Liver fatty acid-binding protein: specific mediator of the mitogenesis induced by two classes of carcinogenic peroxisome proliferators.
Peroxisome proliferators (PP) are a diverse group of chemicals that induce dramatic increases in peroxisomes in rodent hepatocytes, followed by hypertrophy, hepatomegaly, alterations in lipid metabolism, mitogenesis, and finally hepatocarcinomas. Termed nongenotoxic carcinogens, they do not interact with DNA, are not mutagenic in bacterial assays, and fail to elicit many of the phenotypes associated with classic genotoxic carcinogens. We report here that the mitogenesis induced by the major PP class, the amphipathic carboxylates, and by the tetrazole-substituted acetophenones specifically requires liver fatty acid-binding protein (L-FABP) in cultured rat hepatoma cells transfected with the sense cDNA of L-FABP, in contrast to L-FABP-nonexpressing cells transfected with its antisense cDNA. The mitogenic actions of L-FABP were protein-specific, inasmuch as no other protein in the nonexpressing cells could act like L-FABP. L-FABP was previously shown not only (i) to interact covalently with metabolites of the two genotoxic carcinogens 2-acetylaminofluorene and aminoazo dyes during liver carcinogenesis, but also (ii) to bind noncovalently the two classes of PP in vitro with avidities that correlate with their abilities to elicit peroxisomal enzymatic responses, and (iii) together with unsaturated fatty acids, especially linoleic acid, to promote multiplication of the transfected hepatoma cells in culture. The convergence of the two types of genotoxic carcinogens with the two classes of PP nongenotoxic carcinogens, and also with unsaturated fatty acids, at L-FABP actions in inducing mitogenesis allows the following hypothesis. During tumor promotion of carcinogenesis in vivo, these groups of genotoxic and nongenotoxic carcinogens act on the normal process by which L-FABP, functioning as a specific receptor of unsaturated fatty acids or their metabolites, promotes hepatocyte proliferation.
Khan
S H
SH
Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA 19111.
Sorof
S
S
D000098:Acetophenones / Q000633:toxicity; D000818:Animals; D002264:Carboxylic Acids / Q000633:toxicity; D002273:Carcinogens / Q000633:toxicity; D002352:Carrier Proteins / Q000502:physiology*; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D008830:Microbodies / Q000187:drug effects; D008938:Mitosis / Q000187:drug effects / Q000502:physiology*; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D051381:Rats; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism / Q000473:pathology
D000098:Acetophenones; D002264:Carboxylic Acids; D002273:Carcinogens; D002352:Carrier Proteins; C493320:Fabp1 protein, mouse; C493321:Fabp1 protein, rat; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins