The Antitumor Drug Aclacinomycin A, Which Inhibits the Degradation of Ubiquitinated Proteins, Shows Selectivity for the Chymotrypsin-like Activity of the Bovine Pituitary 20 S Proteasome

• Published in: The Journal of biological chemistry Vol. 271; no. 28; pp. 16455 - 16459
• Main Authors: Figueiredo-Pereira, Maria E., Chen, Wei Er, Li, Jingrong, Johdo, Osamu
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 12.07.1996; American Society for Biochemistry and Molecular Biology
• Subjects: Aclarubicin - chemistry; Aclarubicin - pharmacology; Animals; Antibiotics, Antineoplastic - chemistry; Antibiotics, Antineoplastic - pharmacology; Catalysis; Cattle; Chymotrypsin - antagonists & inhibitors; Chymotrypsin - metabolism; Cysteine Endopeptidases - drug effects; Cysteine Endopeptidases - metabolism; Hydrolysis; Molecular Structure; Multienzyme Complexes - drug effects; Multienzyme Complexes - metabolism; Pituitary Gland - enzymology; Proteasome Endopeptidase Complex; Proteins - metabolism; Ubiquitins - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.271.28.16455

The antitumor drug aclacinomycin A was previously shown to inhibit the degradation of ubiquitinated proteins in rabbit reticulocyte lysates with an IC50 of 52 µM (Isoe, T., Naito, M., Shirai, A., Hirai, R., and Tsuruo, T. (1992) Biochim. Biophys. Acta 1117, 131-135). We report here that from all the catalytic activities of the 20 S proteasome tested, the chymotrypsin-like activity was the only one affected by the antitumor drug. An important requirement for inhibition of the chymotrypsin-like activity seemed to be the presence of hydrophobic nonpolar residues in positions P1 to P3. Degradation of Z-E(OtBu)AL-pNA and Z-LLL-AMC at pH 7.5 was dramatically (87-98%) inhibited by 50 µm of the drug, while that of Z-GGL-pNA (containing uncharged polar residues in positions P2 and P3) and succinyl-LLVY-AMC (containing an uncharged polar residue in the P1 position) was inhibited only 11 and 24%, respectively. Aclacinomycin A had no effect on cathepsin B, stimulated trypsin, and inhibited chymotrypsin and, to a lesser extent, calpain. The aglycone and sugar moieties of the cytotoxic drug are essential for inhibition. The results presented here support a major role for the chymotrypsin-like activity in the degradation of ubiquitinated proteins. Aclacinomycin A is the first described non-peptidic inhibitor showing discrete selectivity for the chymotrypsin-like activity of the 20 S proteasome.