Polyunsaturated fatty acids block platelet-activating factor-induced phosphatidylinositol 3 kinase/Akt-mediated apoptosis in intestinal epithelial cells.
We have shown earlier that platelet-activating factor (PAF) causes apoptosis in enterocytes via a mechanism that involves Bax translocation to mitochondria, followed by caspase activation and DNA fragmentation. Herein we report that, in rat small intestinal epithelial cells (IEC-6), these downstream apoptotic effects are mediated by a PAF-induced inhibition of the phosphatidylinositol 3-kinase (PI 3-kinase)/protein kinase B (Akt) signaling pathway. Treatment with PAF results in rapid dephosphorylation of Akt, phosphoinositide-dependent kinase-1, and the YXXM p85 binding motif of several proteins and redistribution of Akt-pleckstrin homology domain-green fluorescent protein, i.e., an in vivo phosphatidylinositol (3,4,5)-trisphosphate sensor, from membrane to cytosol. The proapoptotic effects of PAF were inhibited by both n-3 and n-6 polyunsaturated fatty acids but not by a saturated fatty acid palmitate. Indomethacin, an inhibitor of prostaglandin biosynthesis, did not influence the baseline or PAF-induced apoptosis, but 2-bromopalmitate, an inhibitor of protein palmitoylation, inhibited all of the proapoptotic effects of PAF. Our data strongly suggest that an inhibition of the PI 3-kinase/Akt signaling pathway is the main mechanism of PAF-induced apoptosis in enterocytes and that polyunsaturated fatty acids block this mechanism very early in the signaling cascade independently of any effect on prostaglandin synthesis, and probably directly via an effect on protein palmitoylation.
Lu
Jing
J
Evanston Northwestern Healthcare Research Institute, Evanston, IL 60201, USA.
Caplan
Michael S
MS
Li
Dan
D
Jilling
Tamas
T
D064413:3-Phosphoinositide-Dependent Protein Kinases; D020816:Amino Acid Motifs / Q000187:drug effects; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D016718:Arachidonic Acid / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004281:Docosahexaenoic Acids / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D007213:Indomethacin / Q000494:pharmacology; D007422:Intestines / Q000166:cytology; D054878:Lipoylation / Q000187:drug effects; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D051058:Oncogene Protein v-akt / Q000378:metabolism*; D010168:Palmitates / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D010972:Platelet Activating Factor / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D051381:Rats
D064413:3-Phosphoinositide-Dependent Protein Kinases; D016718:Arachidonic Acid; D053148:Caspase 3; D002867:Chromones; D004281:Docosahexaenoic Acids; D004791:Enzyme Inhibitors; D005231:Fatty Acids, Unsaturated; D007213:Indomethacin; D009025:Morpholines; D051058:Oncogene Protein v-akt; D010168:Palmitates; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010972:Platelet Activating Factor; D017346:Protein Serine-Threonine Kinases; D019253:Proto-Oncogene Proteins c-bcl-2; C022776:2-bromopalmitate; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one