KFERQ Sequence in Ribonuclease A-mediated Cytotoxicity

• Published in: The Journal of biological chemistry 2002-03, Vol.277 (13), p.11576-11581
• Main Authors: Haigis, Marcia C., Kurten, Erin L., Abel, Richele L., Raines, Ronald T.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Antineoplastic Agents - chemistry; Antineoplastic Agents - pharmacology; Cell Division - drug effects; Cell Survival - drug effects; Humans; K562 Cells; Models, Molecular; Molecular Sequence Data; onconase; Protein Conformation; ribonuclease A; Ribonuclease, Pancreatic - chemistry; Ribonuclease, Pancreatic - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112227200

Onconase® (ONC) is an amphibian ribonuclease that is in clinical trials as a cancer chemotherapeutic agent. ONC is a homolog of ribonuclease A (RNase A). RNase A can be made toxic to cancer cells by replacing Gly88 with an arginine residue, thereby enabling the enzyme to evade the endogenous cytosolic ribonuclease inhibitor protein (RI). Unlike ONC, RNase A contains a KFERQ sequence (residues 7–11), which signals for lysosomal degradation. Here, substitution of Arg10 of the KFERQ sequence has no effect on either the cytotoxicity of G88R RNase A or its affinity for RI. In contrast, K7A/G88R RNase A is nearly 10-fold more cytotoxic than G88R RNase A and has more than 10-fold less affinity for RI. Up-regulation of the KFERQ-mediated lysosomal degradation pathway has no effect on the cytotoxicity of these ribonucleases. Thus, KFERQ-mediated degradation does not limit the cytotoxicity of RNase A variants. Moreover, only two amino acid substitutions (K7A and G88R) are shown to endow RNase A with cytotoxic activity that is nearly equal to that of ONC.