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A Comparison of Enzyme-active Membrane Antigens from Two Different 4-Dimethylaminoazobenzene-induced Rat Hepatomas with Those of Adult and Fetal Rat Liver¹

Wenner-Gren Institute, University of Stockholm, Norrtullsgatan 16, S-113 45, Stockholm, Sweden

Neoplastic transformation is accompanied by losses of macromolecules typical for the fully differentiated adult cells, as well as by gains of tumor-specific or tumor-associated components, often related to components present in less differentiated fetal cells. The aim of this study was to investigate possible differences in the pattern of enzyme-active antigens included in the membranes of two different 4-dimethylaminoazobenzene-induced rat hepatomas (D23 and D33), and to compare these patterns with those found in the membranes of normal adult and fetal liver cells. Detergent-solubilized microsomal and plasma membrane fractions were analyzed by means of antisera from rabbits, making use of immunodiffusion methods combined with enzyme-staining reactions.

Only one of the nine immunologically different esterase-active antigens present in adult liver microsomes was detected in the D23 and D33 microsomes. The plasma membrane fractions from the two hepatomas contained one esterase different from the microsomal or liver plasma membrane antigens.

Multienzyme complexes containing nucleoside di- and triphosphatase (NDP-NTPase), acid phosphatase, reduced nicotinamide adenine dinucleotide-neotretrazolium reductase activities were seen in the microsomal fractions from both hepatomas. Similar complexes were also detected in the plasma membrane fractions of the tumors. However, the latter had only NDP-NTPase and reduced nicotinamide adenine dinucleotide-neotetrozolium reductase activities. Only a few of the multienzyme complexes found in membrane extracts of normal adult liver were detected in the hepatomas. However, one NDP-NTPase-active antigen typical for fetal liver was found also in D23 and D33 microsomes.

No -L-glutamyl-ß-naphthylamidase-active antigens were detected in any of the D23 fractions. However, in striking similarity to fetal liver but in contrast to normal adult liver, membrane extracts of tumor D33 contained four antigens with significantly elevated activities of this kind. L-Leucyl-ß-naphthylamidase-active antigens which also expressed NDP-NTPase activity were found in the plasma membrane fractions from liver and the two hepatomas. No association to NDP-NTPase activity was found in the L-leucyl-ß-naphthyl-amidase-active antigens present in the other membrane fractions.

In conclusion, the two hepatomas were strikingly similar in regard both to deletions and to preservation of certain enzyme-active membrane antigens. Furthermore, at least one enzyme-active antigen of fetal origin was common for both tumors. These results suggested that similar dedifferentiation events take place during tumorigenesis. However, a marked difference between the tumors was also found, in that fetal antigens with -L-glutamyl-ß-naphthylamidase activity were present in only one of them. The meaning of this latter finding remains to be established.

¹ This work was supported by Grant 113-B72-07XA from the Swedish Cancer Society.

Received 12/26/73. Accepted 3/ 7/74.