AJP - Endocrinology and Metabolism, Vol 249, Issue 5 461-E469, Copyright © 1985 by American Physiological Society
Nuclear RNA polymerase activity in tumor-host livers
M. Ternell, C. Lonnroth and K. Lundholm
This study has evaluated changes in RNA synthesis in livers under the
distant influence of a malignant tumor. A transplantable-induced sarcoma
(MCG 101), transplanted on inbred adult mice (C57BL/6J), was used.
Activities of DNA-dependent RNA polymerase (EC 2.7.7.6) were measured in
relation to RNA content and translational activity. Liver nuclei from
freely fed sarcoma-bearing mice had increased RNA synthesis. As a
consequence of this, RNA content per DNA was increased in liver tissue.
This was independent of depressed food intake and malnutrition. Elevated
RNA synthesis, proportional to the tumor burden was due to an increased
proportion of chromatin-engaged RNA polymerase I and II activities. RNA
polymerase III activity (template-engaged form) was unchanged when
evaluated in isolated nuclei, but appeared to be increased in partially
purified extracts of nuclei. RNA content in tumor-host liver was a
composite of increased levels of rRNA and tRNA, whereas the levels of
poly(A)+ mRNA could not be measured as increased. Overall translational
activities in vitro of mRNA from liver tissue of tumor-bearing,
pair-weighed, and freely fed tumor-free controls were qualitatively and
quantitatively different. mRNA from tumor-bearing mice directed an
increased synthesis, particularly of larger proteins (above 55,000 daltons)
compared with control animals. The results support the conclusion that
previous evidence of elevated net protein synthesis in tumor-host liver is
accompanied by increased transcription of genes coding for RNA and also for
some or several hepatic proteins.
