Covalent linkage of ribonuclease S-peptide to microinjected proteins causes their intracellular degradation to be enhanced during serum withdrawal

J. M. Backer, J. F. Dice

Research output: Contribution to journalArticle

32 Scopus citations

Abstract

The amino-terminal 20 amino acids are required for microinjected ribonuclease A (RNase A) to be taken up by lysosomes and degraded at an enhanced rate during serum withdrawal. We used water-soluble carbodiimides to covalently attach the RNase S-peptide (residues 1-20) to [3H]RNase S-protein (residues 21-124) at unspecified locations. We then measured catabolism of the [3H]S-protein-S-peptide conjugate after its microinjection into human diploid fibroblasts. The attached S-peptide caused the degradation of S-protein to be enhanced 2-fold in the absence of serum. Control experiments showed that degradation of [3H]RNase S-protein remained unresponsive to serum after conjugation with the inactive fragment, RNase S-peptide (residues 1-10). Covalent attachment of RNase S-peptide had a similar effect on the catabolism of two other proteins. Degradation rates of microinjected 125I-labeled lysozyme and 125I-labeled insulin A chain are normally unresponsive to serum withdrawal. However, breakdown rates of microinjected 125I-labeled lysozyme S-peptide and 125I-labeled insulin A chain-S-peptide conjugates were increased 2-fold during serum deprivation. We suggest that RNase S-peptide acts as a 'signal sequence' that directs cytosolic proteins to lysosomes through a pathway that is activated by deprivation conditions.

Original languageEnglish (US)
Pages (from-to)5830-5834
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume83
Issue number16
DOIs
StatePublished - 1986

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