A study of soluble protein and sulfhydryl levels in the rat liver during rapid normal and premalignant growth

Abstract

FOLLOWING the demonstration by Miller and Miller (1947) and Miller, Miller, Sapp and Weber (1949) that carcinogenic azo dyes are bound covalently to rat liver proteins before the appearance of tumors, the cytoplasmic h protein components of this combination (Sorof and Cohen, 1951; Wirtz and Arcos, 1958) have been extensively investigated. During liver carcinogenesis by the aminoazo dyes and by 2-acetylaminofluorene, the h2 liver proteins contain the greatest portion of the soluble carcinogen-protein conjugates (Sorof, Young and Ott, 1958;Sorof, Young and Fetterman, 1960), and there is at the time of maximum dye binding an increase in the total h protein fraction of the liver (Sorof, Young and Ott, 1958). In contrast, the primary tumors induced by these carcinogens do not form h2 protein-carcinogen conjugates (Sorof, Young McCue and Fetterman, 1963;Sorof, Young, McBride and Coffey, 1965), and the h fraction is considerably decreased in these hepatomas (Sorof and Cohen, 1951;Sorof, Young and Ott, 1958).It has been hypothesized that carcinogens combine with specific growthcontrolling proteins, the deletion of which gives rise to malignant cells (Miller and Miller, 1953; Potter, 1958), and certain h2 proteins of rat liver were postulated to be involved in regulation of cell multiplication (Bakay and Sorof, 1964). Freed and Sorof (1966) provided evidence that the h2 liver proteins do function in normal cells as metabolic regulators: isolated h2 protein fraction strongly inhibits the growth of L strain mouse fibroblasts in suspension tissue culture, and the inhibition of cell multiplication is reversed by removal of the h2 proteins. The inhibitory fraction centred at the slow h2 proteins has been recently identified as arginase (Sorof, Young, Luongo, Kish and Freed, 1967).The present investigations attempt to gain specific information on the possible role of the h proteins in the rapid normal growth of regenerating liver, in the rapid liver growth induced by polycyclic aromatic hydrocarbons, and in nitrosamine hepatocarcinogenesis. Thus, a study of the electrophoretic patterns of soluble rat liver proteins at various time intervals was carried out following partial hepatectomy and following intraperitoneal injection of a single dose of 20-methylcholanthrene. Electrophoretic patterns were also studied in soluble liver proteins obtained from rats which were continuously administered the hepatic carcinogen, diethylnitrosamine. The sulfhydryl levels in the soluble protein preparations and the mitotic indexes of the liver tissues were measured in order to correlate the electrophoretic patterns with these parameters of mitosis.

Microelectrophoresis in Agarose Gel of Soluble Rat Liver Proteins During Aminoazo Dye Carcinogenesis

“…Hence all tissues were homogenized in the presence of chloride ion which in boundary electrophoresis, as stressed by S o r o f et al [10] improves the resolution of h proteins and protects them from pre cipitation and denaturation. In a recent report [2] this point has not been observed and this possibly accounts for their equivocal findings in the case of regenerating rat liver. Repeated observations have shown that the pattern of the electrophoretic profiles of both normal and regenerating rat liver at pH 8.6 is constant and that the ratios of the quantities of protein in each band remain within very narrow limits (Tab.…”