Regulation of catabolism of ribonuclease a microinjected into human fibroblasts
Dice, J.F.; Backer, J.M.; Miao, P.; Bourret, L.; McElligott, M.A.
Progress in Clinical and Biological Research 180: 385-394
1985
ISSN/ISBN: 0361-7742 PMID: 4034548 Document Number: 257185
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.