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Turnover of Messenger RNA in Transplantable Hepatomas and Host Livers of Rats¹

Department of Pathology, University of South Florida, College of Medicine, Tampa, Florida 33620, and Department of Pathology, The George Washington University Medical Center, Washington, D. C. 20037

The turnover of messenger RNA (mRNA) in two intrahepatically transplantable hepatomas (5123 and 19) and host livers of Buffalo rats was evaluated with four different approaches. [¹⁴C]Orotic acid incorporation into the rapidly labeled peak between 18S and 4S of total polyribosomal RNA was measured. In vitro RNase assay of [¹⁴C]orotic acid-labeled mRNA of polyribosomes was utilized. The decay of mRNA as reflected by disaggregation of free and membrane-bound polyribosomes at intervais after actinomycin D treatment was determined. The incorporation of [¹⁴C]orotic acid into polyadenylic acid-mRNA of free and membrane-bound polyribosomes was assayed. The results revealed that the turnover of mRNA of total, free, and membrane-bound polyribosomes was greater in the host livers than it was in the two hepatomas. In host livers the turnover of mRNA of the free polyribosomes was greater than that of the membrane-bound polyribosomes. In the two hepatomas the turnover of mRNA of free polyribosomes was at a similar rate as that of membranebound polyribosomes. Hepatoma 19, which grows more rapidly and is less differentiated morphologically than is hepatoma 5123, appeared to have a slower turnover of mRNA than did hepatoma 5123. Measurement of RNase activity revealed greater activity in host livers than in hepatomas.

¹ This investigation was supported by USPHS Research Grants CA14158 and CA22997 from the National Cancer Institute.

² To whom requests for reprints should be addressed, at Department of Pathology, George Washington University Medical Center, 2300 I Street, N. W., Washington, D. C. 20037.

Received 12/ 9/76. Accepted 3/15/78.