A comparison of enzyme-active membrane antigens from two different 4-dimethylaminoazobenzene-induced rat hepatomas with those of adult and fetal rat liver.

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. Delergenlsolubilized 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 esteraseactive 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 diand triphosphatase (NDP-NTPase), acid phosphatase, reduced nicotinamide adenine dinucleotide-neotetrazolium reducÃ-ase 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 reducÃ-aseactivilies. Only a few of the multienzyme complexes found in membrane extracts of normal adult liver were detecled in Ihe hepatomas. However, one NDP-NTPase-active antigen typical for fetal liver was found also in D23 and D33 microsomes. No 7-L-glutamyl-0-naphlhylamidase-aclive antigens were de tecled in any of Ihe D23 fraclions. However, in slriking similarily lo felal liver bui in conlrasl to normal adult liver, membrane extracts of tumor D33 contained four antigens with significantly elevated activities of this kind. L-Leucyl-0naphlhylamidase-aclive anligens which also expressed NDPNTPase aclivily were found in Ihe plasma membrane fraclions from liver and Ihe two hepatomas. No association to NDP-NTPase activity was found in the L-leucyl-0-naphthylamidase-aclive anligens presenl in Ihe olher membrane fraclions. In conclusion, the two hepatomas were slrikingly similar in regard bolh lo delelions and lo preservalion of certain enzyme-aclive membrane anligens. Furthermore, at least one enzyme-active antigen of fetal origin was common for bolh lumors. These results suggested that similar dedifferenliation events take place during tumorigenesis. However, a marked difference belween Ihe lumors was also found, in lhat fetal antigens with 7-L-glutamyl-j3-naphlhylamidase aclivity were present in only one of them. The meaning of Ihis latter finding remains to be established.