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.