title: Vitamin E forms inhibit IL-13/STAT6-induced eotaxin-3 secretion by up-regulation of PAR4, an endogenous inhibitor of atypical PKC in human lung epithelial cells.
abstract: Eotaxin-3 (CCL-26), a potent chemokine for eosinophil recruitment and contributing significantly to the pathogenesis of asthma, is secreted by lung epithelial cells in response to T helper 2 cytokines including interleukin 13 (IL-13). Here we showed that vitamin E forms, but not their metabolites, differentially inhibited IL-13-stimulated generation of eotaxin-3 in human lung epithelial A549 cells. The relative inhibitory potency was γ-tocotrienol (γ-TE) (IC50 ~15 μM)>γ-tocopherol, δ-tocopherol (IC50 ~25-50 μM)>α-tocopherol. Consistent with suppression of eotaxin, γ-TE treatment impaired IL-13-induced phosphorylation of STAT6, the key transcription factor for activation of eotaxin expression, and consequently blocked IL-13-stimulated DNA-binding activity of STAT6. In search of the upstream target of γTE by using inhibitor and siRNA approaches, we discovered that the atypical protein kinase C (aPKC) signaling, instead of classical PKC, p38 MAPK, JNK or ERK, played a critical role in IL-13-stimulated eotaxin generation and STAT6 activation. While showing no obvious effect on aPKC expression or phosphorylation, γ-TE treatment resulted in increased expression of prostate-apoptosis-response 4 (PAR4), an endogenous negative regulator of aPKCs. Importantly, γ-TE treatment led to enhanced formation of aPKC/PAR4 complex that is known to reduce aPKC activity via protein-protein crosstalk. Our study demonstrated that γ-TE inhibited IL-13/STAT6-activated eotaxin secretion via up-regulation of PAR4 expression and enhancement of aPKC-PAR4 complex formation. These results support the notion that specific vitamin E forms may be useful anti-asthmatic agents.
authors.affiliation: Department of Foods and Nutrition, Purdue University, Stone Hall, West Lafayette, IN 47907, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Wang
authors.forename: Michelle
authors.initials: M
authors.lastname: Moreland
authors.forename: James G
authors.initials: JG
authors.lastname: Wagner
authors.forename: Bruce N
authors.initials: BN
authors.lastname: Ames
authors.forename: Beate
authors.initials: B
authors.lastname: Illek
authors.forename: David B
authors.initials: DB
authors.lastname: Peden
authors.forename: Qing
authors.initials: Q
authors.lastname: Jiang
mesh_terms: D018927:Anti-Asthmatic Agents / Q000494:pharmacology; D051017:Apoptosis Regulatory Proteins / Q000235:genetics* / Q000378:metabolism; D000075906:Chemokine CCL26; D019742:Chemokines, CC / Q000378:metabolism*; D002839:Chromans / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects*; D006801:Humans; D018793:Interleukin-13 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism; D050800:STAT6 Transcription Factor / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D024505:Tocopherols / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D014810:Vitamin E / Q000031:analogs & derivatives / Q000494:pharmacology*; D024502:alpha-Tocopherol / Q000494:pharmacology; D024504:gamma-Tocopherol / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D018927:Anti-Asthmatic Agents; D051017:Apoptosis Regulatory Proteins; C120429:CCL26 protein, human; D000075906:Chemokine CCL26; D019742:Chemokines, CC; D002839:Chromans; D018793:Interleukin-13; D050800:STAT6 Transcription Factor; C494101:STAT6 protein, human; D014157:Transcription Factors; C101296:prostate apoptosis response-4 protein; D014810:Vitamin E; C013649:plastochromanol 8; D024504:gamma-Tocopherol; D011493:Protein Kinase C; D048051:p38 Mitogen-Activated Protein Kinases; D024502:alpha-Tocopherol; C479072:delta-tocopherol; D024505:Tocopherols