Genetic mutations of precore region of hepatitis B virus in hepatitis B e antigen-negative patients with fulminant hepatitis B and translation of precore variants in vitro

OBJECTIVE

To detect mutations in precore region of hepatitis B virus of HBeAg negative- patients with fulminant hepatitis and to determine the effect of T1862 mutants on synthesis of precursor of hepatitis B e antigen.

METHODS

The entire precore and core region were amplified from sera of nine HBeAg negative-patients with fulminant hepatitis B by polymerase chain reaction (PCR). PCR products were cloned into plasmid pUC18, and sequencing for analysis of precore mutations. Precore and core sequence of T1862 variant were also cloned into expression plasmid pGEMT for in vitro transcription and translation study on synthesis and procession of e antigen.

RESULTS

Three variants, A1896, A1899 and T1862, whose nucleotide mutation led to amino acids substitutions, were detected in patients with fulminant hepatitis. T1862 variant didn't effect the synthesis of precursor of e antigen. Also there was no variant detected in precore region of hepatitis B virus in two patients.

CONCLUSIONS

The causes for negative of e antigen in fulminant hepatitis patients may be partially explained by precore mutation of A1896 and T1862, and the latter variant may effect the process of precursor of e antigen, rather than the synthesis of precursor protein.

Ski represses bone morphogenic protein signaling in Xenopus and mammalian cells

The bone morphogenic proteins (BMPs) play important roles in vertebrate development. In Xenopus, BMPs act as epidermal inducers and also as negative regulators of neurogenesis. Antagonism of BMP signaling results in neuralization. BMPs signal through the cell-surface receptors and downstream Smad molecules. Upon stimulation with BMP, Smad1, Smad5, and Smad8 are phosphorylated by the activated BMP receptors, form a complex with Smad4, and translocate into the nucleus, where they regulate the expression of BMP target genes. Here, we show that the Ski oncoprotein can block BMP signaling and the expression of BMP-responsive genes in both Xenopus and mammalian cells by directly interacting with and repressing the activity of BMP-specific Smad complexes. This ability to antagonize BMP signaling results in neuralization by Ski in the Xenopus embryo and blocking of osteoblast differentiation of murine W-20-17 cells. Thus, Ski is able to repress the activity of all receptor-associated Smads and may regulate vertebrate development by modulating the signaling activity of transforming growth factor-beta family members.

Effects of huang qi wu wu decoction on plasma proteins in 70 cases of chronic pulmonary heart disease

Simple immune agar diffusion test was used to assay the contents of 12 plasma proteins in 70 cases of chronic pulmonary heart disease treated by Huang Qi Wu Wu Decoction ([symbol: see text]), with the other 70 cases who were not given Huang Qi Wu Wu Decoction as the control group. The total clinical effective rate in the treatment group was 90.0%, while that in the control group was 75.7%, with a statistically significant difference between the two groups (P < 0.05). In the treatment group, the levels of prealbumin, transferrin and fibronectin elevated obviously after treatment, and the contents of C-reactive protein, ceruloplasmin, haptoglobin, alpha 1-antitrypsin and alpha 1-acid glycoprotein decreased markedly (P < 0.01). In the control group, only the levels of ceruloplasmin and C-reactive protein decreased significantly (P < 0.05). It is shown that Huang Qi Wu Wu Decoction may enhance the therapeutic effects for pulmonary heart disease, regulate the metabolism of plasma proteins, and improve the life quality of the patients.

Determination of low-level mercury based on a renewable-drops sensing technique

The design and characteristics of a novel drop-based fluorescence-detection technique for the determination of mercury(II) are described. The method, using a flow injection technique, is based on the renewable-drops of 3,3',5,5'-tetramethylbenzidine(TMB), which are formed at the bottom tip of a silica capillary tube connected to the end of the flow system. An excitation beam from a high-pressure Hg lamp directly illuminates the drops, the fluorescence emission is conducted to a photodiode (PD) to convert the photocurrent into a voltage signal (mV). Optimum analytical conditions for Hg(II) assays have been established. In NaAc/HAc buffer at pH 3.09 this assay has a wide linear range for Hg(II) from 8.0 x 10(-8) to 2.0 x 10(-5) mol/L with a detection limit of 2.0 x 10(-8) mol/L. The use of renewable drops allowing a fresh reaction surface for each sample is of particular value to solving the problems of irreversible reactions. Besides its high sensitivity, the method permits a simple, fast, and inexpensive measurement with only micro-quantities of reagent consumption. The technique described provides a simple and sensitive way to fabricate sensors of feasible prospects and commercial advantages.

Hepatotropism of nonenveloped DNA virus in rhesus monkey infected by transfusion-transmitted virus

OBJECTIVE

To study wether the nonenveloped DNA virus transmitted via blood transfusion is hepatotropic.

METHODS

Total DNA was extracted from tissues of 5 experimentally infected Rhesus monkeys. A dot hybridization was done with virus double DNA strand probe or single antisense strand probe.

RESULTS

Both single- and double-strand probes were hybridized with DNA of the liver, spleen, stomach, small intestine and colon. The virus was conformed present in most of all the organs when double-strand probe was used. The positive was noted only in the liver and small intestine when single-strand antisense probe was used, which showed that in liver and small intestine might have replicative intermediates of the virus.

CONCLUSION

It suggests that nonenveloped DNA virus replicate in the liver and small intestine, so it might be hepatotropic.

[Experimental infection of a novel nonenveloped DNA hepatitis virus in Rhesus monkey]

OBJECTIVE

To test the susceptibility of the Rhesus monkey to the TT virus and to establish its transmission route.

METHODS

Rhesus monkeys were administered orally and intravenously with the inoculum that was prepared with feces collected from a patient at the incubation period. Passage study was done with monkey' s positive feces. The blood, bile and feces were tested with polymerase chain reaction (PCR), and the liver, the jejunum tissues with in situ hybridization.

RESULTS

The viremia occurred 4-7 days after intravenous inoculation and 7-10 days after oral administration. The virus was also excreted in the feces in a few days after oral infection and simultaneously with viremia after intravenous inoculation. The virus was also detected in the bile during the viremic phase. There was a prolonged carrier state that the viremia and fecal virus excretion persisted for more than 6 months. No serum transaminase elevation was found during the infection. There were virus signals in hepatocytes in columnar epithelium and lamina propria cells of jejunum villi, but no significant pathology was demonstrated in both sites.

CONCLUSIONS

The liver infection of Rhesus monkey was established hb either oral or parenteral virus Inoculation. The virus may be released from liver into blood and intestine vial the bile or just from the gut wall into feces, and hence it may be transmitted by both routes.

Experimental infection of nonenveloped DNA virus (TTV) in rhesus monkey

Virus fragments homologous to TTV were detected previously from an enterically transmitted outbreak of non-A-E hepatitis [Luo et al., 1999]. To test the susceptibility of the Rhesus monkey to this virus and to establish its transmission routes, 6 Rhesus monkeys were inoculated, 3 orally and another 3 intravenously. The inoculum was prepared by extracting and filtering feces collected from a patient during the incubation period identified in the described outbreak. A second group of 3 monkeys was used for the passage study. The feces and blood samples were collected for detection of the virus by polymerase chain reaction (PCR). Four animals were subjected to liver biopsies and bile aspiration by open surgery for in situ virus detection. Viremia occurred in 4-7 days after intravenous and 7-10 days after oral inoculation. The virus was excreted in feces a few days after oral infection and simultaneously with viremia after intravenous inoculation. The virus was also detected in bile during the viremic phase. There was a prolonged carrier state with persistent viremia and virus excretion in feces for more than 6 months. Serum transaminase levels were not raised during the infection. The virus was present in both the cytoplasm and nuclei of hepatocytes, but no significant pathology was found. Therefore, the Rhesus monkey is susceptible to TT virus infection, but the virus seems nonpathogenic. Infection of the liver may be established either by oral or parenteral inoculation. The virus may be released from liver into the blood or via bile into feces, so it may be transmitted by both blood and fecal routes.

Experimental infection of nonenveloped DNA virus (TTV) in rhesus monkey

Virus fragments homologous to TTV were detected previously from an enterically transmitted outbreak of non-A-E hepatitis [Luo et al., 1999]. To test the susceptibility of the Rhesus monkey to this virus and to establish its transmission routes, 6 Rhesus monkeys were inoculated, 3 orally and another 3 intravenously. The inoculum was prepared by extracting and filtering feces collected from a patient during the incubation period identified in the described outbreak. A second group of 3 monkeys was used for the passage study. The feces and blood samples were collected for detection of the virus by polymerase chain reaction (PCR). Four animals were subjected to liver biopsies and bile aspiration by open surgery for in situ virus detection. Viremia occurred in 4-7 days after intravenous and 7-10 days after oral inoculation. The virus was excreted in feces a few days after oral infection and simultaneously with viremia after intravenous inoculation. The virus was also detected in bile during the viremic phase. There was a prolonged carrier state with persistent viremia and virus excretion in feces for more than 6 months. Serum transaminase levels were not raised during the infection. The virus was present in both the cytoplasm and nuclei of hepatocytes, but no significant pathology was found. Therefore, the Rhesus monkey is susceptible to TT virus infection, but the virus seems nonpathogenic. Infection of the liver may be established either by oral or parenteral inoculation. The virus may be released from liver into the blood or via bile into feces, so it may be transmitted by both blood and fecal routes.

[Influence of HBV/C mutation on HLA expression of host cells]

OBJECTIVE

To study the influence of HBV/C mutation on host cellular HLA expression.

METHODS

HBV expression vectors carrying wild or variant HBV/C gene were constructed and transferred into HepG(2) cells. HBV/C gene expression on the host cells was identified. The expression of HLA-I and HLA-DR on the host cell membrane was detected.

RESULTS

DNA segments similar with HBV/C gene size and HBcAg were detected by PCR and Western blot analysis, respectively. Almost all HepG(2) cells expressed HLA-I but not HLA-DR. The fluorescence intensity of HLA-I expression on host cells was different: HepG(2) was 57.8 and wild vector 54.3. The wild HBV/C gene declined significantly to 31.2. While V60, G87 and L97 increased to 43.0, 54.0 and 69.4, respectively. L97 was greatly increased with 11.6 higher than HepG(2). HLA-DR had no significant expression.

CONCLUSION

Replication and expression of HBV/C gene can influence HLA-I expression on the host cells directly. Influence of variant gene on HLA-I expression is different from the wild gene. This might relate with the exacerbation of diseases resulting from HBV mutation.

[Determination of rufloxacin in human plasma by high performance liquid chromatography]

A high performance liquid chromatographic method has been developed for the determination of rufloxacin in human plasma. Rufloxacin was extracted from plasma with dichloromethane for three times. It was chromatographed on an Ultrasphere ODS column with Pefloxacin as internal standard with a mobile phase consisting of methanol-tetrabutylammonium bromide-triethanolamine (32:68:0.5, V/V) adjusted to pH 2.8 with orthophosphoric acid. The flow rate was 1.2 mL/min and the monitoring wavelength was 295 nm. The calibration curve was linear from 0.1 to 10 mg/L of plasma. The detection limit of rufloxacin was 0.05 mg/L for plasma and the recovery was (97.7 +/- 2.1)%. The intra-day RSD and inter-day RSD were 2.33% and 3.38% respectively. The method is simple, rapid, accurate and can be used to determine the rufloxacin concentration in plasma and for pharmacokinetic study.

[Establishment of a method for classification of HBV genome and it's application]

OBJECTIVE

By using the techniques of PCR and restriction fragment length polymorphism (RFLP), we established a classification method for HBV genome based on viral S gene of asymptomatic HBV carriers (AsC).

METHODS

By using this method we classified HBV DNA of AsC living in Guangzhou, Shenyang, Beijing and Chongqing.

RESULTS

Among the AsC of Guangzhou, genotype B was 32.8%, genotype C 42.7%, mixed genotypes B and C 23.0%, others 1.6%; among the AsC of Chongqing, genotype B was 35.0%, genotype C 40.0%, mixed genotypes B and C 25.0%; among the AsC of Beijing, genotype B was 25.0%, genotype C 50.0%, mixed genotypes B and C 25.0%; among the AsC of Shenyang, genotype B was 11.1%, genotype C 88.9%. The prevalent HBV strains in China are genotype C and genotype B, and genotype C is the main genotype in west China.

CONCLUSION

The established method for genotyping is simple and convenient. Using this method, we also classified HBV DNA of the patients with chronic hepatitis B and liver cirrhosis living in Guangzhou, and found that mixed genotypes B and C was in 50.0% of the patients detected, suggesting the mixed infection might lead to a severe damage of the liver tissue.

Negative feedback regulation of TGF-beta signaling by the SnoN oncoprotein

Smad proteins mediate transforming growth factor-beta (TGF-beta) signaling to regulate cell growth and differentiation. The SnoN oncoprotein was found to interact with Smad2 and Smad4 and to repress their abilities to activate transcription through recruitment of the transcriptional corepressor N-CoR. Immediately after TGF-beta stimulation, SnoN is rapidly degraded by the nuclear accumulation of Smad3, allowing the activation of TGF-beta target genes. By 2 hours, TGF-beta induces a marked increase in SnoN expression, resulting in termination of Smad-mediated transactivation. Thus, SnoN maintains the repressed state of TGF-beta-responsive genes in the absence of ligand and participates in negative feedback regulation of TGF-beta signaling.

T1762/A1764 variants of the basal core promoter of hepatitis B virus; serological and clinical correlations in Chinese patients

BACKGROUND

A double variant in the basal core promoter, converting nucleotide 1762 from A to T (T1762) and nucleotide 1764 from G to A (A[764), has been described in patients with chronic hepatitis B infection. Its prevalence and significance in Chinese chronic HBV carriers are unknown.

METHODS

We studied 177 Chinese patients with chronic HBV infection (chronic hepatitis/asymptomatic: 89/88; hepatitis B e antigen positive/negative: 84/93). The double variant was detected by mismatched polymerase chain reaction and restriction fragment length polymorphism analysis. The reliability of this method was verified by sequencing in 41 serum samples with 100% matching.

RESULTS

The double variant T1762/ A1764 was found in 52 of 89 patients with chronic hepatitis, but in only 6 of 59 asymptomatic carriers (p<0.001). The prevalence was significantly lower in hepatitis B e antigen positive patients (23/84) than in hepatitis B e antigen negative patients (35/64) (p<0.005). Precore variant, A1896 was detected in 40 individuals; 31 of them suffered from chronic hepatitis and 9 were asymptomatic (p<0.001). A combination of both variants T1762/A1764 and A1896 was seen in 3 of 59 asymptomatic and 22 of 89 patients with chronic hepatitis (p<0.005).

CONCLUSIONS

Mismatched polymerase chain reaction with restriction fragment length polymorphism provides a reliable, easy and fast method for detection of the presence of the T1762/A1764 variant. In Chinese chronic hepatitis B carriers, T1762/A1764 variant was associated with both active liver disease and hepatitis B e antigen negativity.

Expression of a glycosylphosphatidylinositol-linked Manduca sexta aminopeptidase N in insect cells

Aminopeptidase N (APN; EC 3.4.11.2) is an exopeptidase that is attached to cell membranes by a hydrophobic amino-terminal stalk in vertebrates or a glycosylphosphatidylinositol (GPI) anchor in insects. In this study, we report the cloning, expression, and characterization of an aminopeptidase N from Manduca sexta midgut. The full-length aminopeptidase N cDNA (APN1a) encodes a 995-amino-acid protein. The predicted amino acid sequence differs by 8 amino acids from M. sexta APN1. These different amino acids do not modify any putative glycosylation or glycosylphosphatidylinositol anchor sites. The full-length cDNA was cloned into an expression plasmid, pHSP-HR5, and transiently expressed in an insect cell line derived from Spodoptera frugiperda (Sf21 cells). Immunoblot analysis with anti-APN antiserum showed that APN1a expressed in Sf21 cells is the same size (120 kDa) as APN found in midgut brush border membranes. After treatment with phosphatidylinositol-specific phospholipase C (PIPLC), anti-cross-reacting determinant antibody specific for PIPLC cleavage products recognized the expressed 120-kDa APN1a, but not endogenous Sf21 proteins, indicating that APN1a has an intact glycosylphosphatidylinositol anchor. These results are evidence that Sf21 cells synthesize few, if any, endogenous GPI-linked proteins. Immunofluorescence staining showed that the expressed APN1a was located on the surface of Sf21 cells.

[Hepatitis B virus core promoter mutations in patients with fulminant hepatitis]

OBJECTIVE

To detect hepatitis B virus core promoter (CP) mutations in patients with fulminant hepatitis.

METHODS

Polymerase chain reaction amplified serum HBV DNA fragments were directly sequenced.

RESULTS

There were 2-12 nucleotide substitutions in CP region in the 7 subacute fulminant hepatitis patients studied. An 11 bp nucleotides insertion was found in one patient. Mutations in CP were usually seen in the first and the second A T rich regions. The A to T mutation at nt 1,762 and G to A mutation at nt 1,764 were found in 4 cases, 3 of them were HBeAg negative. The third A T rich region was kept intact in all the 7 patients, so did the initial site of HBV replication (DR1) and the initial site of mRNA transcription (1,783/1784 or 1,790 +/- 1 for precore mRNA and 1818 for pregenome-C/P mRNA).

CONCLUSION

CP mutations in patients with fulminant hepatitis are common, most of the CP variations occur in the first and the second A T rich regions, and these mutations may impede the transcription of precore mRNA and affect the expression of HBeAg.

The Ski oncoprotein interacts with the Smad proteins to repress TGFbeta signaling

Smad proteins are critical signal transducers downstream of the receptors of the transforming growth factor-beta (TGFbeta) superfamily. On phosphorylation and activation by the active TGFbeta receptor complex, Smad2 and Smad3 form hetero-oligomers with Smad4 and translocate into the nucleus, where they interact with different cellular partners, bind to DNA, regulate transcription of various downstream response genes, and cross-talk with other signaling pathways. Here we show that a nuclear oncoprotein, Ski, can interact directly with Smad2, Smad3, and Smad4 on a TGFbeta-responsive promoter element and repress their abilities to activate transcription through recruitment of the nuclear transcriptional corepressor N-CoR and possibly its associated histone deacetylase complex. Overexpression of Ski in a TGFbeta-responsive cell line renders it resistant to TGFbeta-induced growth inhibition and defective in activation of JunB expression. This ability to overcome TGFbeta-induced growth arrest may be responsible for the transforming activity of Ski in human and avian cancer cells. Our studies suggest a new paradigm for inactivation of the Smad proteins by an oncoprotein through transcriptional repression.

[Tolerance of HepG2 and HepG2.2.15 cell lines to different apoptotic stimuli]

OBJECTIVE

To elucidate the effect of HBV on hepatocyte apoptosis.

METHODS

The HepG2 cells and the HBV transfected HepG2.2.15 cells were cultured with MIX or ActD or cultured in DMEM medium without serum, The apoptosis was examined with FCM.

RESULTS

The apoptotic rates of HepG2.2.15 cells at 24 h and 48 h after MTX addition were 10.8% and 13.3%, at 24 h and 48 h after Act D addition were 16.8% and 37.7%, and at 4th and 6th day after serum withdrawal were 13.2% and 14.8%, respectively. While those of HepG2 cells were 12.6% and 65.3%, 44.5% and 89.7%, and 19.8% and 28.8%, correspondingly.

CONCLUSION

HepG2.2.15 cell was tolerant to these apoptotic stimuli, and it might be inferred that HBV inhibits hepatocyte apoptosis.

[Cytotoxic effect of HepG2 cell expressing CD95L in an autocrine and paracrine way]

OBJECTIVE

The clearance of HBV-infected hepatocyte is mainly mediated by the CTL expressing CD95L. We have found that the hepatocytes also express CD95L in hepatitis B, a molecule with cytotoxic effect. This study was to elucidate its effect mechanism.

METHODS

The HepG2 cell was induced to express CD95L and coincubated with HepG2.2.15 cell. The supernate from the induced HepG2 cell culture was added to another untreated HepG2 fraction. The apoptosis rates were examined with flow cytometry. The apoptosis of individual HepG2 cell incubation was also examined.

RESULTS

The HepG2 cell expressing CD95L was able to kill the HepG2.2.15 cell with CD95 expression, apoptotic rates were 16.5% at 24 h and 43.0% at 48 h incubation. The supernate induced apoptosis rates of 38.7% and 73.3%, and the suicide rates of individual HepG2 cell incubation were 43.8% at 24 h. All these data were higher than those in controls. The apoptosis could be blocked with addition of anti-CD95L monoclonal antibody.

CONCLUSION

The HepG2 cell expressing CD95L mediated cytotoxic effect by an autocrine and paracrine mechanism.

[Clearance of intrahepatic hepatitis B virus by a nonimmune mechanism]

OBJECTIVE

The clearance of intrahepatic hepatitis B virus (HBV) is mainly by the cytotoxicity of immune cells with ways including CD95 ligand/CD95 induction. We found that the liver cells do express CD95 ligand (CD95L), a cytotoxic cell surface molecule. This paper studied the mechanism and implications of the hepatocytes themselves to clear the virus.

METHODS

The HepG2 cells with induced CD95L and the HepG2.2.15 cells with constitutive CD95 expression were coincubated. The apoptotic cells were examined under fluorescence microscope and with flow cytometry.

RESULTS

In chronic hepatitis B intrahepatic expressions of CD95L and/or CD95 were detected at both mRNA and protein level. Methotrexate induced CD95L expression of HepG2 cell. The HepG2 cells with CD95L could kill the HepG2.2.15 cells with CD95 molecule with apoptotic rates of 16.5% at 24h and 43.0% at 48h. This apoptosis effect could be blocked by using anti-CD95L antibody.

CONCLUSION

The hepatocyte might induce apoptosis mutually and clear the virus themselves with a nonimmune mechanism.

Cooperative binding of Smad proteins to two adjacent DNA elements in the plasminogen activator inhibitor-1 promoter mediates transforming growth factor beta-induced smad-dependent transcriptional activation

Transforming growth factor beta (TGFbeta) activates transcription of the plasminogen activator inhibitor type-1 (PAI-1) gene through a major TGFbeta-responsive region (-740 and -647) in the PAI-1 promoter. This process requires the Smad family of signaling molecules. Upon phosphorylation by the TGFbeta receptors, Smad2 and Smad3 homoligomerize and heteroligomerize with Smad4, translocate to the nucleus and activate transcription of TGFbeta responsive genes. Smad3 and Smad4 have been shown to bind to various sites in the PAI-1 promoter. To determine the number of Smad-binding sites within the 94-base pair major TGFbeta-responsive region and the mechanism of Smad-mediated transactivation, we systematically mapped the Smad-binding sites and show that Smad4 and Smad3 bind cooperatively to two adjacent DNA elements in this region. Both elements were required for TGFbeta-induced, Smad3- and Smad4-dependent activation of PAI-1 transcription. Contrary to previous reports, transactivation of the PAI-1 promoter was mediated by the amino- but not carboxyl-terminal domains of the Smads. Furthermore, oligomerization of Smad3 markedly enhanced its binding to the two binding sites. Finally, a Smad4 mutation identified in a human pancreatic carcinoma that inactivates Smad4 signaling abolished Smad4 DNA binding activity, hence preventing transactivation of TGFbeta-responsive genes. These results underscore the importance of the Smad4 DNA binding activity in controlling cell growth and carcinogenesis.

Kaposi's sarcoma-associated herpesvirus: a sexually transmissible infection?

We examined sexual behavior as a risk factor for Kaposi's sarcoma-associated herpesvirus (KSHV) infection and examined the relation between KSHV seropositivity and development of KS in cross-sectional and cohort studies of 130 homosexual men diagnosed with AIDS in Sydney, Australia during the period from 1991 to 1993. KSHV serology was measured using antibody tests to latency-associated nuclear antigen (LANA) and lytically expressed open reading frame (ORF) 65.2. In the cross-sectional analysis, 52% (68) of study subjects were KSHV-seropositive by either assay. KSHV-seropositive men were significantly more likely to be seropositive to both herpes simplex type 2 (odds ratio [OR] 3.0; 95% confidence interval [CI], 1.2-7.5 for LANA and OR 2.8; 95% CI, 1.3-6.0 for ORF 65) and hepatitis A virus (OR 2.2; 95% CI, 1.1-4.5 for ORF 65). KSHV-seropositive men reported nonsignificantly more casual sexual partners and were nonsignificantly more likely to report insertive oroanal contact with casual partners. These data suggest that KSHV might be sexually transmitted among homosexual men. Men were observed until October 1996 for development of KS. Those seropositive to either KSHV assay at baseline were more likely than the seronegative to develop KS during follow-up (rate ratio [RR] 4.4; 95% CI, 1.9-10.2). Of those seropositive for KSHV, 53% developed KS.

Hot spot mutations of hepatitis B virus pre-C/C gene and its promotor in Chinese patients and the clinical implications

OBJECTIVE

To study if the functions of C gene and its promotor are related to the pathogenesis of hepatitis B and to describe their hot spot mutations in Chinese patients.

DATA SOURCES

We have studied this subject in recent years. A mini-review is based on some unpublished works.

DATA SELECTION

The sequence data of C gene and core promotor (cp) of hepatitis B virus (HBV) were analysed in the asymptomatic carriers (AsC) and the patients of hepatitis with various severity.

RESULTS

Pre-C A1896 mutation occurred in 67% of anti-HBe-positive and 38% of HBeAg-positive cases. All were chronic infections. In C gene, 8 missense mutations in the segment of codon 48-60, and 28 in codon 84-101 were found, more in severe patients. The cp mutations of nt 1762 and nt 1764 occurred more in HBeAg-negative than in positive cases (49% vs 20%), and more in patients than in AsC (56% vs 10%).

CONCLUSIONS

A1896 often occurred in nature infection course. The cp and clustering C gene mutations would more frequently lead to prolonged active infection and advanced liver diseases.

Toxicity, binding, and permeability analyses of four Bacillus thuringiensis Cry1 delta-endotoxins using brush border membrane vesicles of Spodoptera exigua and Spodoptera frugiperda

The binding and pore formation properties of four Bacillus thuringiensis Cry1 toxins were analyzed by using brush border membrane vesicles from Spodoptera exigua and Spodoptera frugiperda, and the results were compared to the results of toxicity bioassays. Cry1Fa was highly toxic and Cry1Ac was nontoxic to S. exigua and S. frugiperda larvae, while Cry1Ca was highly toxic to S. exigua and weakly toxic to S. frugiperda. In contrast, Cry1Bb was active against S. frugiperda but only marginally active against S. exigua. Bioassays performed with iodinated Cry1Bb, Cry1Fa, and Cry1Ca showed that the effects of iodination on toxin activity were different. The toxicities of I-labeled Cry1Bb and Cry1Fa against Spodoptera species were significantly less than the toxicities of the unlabeled toxins, while Cry1Ca retained its insecticidal activity when it was labeled with 125I. Binding assays showed that iodination prevented Cry1Fa from binding to Spodoptera brush border membrane vesicles. 125I-labeled Cry1Ac, Cry1Bb, and Cry1Ca bound with high-affinities to brush border membrane vesicles from S. exigua and S. frugiperda. Competition binding experiments performed with heterologous toxins revealed two major binding sites. Cry1Ac and Cry1Fa have a common binding site, and Cry1Bb, Cry1C, and Cry1Fa have a second common binding site. No obvious relationship between dissociation of bound toxins from brush border membrane vesicles and toxicity was detected. Cry1 toxins were also tested for the ability to alter the permeability of membrane vesicles, as measured by a light scattering assay. Cry1 proteins toxic to Spodoptera larvae permeabilized brush border membrane vesicles, but the extent of permeabilization did not necessarily correlate with in vivo toxicity.

Infection with HIV and hepatitis C virus among injecting drug users in a prevention setting: retrospective cohort study

OBJECTIVES

To estimate the incidence of HIV and hepatitis C virus and risk factors for seroconversion among a cohort of injecting drug users.

DESIGN

Retrospective cohort study.

SETTING

Primary healthcare facility in central Sydney.

SUBJECTS

Injecting drug users tested for HIV-1 antibody (n=1179) and antibodies to hepatitis C virus (n=1078) from February 1992 to October 1995.

MAIN OUTCOME MEASURES

Incidence of HIV-1 and hepatitis C virus among seronegative subjects who injected drugs and underwent repeat testing. Demographic and behavioural risk factors for hepatitis seroconversion.

RESULTS

Incidence of HIV-1 among 426 initially seronegative injecting drug users was 0.17/100 person years (two seroconversions) compared with an incidence of hepatitis C virus of 20.9/100 person years (31 seroconversions) among 152 injecting drug users initially negative for hepatitis C virus. Incidence of hepatitis C virus among injecting drug users aged less than 20 years was 75.6/100 person years. Independent risk factors for hepatitis C virus seroconversion were age less than 20 years and a history of imprisonment.

CONCLUSIONS

In a setting where prevention measures have contributed to the maintenance of low prevalence and incidence of HIV-1, transmission of hepatitis C virus continues at extremely high levels, particularly among young injecting drug users.

Transcription elongation factor P-TEFb mediates Tat activation of HIV-1 transcription at multiple stages

Tat stimulates human immunodeficiency virus type 1 (HIV-1) transcription elongation through recognition of the transactivation response (TAR) RNA stem-loop structure at the 5' end of nascent viral transcripts. Recently, a human transcription elongation factor P-TEFb, consisting of CDK9 kinase, cyclin T and other associated factors, has been shown to interact with Tat to restore Tat activation in HeLa nuclear extract depleted of P-TEFb. Here, we report the purification of a P-TEFb complex fraction containing epitope-tagged wild-type CDK9 or kinase-inactive CDK9 and five tightly associated polypeptides. Only wild-type P-TEFb complex with an active CDK9 kinase was able to hyperphosphorylate the C-terminal domain of RNA polymerase II and mediate Tat transactivation in P-TEFb-depleted HeLa nuclear extract. Tat also stimulated transcription elongation by recruitment of the P-TEFb complex to the HIV-1 promoter through a Tat-TAR interaction. A possible mechanism for P-TEFb to become associated with polymerase elongation complexes and function as a general elongation factor was demonstrated by an interaction of P-TEFb with double-stranded RNA molecules through an 87 kDa subunit. Finally, P-TEFb was found to interact with and phosphorylate Tat-SF1, a Tat cofactor required for Tat transactivation. Our data indicate that the various subunits of the human P-TEFb complex may play distinct roles at multiple stages to mediate Tat activation of HIV-1 transcription elongation.

[Study on the physiological activities of the metabolites from Paecilomyces arovirens]

The metabolites of Paecilomyces arovirens exhibited insecticidal activities to many inscct pcsts, including cotton aphid, Aphis gossypii, hawthorn Ispidcr mitc, Tetranychus viennensis and larvae of imported cabbage worm, Pietis rapae. A comparison was made between the metabolites of P. arovirens and naphthyl acetic acid (NAA) in wheat (Triticum aestivum) and water melon (Cucumis sativus) bioassays on their physiological effects. Results demonstrated that some of the metabolites physiological activities of P. arovirens are same to that of NAA, some are different between them. It indicate that there is a new kind or many kinds of plant growth regulator in the metabolites and need further analysized. The results can offer reference for exploiting a new insecticid which not only can control insect pests, but also increase plant growth.

[The comparison of conventional open cholecystectomy, laparoscopic cholecystectomy and minor-incision cholecystectomy]

To study the clinical value of minor incision for cholecystectomy, compared conventional open cholecystectomy (300 patients, group A), alparoscopic cholecytectomy (300 patients, group B), and minor-incision cholecystectomy (300 patients, group C) with regard to duration (day) of operation, amount of intraoperative bleeding, complications, time (day) of gastrointestinal function recovery, intravenous infusion, and expense and time (day) of hospitalization. The results showed that the operating time, amount of bleeding, duration of intravenous infusion, time of gastrointestinal function recovery and hospitalization in group A were significantly different from those in group B and C (P < 0.05), but the incidence in group A was lower than that in group B. The operating time, amount of intraoperative bleeding, and the time of gastrointestinal function recovery and intravenous infusion in group B were similar to those in group C, but there was a high rate of intraoperative and postoperative complication in group B (1.66%). There was no complication in group C (P < 0.05). Comparison of the effects among group A, B and C showed that it was superior in group C to those in group A and B.

The heliothis virescens 170 kDa aminopeptidase functions as "receptor A" by mediating specific Bacillus thuringiensis Cry1A delta-endotoxin binding and pore formation

The relationship between Bacillus thuringiensis Cry1Aa, Cry1Ab and Cry1Ac delta-endotoxin binding and pore formation was investigated using a purified 170 kDa aminopeptidase N (APN) from Heliothis virescens brush border membranes. Aminopeptidases with molecular sizes of 110, 140 and 170 kDa were eluted from a Cry1Ac toxin affinity column using N-acetylgalactosamine. The 140 kDa aminopeptidase has a cross-reacting determinant typical of a cleaved glycosyl-phosphatidylinositol anchor. After mild base treatment to de-acylate the glycosyl-phosphatidylinositol linkage and incubation in phosphatidyl inositol phospholipase C, anti-cross-reacting determinant antibody recognized the 170 kDa protein. Kinetic binding characteristics of Cry1A toxins to purified 170 kDa APN were determined using surface plasmon resonance. Cry1Aa, Cry1Ab and Cry1Ac, but not Cry1C and Cry1E toxins recognized 170 kDa APN. Each Cry1A toxin recognized two binding sites: a high affinity site with KD ranging from 41 to 95 nM and a lower affinity site with KD in the 325 to 623 nM range. N-acetylgalactosamine inhibited Cry1Ac but not Cry1Aa and Cry1Ab binding to 170 kDa APN. When reconstituted into phospholipid vesicles, the 170 kDa APN promoted toxin-induced 86Rb+ release for Cry1A toxins, but not Cry1C toxin. Furthermore Cry1Ac, the Cry protein most toxic to H. virescens larvae, caused 86Rb+ release at lower concentrations, and to a greater extent than Cry1Aa and Cry1Ab toxins. The correlation between toxin-binding specificity and 86Rb+ release strongly suggests that the purified 170 kDa APN is the functional receptor A in the H. virescens midgut epithelial cell brush border membranes.

[In vitro expression of wild type and precore mutant woodchuck hepatitis virus]

Hepatitis B virus (HBV) precore 1896 and 1898 G-->A mutations are regarded as hot spots to study. Such mutants have been considered associating with molecular and biological changes of HBV and causing chronic hepatitis and severe forms of hepatitis, including fulminant hepatitis. Using oligonucleotide-directed mutagenesis, we have conducted the same point mutations in the precore gene of an infectious clone of woodchuck hepatitis virus (WHV-8). Transfection of mutant WHV DNA, 1896 mutant (WHV-M1) or both 1896 and 1898 mutants (WHV-M2) resulted in WHV replication. Southern blot and Northern blot tests showed that wild type and mutants both had similar DNA replication and transcription. It was concluded that the precore gene of the WHV genome is not essential for virus replication.

Risk of Kaposi's sarcoma and oroanal sexual contact

After contradictory findings from a number of previous studies, behavioral risk factors for Kaposi's sarcoma were examined in a case-control study of 202 people diagnosed with acquired immunodeficiency syndrome (AIDS) in 1991-1993 in Sydney, Australia. Cases comprised 67 men who developed Kaposi's sarcoma at or after a diagnosis of acquired immunodeficiency syndrome, and controls were 135 people who did not have Kaposi's sarcoma at the time of diagnosis of acquired immunodeficiency syndrome or during follow-up until 1995. Men who developed Kaposi's sarcoma were more likely to report having a history of sexually transmissible diseases and having engaged more frequently than controls in a number of sexual practices with casual partners in the period before they became aware of their human immunodeficiency virus (HIV) infection. However, the only sexual practice reported significantly more often by cases at the 0.05 significance level was insertive oroanal contact with casual partners (odds ratio = 2.6, 95 percent confidence interval 1.3-5.3). This association was not present for insertive oroanal contact with regular partners or for insertive oroanal contact after subjects became aware of their HIV infection. The relation was present both in men who had Kaposi's sarcoma at the time of interview and in those who developed it later. The relation was not affected by adjustment for time of HIV infection and diagnosis or for other sexual practices. These results can be interpreted as supporting the hypothesis that Kaposi's sarcoma in people with HIV is caused by an infectious agent transmitted by oral contact with feces.

Positive and negative regulation of type II TGF-beta receptor signal transduction by autophosphorylation on multiple serine residues

The type II transforming growth factor-beta (TGF-beta) receptor Ser/Thr kinase (TbetaRII) is responsible for the initiation of multiple TGF-beta signaling pathways, and loss of its function is associated with many types of human cancer. Here we show that TbetaRII kinase is regulated intricately by autophosphorylation on at least three serine residues. Ser213, in the membrane-proximal segment outside the kinase domain, undergoes intra-molecular autophosphorylation which is essential for the activation of TbetaRII kinase activity, activation of TbetaRI and TGF-beta-induced growth inhibition. In contrast, phosphorylation of Ser409 and Ser416, located in a segment corresponding to the substrate recognition T-loop region in a three-dimensional structural model of protein kinases, is enhanced by receptor dimerization and can occur via an intermolecular mechanism. Phosphorylation of Ser409 is essential for TbetaRII kinase signaling, while phosphorylation of Ser416 inhibits receptor function. Mutation of Ser416 to alanine results in a hyperactive receptor that is better able than wild-type to induce TbetaRI activation and subsequent cell cycle arrest. Since on a single receptor either Ser409 or Ser416, but not both simultaneously, can become autophosphorylated, our results show that TbetaRII phosphorylation is regulated intricately and affects TGF-beta receptor signal transduction both positively and negatively.

Binding of Bacillus thuringiensis Cry1Ac Toxin to Aminopeptidase in Susceptible and Resistant Diamondback Moths (Plutella xylostella)

Bacillus thuringiensis Cry1Ac toxin bound to a 120-kDa protein isolated from the brush border membranes of both susceptible and resistant larvae of Plutella xylostella, the diamondback moth. The 120-kDa protein was purified by Cry1Ac toxin affinity chromatography. Like Cry1Ac-binding aminopeptidase N (EC 3.4.11.2) from other insects, this protein was eluted from the affinity column with 200 mM N-acetylgalactosamine. The purified protein had aminopeptidase activity and bound Cry1Ac toxin on ligand blots. Purified aminopeptidase was recognized by antibodies to the cross-reacting determinant found on phosphatidylinositol-specific phospholipase C-solubilized proteins. The results show that the presence of Cry1Ac-binding aminopeptidase in the brush border membrane is not sufficient to confer susceptibility to Cry1Ac. Furthermore, the results do not support the hypothesis that resistance to Cry1Ac was caused by lack of a Cry1Ac-binding aminopeptidase.

[Hot-point mutations of viral C gene during hepatitis B virus infection]

To investigate the relationship of the HBV C gene mutations with the disease progress, the hotpoint mutations of pre- C stop28 and C region L97 were examined with restrictio-fragment-length-polymorphism (RFLP) technique in 91 hepatitis patients with diverse clinical features and HBe status. Both mutations were almost not seen in acute hepatitis B and chronic asymptomatic virus carriers; rarely in chronic persistent hepatitis and frequently in chronic active hepatitis (CAH) and active liver cirrhosis (ALC), accounting for 80% and 78% in CAH and ALC respectively. The pre-C mutant was mixed with wild strain in 11 of 31 patients who were HBeAg-positive CAH and ALC; on the other hand, the wild strain also coexisted with variant in anti-HBe-positive cases. So did the L97 in both HBeAg- and anti- HBe-positive cases. Possibly, both the mutant and the wild strain are usually in a relatively growth and decline status. So, the hot-point mutations of HBV C gene were closely related with the disease activity.

SIR2 and SIR4 interactions differ in core and extended telomeric heterochromatin in yeast

Yeast core telomeric heterochromatin can silence adjacent genes and requires RAP1, SIR2, SIR3, and SIR4 and histones H3 and H4 for this telomere position effect. SIR3 overproduction can extend the silenced domain. We examine here the nature of these multiprotein complexes. SIR2 and SIR4 were immunoprecipitated from whole-cell extracts. In addition, using formaldehyde cross-linking we have mapped SIR2, SIR4, and RAP1 along telomeric chromatin before and after SIR3 overexpression. Our data demonstrate that SIR2 and SIR4 interact in a protein complex and that SIR2, SIR3, SIR4, and RAP1 map to the same sites along telomeric heterochromatin in wild-type cells. However, when overexpressed, SIR3 spreads along the chromosome and its interactions are dominant to those of SIR4 and especially SIR2, whose detection is decreased in extended heterochromatin. RAP1 binding at the core region is unaffected by SIR3 overproduction and RAP1 shows no evidence of spreading. Thus, we propose that the structure of core telomeric heterochromatin differs from that extended by SIR3.

[Fas expression and DNA impairment of hepatocyte in chronic hepatitis B]

To elucidate the role of apoptosis in the pathological lesion of hepatitis B virus (HBV) infection, biopsied liver tissue specimens of 38 patients with chronic hepatitis B of varying severity were investigated with in situ immunohistochemistry and TUNEL test. Apoptotic hepatocytes were found to be rare, while the nuclei of many cells were positively stained with TUNEL, suggesting 3'-OH ends generated as the DNA was impaired. Of the 17 cases with mild lesion or without piecemeal necrosis, 14 were negative or weakly positive with both Fas and TUNEL test. Of the 7 cases with piecemeal and bridging necrosis, none was strongly positive. In the 14 cases with active hepatitis and early cirrhosis, strongly positive results with Fas were found in 9 and with TUNEL in 3 respectively. It is suggested that the cytotoxic T lymphocyte (CTL)-Fas-apoptosis mechanism was involved in the hepatocyte death of hepatitis B as well. The Fas expression, DNA damage and apoptotic cells distributed mostly in the piecemeal necrosis region, and the ballooning and the necrotic hepatocytes were also clustering in this region. As both the apoptosis and necrosis are mediated by CTL, they are closely related: while transducted by different ways, they occurred independently.

Signaling by chimeric erythropoietin-TGF-beta receptors: homodimerization of the cytoplasmic domain of the type I TGF-beta receptor and heterodimerization with the type II receptor are both required for intracellular signal transduction

Transforming growth factor-beta (TGF-beta) affects multiple cellular functions through the type I and type II receptor Ser/Thr kinases (TbetaRI and TbetaRII). Analysis of TGF-beta signaling pathways has been hampered by the lack of cell lines in which both TbetaRI and TbetaRII are deleted, and by the inability to study signal transduction by TbetaRI independently of TbetaRII since TbetaRI does not bind TGF-beta directly. To overcome these problems, we constructed and expressed chimeric receptors with the extracellular domain of the erythropoietin receptor (EpoR) and the cytoplasmic domains of TbetaRI or TbetaRII. When expressed in Ba/F3 cells, which do not express EpoR, Epo induces the formation of a heteromeric complex between cell surface EpoR-TbetaRI and EpoR-TbetaRII chimeras. Neither the EpoR-TbetaRI nor the EpoR-TbetaRII chimera interacts with endogenous TGF-beta receptors. Ba/F3 cells expressing both EpoR-TbetaRI and EpoR-TbetaRII chimeras, but not EpoR-TbetaRI or EpoR-TbetaRII alone, undergo Epo-induced growth arrest. When expressed in Ba/F3 cells in the absence of the EpoR-TbetaRII chimera, EpoR-TbetaRI(T204D), a chimeric receptor with a point mutation in the GS domain of TbetaRI that is autophosphorylated constitutively, triggers growth inhibition in response to Epo. Thus, both homo- and heterodimerization of the cytoplasmic domain of the type I TGF-beta receptor are required for intracellular signal transduction leading to inhibition of cell proliferation. These chimeric receptors provide a unique system to study the function and signal transduction of individual TGF-beta receptor subunits independently of endogenous TGF-beta receptors.

Whole genome analysis of hepatitis B virus from four cases of fulminant hepatitis: genetic variability and its potential role in disease pathogenicity

The precore stop-codon variant of hepatitis B virus (HBV) has been associated with fulminant hepatitis but is also found in patients with persistent infection and chronic hepatitis. We have examined the possibility that the severe outcome of infection in patients with fulminant disease may be a result of additional genomic variation. We sequenced the entire HBV genome from three patients of Greek and one patient of Chinese origin with fulminant hepatitis, and from two patients with hepatitis B e antigen (HBeAg) positive chronic infection from the same regions, using direct sequencing of amplified viral DNA. Three of the fulminant cases were infected with the precore stop-codon variant HBeAg negative) and the fourth with the wild-type (HBeAg) positive virus. We compared sequences from our four fulminant isolates, and an additional fulminant isolate reported by others, with HBeAg positive carriers from the same regions and 12 published HBV genomes. There was a higher number of nucleotide and amino-acid substitutions throughout the HBV genome in the precore variant fulminant sequences than in the wild type. A cluster of mutations previously identified in the X region (126-132) in sequences reported in Japanese patients and encompassing the Enhancer II-Core Promoter region (1751-1768), were not found in our patients. We conclude that although there are no changes common to all sequences of HBV isolates from fulminant cases, some of these changes are in recognized cis-acting regulatory elements, whilst others are in the immediate vicinity of such elements. The effect of these mutations on viral genome transcription must now be determined.

[Identification of vertical transmission of hepatitis B virus from mother to children by direct sequencing a segment of surface gene of hepatitis B virus]

SUBJECTIVE

To explore the reason for the failure to interrupt vertical transmission of hepatitis B virus (HBV) from mother to children in Chinese subjects by vaccination.

METHODS

HBV nucleotide sequences isolated from three sets of mother/children pairs were analyzed. HBV DNA from the surface antigen region encoding the amino acids 101 to 160 of hepatitis B surface antigen (HBsAg) was amplified and sequenced from HBsAg positive mother and their children.

RESULTS

Nucleotide and deduced amino acid sequences were absolutely identical in the mother and children in family one and two respectively. However, there were five nucleotides different in family one's isolates compared with the family two's isolates. All of them were a subtype. In one child of family three, with coexisted HBsAg and anti-HBs, sequencing result revealed a point mutation which predicted a change from glycine to arginine at residue 145 in the second loop of the determinant. The mother and another child had a glycine at this position.

CONCLUSION

This study revealed the vertical transmission linkage of HBV between the mother and children in a molecular level, and also first described a codon 145 immune escape mutant in Chinese vaccinated children.

The specificity of the transforming growth factor beta receptor kinases determined by a spatially addressable peptide library

Type I and II receptors for the transforming growth factor beta (TGF-beta) are transmembrane serine/threonine kinases that are essential for TGF-beta signaling. However, little is known about their in vivo substrates or signal transduction pathways. To determine the substrate specificity of these kinases, we developed combinatorial peptide libraries synthesized on a hydrophilic matrix that is easily accessible to proteins in aqueous solutions. When we subjected these libraries to phosphorylation by the cAMP-dependent protein kinase, we obtained the optimal peptide sequence RRXS (I/L/V), in perfect agreement with the substrate sequence deduced from mutagenesis and crystal structure analyses. By using the same libraries, we showed that the optimal substrate peptide for both the type I and II TGF-beta receptors was KKKKKK(S/T)XXX. Since the two kinases are thought to play different roles in intracellular signal transduction, it was a surprise to find that they have almost identical substrate specificity. Our method is direct, sensitive, and simple and provides information about the kinase specificity for all the amino acid residues at each position.

[Genetic variation in the cleavage site of the precore region of hepatitis B virus in Chinese patients with fulminant hepatitis]

In this study, a previously not documented variant of hepatitis B virus was described in Chinese patients with fulminant hepatitis. The entire precore/core region amplified from samples was cloned into a bacterial vector and sequenced by dideoxy chain termination reaction. Double amino acid substitutions were seen in the precore region in the isolates: one from glycine to aspartic acid at codon 29 previously reported; the other substitution of phenylalanine for valine at codon 17 in the cleavage site of hepatitis B virus. Loss of hepatitis B virus e antigen in these patients with fulminant hepatitis might therefore be due to the mutation in the cleavage site, rather than the emergence of a stop codon in the precore region of hepatitis B virus. Accumulation of hepatitis B e antigen precursor within the hepatocytes might account for the fulminant hepatitis exacerbation.

Development of Bacillus thuringiensis CryIC Resistance by Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae)

Selection of resistance in Spodoptera exigua (Hubner) to an HD-1 spore-crystal mixture, CryIC (HD-133) inclusion bodies, and trypsinized toxin from Bacillus thuringiensis subsp. aizawai and B. thuringiensis subsp. entomocidus was attempted by using laboratory bioassays. No resistance to the HD-1 spore-crystal mixture could be achieved after 20 generations of selection. Significant levels of resistance (11-fold) to CryIC inclusion bodies expressed in Escherichia coli were observed after seven generations. Subsequent selection of the CryIC-resistant population with trypsinized CryIC toxin resulted, after 21 generations of CryIC selection, in a population of S. exigua that exhibited only 8% mortality at the highest toxin concentration tested (320 (mu)g/g), whereas the 50% lethal concentration was 4.30 (mu)g/g for the susceptible colony. Insects resistant to CryIC toxin from HD-133 also were resistant to trypsinized CryIA(b), CryIC from B. thuringiensis subsp. entomocidus, CryIE-CryIC fusion protein (G27), CryIH, and CryIIA. In vitro binding experiments with brush border membrane vesicles showed a twofold decrease in maximum CryIC binding, a fivefold difference in K(infd), and no difference in the concentration of binding sites for the CryIC-resistant insects compared with those for the susceptible insects. Resistance to CryIC was significantly reduced by the addition of HD-1 spores. Resistance to the CryIC toxin was still observed 12 generations after CryIC selection was removed. These results suggest that, in S. exigua, resistance to a single protein is more likely to occur than resistance to spore-crystal mixtures and that once resistance occurs, insects will be resistant to many other Cry proteins. These results have important implications for devising S. exigua resistance management strategies in the field.