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

Molecular Characterization of Cellular Proteins from Colorectal Tumors

Aims and background

Recent evidence has suggested that progressive stages of colorectal tumorigenesis can be defined by a sequence of genetic events characterized by altered expression of certain genes and the appearance of cancer-specific proteins. Although the significance of these events is still not clear, expression of cancer-specific protein components may be directly involved in the neoplastic transformation. The purpose of the present study was to compare molecular characteristics of cellular proteins from human colorectal tumors and normal colonic mucosa.

Methods

Normal mucosa and colorectal tumors from 18 patients were fractionated by a differential centrifugation scheme into four cellular fractions, i.e., nuclear, mitochondrial (10P), microsomal (100P) and cytosolic (100S). The proteins of these fractions from normal and tumorigenic mucosa were analyzed by one-dimensional polyacrylamide gel electrophoresis followed by Coomassie brilliant blue R-250 and silver nitrate staining. Nuclear proteins from normal and neoplastic tissues which had revealed the most significant diversities were further characterized by two-dimensional gel electrophoresis. Electrophoretically cancer-specific nuclear proteins in the molecular mass zone 35-40 kDa were used as immunogen to produce rabbit polyclonal antibodies.

Results

Electrophoretic analysis by one-dimensional gel electrophoresis showed clear differences in molecular characteristics of cellular proteins between normal and tumorigenic mucosa, especially among nuclear fractions. The latter were also confirmed by their two-dimensional electrophoresis results. Rabbit antibodies raised against electrophoretically specific nuclear proteins characterized by molecular mass of 35-40 kDa cross-reacted with 36 kDa polypeptide in 15 of 18 (83.3%) studied nuclear fractions of colorectal tumors but not with any normal mucosa. In some cases, nuclear cancer-associated components of 38 and 40 kDa were also recognized by these antibodies.

Conclusions

During colorectal carcinogenesis, specific expression of several nuclear proteins takes place. One of them, the polypeptide of 36 kDa not found in normal colonic epithelium, was shared by over 83% of the studied carcinomas despite variations in detailed cancer properties. This particular nuclear protein may be considered as a potential marker for the colon malignancy.

Diversity of nuclear protein fractions of hamster liver and hepatoma produced by DNaseI

The structural and functional diversity between active and inactive chromatin is thought to depend, in part, upon differences in DNA-bound protein composition, including changes in the number of sulfhydryl groups. The aim of the present study was to compare protein composition in untreated nuclei, DNaseI-released and resistant nuclear fractions of hamster liver and Kirkman-Robbins hepatoma cells. Electrophoretic analysis of nuclear proteins showed some evident quantitative and qualitative differences between normal and neoplastic cells. The most significant diversities were noticed in DNaseI solubilized fraction of both types of cells. Nuclease attack released a characteristic set of non-histones with mol. wt 37,000, 50,000, 74,000 and 130,000-160,000 from transformed cells, and polypeptides of mol. wt 45,000 and 76,000 from normal cells. Cell-specific distribution within examined nuclear polypeptides was revealed using selective staining of their protein-bound sulfhydryls. Immunoblot analysis demonstrated that a non-histone protein with mol. wt 48,000, overexpressed in rodent tumour cells, was exclusively concentrated in liver DNaseI-sensitive fraction, which amounted only to 8.3% +/- 2.0% of total nuclear DNA. In hepatoma cells, however, this particular polypeptide is distributed between nuclease-sensitive and nuclease-resistant nuclear fractions. Non-histone protein of mol. wt 48,000 appeared to contain free sulfhydryl groups. In summary, these results show molecular specificity of nuclear proteins from normal and tumour cells and differences in their distribution among nuclease-released and nuclease-resistant nuclear fractions. The diversity in molecular characteristics and sulfhydryl group patterns observed among the examined proteins of normal and neoplastic cells may suggest their involvement in some changes in the rearrangement of nuclei during neoplastic transformation.

Nuclear glycoproteins of hamster liver and Kirkman-Robbins hepatoma recognized by concanavalin A

1. Glycoproteins recognized by Concanavalin A (ConA) have been identified in nuclei and nuclear fractions differing in sensitivity to micrococcal nuclease digestion from hamster liver and Kirkman-Robbins hepatoma. 2. The major ConA binding proteins from hamster liver and Kirkman-Robbins hepatoma nuclei have molecular weights about 27,000 and 57,000, and 38,000 and 49,000, respectively. 3. A distinct distribution of glycoproteins between fractions differing in sensitivity to nuclease digestion has not been observed.

Nuclear distribution pattern of tumour-associated nonhistone protein of mol. wt 48,000

1. As a further step toward characterizing nonhistone protein of mol. wt 48,000 which was found to be much more abundant in animal tumour cells than in normal ones [Krajewska W.M., Lipínska A., Marszatek M., Kiliańska Z., Wojtkowiak Z. and Kłyszejko-Stefanowicz L. Cell. Biochem. Funct. 8, 79-89 (1990)] its intranuclear localization in hamster liver and Kirkman-Robbins hepatoma was studied. The protein was identified by immunoblotting technique in the presence of antibodies against polypeptide of mol. wt about 48,000 from Kirkman-Robbins hepatoma. 2. Distribution of antigen with mol. wt of 48,000 in nuclear fractions representing different levels of nuclear material organization, i.e. in nucleoli, nuclease-sensitive and nuclease-resistant fractions, and extensive nuclease digestion products separated by size on Bio-Gel A-50m; implied the structural role of this component. 3. Fractionation of endogenously digested nuclei into low salt extract, high salt extract and nuclear matrix revealed that in normal liver the antigen studied is associated with nuclear matrix while in hepatoma this component appeared in high salt extract. 4. These results suggest that polypeptide with mol. wt of 48,000 is a shuttling protein which may be involved in reorganization of nuclear matrix during neoplastic transformation.

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.

Studies on low molecular weight nuclear protein of tumour and normal cells

1. Preliminary results of comparative electrophoretical and immunological analyses of the components of two classes of non-histone proteins, i.e. NHP1 and NHP2 eluted from hydroxyapatite allowed to suppose that protein of Mw 18,000 is specific for animal tumour cells. 2. However, the studies on cellular distribution of this polypeptide indicated that it is exclusively located in nuclei of hepatoma and normal liver as well. 3. The former observation seems to be the result of changes of the affinity of this protein to DNA during neoplastic transformation.