilic and Thermostable Esterase with Sequence Similarity to the Hormone-Sensitive Lipase Family, Cloned from a Metagenomic Library

ABSTRACT A gene coding for a thermostable esterase was isolated by functional screening of Escherichia coli cells that had been transformed with fosmid environmental DNA libraries constructed with metagenomes from thermal environmental samples. The gene conferring esterase activity on E. coli grown on tributyrin agar was composed of 936 bp, corresponding to 311 amino acid residues with a molecular mass of 34 kDa. The enzyme showed significant amino acid similarity (64%) to the enzyme from a hyperthermophilic archaeon, Pyrobaculum calidifontis. An amino acid sequence comparison with other esterases and lipases revealed that the enzyme should be classified as a new member of the hormone-sensitive lipase family. The recombinant esterase that was overexpressed and purified from E. coli was active above 30°C up to 95°C and had a high thermal stability. It displayed a high degree of activity in a pH range of 5.5 to 7.5, with an optimal pH of approximately 6.0. The best substrate for the enzyme among the p-nitrophenyl esters (C4 to C16) examined was p-nitrophenyl caproate (C6), and no lipolytic activity was observed with esters containing an acyl chain length of longer than 10 carbon atoms, indicating that the enzyme is an esterase and not a lipase.

Liver Extracellular Matrix Providing Dual Functions of Two-Dimensional Substrate Coating and Three-Dimensional Injectable Hydrogel Platform for Liver Tissue Engineering

Decellularization of tissues or organs can provide an efficient strategy for preparing functional scaffolds for tissue engineering. Microstructures of native extracellular matrices and their biochemical compositions can be retained in the decellularized matrices, providing tissue-specific microenvironments for efficient tissue regeneration. Here, we report the versatility of liver extracellular matrix (LEM) that can be used for two-dimensional (2D) coating and three-dimensional (3D) hydrogel platforms for culture and transplantation of primary hepatocytes. Collagen type I (Col I) has typically been used for hepatocyte culture and transplantation. In this study, LEM was compared with Col I in terms of biophysical and mechanical characteristics and biological performance for enhancing cell viability, differentiation, and hepatic functions. Surface properties of LEM coating and mechanical properties and gelation kinetics of LEM hydrogel could be manipulated by adjusting the LEM concentration. In addition, LEM hydrogel exhibited improved elastic properties, rapid gelation, and volume maintenance compared to Col I hydrogel. LEM coating significantly improved hepatocyte functions such as albumin secretion and urea synthesis. More interestingly, LEM coating upregulated hepatic gene expression of human adipose-derived stem cells, indicating enhanced hepatic differentiation of these stem cells. The viability and hepatic functions of primary hepatocytes were also significantly improved in LEM hydrogel compared to Col I hydrogel both in vitro and in vivo. Albumin and hepatocyte transcription factor expression was upregulated in hepatocytes transplanted in LEM hydrogels. In conclusion, LEM can provide functional biomaterial platforms for diverse applications in liver tissue engineering by promoting survival and maturation of hepatocytes and hepatic commitment of stem cells. This study demonstrates the feasibility of decellularized matrix for both 2D coating and 3D hydrogel in liver tissue engineering.

Protein Kinase C-related Kinase 2 Regulates Hepatitis C Virus RNA Polymerase Function by Phosphorylation

The hepatitis C virus (HCV) NS5B protein is the viral RNA-dependent RNA polymerase required for replication of the HCV RNA genome. We have identified a peptide that most closely resembles a short region of the protein kinase C-related kinase 2 (PRK2) by screening of a random 12-mer peptide library displayed on the surface of the M13 bacteriophage with NS5B proteins immobilized on microwell plates. Competitive phage enzyme-linked immunosorbent assay with a synthetic peptide showed that the phage clone displaying this peptide could bind HCV RNA polymerase with a high affinity. Coimmunoprecipitation and colocalization studies demonstrated in vivo interaction of NS5B with PRK2. In vitro kinase assays demonstrated that PRK2 specifically phosphorylates NS5B by interaction with the N-terminal finger domain of NS5B (amino acids 1–187). Consistent with the in vitro NS5B-phosphorylating activity of PRK2, we detected the phosphorylated form of NS5B by metabolic cell labeling. Furthermore, HCV NS5B immunoprecipitated from HCV subgenomic replicon cells was specifically recognized by an antiphosphoserine antibody. Knock-down of the endogenous PRK2 expression using a PRK2-specific small interfering RNA inhibited HCV RNA replication. In contrast, PRK2 overexpression, which was accompanied by an increase of in the level of its active form, dramatically enhanced HCV RNA replication. Altogether, our results indicate that HCV RNA replication is regulated by NS5B phosphorylation by PRK2.

Reciprocal expressions of cyclin E and cyclin D1 in hepatocellular carcinoma

Deregulation of the cell cycle by overexpression of G1 cyclins, cyclin E and cyclin D1 genes, has been demonstrated to be a prerequisite for the development of human cancer. Recently, cyclin E is proposed to be sufficient for the progression of the G1 cell cycle without cyclin D1. Here we show that the proposed model system was specifically present in human hepatocellular carcinoma (HCC) unlike other human cancers. Of 31 HCC tissues analyzed, 21 (67.7%) exhibited an overexpression of cyclin E protein. In contrast to cyclin E gene expression, cyclin D1 expression was strongly downregulated in 19 (61.2%) HCCs. Interestingly, 65% of HCC tissues with overexpression of the cyclin E gene exhibited downregulation of cyclin D1, suggesting reciprocal deregulation of these cyclins in the G1 progression of the cell cycle. Southern blot analysis proved the amplification of cyclin E gene in HCC with a high level of overexpression. The present findings suggest that the reciprocal deregulation of cyclin E lacking cyclin D1 expression might play a role in G1 progression and the development of HCC.

Interaction of hepatitis C virus core protein with Hsp60 triggers the production of reactive oxygen species and enhances TNF-α-mediated apoptosis

The hepatitis C virus (HCV) core protein is the primary protein component of the nucleocapsid that encapsidates the viral RNA genome. Besides its role as a viral structural protein, the core protein is implicated in HCV chronic infection-associated liver diseases by induction of reactive oxygen species (ROS) production and modulation of apoptosis. Here, we show that interaction of the core protein, through its N-terminal domain (amino acids 1-75), with heat shock protein (Hsp60) is critical for the induction of ROS production, leading to sensitization of core protein-expressing cells to apoptosis induced by tumor necrosis factor-alpha (TNF-alpha). Moreover, overexpression of Hsp60 rescued the core protein-expressing cells from cell death by reducing ROS production. Collectively, our results suggest that impairment of Hsp60 function through binding of HCV core protein contributes to HCV viral pathogenesis by ROS generation and amplification of the apoptotic effect of TNF-alpha.

Troglitazone activates p21Cip/WAF1 through the ERK pathway in HCT15 human colorectal cancer cells

In this study, we identified a new mechanism for the anti-proliferation of HCT15 colorectal cancer cells by troglitazone (TRO). Treating HCT15 cells with 20 microM of TRO transiently increased extracellular signal regulated kinase (ERK) activity within 15 min, and this subsequently induced p21Cip/WAF1 cell cycle regulator and localized in the nucleus. Raf-1 modification and MEK activation also occurred after TRO treatment, and Elk-1-dependent trans-reporter gene expression was concomitantly induced. The induction and nuclear localization of p21Cip/WAF1 by TRO were blocked by PD98059 pre-treatment, which suggested a role for the ERK pathway in p21Cip/WAF1 activation. TRO inhibited BrdU incorporation and no BrdU incorporation was observed in most p21Cip/WAF1-activated cells. Therefore, TRO regulates the proliferation of HCT15 cells at least partly by a mechanism involving the activation of p21Cip/WAF1.

Interference of ribosomal frameshifting by antisense peptide nucleic acids suppresses SARS coronavirus replication.

Abstract The programmed −1 ribosomal frameshifting (−1 PRF) utilized by eukaryotic RNA viruses plays a crucial role for the controlled, limited synthesis of viral RNA replicase polyproteins required for genome replication. The viral RNA replicase polyproteins of severe acute respiratory syndrome coronavirus (SARS-CoV) are encoded by the two overlapping open reading frames 1a and 1b, which are connected by a −1 PRF signal. We evaluated the antiviral effects of antisense peptide nucleic acids (PNAs) targeting a highly conserved RNA sequence on the – PRF signal. The ribosomal frameshifting was inhibited by the PNA, which bound sequence-specifically a pseudoknot structure in the −1 PRF signal, in cell lines as assessed using a dual luciferase-based reporter plasmid containing the −1 PRF signal. Treatment of cells, which were transfected with a SARS-CoV-replicon expressing firefly luciferase, with the PNA fused to a cell-penetrating peptide (CPP) resulted in suppression of the replication of the SARS-CoV replicon, with a 50% inhibitory concentration of 4.4μM. There was no induction of type I interferon responses by PNA treatment, suggesting that the effect of PNA is not due to innate immune responses. Our results demonstrate that −1 PRF, critical for SARS-CoV viral replication, can be inhibited by CPP-PNA, providing an effective antisense strategy for blocking −1 PRF signals.

Lipoteichoic acid of Enterococcus faecalis induces the expression of chemokines via TLR2 and PAFR signaling pathways

Enterococcus faecalis is one of the most common opportunistic pathogens responsible for nosocomial infections, and its LTA is known as an important virulence factor causing inflammatory responses. As chemokines play a key role in inflammatory diseases by triggering leukocyte infiltration into the infection site, we purified EfLTA and investigated its effect on the expression of chemokines, IP‐10, MIP‐1α, and MCP‐1, in murine macrophages. EfLTA induced the expression of these chemokines at the mRNA and protein levels. TLR2, CD14, and MyD88 were involved in the EfLTA‐induced chemokine expression, as the expression was reduced remarkably in macrophages derived from TLR2‐, CD14‐, or MyD88‐deficient mice. EfLTA induced phosphorylation of MAPKs and enhanced the DNA‐binding activity of NF‐κB, AP‐1, and NF‐IL6 transcription factors. The induction of IP‐10 required ERK, JNK, p38 MAPK, PKC, PTK, PI3K, and ROS. We noticed that all of these signaling molecules, except p38 MAPK and ROS, were indispensable for the induction of MCP‐1 and MIP‐1α. Interestingly, the EfLTA‐induced chemokine expression was mediated through PAFR/JAK/STAT1 signaling pathways without IFN‐β involvement, which is different from LPS‐induced chemokine expression requiring IFN‐β/JAK/STAT1 signaling pathways. Furthermore, the culture supernatant of EfLTA‐treated RAW 264.7 cells promoted the platelet aggregation, and exogenous PAF induced the chemokine expression in macrophages derived from WT and TLR2‐deficient mice. These results suggest that EfLTA induces the expression of chemokines via signaling pathways requiring TLR2 and PAFR, which is distinct from that of LPS‐induced chemokine expression.

NM23H2 inhibits EGF- and Ras-induced proliferation of NIH3T3 cells by blocking the ERK pathway

The NM23 family proteins are involved in a variety of biological processes including tumor metastasis, development, and differentiation; however, their functions in the regulation of cellular proliferation are poorly understood. We have investigated the role of one NM23 family protein, NM23H2, in the regulation of cellular proliferation directed by the extracellular signal regulated kinase (ERK) pathway. The activity of ERKs was enhanced by knockdown of endogenous NM23H2 and blocked by overexpression of NM23H2 in both NIH3T3 and HEK293 cells. Additionally, the epidermal growth factor (EGF)- and oncogenic Ras(G12R)-induced proliferation of both HEK293 and NIH3T3 cells was reduced by NM23H2 overexpression. Furthermore, activation of Raf-1, MEK and the ERKs by either EGF or Ras(G12R) was inhibited by NM23H2 overexpression. Together, our data indicate that NM23H2 is a negative regulator of cellular proliferation stimulated by EGF- and Ras-mediated activation of the ERK pathway.

A thermodynamic study of mesophilic, thermophilic, and hyperthermophilic L-arabinose isomerases: The effects of divalent metal ions on protein stability at elevated temperatures

To gain insight into the structural stability of homologous homo‐tetrameric l‐arabinose isomerases (AI), we have examined the isothermal guanidine hydrochloride (GdnHCl)‐induced unfolding of AIs from mesophilic Bacillus halodurans (BHAI), thermophilic Geobacillus stearothermophilus (GSAI), and hyperthermophilic Thermotoga maritima (TMAI) using circular dichroism spectroscopy. The GdnHCl‐induced unfolding of the AIs can be well described by a two‐state reaction between native tetramers and unfolded monomers, which directly confirms the validity of the linear extrapolation method to obtain the intrinsic stabilities of these proteins. The resulting unfolding free energy (ΔG U) values of the AIs as a function of temperature were fit to the Gibbs–Helmholtz equation to determine their thermodynamic parameters based on a two‐state mechanism. Compared with the stability curves of BHAI in the presence and absence of Mn2+, those of holo GSAI and TMAI were more broadened than those of the apo enzymes at all temperatures, indicating increased melting temperatures (T m) due to decreased heat capacity (ΔC p). Moreover, the extent of difference in ΔC p between the apo and holo thermophilic AIs is larger than that of BHAI. From these studies, we suggest that the metal dependence of the thermophilic AIs, resulting in the reduced ΔC p, may play a significant role in structural stability compared to their mesophilic analogues, and that the extent of metal dependence of AI stability seems to be highly correlated to oligomerization.