Anticolon Cancer Effect of Korean Red Ginseng via Autophagy- and Apoptosis-Mediated Cell Death

Ginseng (Panax ginseng Meyer) has been used in East Asian traditional medicine for a long time. Korean red ginseng (KRG) is effective against several disorders, including cancer. The cytotoxic effects of KRG extract in terms of autophagy- and apoptosis-mediated cell death and its mechanisms were investigated using human colorectal cancer lines. KRG induced autophagy-mediated cell death with enhanced expression of Atg5, Beclin-1, and LC3, and formed characteristic vacuoles in HCT-116 and SNU-1033 cells. An autophagy inhibitor prevented cell death induced by KRG. KRG generated mitochondrial reactive oxygen species (ROS); antioxidant countered this effect and decreased autophagy. KRG caused apoptotic cell death by increasing apoptotic cells and sub-G₁ cells, and by activating caspases. A caspase inhibitor suppressed cell death induced by KRG. KRG increased phospho-Bcl-2 expression, but decreased Bcl-2 expression. Moreover, interaction of Bcl-2 with Beclin-1 was attenuated by KRG. Ginsenoside Rg2 was the most effective ginsenoside responsible for KRG-induced autophagy- and apoptosis-mediated cell death. KRG induced autophagy- and apoptosis-mediated cell death via mitochondrial ROS generation, and thus its administration may inhibit colon carcinogenesis.

Reduced Autophagy in 5-Fluorouracil Resistant Colon Cancer Cells

We investigated the role of autophagy in SNUC5/5-FUR, 5-fluorouracil (5-FU) resistant SNUC5 colon cancer cells. SNUC5/5-FUR cells exhibited low level of autophagy, as determined by light microscopy, confocal microscopy, and flow cytometry following acridine orange staining, and the decreased level of GFP-LC3 puncta. In addition, expression of critical autophagic proteins such as Atg5, Beclin-1 and LC3-II and autophagic flux was diminished in SNUC5/5-FUR cells. Whereas production of reactive oxygen species (ROS) was significantly elevated in SNUC5/5-FUR cells, treatment with the ROS inhibitor N-acetyl cysteine further reduced the level of autophagy. Taken together, these results indicate that decreased autophagy is linked to 5-FU resistance in SNUC5 colon cancer cells.

Cytoprotective effect of eckol against oxidative stress-induced mitochondrial dysfunction: involvement of the FoxO3a/AMPK pathway

This study investigated the cytoprotective effect of Ecklonia cava-derived eckol against H2O2-induced mitochondrial dysfunction in Chang liver cells. While H2O2 augmented levels of mitochondrial reactive oxygen species (ROS), eckol decreased it. Eckol also attenuated high intracellular Ca(2+) levels stimulated by H2O2 and recovered H2O2-diminished ATP levels and succinate dehydrogenase activity. Eckol time-dependently increased the expression of manganese superoxide dismutase (Mn SOD), a mitochondrial antioxidant enzyme with cytoprotective effect against oxidative stress. Eckol recovered Mn SOD expression and activity that were decreased by H2O2. Finally, eckol induced Mn SOD through phosphorylated AMP-activated protein kinase (AMPK) and forkhead box O3a (FoxO3a). Specific silencing RNAs (siRNAs) against FoxO3a and AMPK reduced eckol-stimulated Mn SOD expression, and diethyldithiocarbamate (Mn SOD inhibitor) and siRNA against Mn SOD reduced the cytoprotective effect of eckol against H2O2-provoked cell death. These results demonstrate that eckol protects cells from mitochondrial oxidative stress by activating AMPK/FoxO3a-mediated induction of Mn SOD.

Photo-protective effect of americanin B against ultraviolet B-induced damage in cultured human keratinocytes

Excessive ultraviolet (UV) radiation, a constituent of sunlight, can induce multiple types of skin damage. We recently demonstrated that americanin B, a lignin compound, protected cells against hydrogen peroxide (H2O2)-induced damage by exerting antioxidant effects and inhibiting apoptosis. In this study, we investigated the ability of americanin B to protect against cell injury induced by UVB (280-320nm), the most harmful UV wavelengths, in human HaCaT keratinocytes. Americanin B absorbed UVB, eliminated UVB-induced intracellular reactive oxygen species (ROS), and decreased the extent of UVB-induced oxidative modification of lipids, proteins, and DNA. In addition, americanin B inhibited UVB-induced apoptosis, as indicated by reductions in apoptotic body formation and DNA fragmentation. Furthermore, americanin B reversed the depolarization of the mitochondrial membrane induced by UVB exposure. These protective activities were associated with down-regulation of apoptosis-promoting proteins, Bax, caspase-9, and caspase-3 and up-regulation of an apoptosis inhibitor, Bcl-2. These results suggest that americanin B can protect human keratinocytes against UVB-induced cell damage.

The ethyl acetate fraction of Sargassum muticum attenuates ultraviolet B radiation-induced apoptotic cell death via regulation of MAPK- and caspase-dependent signaling pathways in human HaCaT keratinocytes

CONTEXT

Our previous work demonstrated that an ethyl acetate extract derived from Sargassum muticum (Yendo) Fenshol (SME) protected human HaCaT keratinocytes against ultraviolet B (UVB)-induced oxidative stress by increasing antioxidant activity in the cells, thereby inhibiting apoptosis.

OBJECTIVE

The aim of the current study was to further elucidate the anti-apoptotic mechanism of SME against UVB-induced cell damage.

MATERIALS AND METHODS

The expression levels of several apoptotic-associated and mitogen-activated kinase (MAPK) signaling proteins were determined by western blot analysis of UVB-irradiated HaCaT cells with or without prior SME treatment. In addition, the loss of mitochondrial membrane potential (Δψm) was detected using flow cytometry or confocal microscopy and the mitochondria membrane-permeate dye, JC-1. Apoptosis was assessed by quantifying DNA fragmentation and apoptotic body formation. Furthermore, cell viability was evaluated using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.

RESULTS

SME absorbed electromagnetic radiation in the UVB range (280-320 nm) of the UV/visible light spectrum. SME also increased Bcl-2 and Mcl-1 expression in UVB-irradiated cells and decreased the Bax expression. Moreover, SME inhibited the UVB-induced disruption of mitochondrial membrane potential and prevented UVB-mediated increases in activated caspase-9 and caspase-3 (an apoptotic initiator and executor, respectively) levels. Notably, treatment with a pan-caspase inhibitor enhanced the anti-apoptotic effects of SME in UVB-irradiated cells. Finally, SME reduced the UVB-mediated phosphorylation of p38 MAPK and JNK, and prevented the UVB-mediated dephosphorylation of Erk1/2 and Akt.

DISCUSSION AND CONCLUSION

The present results indicate that SME safeguards HaCaT keratinocytes from UVB-mediated apoptosis by inhibiting a caspase-dependent signaling pathway.

Fucodiphlorethol G Purified from Ecklonia cava Suppresses Ultraviolet B Radiation-Induced Oxidative Stress and Cellular Damage

Fucodiphlorethol G (6’-[2,4-dihydroxy-6-(2,4,6-trihydroxyphenoxy)phenoxy]biphenyl-2,2’,4,4’,6-pentol) is a compound purified from Ecklonia cava, a brown alga that is widely distributed offshore of Jeju Island. This study investigated the protective effects of fucodiphlorethol G against oxidative damage-mediated apoptosis induced by ultraviolet B (UVB) irradiation. Fucodiphlorethol G attenuated the generation of 2, 2-diphenyl-1-picrylhydrazyl radicals and intracellular reactive oxygen species in response to UVB irradiation. Fucodiphlorethol G suppressed the inhibition of human keratinocyte growth by UVB irradiation. Additionally, the wavelength of light absorbed by fucodiphlorethol G was close to the UVB spectrum. Fucodiphlorethol G reduced UVB radiation-induced 8-isoprostane generation and DNA fragmentation in human keratinocytes. Moreover, fucodiphlorethol G reduced UVB radiation-induced loss of mitochondrial membrane potential, generation of apoptotic cells, and active caspase-9 expression. Taken together, fucodiphlorethol G protected human keratinocytes against UVB radiation-induced cell damage and apoptosis by absorbing UVB radiation and scavenging reactive oxygen species.

Fucoxanthin enhances the level of reduced glutathione via the Nrf2-mediated pathway in human keratinocytes

Fucoxanthin, a natural carotenoid, is abundant in seaweed with antioxidant properties. This study investigated the role of fucoxanthin in the induction of antioxidant enzymes involved in the synthesis of reduced glutathione (GSH), synthesized by glutamate-cysteine ligase catalytic subunit (GCLC) and glutathione synthetase (GSS), via Akt/nuclear factor-erythroid 2-related (Nrf2) pathway in human keratinocytes (HaCaT) and elucidated the underlying mechanism. Fucoxanthin treatment increased the mRNA and protein levels of GCLC and GSS in HaCaT cells. In addition, fucoxanthin treatment promoted the nuclear translocation and phosphorylation of Nrf2, a transcription factor for the genes encoding GCLC and GSS. Chromatin immune-precipitation and luciferase reporter gene assays revealed that fucoxanthin treatment increased the binding of Nrf2 to the antioxidant response element (ARE) sequence and transcriptional activity of Nrf2. Fucoxanthin treatment increased phosphorylation of Akt (active form), an up-regulator of Nrf2 and exposure to LY294002, a phosphoinositide 3-kinase (PI3K)/Akt inhibitor, suppressed the fucoxanthin-induced activation of Akt, Nrf2, resulting in decreased GCLC and GSS expression. In accordance with the effects on GCLC and GSS expression, fucoxanthin induced the level of GSH. In addition, fucoxanthin treatment recovered the level of GSH reduced by ultraviolet B irradiation. Taken together, these findings suggest that fucoxanthin treatment augments cellular antioxidant defense by inducing Nrf2-driven expression of enzymes involved in GSH synthesis via PI3K/Akt signaling.

The Polyphenol Chlorogenic Acid Attenuates UVB-mediated Oxidative Stress in Human HaCaT Keratinocytes

We investigated the protective effects of chlorogenic acid (CGA), a polyphenol compound, on oxidative damage induced by UVB exposure on human HaCaT cells. In a cell-free system, CGA scavenged 1,1-diphenyl-2-picrylhydrazyl radicals, superoxide anions, hydroxyl radicals, and intracellular reactive oxygen species (ROS) generated by hydrogen peroxide and ultraviolet B (UVB). Furthermore, CGA absorbed electromagnetic radiation in the UVB range (280–320 nm). UVB exposure resulted in damage to cellular DNA, as demonstrated in a comet assay; pre-treatment of cells with CGA prior to UVB irradiation prevented DNA damage and increased cell viability. Furthermore, CGA pre-treatment prevented or ameliorated apoptosis-related changes in UVB-exposed cells, including the formation of apoptotic bodies, disruption of mitochondrial membrane potential, and alterations in the levels of the apoptosis-related proteins Bcl-2, Bax, and caspase-3. Our findings suggest that CGA protects cells from oxidative stress induced by UVB radiation.

Effect of 7, 8-dihydroxyflavone on the up-regulation of Nrf2-mediated heme oxygenase-1 expression in hamster lung fibroblasts

The cytoprotective mechanism of 7, 8-dihydroxyflavone (DHF) against oxidative stress-induced cell damage with respect to its stimulatory effect on the expression of heme oxygenase-1 (HO-1), a potent antioxidant enzyme, was investigated in the present study. Up-regulation of HO-1 expression by DHF was both dose and time dependent in lung fibroblast V79-4 cells. DHF also increased the protein expression level of the transcription factor nuclear factor erythroid-2-related factor 2 (Nrf2), and induced the translocation of Nrf2 from the cytosol into the nucleus, leading to elevated HO-1 expression. The siNrf2 RNA-transfection attenuated HO-1 expression induced by DHF treatment. In addition, DHF induced the activation of extracellular signal-regulated kinase (ERK), while U0126 (a specific pharmacological inhibitor of ERK kinase) abrogated DHF-activated Nrf2 and HO-1 expression. This suggests that DHF increased the levels of Nrf2 and HO-1 via ERK-dependent pathways. Furthermore, DHF significantly prevented the reduction of cell viability in response to oxidative stress; however, U0126 attenuated the protective effect of DHF. Taken together, these results demonstrate that DHF protected cells from oxidative stress via the activation of an ERK/Nrf2/HO-1 signaling pathway.

7,8-Dihydroxyflavone protects human keratinocytes against oxidative stress-induced cell damage via the ERK and PI3K/Akt-mediated Nrf2/HO-1 signaling pathways

This study investigated the effect of 7,8-dihydroxyflavone (DHF) on the expression and activity of heme oxygenase-1 (HO-1), an enzyme with potent antioxidant properties, as well as the molecular mechanisms involved. DHF markedly upregulated HO-1 mRNA and protein expression in human keratinocytes (HaCaT cells), resulting in increased HO-1 activity. DHF also increased the protein level of transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which regulates HO-1 expression by binding to the antioxidant response element (ARE) within the HO-1 gene promoter, in a time-dependent manner. Moreover, DHF decreased the expression of Kelch-like ECH-associated protein 1, a repressor of Nrf2 activity, and induced the translocation of Nrf2 from the cytosol into the nucleus, thereby allowing its association with the ARE site. DHF activated extracellular-regulated kinase (ERK) and protein kinase B (PKB, Akt) in keratinocytes, while the ERK and Akt inhibitors attenuated DHF-enhanced Nrf2 and HO-1 expression. DHF also protected the keratinocytes against hydrogen peroxide- and ultraviolet B-induced oxidative damage, while HO-1, ERK and Akt inhibitors markedly suppressed DHF-mediated cytoprotection. Taken together, the results suggested that DHF activates ERK- and Akt-Nrf2 signaling cascades in HaCaT cells, leading to the upregulation of HO-1 and cytoprotection against oxidative stress.

6'-o-galloylpaeoniflorin protects human keratinocytes against oxidative stress-induced cell damage

6'-O-galloylpaeoniflorin (GPF) is a galloylated derivate of paeoniflorin and a key chemical constituent of the peony root, a perennial flowering plant that is widely used as an herbal medicine in East Asia. This study is the first investigation of the cytoprotective effects of GPF against hydrogen peroxide (H₂O₂)-induced cell injury and death in human HaCaT keratinocytes. GPF demonstrated a significant scavenging capacity against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical, H₂O₂-generated intracellular reactive oxygen species (ROS), the superoxide anion radical (O₂^-), and the hydroxyl radical (•OH). GPF also safeguarded HaCaT keratinocytes against H₂O₂-provoked apoptotic cell death and attenuated oxidative macromolecular damage to DNA, lipids, and proteins. The compound exerted its cytoprotective actions in keratinocytes at least in part by decreasing the number of DNA strand breaks, the levels of 8-isoprostane (a stable end-product of lipid peroxidation), and the formation of carbonylated protein species. Taken together, these results indicate that GPF may be developed as a cytoprotector against ROS-mediated oxidative stress.

Compound K, a metabolite of ginseng saponin, inhibits colorectal cancer cell growth and induces apoptosis through inhibition of histone deacetylase activity

In this study, we investigated the molecular mechanisms underlying the anti-proliferative effects of Compound K, with specific reference to histone modification. Exposure of HT-29 human colon cancer cells to Compound K resulted in time-dependent inhibition of histone deacetylase (HDAC) activity, mRNA and protein expression. Compound K treatment induced unmethylation of the RUNX3 promoter region such as TSA treatment and an accumulation of acetylated histones H3 and H4 within the total cellular chromatin, resulting in an enhanced ability of these histones to bind to the promoter sequences of the tumor suppressor gene Runt-related transcription factor 3 (RUNX3). Treatment of cells with Compound K increased the mRNA and protein expression of RUNX3, as well as p21, a downstream target of RUNX3. These alterations were consistent with cell cycle arrest at the G0/G1 phases and induction of apoptosis. Our results provide new insights into the mechanisms of Compound K action in human colorectal cancer cells and suggest that HDAC inhibition presents a novel approach to prevent or treat colorectal cancer.

High-level expression of recombinant dengue viral NS-1 protein and its potential use as a diagnostic antigen

The prevalence of NS1 Ab response in patients with dengue viral infection and the potential of using recombinant NS1 protein as a diagnostic antigen for dengue viral infection were investigated. In this study, the full-length and C-terminal half of NS1 proteins (rNS1, rNS1-C) were highly expressed (10-30 mg/l) and further purified and refolded. The good antigenicity of the full-length rNS1 protein was confirmed by interaction with 19 dengue NS1-specific monoclonal antibodies (MAbs) in ELISA; however, the antigenicity of rNS1-C was relatively lower. The full-length rNS1 antigen also differentiated reliably between sera from dengue virus-infected patients and sera from normal controls. When rNS1 was used as an antigen to detect human anti-NS1 IgM and IgG Ab, the anti-NS1 Ab response was found in 15 of 17 patients (88%) with primary dengue infection and all 16 patients (100%) with secondary dengue infection. These results indicated that using the full-length rNS1 whose antigenicity is restored as ELISA antigen, a high anti-NS1 antibody prevalence could be detected in patients with either primary or secondary dengue infection. This finding suggested that the anti-NS1 antibody appeared not only in secondary and severe dengue virus infection and might not correlate the pathogenesis of dengue hemorrhagic fever. The study also verified that our purified rNS1 protein showed similar immunological properties as native dengue viral proteins. Genetic engineering production of recombinant NS1 antigen could provide a safe and valuable resource for dengue virus serodiagnosis.

Vector competence of Culex pipiens molestus (Diptera: Culicidae) from Taiwan for a sympatric strain of Japanese encephalitis virus

Laboratory strains of Culex pipiens molestus Forskal and Culex tritaeniorhynchus Giles from northern Taiwan were compared for their susceptibility to the Sanhsia MQ1-2 (SH) strain of Japanese encephalitis (JE) virus isolated from Taiwan. After feeding on a sweetened blood-virus mixture, viral titers in Cx. p. molestus during the 14-d incubation period ranged from a minimum of 2.9 log10PFU (plaque forming units) per mosquito on day 3 after ingestion to a maximum of 4.65 log10PFU at day 8 and in Cx. tritaeniorhynchus from 2.6 on day 10-5.18 log10PFU per mosquito on day 13. Although virus titer in Cx. p. molestus was lower than in Cx. tritaeniorhynchus at the end of the experiment, this difference was not statistically significant. The median infective dose (ID50) for Cx. p. molestus was 2.83 log10PFU and for Cx. tritaeniorhynchus was 1.02 log10PFU per mosquito, and this difference also was not significant. There also was no significant difference between the median infective dose for transmission (TID50) per mosquito for Cx. p. molestus (5.34 log10PFU) and Cx. tritaeniorhynchus (4.59 log10PFU). We concluded that Cx. p. molestus is an effective laboratory vector of JE virus.

Failure of dengue-2 virus antibody to interfere with the isolation of dengue-2 virus from Aedes aegypti (Diptera: Culicidae)

When isolating dengue virus (DEN) from mosquitoes collected in endemic areas, pools may contain both anti-dengue antibodies from freshly engorged females and virus from DEN infected females. To determine if these antibodies may interfere with virus isolation, we simulated the isolation procedure using Aedes aegypti (L.) that we infected with the 16,681 strain of dengue type 2 virus by intrathoracic inoculation. At 7 d postinfection, we allowed females to engorge on immunized or normal mouse blood. Virus in a mixture of anti-dengue-2 antibodies and dengue-2 virus became inactive after incubation at 37 degrees C for 1 h, but remained infective without incubation. Therefore, at ambient conditions antibodies would not interfere with virus isolation from field-collected Ae. aegypti from endemic areas. In addition, DEN antibodies enhanced virus replication when inoculated into Ae. aegypti, but not C6/36 cells. The mechanism for this in vitro antibody enhancement of infection remains unclear.

Identification of free deaminated sialic acid (2-keto-3-deoxy-D-glycero-D-galacto-nononic acid) in human red blood cells and its elevated expression in fetal cord red blood cells and ovarian cancer cells

Chemical studies have shown the occurrence of the deaminated sialic acid 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN) in paired samples of blood obtained from mothers and newborns of healthy human individuals. Most of the KDN was found in red blood cells, although low levels were detected in mononuclear cells. No N-glycolylneuraminic acid was detected. Unexpectedly, nearly all of the KDN in fetal cord and matched maternal red blood cells was present as the free sugar and comparatively little occurred conjugated or as cytidine 5'-KDN phosphate. The amount of free KDN in fetal newborn red blood cells was 2.4-fold higher than in red blood cells from the mothers or from healthy nonpregnant women. Free KDN was also identified in normal human ovaries, in ovarian tumors, and in ascites cells obtained from ovarian cancer patients. Importantly, as in fetal cord red blood cells, a distinguishing feature of KDN expression in ovarian tumor cells was an elevated level of free KDN compared with normal controls. A positive correlation was found between an increase in the ratio of free KDN/N-acetylneuraminic acid in ovarian adenocarcinomas and the stage of malignancy. This was particularly evident in tumor cells isolated from the ascites fluid. The central importance of these new findings is 2-fold. First, they show that free KDN is a minor but ubiquitous sialic acid in human red blood cells and that its elevated expression in red blood cells from fetal cord blood compared with maternal red blood cells may be developmentally related to blood cell formation during embryogenesis. Second, the enhanced expression of KDN in ovarian cancer cells suggests that this sialic acid, like the alpha2,8-linked polysialic acid glycotope, may be an oncofetal antigen in these tumors and thus could be an "early warning" signal for onset of disease and/or a marker for detection of recurrence of disease. These new findings highlight the importance of elucidating the role that KDN and KDN-containing glycoconjugates may play in normal development and malignancy.

Genomic organization and characterization of the promoter region of the round-spotted pufferfish (Tetraodon fluviatilis) JAK1 kinase gene

Seventeen kilobases of genomic DNA containing the promoter and the coding region of the round-spotted pufferfish JAK1 gene was isolated and completely sequenced. This gene consists of 25 exons and 24 introns spanning about 13.5 kb, compared to > 30kb in carp JAK1 gene. Primer extension analysis revealed one transcription initiation site which was 376 bp upstream of the translation initiation site. The sequence of the 2.9 kb region upstream of the transcription initiation site contains numerous potential binding sites for transcription factors including HNF-5, GCF, Sp1, CRE, AP2, GATA, GAGA, E2A, p53, and NF-IL6. When this region was placed upstream of the chloramphenicol acetyltransferase (CAT) reporter gene and transfected into a carp CF cell line, it could drive the synthesis of CAT enzyme three times more efficiently than could the common carp JAK1 promoter.

Round-spotted pufferfish (Tetraodon fluviatilis) snf5 gene is oriented in a tail-to-tail manner with the set gene which encodes an inhibitor of protein phosphatase 2A

The round-spotted pufferfish Tetraodon fluviatilis has a genome size of 380 Mb which is slightly smaller than that of another pufferfish Fugu rubripes rubripes (Fugu). Due to its compact genome and small introns, Fugu has been introduced as a model for genome studies. Recently, the round-spotted pufferfish has also been proposed as a new model for genome studies because of the ease in obtaining material and high-sequence homology to that of Fugu. In this study, we have cloned and characterized the snf5 and set genes from the round-spotted pufferfish. The snf5 gene is composed of 9 exons spanning about 2.9 kb whereas the set gene consists of 8 exons spanning about 2.7 kb. They are linked in a tail-to-tail manner with an intergenic region of about 6.5 kb. So far, the genomic structures of human snf5 and set genes are unknown. Based on our data, the pufferfish SNF5 and SET display high amino acid sequence identity (>90%) with the respective human genes. By primer extension and sequence analysis, we found that putative promoter region of the snf5 gene contains a typical TATA box and numerous potential binding sites for transcription factors including AP1, AP2, AP3, c-Myb, HNF-5, and NF-IL6. As for the set gene, its promoter region does not have any TATA or CCAAT motif and contains a few potential binding sites for transcriptional factors such as c-Myb and gamma-IRE. When these promoter regions were placed upstream of the CAT reporter gene and transfected into a carp CF cell line, the 5'-upstream 1.6-kb DNA fragment of the snf5 gene displayed stronger promoter activity, approximately three-fold higher than that of the 5'-upstream 1.3 kb DNA fragment of the set gene. By transient expression and immunofluorescent staining, we also showed that the pufferfish SNF5 and SET are nuclear proteins, consistent with their postulated roles as transcriptional factors.

In vitro processing of dengue virus type 2 nonstructural proteins NS2A, NS2B, and NS3

We have tested the hypothesis that the flavivirus nonstructural protein NS3 is a viral proteinase that generates the termini of several nonstructural proteins by using an efficient in vitro expression system and monospecific antisera directed against the nonstructural proteins NS2B and NS3. A series of cDNA constructs was transcribed by using T7 RNA polymerase, and the RNA was translated in reticulocyte lysates. The resulting protein patterns indicated that proteolytic processing occurred in vitro to generate NS2B and NS3. The amino termini of NS2B and NS3 produced in vitro were found to be the same as the termini of NS2B and NS3 isolated from infected cells. Deletion analysis of cDNA constructs localized the protease domain within NS3 to the first 184 amino acids but did not eliminate the possibility that sequences within NS2B were also required for proper cleavage. Kinetic analysis of processing events in vitro and experiments to examine the sensitivity of processing to dilution suggested that an intramolecular cleavage between NS2A and NS2B preceded an intramolecular cleavage between NS2B and NS3. The data from these expression experiments confirm that NS3 is the viral proteinase responsible for cleavage events generating the amino termini of NS2B and NS3 and presumably for cleavages generating the termini of NS4A and NS5 as well.