In vivo and in vitro evidence suggests that synthesis of intracellular and secretory proteins occurs in separate compartments of liver and other mammalian cells. The mechanism for regulating protein synthesis in these compartments, however, has remained unclear. As a result of improved methods for isolating natural mRNAs and initiation factors from mammalian systems, attention can now be focused on the mechanism for subcellular regulation of protein synthesis in higher organisms. The main objectives of this proposal are to determine 1) whether the translation of specific mRNAs from membrane-bound and free liver polysomes is controlled by specific enzyme factors and 2) whether changes in the amount or functional activity of specific mRNAs or translational control factors can account for changes occurring after specific protein induction. Liver ferritin synthesis will be induced by intramuscular injection of an iron-dextran solution, albumin synthesis will be augmented by introduction of nephrosis by puromycin amino-nucleoside or antibodies to glomerular basement membrane, and overall protein synthesis will be stimulated by partial hepatectomy. Using cell-free systems developed in our laboratory to determine levels of messenger RNA and specific initiation or translational control factors, synthesis of total protein, albumin and ferritin will be studied in both induced and regenerating liver. Other studies will examine the suppression of cell-free protein synthesis in amino acid depleted and/or ethanol treated animals. These studies will hopefully increase our understanding of important cellular events occurring in liver regeneration and may provide important insight into factors responsible for derangements in protein metabolism in such conditions as protein-calorie malnutrition, toxic liver injury, and alcoholic liver disease.
NIH ExPorter
NIH ExPorter