Messenger RNA activities for two liver enzymes, tyrosine aminotransferase and tryptophan oxygenase, in Morris hepatoma 5123C and 9618A and in HTC cells. Correlation with enzyme activities.

Abstract

Messenger RNA activities for tyrosine aminotransferase and tryptophan oxygenase have been determined in two Morris hepatomas, 5123C and 9618A and in HTC cells by translation in vitro of poly(A)-containing RNA in a wheat germ system, followed by immunoprecipitation of the synthesized enzyme subunits. The amount of specific translatable mRNA was correlated to the respective enzyme activity in the tumors and in the host livers of untreated and hydrocortisone-treated rats. In hepatoma 5123C, the activities of tyrosine aminotransferase mRNA parallel the corresponding enzyme activities. The basal levels of enzyme activity and of mRNA activity are several-fold higher than in the host liver and can be induced by hydrocortisone, reaching levels somewhat higher than in maximally induced liver. In hepatoma 9618A, tyrosine aminotransferase activity and the respective mRNA activity is virtually absent in non-induced animals. Enzyme activity is only slightly induced by treatment with hydrocortisone, whereas translatable tyrosine aminotransferase mRNA accumulates after hormone administration, reaching levels of approximately one third of the maximum liver values. Tryptophan oxygenase activity and the corresponding mRNA activity is virtually absent in both Morris hepatomas tested and cannot be unequivocally detected after administration of hydrocortisone. Dexamethasone-treated HTC cells accumulate translatable tyrosine aminotransferase mRNA in direct correlation with the increased activity of the respective enzyme, whereas no tryptophan oxygenase or its respective mRNA could be detected either in untreated or dexamethasone-treated cells. The patterns of the major proteins synthesized in the wheat germ system under the direction of poly(A)-containing RNA from liver, hepatoma 5123C, hepatoma 9618A and HTC cells show striking differences. A mRNA coding for a protein of Mr approximately 40 000 is induced by dexamethasone solely in HTC cells.