Hepatoma-associated nonhistone chromosomal proteins are present in active chromatin

Hepatoma-associated nuclear matrix nonhistone antigens

Polyclonal antibodies generated against a group of high molecular weight nonhistone proteins from Morris hepatoma 7777 were used in immunological studies of hepatoma-associated nonhistone proteins in rat and hamster. We revealed the presence of cross-reactive antigens in rat Morris hepatomas 7777 and 8994, and in hamster Kirkman-Robbins hepatoma, but not in normal rat or hamster livers. These specific nonhistone proteins were found to be preferentially localized in the nuclear matrix of rat Morris hepatoma 7777 as well as hamster Kirkman-Robbins hepatoma.

Nuclear antigen with a molecular weight of 48,000 associated with malignant transformation

1. Analysis of immunoblots of one- and two-dimensional electropherograms of non-histone proteins from Kirkman-Robbins hepatoma, Morris hepatoma 7777, regenerating liver and normal liver demonstrated the presence of elevated level of nuclear antigen with mol. wt of 48,000 and pI of 5.4 in tumour cells. 2. Small amounts only were detected in proliferating and quiescent cells suggesting that different expression of this component may reflect biochemical events related to malignant transformation rather than to general cell activation.

Association of fibronectin-like antigens in chromatin preparations from rat hepatoma cells

High molecular weight hepatoma-associated nonhistone chromosomal proteins (NHPs) in transplantable rat hepatoma cells were reported previously from this laboratory. A cDNA library prepared from Morris hepatoma 7777 cells was screened with the polyclonal antibodies against hepatoma NHPs and a positive cDNA clone (lambda P2A1) was isolated. DNA sequence analysis revealed that the cDNA clone was identical to that of rat fibronectin (FN). The polyclonal antibodies against hepatoma NHPs were shown to bind specifically to both rat plasma FN and the fusion proteins encoded by lambda P2A1. A monoclonal antibody specific to rat plasma FN also recognized high molecular weight antigens of hepatoma NHPs in a pattern similar to that demonstrated with the polyclonal antibodies. These results suggest the existence of FN or FN-like antigens in the chromatin preparations from rat hepatoma cells. The antigenic proteins are localized in the nuclei of neoplastic foci of liver undergoing hepatocarcinogenesis.

Identification of a nuclear antigen with molecular weight of 48,000 differentially expressed in tumour and normal cells

A non-histone protein with mol. wt of 48,000 differentially expressed in normal and tumour cells was identified using immunological criteria. Antibodies were raised against a component specific for Kirkman-Robbins hepatoma of mol. wt about 48,000 separated from hepatoma non-histone proteins by preparative electrophoresis in polyacrylamide gel. It was demonstrated by immunoblotting that Morris hepatoma 7777 and Ehrlich ascites cells share an antigenic non-histone protein with Kirman-Robbins hepatoma. Tumour cells when compared with normal cells, i.e. hamster and rat liver, are characterized by significant enrichment of this component. Intracellular distribution of the polypeptide with mol. wt 48,000 suggests that this component may be a structural protein the biosynthesis of which increases or the antigenic determinants of which change in tumour cells.

The role of methylation in regulating the expression of the alpha-fetoprotein gene in developing rat liver and hepatoma cell lines

We have examined four possible sites of methylation in the 5' flanking region of the alpha-fetoprotein (AFP) gene during liver development in the rat, paying particular attention to the neonatal period, in which AFP gene transcription changes rapidly. These sites are found in MspI/HpaII sites located at -4197, -3038, -2431, and +3 bp relative to the transcription start site. Three of these sites are associated with sequence regions important for the regulation of AFP gene transcription. We found that, in general, the 5' flanking region of the gene was methylated more in the adult liver than in the livers of fetal and neonatal rats. In addition, the degree of methylation of all four sites examined was increased in the adult liver. One of these sites showed increased methylation as AFP gene activity decreased, whereas the other became more methylated only after transcriptional activity of the gene had ceased. In particular, the site (+3 bp) just adjacent to the transcriptional initiation site of the gene was fully methylated in the adult liver. In various rat hepatoma and liver cell lines methylation of this same site showed a particularly close correlation with the amount of transcriptional activity of the AFP promoter in these cell lines. Treatment of the hepatoma and liver cell lines with dexamethasone, which influences AFP gene expression, did not result in any changes in methylation of these sites in the 5' flanking region.