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T J Liang

Publications and source records attributed to T J Liang.

At least 55 records · Page 3Linked to original sources
PubMed1996

Proteasome complex as a potential cellular target of hepatitis B virus X protein.

Although the biological importance of hepatitis B virus X protein (HBX) in the life cycle of hepatitis B virus has been well established, the cellular and molecular basis of its function remains largely undefined. Despite the association of multiple activities with HBX, none of them appear to provide a unifying hypothesis regarding the true biological function of HBX. Identification and characterization of cellular targets of HBX remain an essential goal in the elucidation of the molecular mechanisms of HBX. Using the Saccharomyces cerevisiae two-hybrid system, we have identified and characterized a novel subunit of the proteasome complex (XAPC7) that interacts specifically with HBX. We also showed that HBX binds specifically to XAPC7 in vitro. Mutagenesis studies have defined the domains of interaction to be critical for the function of HBX. Furthermore, overexpression of XAPC7 appeared to activate transcription by itself and antisense expression of XAPC7 was able to block transactivation by HBX. Therefore, the proteasome complex is possibly a functional target of HBX in cells.

Amino Acid Sequence↗
PubMed1995

Molecular cloning of two types of cDNA encoding subunit RC6-I of rat proteasomes.

A new subunit, named RC6-I, of the rat 20 S proteasome was purified and the partial amino acid sequences of several peptide fragments obtained by digestion with lysyl-endopeptidase were determined by Edman degradation. Amplification of cDNAs encoding RC6-I by the polymerase chain reaction (PCR) technique revealed two types of cDNA, tentatively designated as RC6-IL and RC6-IS in order of size. The nucleotide sequences of the two cDNAs are identical except that RC6-IL contains an insertion of 18 nucleotides in the coding region compared with RC6-IS. The polypeptide predicted from the open reading frame of RC6-IS cDNA consists of 248 amino acid residues with a calculated molecular weight of 27,783. These values are consistent with those obtained by protein chemical analyses. Computer-assisted homology analysis showed that RC6-I belongs to the alpha-type subfamily of the proteasome gene family, which shows similarity to the alpha-subunit of the archaebacterium Thermoplasma acidophilum proteasome, and that the 18 nucleotide insert, encoding six amino acid residues, VVASVS, appears to be unique to RC6-IL, because this motif has not been conserved in any other alpha-type subunit. By reverse transcription (RT)-PCR analysis, the mRNAs for both RC6-IL and RC6-IS were found in all the rat tissues examined. These results suggest that proteasomes are present as a heterogeneous population, possibly for acquisition of diversity of functions.

Amino Acid Sequence↗
PubMed1995

Chronic leukocytoclastic vasculitis complicating HBV infection. Possible role of mutant forms of HBV in pathogenesis and persistence of disease.

A young woman developed arthritis and leukocytoclastic vasculitis, followed by hepatitis due to a precore mutant strain of hepatitis B virus (HBV) incapable of synthesizing HBe antigen. Tests for antibodies to HCV were persistently negative. Treatment of the patient with alpha interferon initially led to a severe exacerbation of hepatitis. Later, higher doses of interferon were tolerated and were associated with reduction of HBV replication and improvement in liver histopathology and serum aminotransferases. After interferon therapy, sequencing of HBV DNA from a repeat liver biopsy showed a cluster of new mutations, which may have led to alterations in immunodominant epitopes of viral proteins. The findings suggest that a "naturally occurring" mutant form of HBV was associated with chronic hepatitis and vasculitis in the patient, and that the immunological pressure on HBV produced by therapy with interferon may have led to other mutations in the viral genome with persistence of low-level HBV infection.

Adult↗
PubMed1995

[Relationship between anti-coagulation system changes of coronary heart disease patients and different syndrome-type in TCM].

The level of Antithrombin-III : antibody (ATIII : A), Antithrombin III: antigen (ATIII : Ag), protein C antigen (PC : Ag), Total protein S : antigen (TPS : Ag) and Free protein S : antigen (FPS : Ag) were determined in 46 cases of coronary heart disease (CHD) and 40 cases normal control with the thrombin gelplaque technique and the immunoelectrophoresis assay. The results showed: the level of the PC: Ag and TPS: Ag of Qi stagnation type of CHD were significantly higher than those in normal control group (P < 0.05), the level of the AIII: Ag, ATIII : Ag in blood stasis type of CHD were significantly less than those in control (P < 0.05). These suggested that the level of PC: Ag and TPS: Ag might be used as referential indices of the Qi stagnation type; the level of ATIII: A, ATIII : Ag might be used as those of blood stasis type in CHD.

Adult↗
PubMed1995

Association of hepatitis C virus and hepatocellular carcinoma in the United States.

Hepatocellular carcinoma (HCC) is a common cause of death from cancer on a worldwide basis. Chronic hepatitis B virus (HBV) infection is a well-documented pathogenic factor in the etiology of HCC, accounting for the majority of cases in certain geographic areas where HBV chronic-infection rates are high. Recent studies have implicated hepatitis C virus (HCV) infection as another major etiologic agent of hepatitis B surface antigen (HBsAg)-negative HCC. Studies in Europe have demonstrated that HCV infection is commonly associated with HCC; the prevalence rates of HCV ranged from 39% to 77% of HCC patients in these studies. In areas where HBV infection is endemic, such as Africa and Japan, the prevalence rates of anti-HCV in individuals with HCC have been reported at 29% and 68%, respectively. The significance of HCV and HBV infections in contributing to the occurrence of HBsAg-negative HCC has not been well established in the United States. The clinical consequences of infection with different genotypes of HCV (defined by nucleotide sequence divergence) are largely unknown: several studies have suggested differences among genotypes in terms of clinical expression, disease progression, and response to treatment with interferon. Our recent studies demonstrated that HCV and occult HBV infections account for the majority of cryptogenic HCC cases in the United States. Preliminary studies on the prevalence of HCV genotypes in patients with or without HCC but otherwise matched for hepatic histology did not reveal any association of specific genotype(s) with development of HCC.

Carcinoma, Hepatocellular↗
PubMed1994

Presence of hepatitis B and C viral genomes in US blood donors as detected by polymerase chain reaction amplification.

Hepatitis C virus (HCV) represents a major cause of posttransfusion hepatitis worldwide. Posttransfusion hepatitis associated with hepatitis B virus (HBV) continues to occur. HBsAg-negative donor sera from the Rhode Island Blood Center between 1987 and 1988 were screened using more sensitive techniques to assess the prevalence of low level HBV infection. Group I consists of 866 healthy blood donors without HBV serologic markers, group II consists of 377 donors with ALT elevations (> 45 IU/L), group II consists of 148 donors positive for anti-HBc, and group IV consists of eight donors positive for both surrogate markers. A sensitive monoclonal immunoradiometric assay (M-IRMA) was employed for detection of HBsAg-associated epitopes (detection limit of 20 pg/ml) in serum. A subset of sera were analyzed for the presence of HBV DNA using the method of anti-HBs capture of HBV related virions in serum followed by polymerase chain reaction (PCR) amplification. Using these techniques, 0.8% and 1.7% of donors were positive for HBsAg and HBV DNA respectively in group I. In contrast, 0.9% and 9.5% in group II and 0.7% and 18.1% in group III were positive, respectively. There were eight donors with both ALT elevation and anti-HBc; and four (50%) of these were positive for HBV DNA. In the group with anti-HBc, the majority (80%) of donors with HBV DNA had either no or low (signal to noise ratio < 10) anti-HBs titer. Using anti-HCV testing and reverse transcription-PCR for detection of HCV genomes, we detected evidence of HCV infection in nine of the 49 donors with low level HBV DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Donors↗
PubMed1994

Enhanced replication of a hepatitis B virus mutant associated with an epidemic of fulminant hepatitis.

Hepatitis B virus (HBV) mutants unable to synthesize HBV e antigen have been described in association with fulminant hepatitis. We have cloned and sequenced the entire viral genome of an HBV strain associated with an epidemic of fulminant hepatitis. This strain contained, in addition to two G-to-A mutations in the precore region (nucleotides 1898 and 1901), numerous other mutations in conserved nucleotide positions resulting in significant amino acid substitutions in HBV gene products. We introduced either or both of the two G-to-A mutations into wild-type HBV by oligonucleotide-directed mutagenesis and generated replication-competent constructs of these mutants as well as the fulminant strain. Viral antigen synthesis, transcription, and replication were analyzed after transfection into human hepatoma cells. All viral constructs produced and secreted similar levels of envelope proteins (HBV surface antigen). Analysis of cellular lysate for core-specific immunoreactivity demonstrated a much higher level of core-associated antigens in cells transfected with the fulminant strain. While cells transfected with mutant and wild-type HBV DNAs synthesized similar levels of viral RNAs, the fulminant strain directed the synthesis of a much higher level of core-associated replicative intermediates (as well as virion particles) than the wild type and mutants with either or both of the precore mutations. Increase in the encapsidation of pregenomic RNA into core particles likely the basis for the enhanced replication associated with the fulminant strain. Our study suggests that an HBV mutant with enhanced viral replication may be important in the pathogenesis of fulminant hepatic failure, and mutations other than the precore mutations may be responsible for this variant behavior.

Base Sequence↗
PubMed1994

Hepatitis B virus precore mutation and fulminant hepatitis in the United States. A polymerase chain reaction-based assay for the detection of specific mutation.

Hepatitis B virus (HBV) variants with precore mutation(s) resulting in the absence of HBeAg production have been associated with the occurrence of fulminant hepatitis in Japan, Israel, and southern Europe, where the prevalence of this HBV strain appears common. In areas such as United States, where HBV infection is not endemic, the role of this mutant virus in fulminant hepatitis is unknown. We developed an amplification refractory mutation detection system to detect specifically the presence of the G to A mutation at nucleotide position 1898, which is the most frequently observed mutation resulting in a precore stop codon. In addition, this method provided a quantitative measurement of the relative ratio of one strain to the other. Using this system, we tested HBV strains for the presence of the stop codon mutation in sera from 40 cases of fulminant hepatitis B occurring in the United States. Serum HBV DNAs from 28 patients were analyzed successfully. A mixture of wild-type and mutant strains in various ratios were observed in 15 patients, wild type exclusively in 11, and mutant exclusively in 2. Four of these patients had undergone liver transplantation for HBV-associated cirrhosis and developed fulminant HBV-associated hepatitis after transplantation. Pre- and posttransplant serum samples from one patient were analyzed: a mixture of wild-type and mutant HBV strains was detected in both samples. Our study demonstrated that both wild-type and mutant HBV strains are associated with fulminant hepatitis, and that in some patients in the United States, factors other than precore mutations contribute to the development of fulminant hepatitis.

Adolescent↗
PubMed1993

HCV RNA in patients with chronic hepatitis C treated with interferon-alpha.

In order to assess the efficacy of interferon-alpha on hepatitis C viral RNA in patients with chronic hepatitis C, we analyzed the levels of HCV RNA in sera and liver tissues of 16 patients pre- and posttreatment using a semiquantitative polymerase chain reaction method. Fifteen of 16 patients were positive for anti-HCV antibodies by four-antigen recombinant immunoblot assay (4-RIBA). Only two patients demonstrated normalization of ALT in response to interferon; three patients showed a partial response. Only one patient from the partial responder group displayed a significant reduction of HCV RNA level posttreatment. In the nonresponder group, several patients, although their ALTs remained elevated, demonstrated significant decreases in HCV RNA levels in either serum or liver in response to interferon. Our data suggest that interferon treatment of chronic hepatitis C may not be effective in eradicating HCV infection and a reduction in ALT is infrequently associated with a decrease in HCV RNA level in either serum or liver. Cessation of treatment is frequently associated with the recrudescence of HCV replication and disease.

Adult↗
PubMed1993

Fulminant or subfulminant non-A, non-B viral hepatitis: the role of hepatitis C and E viruses.

BACKGROUND: Although non-A, non-B (NANB) viral hepatitis has been implicated as an etiology of fulminant hepatitis, hepatitis C virus (HCV) has not been shown to result in acute hepatic failure and hepatitis E virus (HEV) has predominantly been associated with fulminant hepatitis among pregnant women. METHODS: Using polymerase chain reaction to detect HCV and HEV genomes, four-antigen radioimmunoblot assay (4-RIBA) to measure anti-HCV antibodies, and enzyme-linked immunosorbent assay (ELISA) to detect anti-HEV immunoglobulin M (IgM) antibodies, 17 patients with sporadic fulminant or subfulminant hepatitis of presumed NANB viral etiology were studied. RESULTS: The diagnosis of acute NANB viral hepatitis was made based on clinical information, serological tests, biochemical profiles, and pathological features. All 17 patients were negative for anti-HEV IgM antibodies and HEV RNA in either serum and/or liver. HCV RNAs were detected in 2 patients although anti-HCV antibodies were negative in all of them. CONCLUSIONS: It is shown that HCV is infrequently associated with and HEV is not an identifiable cause of presumed NANB fulminant or subfulminant hepatitis in this patient population. Although further studies will be required for identification of the causative agent, it is possible that another agent is responsible for the occurrence of sporadic NANB fulminant or subfulminant hepatitis.

Acute Disease↗
PubMed1993

A novel hepatitis B virus (HBV) genetic element with Rev response element-like properties that is essential for expression of HBV gene products.

Many viruses possess complex mechanisms involving multiple gene products and cis-regulatory elements in order to achieve a fine control of their gene expression at both transcriptional and posttranscriptional levels. Hepatitis B virus (HBV) and retroviruses share many structural and functional similarities. In this study, by genetic and biochemical analyses, we have demonstrated the existence of a novel genetic element within the HBV genome which is essential for high-level expression of viral gene products. This element is located 3' to the envelope coding region. We have shown that this genetic element is cis acting at the posttranscriptional level and that its function is exerted at the level of RNA processing as part of transcribed sequences. This RNA element is also functional in the context of a heterologous gene. Similar to the function of Rev-Rev response element interaction of human immunodeficiency virus type 1, this element appears to inhibit the splicing process and facilitate the transport and utilization of HBV transcripts.

Base Sequence↗
PubMed1993

Targeted transfection and expression of hepatitis B viral DNA in human hepatoma cells.

A soluble DNA carrier system consisting of an asialoglycoprotein covalently linked to poly-L-lysine was used to bind DNA and deliver hepatitis B virus (HBV) DNA constructs to asialoglycoprotein receptor-positive human hepatoma cells. 4 d after transfection with surface or core gene expression constructs, HBsAg and HBeAg in the media were measured to be 16 ng/ml and 32 U/ml per 10(7) cells, respectively. Antigen production was completely inhibited by the addition of an excess of asialoorosomucoid. On the other hand, asialoglycoprotein receptor-negative human hepatoma cells, SK-Hep1, did not produce any viral antigens under identical conditions after incubation with HBV DNA complexed to a conjugate composed of asialoorosomucoid and poly-L-lysine. Using a complete HBV genome construct, HBsAg and HBeAg levels reached 16 ng/ml and 16 U/ml per 10(7) cells, respectively. Northern blots revealed characteristic HBV RNA transcripts including 3.5-, 2.4-, and 2.1-kb fragments. Intracellular and extracellular HBV DNA sequences including relaxed circular, linear and single stranded forms were detected by Southern blot hybridization. Finally, 42-nm Dane particles purified from the spent cultures medium were visualized by electron microscopy. This study demonstrates that a targetable DNA carrier system can transfect HBV DNA in vitro resulting in the production of complete HBV virions.

Carcinoma, Hepatocellular↗
PubMed1993

Viral pathogenesis of hepatocellular carcinoma in the United States.

Chronic hepatitis B virus infection is closely associated with the development of hepatocellular carcinoma, which is a major cause of cancer death worldwide. Recent studies have implicated hepatitis C virus infection as a major pathogenic agent of HBsAg-negative hepatocellular carcinoma. The significance of hepatitis C virus and hepatitis B virus infections in the occurrence of HBsAg-negative hepatocellular carcinoma has not been well established in the United States. We studied 91 HBsAg-negative American patients with hepatocellular carcinoma for evidence of hepatitis C virus or hepatitis B virus infection. These patients had no other predisposing factors to hepatocellular carcinoma. A sensitive polymerase chain reaction was employed to detect hepatitis C virus RNA and hepatitis B virus DNA in serum and liver. Three sets of hepatitis C virus and hepatitis B virus primers were used to optimize the detection of viral genomes. Hepatitis C virus antibodies were measured with second-generation immunoassays. Twenty-six (29%) of these patients carried low levels of hepatitis B virus DNA in either serum, liver/tumor tissue or both. On the basis of the results from serological and polymerase chain reaction analyses of serum and liver, we found that 53 of 91 patients (58%) exhibited evidence of hepatitis C virus infection. When data were combined, 14 patients (15%) had evidence of hepatitis B virus/hepatitis C virus coinfection, whereas 12 (13%) were infected with hepatitis B virus alone and 39 (43%) had hepatitis C virus only. Twenty-six (29%) had no markers of hepatitis B virus or hepatitis C virus infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗