leupeptins and 7-ketocholesterol

Akt plays a role in protecting macrophages from apoptosis induced by some oxysterols. Previously we observed enhanced degradation of Akt in P388D1 moncocyte/macrophages following treatment with 25-hydroxycholesterol (25-OH) or 7-ketocholesterol (7-KC). In the present report we examine the role of the ubiquitin proteasomal pathway in this process. We show that treatment with 25-OH or 7-KC results in the accumulation of poly-ubiquitinated Akt, an effect that is enhanced by co-treatment with the proteasome inhibitor MG-132. Modification of Akt by the addition of a Gly-Ala repeat (GAr), a domain known to block ubiquitin-dependent targeting of proteins to the proteasome, resulted in a chimeric protein that is resistant to turn-over induced by 25-OH or 7-KC and provides protection from apoptosis induced by these oxysterols. These results uncover a new aspect of oxysterol regulation of Akt in macrophages; oxysterol-stimulated poly-ubiquitination of Akt and degradation by the proteasomal pathway.

Topics: Animals; Apoptosis; Base Sequence; Cell Line, Tumor; Hydroxycholesterols; Ketocholesterols; Leukemia P388; Leupeptins; Macrophages; Mice; Plasmids; Protease Inhibitors; Proteasome Endopeptidase Complex; Proto-Oncogene Proteins c-akt; Recombinant Fusion Proteins; Transfection; Ubiquitination