Inhibition of peroxisome-proliferator-activated receptor (PPAR)alpha by MK886

Although MK886 was originally identified as an inhibitor of 5-lipoxygenase activating protein (FLAP), recent data demonstrate that this activity does not underlie its ability to induce apoptosis [Datta, Biswal and Kehrer (199 9) Biochem, J. 340, 371-375], Since FLAP is a fatty-acid binding protein, i t is conceivable that MK886 may affect other such proteins. A family of nuc lear receptors that are activated by fatty acids and their metabolites. the peroxisome-proliferator-activated receptors (PPARs). have been implicated in apoptosis and may represent a target for MK886, The ability of MK886 to inhibit PPAR-alpha, -beta and -gamma activity was assessed using reporter a ssay systems (peroxisomeproliferator response element-luciferase), Using a transient transfection system in monkey kidney fibroblast CV-1 cells, mouse keratinocyte 308 cells and human lung adenocarcinoma A549 cells, 10-20 muM MK886 inhibited Wy14,643 activation of PPAR alpha by approximately 80%, Si milar inhibition of PPAR alpha by MK886 was observed with a stable transfec tion reporter system in CV-1 cells. Only minimal inhibitory effects were se en on PPAR beta and PPAR gamma. MK886 inhibited PPAR alpha by a noncompetit ive mechanism as shown by its effects on the binding of arachidonic acid to PPARs protein, and a dose-response study using a transient transfection re porter assay in COS-1 cells. An assay assessing PPAR ligand-receptor intera ctions showed that MK886 prevents the conformational change necessary for a ctive-complex formation. The expression of keratin-1, a protein encoded by a PPAR alpha -responsive gene, was reduced by MK886 in a culture of mouse p rimary keratinocytes, suggesting that PPAR inhibition has functional conseq uences in normal cells. Although Jurkat cells express all PPAR isoforms, va rious PPAR alpha and PPAR gamma agonists were unable to prevent MK886-induc ed apoptosis. This is consistent with MK886 functioning as a non-competitiv e inhibitor of PPARa, but may also indicate that PPAR alpha is not directly involved in MK886-induced apoptosis. Although numerous PPAR activators hav e been identified, the results show that MK886 can inhibit PPAR alpha, maki ng it the first compound identified to have such an effect.