Evidence for a receptor protein of activated carcinogen

Abstract

During carcinogenesis in rat liver by 3'-methyl-4-dimethylaminoazobenzene, the two moieties of the principal liver carcinogen-protein complex have considerably different turnover rates. With continued ingestion of the azocarcinogen by rats, the bound azo dye in the complex has a half-life of 2.5 ± 0.25 (SD) days, while the protein moiety has a half-life of 8.7 + 1.6 days (probability of identity <0.001). In addition, the interaction of the azocarcinogen with the principal target protein in vivo appears to extend the half-life of the protein itself from 3.3 i 0.2 days in normal liver to 8.7 i 1.6 days (P < 0.001). The slowing of the turnover of the protein by the carcinogen appears to be readily reversible, since soon after the cessation of azocarcinogen feeding, the half-life of the protein returns to that of the target protein in normal liver.The considerable difference in turnover rates of the two moieties of the complex and the reversible effects of the carcinogen in slowing the turnover of the protein moiety suggest that the two moieties of the native azoprotein are noncovalently linked and that they have different biological activities. The native complex appears to contain azo dye in an activated state that is capable of yielding a reactive electrophile, because after protein denaturation the bound azo dye was previously found to have properties that are indicative of covalent linkage to the protein. The retardation in the biological turnover rate of the protein moiety, apparently resulting from interaction with azocarcinogen, is in agreement with the known ligand-induced stabilization in vitro and reduced rate of proteolytic degradation in vivo of other proteins that result from conformational change to a more compact configuration. Our evidence is consistent with the hypothesis that the principal liver carcinogen-protein complex contains hydrophobicalfy bound activated azocarcinogen, whose specificity of reaction with critical macromolecule(s) in nuclei may be directed by the conformationally altered protein of an activated carcinogen-protein complex, i.e., a specific receptor protein containing activated azocarcinogen.

In vitro evaluation of some derivatives of the carcinogen butter yellow: implications for environmental screening

“…It has been suggested that intracellular transport of this activated species occurs via a receptor protein (Mainigi and Sorof, 1977). The active ester formed from compounds such as III has generally been assumed to be the sulphate derivative, but this idea has recently been questioned in the case of the metabolic activation of the carcinogen 2-acetylaminofluorene.…”

Hepatocellular Ligandin during N-2-Fluorenylacetamide Carcinogenesis

“…Smith et al [5] sum marized evidence suggesting an inverse relationship between hepatic ligandin levels and susceptibility to hepatocarcinogenesis. Presence of ligandin in the nucleus [7,10] and receptor role of the carcinogen-binding proteins [15,16] suggest that ligandin may be involved in translocation of the carcinogen metabolites into the nucleus. Ligandin [6,7] and other azodye-binding proteins [8][9][10][11][12][13][14] are reduced or absent after azodye administration and in azodye-induced carcinomas.…”