Protein synthesis in tumor host. I. Enhanced peptide elongation in transplantable tumors and host liver

Protein synthesis was significantly enhanced in subcellular systems containing ribosomes and cytosol from the liver of Walker tumor-bearing rats from the second week following the tumor transplantation and this enhancement persisted for the whole period of tumor growth. Homologous systems from Zajdela hepatoma and host liver showed a markedly increased poly(U)-dependent peptide elongation when compared with normal liver tissue. A stimulation of polyphenylalanine synthesis resulted from the addition of cytosols from tumors or host liver to ribosomes from normal rat liver. Similar results were found for the binding of phenylalanyl-tRNA to ribosomes. Ribosomes from tumors and host liver are more active in peptide elongation than particles from normal liver tissue. A more than 10-fold stimulation of phenylalanine polymerization resulted from the addition of poly(U) to ribosomes from Zajdela hepatoma whereas only less than 2-fold enhancement was found when using ribosomes from normal or host liver. Hepatoma ribosomes apparently contain only a low proportion of polyribosomes carrying natural message. Enhanced protein synthesis in tumors and host liver is apparently due, in particular, to an increased activity of soluble factors required for protein synthesis and less due to an increased activity of ribosomes.