Ubiquitination of Protein Kinase C-α and Degradation by the Proteasome

• Published in: The Journal of biological chemistry 1996-08, Vol.271 (35), p.20973
• Main Authors: Hyeon-Woo Lee, Lucinda Smith, George R. Pettit, Alexander Vinitsky, Jeffrey Bingham Smith
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.271.35.20973

Bryostatins and phorbol esters acutely activate and subsequently down-regulate protein kinase C (PKC) by inducing its proteolysis via an unknown pathway. Here we show that treatment of renal epithelial cells with bryostatin 1 (Bryo) produced novel PKC-α species, which were larger than the native protein (80 kDa). The >80 kDa PKC-α species contained Ubi as indicated by immunostaining and accumulated in the presence of lactacystin, a selective inhibitor of proteolysis by the proteasome. In vitro experiments with 125 I-ubiquitin and membranes from Bryo-treated cells showed that PKC-α became ubiquitinated by a reaction that depended on ATP and a cytosolic fraction. Lactacystin or a peptidyl aldehyde, Bz-Gly-Leu-Ala-leucinal, which inhibits certain proteinase activities of the proteasome, inhibited Bryo-evoked disappearance of PKC-α protein from the cells. Lacta preserved Bryo-induced 32 P-labeled PKC-α indicating that the proteasome inhibitor spared activated enzyme from down-regulation in vivo . These findings show that Bryo induces the degradation of PKC-α by the ubiquitin-proteasome complex.