Dye Carcinogenesis*

With the use of 2.1 M sucrose solution, nuclei were isolated from normal, control, and azo preneoplastic livers, and from azo dye-inducedliver tumors of rats. Four consecu tive extractions of nuclear sap in isotonic saline-phosphate buffer solubiized 49 and 37 per cent of the nitrogen of liver and tumor nuclei, respectively. Velocity sedimentation analyses revealed that the soluble nuclear macromolecules consist of the following size classes: 41 S, 18 S, 14 8, 8 2, 6 8, 4 S, and 2 S, and two diffuse groups sedimenting at greater than 41 8 and at 18—41S. No significant dii ference in sedimentation could be attributed to early preneoplasia induced by the liver carcinogen, 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB). However, nuclear extracts of 3'-Me-DAB-induced liver tumor contain considerably more 4 2 and much less 6 8 and 8 2 proteins than do nuclear extracts of liver. Extensive resolution of the soluble macromolecules of liver nuclei by free boundary electrophoresis yielded profiles which have been extrapolated into eighteen hypotheti cal classes. These have been grouped into five charge types : basic, near-neutral, weakly acidic, highly acidic, and strongly polyanionic. The mobilities of most of the classes coincide with those previously found in liver extracts of essentially cytoplasmic origin. This applies in particular to the five near-neutral nuclear components and the five cytoplasmic h components, which previously have been implicated in the causal mechanisms of three different types of chemical carcinogeneses. The only difference in the electrophoresis of liver nuclear extracts which could be at tributed to early hepatic preneoplasia induced by azocarcinogen was the frequency of absence of the most basic component. In contrast, nuclear extracts of dye-induced liver tumors exhibit a marked reduction of near-neutral (h-like) and basic proteins and an increase in amount of highly acidic components. Parallel alterations have previously been found with cytoplasmic extracts. On the basis of present and past findings, a causal mechanism of carcinogenesis by certain chemicals is discussed, involving carcinogen binding to the h@type of proteins and the subsequent deletion of h (near-neutral) and basic proteins in nucleus and cyto plasm of target cells.