Biomedical subjects
Publications and source records attributed to R Koshy.
We have studied the c-myc gene as a possible target of HBV X protein in liver carcinogenesis. Our results indicate that trans-activation by X protein occurs via PKC/AP1 signal transduction, suggesting a possible two-step mechanism in HBV related liver carcinogenesis.
A new enhancer ENII, located in the X open reading frame and immediately upstream of the core gene promoter, has recently been identified in the genome of hepatitis B virus. We have studied the functional constituents of this new enhancer in different cell lines. ENII can be divided into two functional elements, A and B, corresponding to two major binding sequences for nuclear protein factors. Element A alone gave very low activity; however, it was a modulatory element important for cell-type specificity. Element B was shown to be the basic functional element of ENII, which retained about 70% of the enhancer activity of the complete ENII in HepG2 cells. Element B can be further dissected into three subunits, B1, B2, and B3, which act synergistically. A 52-bp sequence is identified as the core sequences of element B. A model for the mechanism of ENII function is proposed.
A hepatoblastoma cell line transfected with hepatitis B virus (HBV) DNA (Hep G2.2.15) was used to investigate the effects of interferons (IFNs) on HBV replication and hepatocellular gene expression. IFN-alpha 2b or -beta inhibited HBV replication transiently. In parallel, there was a decrease in the amount of HBV mRNA. Hepatitis B surface antigen and early antigen secretion were not influenced; however, their intracellular levels diminished during treatment. The cellular 2',5'-oligoadenylate synthetase activity was increased 9- to 18-fold during treatment of cells with IFN-gamma, -alpha, or -beta. The number of IFN-alpha and -beta receptors was down-regulated, while the number of IFN-gamma receptors remained constant. The expression of major histocompatibility complex class I antigens was stimulated by addition of IFN-alpha or -beta. These data show that both IFN-alpha and -beta can effectively inhibit HBV replication and induce a cellular IFN response in Hep G2.2.15 cells similar to that seen in humans.
Hepatitis B virus (HBV) is regarded as the main aetiologic factor in the development of human hepatocellular carcinoma (HCC), one of the most frequent fatal malignancies worldwide. Detection of integrated HBV sequences in the cellular DNA of almost all HCCs studied, and the recent finding that the integrated HBV open reading frame (orf) X encodes a transactivating activity, supports the notion that integrated HBV DNA could contribute to liver carcinogenesis by activation of cellular genes in trans. But not all HCCs seem to harbour a functional orf X. We report here that 3'-truncated preS2/S sequences in integrated HBV DNA of liver cell carcinomas encode a so far unidentified transcriptional trans-activation activity. This activity is also produced by an artificially 3'-truncated preS2/S gene of the wild-type HBV genome. Besides the simian virus 40 promoter of the reporter plasmid pSV2CAT, the promoter of the human c-myc oncogene can also be activated. These results, taken together with the fact that preS/S is the only HBV gene found to be integrated in almost every HBV-related HCC analysed so far, indicate that trans-activation by integrated preS2/S sequences is a possible mechanism for HBV-associated oncogenesis.
The X gene of wild-type hepatitis B virus or integrated DNA has recently been shown to stimulate transcription of a variety of enhancers and promoters. To further delineate the viral sequences responsible for trans-activation in hepatomas, we cloned the single hepatitis B virus insert from human hepatocellular carcinoma DNA M1. The plasmid pM1 contains 2004 base pairs of hepatitis B virus DNA subtype adr, including truncated preS/S sequences and the enhancer element. The X promoter and 422 nucleotides of the X coding region are present. The entire preC/C gene is deleted. In transient cotransfection assays using Chang liver cells (CCL 13), pM1 DNA exerts a 6- to 10-fold trans-activating effect on the expression of the pSV2CAT reporter plasmid. The trans-activation occurs by stimulation of transcription and is dependent on the simian virus 40 enhancer in the reporter plasmid. Deletion analysis of pM1 subclones reveals that the trans-activator is encoded by preS/S and not by X sequences. A frameshift mutation within the preS2 open reading frame shows that this portion is indispensable for the trans-activating function. Initiation of transcription has been mapped to the S1 promoter. A comparable trans-activating effect is also observed with cloned wild-type hepatitis B virus sequences similarly truncated. These results show that a transcriptional trans-activator function not present in the intact gene is generated by 3' truncation of integrated hepatitis B virus DNA preS/S sequences.
We have identified a tumour-related 43 kd cytoplasmic protein (LC/p43) using a monoclonal antibody against the total proteins of human hepatoma cell line PLC/PRF/5. LC/p43 is preferentially expressed in a variety of tumours of human and animal origin, whereas no expression was detected in several normal adult tissues tested. LC/p43 expression was induced in rodent fibroblasts upon transfection with several viral oncogenes. Expression in non-transformed peripheral blood lymphocytes could be induced by treatment with phytohaemagglutinin (PHA) and subsequent culture with interleukin II, whereas retinoic acid treatment of transformed cells caused a drastic reduction of the antigen in the cells. Sequence analysis of three tryptic peptides of LC/p43 revealed 50-70% homology to different domains of the eukaryotic and prokaryotic translation-elongation factors EF1-alpha and EF-Tu, respectively.
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A controlled, randomized trial of a short-term, medium-dose combination therapy of beta- and gamma-interferon was performed in 20 patients with chronic active hepatitis B. According to clinical, biochemical, and histologic findings that were followed up for 16-24 mo, the combined treatment was successful in 5 of 10 patients. Two of the patients eliminated the virus completely, as confirmed by Southern blotting of hepatocellular deoxyribonucleic acid (DNA) against hepatitis B virus DNA. In the other 3 responders hepatitis B surface antigen persisted in the absence of hepatitis B e antigen, replicating hepatitis B virus DNA in the liver and inflammatory disease activity. Two of these responders with persistent hepatitis B surface antigen had hepatitis B virus DNA integrated into the hepatocyte genome and 1 responder had nonreplicating, episomal virus DNA. In the control group of 10 patients one spontaneous remission occurred. Antiviral treatment was significantly (p less than 0.05) more successful within the first 4 yr after infection (5 responders of 6 treated patients) than after longer disease duration (no responder of 4 treated patients). The results of this pilot study suggest that a combination of beta- and gamma-interferon may be an effective therapy for chronic active hepatitis B when started early after infection.
We describe in this report a unique cDNA clone isolated from a cDNA library of the human hepatoma cell line PLC/PRF/5. The clone which was isolated by using a hepatitis B virus (HBV) hybridization probe consists of HBV DNA sequences flanked by cellular sequences on either side. 5' flanking sequences are homologous to a nuclear integrate of the mitochondrial gene URF4 (1) and are in antisense orientation with respect to the viral DNA. The 3' sequences are homologous to the flanking sequences in the previously described genomic PLC/PRF/5 clones pAL10.5 and pAL10.7 (2), or clones AL26 and AL26a, respectively (3). Nucleotide sequencing and hybridization data suggest that the mRNA from which the cDNA was derived was spliced and could have been transcribed from one of the above-mentioned integrates. Consensus promoter sequences located on the antisense strand of the mitochondrial URF4 and predicted to lie 5' to the HBV sequences might have allowed the expression of the transcript.
We report here on a transactivating function of HBV DNA. The effect is shown by stimulation of transient expression of pSV2cat DNA in cotransfected human liver CCL13 cells. Transfection experiments with plasmid constructs containing different HBV DNA fragments and Northern analyses of RNA from cells transfected with these recombinant plasmids indicate that a transactivating function is encoded within the X-ORF. A frameshift mutation within the X gene causes loss of activity thus demonstrating requirement of a protein. The increase in the level of CAT-specific RNA suggests that the transactivation is by transcriptional enhancement. Constitutive expression of the transactivator function was also observed in cells stably transfected with HBV DNA. A number of eukaryotic promoters, SV40-early, HSV-TK, HTLV-I and RSV LTRs were responsive to transactivation by HBV DNA. However, the MMTV LTR and the human metallothionein promoter (MTIIA) were considerably less responsive than the others. The transactivational potential of HBV DNA was much higher in human cells and cells of higher primates than in rodent cells, thereby indicating interacting cellular factors. These results introduce additional considerations for the role of HBV in the development of hepatocellular tumors.
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We have previously reported the cloning and structural analysis of integrated hepatitis B virus DNA copies from the human hepatoma cell line PLC/PRF/5. Here we show that the cloned DNA fragments of 10.7 kb and 10.5 kb contain intact coding sequences for HBsAg since Ltk- cells transfected with these DNAs secrete considerable amounts of HBsAg. We show for the 10.7-kb fragment that multiple readthrough messages composed of viral as well as cellular sequences are transcribed. These RNAs differ only in their 3' sequences. Furthermore, the 10.7-kb insert leads to a substantial increase in HBsAg produced compared with HBV DNA and with the 10.5-kb insert. We provide evidence that the different 3' sequences on the HBsAg transcripts account for the augmentation of expression.
Hepatitis B virus (HBV) DNA is often found integrated in the genome of infected human liver cells and is supposed to be related to the development of primary liver carcinoma (PLC). Four clones of HBV DNA-containing sequences derived from DNA of the human PLC-derived cell line PLC/PRF/5 are discussed. The viral sequences show no intricate rearrangements excepting for a duplication and an inversion in one case, and a deletion in another. In all cases integration of the viral DNA was seen to be in a region which is single-stranded in the unintegrated HBV DNA. Sequence homologies between human and viral DNA flanking the integration sites have been detected. That may have a functional role in integration. Nucleotide sequence analyses of regions encompassing the viral-human junctions reveal open reading frames which consist of viral and/or human information. The possible expression of chimeric or cellular proteins may play a role in tumour development, and offers directions for further investigations.
DNA of hepatitis B virus is found to be integrated into the genome of infected human liver cells and may be related to the development of primary liver carcinoma. We have previously reported the cloning of cellular DNA with integrated HBV sequences from the PLC/PRF/5 cell line which derives from a human primary liver carcinoma. Two clones, designated as A-10.7 and A-10.5, and a third uncloned fragment are compared by restriction enzyme mapping, hybridization and nucleotide sequencing. The results indicate that amplification of integrated viral DNA and host flanking regions has occurred, followed by transposition and/or major deletions. The implications of these findings for the development of primary liver carcinoma are discussed.
The human hepatoma cell line PLC/PRF/5 produces tumours and lung metastases in nude athymic mice. Here we describe how detection of hepatitis B virus surface antigen, a marker of these cells, as led to identification of pancreatic and muscle metastases. The antigen was shown in the tissues, and antigen-producing PLC/PRF/5 cells were isolated from them. The number of cells detectable by this method is between 5 and 10 million. The principle used here may be adaptable be useful in studying micrometastasis formation in other systems.
The DNA of hepatitis B virus (HBV) can integrate into the genomes of infected human liver cells and may be related to the development of primary liver carcinoma (PLC). This report describes the analysis of three integrated HBV DNA sequences cloned from DNA of the human PLC cell line PLC/PRF/5. In all these sequences, integration of the viral DNA is at a site that is single-stranded (gap) in the unintegrated HBV DNA. Contrary to some speculations, there are no large terminal redundancies flanking the inserts as found in retroviral proviruses. The viral sequences show no obvious rearrangements in these clones, but integration can be associated with deletions in the viral DNA and also apparently in the host DNA.
Hepatitis B virus-related DNA was detected in the chromosomal DNA of three out of seven hepatocellular carcinomas and two out of five cirrhosis samples examined, by means of the blot-hybridization technique, described by Southern (1975). The integration patterns were not identical but some similarities raise the question of whether there are some preferred sites of viral integration.
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