title: Regulation of catabolism of ribonuclease A microinjected into human fibroblasts.
abstract: We are using ribonuclease A (RNase A) as a model protein to study how the degradative rates of proteins are regulated within cells. RNase A and several derivatives can be microinjected into confluent cultures of human fibroblasts using red cell-mediated microinjection. The half-life of RNase A is 80-100 hrs in cells maintained in the presence of serum, and the degradative rate is enhanced approximately two-fold upon serum withdrawal. The ability of fibroblasts to regulate breakdown of this protein depends on a small peptide region within the amino terminal twenty amino acids. This amino terminal peptide from RNase A can be covalently attached to unrelated proteins and will cause their catabolism to become serum responsive. The mechanism of degradation of RNase A involves lysosomal pathways both in the presence and absence of serum, and the enhanced catabolism during serum deprivation results from a two-fold increase in the rate of uptake of the protein by lysosomes. These findings suggest that autophagy, or some other process occuring in serum-deprived cells, can be highly selective.
mesh_terms: D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D008845:Microinjections; D010446:Peptide Fragments / Q000032:analysis; D012259:Ribonuclease, Pancreatic / Q000378:metabolism*; D012260:Ribonucleases / Q000378:metabolism; D014316:Tritium
chemical_list: D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D014316:Tritium; D012260:Ribonucleases; D012259:Ribonuclease, Pancreatic; C022542:ribonuclease S