p53 overexpression in small hepatocellular carcinomas containing two different histologic grades.

There is evidence to suggest that a focus of less-differentiated hepatocellular carcinoma (HCC) may arise within a pre-existing well-differentiated HCC, eventually replacing it. In the present study, the p53 tumor suppressor gene was analyzed by immunohistochemistry in 31 hepato-cellular carcinomas (HCCs) containing two or more regions in the same nodule with different histologic grades. p53 was overexpressed in the nucleus in 13 of 31 HCCs (42%), in seven of which p53 overexpression was seen only in the less-differentiated area of the tumor. This suggests that overexpression of presumed mutant p53 may have contributed to dedifferentiation during the development of HCC.

Binding of wild-type p53 by topoisomerase II and overexpression of topoisomerase II in human hepatocellular carcinoma.

In order to study the mechanisms by which p53 function is regulated, human wild-type p53 cDNA was cloned into a vaccinia virus vector and the expressed p53 protein was used to investigate binding of the p53 by cellular proteins from a cDNA expression library from human liver. One protein that bound wild-type p53 had > 99% homology with DNA topoisomerase IIb. p53 protein was coimmunoprecipitated from topoisomerase II-rich cell lysates (but not from topoisomerase II-deficient cell lysates) by an antibody to topoisomerase IIa and IIb. This binding was shown to occur without a dsDNA intermediary. Hepatocellular carcinomas (HCCs) and adjacent nontumorous liver tissues from ten patients were studied to determine the level of expression of topoisomerase II and p53. Overexpressed topoisomerase II proteins were detected by western blot in six of ten HCCs (60%), including several in which presumed wild-type p53 was detected by immunohistochemistry. No topoisomerase II expression was detectable in the ten nontumorous liver tissues from the same patients or in a sample of normal human liver.

Sequence characterization of the 5' noncoding region of GB virus C/hepatitis G virus.

The nucleotide sequences of the 5' noncoding region of the GB virus C/hepatitis G virus (GBV-C/HGV) were determined in 18 isolates from the United States. Two genotypes have been classified based on the sequence heterogeneity within the 5' noncoding region of GBV-C/HGV. The most distantly related isolates between the two genotypes were 84.6% identical. Sequence identity of the isolates within a genotype was 95-99%. The 5' noncoding region of this virus contains four highly conserved domains. These conserved elements would facilitate the selection of optimal primers for the sensitive detection of GBV-C/HGV RNA by PCR. In addition, they suggest a crucial role for this region in viral replication and/or gene expression. Detection of genotypic variation among GBV-C/HGV infected individuals may provide further insight into the possible pathogenicity and into the transmission of the virus.

Identification of two p53-binding proteins using a recombinant vaccinia virus containing the wild-type human p53 gene.

A recombinant vaccinia virus was constructed using the wild-type human p53 gene as an insert. The p 53 protein produced by this recombinant virus was used to investigate p53 binding proteins in seventeen cell lines, including 10 derived from human hepatocellular carcinoma, four from other human cancers, and three from non-human primate tissues. In all 17 cell lines tested, two proteins of 40 kD and 50 kD were identified that bound to wild-type p53 and that may be cellular regulators of p53 function.

Nuclear localization of a double-stranded RNA-binding protein encoded by the vaccinia virus E3L gene.

We produced a B cell hybridoma (TW2.3) from vaccinia virus-infected mice that secreted a monoclonal antibody (MAb) reactive with a 25-kDA early viral protein that was localized by laser scanning confocal microscopy to the nucleus and cytoplasmic viral factory regions of infected cells. By cell-free translation of mRNA selected by hybridization to a complete library of vaccinia virus DNA fragments, the immunoreactive polypeptide was mapped to open reading frame E3L. The RNA start site of an early promoter was located 26 nucleotides upstream of the first methionine codon of E3L. Evidence was obtained that translation initiation occurs in vivo and in vitro at both the first and second methionine codons to produce major and minor polypeptides of 25 and 19 kDa, respectively. Both polypeptides bound double-stranded RNA, confirming the recent report of H.-W. Chang, J. C. Watson, and B. L. Jacobs (Proc. Natl. Acad. Sci. USA 89, 4825-4829, 1992). Other vaccinia virus proteins were not required for the nuclear localization of the E3L protein, since MAb TW2.3 bound to the nuclei of uninfected cells that were transfected with the E3L gene under the control of the SV40 early promoter. We also demonstrated that the E3L protein can bind to nuclei of aldehyde fixed and detergent permeabilized uninfected cells. This binding was abrogated by treatment of the cells with RNase but not DNase. The nuclear and cytoplasmic locations of the double-stranded RNA binding protein are consistent with multiple functions in the vaccinia virus infectious cycle.