RNA polymerase activity and protein synthesis in mouse tumor-host liver compared to benign para-neoplastic reactions

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Abstract
Elevated protein synthesis in mouse tumor‐host liver is the net result of both stimulatory and inhibitory responses. This study compares the directional change in transcription and synthesis of liver and plasma proteins in tumor‐host liver as compared with para‐neoplastic conditions, such as malnutrition, inflammation, benign cell proliferation and protein deficiency. A methylcholanthrene‐induced sarcoma was used in weight stable mice (C57B1/6J). Inflammation was induced by s. c. turpentine injection, and benign cell proliferation by injection of heat‐killed Corynebacterium parvum. DNA‐dependent RNA‐polymerase activity (I, II and III) (EC2.7. 7.6) was measured in isolated hepatic nuclei. Protein synthesis was measured by labelling of hepatic and plasma proteins following the injection of a “flooding dose” of the labelled amino acid. Benign hepatic cell proliferation and sterile inflammation caused increased rates of transcription, while malnourished and healthy control animals had lower hepatic transcription than animals bearing a malignant tumor. Inflammation was associated with increased activities of free (nonchromatin engaged) RNA polymerase, which was not found in any other para‐neoplastic condition or in the tumor‐host liver. A protein‐ and calorie‐deficient state was associated with depressed hepatic and plasma protein synthesis compared with the tumor condition. Tumor‐host livers had a nonsecretory protein synthesis rate equal to that of normal livers, but 45% higher plasma protein synthesis. Animals with inflammation and benign cell growth had liver protein synthesis rates which were approximately 50% higher than in tumorbearing animals, but plasma protein synthesis in tumor‐bearing animals was comparable with that of animals which had inflammation. Benign cell growth was not associated with an overall elevated plasma protein synthesis. The translation rate per transcription activity was highest in normal animals and decreased in animals suffering from either tumor, protein deficiency or benign cell proliferation. Hepatic protein synthesis in tumor‐host livers is high considering the degree of anorexia and malnutrition, although not as high as in livers from animals with pronounced inflammation. This counter‐regulation in tumor‐host livers may indicate a compensatory state to maintain protein synthesis against attenuating factors such as the declining food intake. Protein metabolism in tumorhost livers represents an unusual combination of findings.