title: Conjugated linoleic acid stimulates an anti-tumorigenic protein NAG-1 in an isomer specific manner.
abstract: Conjugated linoleic acids (CLAs), naturally occurring fatty acids in ruminant food products, have anti-tumorigenic and pro-apoptotic properties in animal as well as in vitro models of cancer. However, the cellular mechanism has not been fully understood. NAG-1 (non-steroidal anti-inflammatory drug-activated gene-1) is induced by several dietary compounds and belongs to a TGF-beta superfamily gene associated with pro-apoptotic and anti-tumorigenic activities. The present study was performed to elucidate the molecular mechanism by which CLA stimulates anti-tumorigenic activity in human colorectal cancer (CRC) cells. The trans-10, cis-12-CLA (t10,c12-CLA) repressed cell proliferation and induced apoptosis, whereas linoleic acid or c9,t11-CLA showed no effect on cell proliferation and apoptosis. We also found that t10,c12-CLA induced the expression of a pro-apoptotic gene, NAG-1, in human CRC cells. Inhibition of NAG-1 expression by small interference RNA (siRNA) results in repression of t10,c12-CLA-induced apoptosis. Microarray analysis using t10,c12-CLA-treated HCT-116 cells revealed that activating transcription factor 3 (ATF3) was induced and its expression was confirmed by western analysis. The t10,c12-CLA treatment followed by the overexpression of ATF3 increased NAG-1 promoter activity in HCT-116 cells. We further provide the evidence that t10,c12-CLA inhibited the phosphorylation of AKT and the blockage of GSK-3 by siRNA abolished t10,c12-CLA-induced ATF3 and NAG-1 expression. The current study demonstrates that t10,c12-CLA stimulates ATF3/NAG-1 expression and subsequently induces apoptosis in an isomer specific manner. These effects may be through inhibition of AKT/GSK-3beta pathway in human CRC cells.
authors.affiliation: Department of Pathobiology, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.
authors.forename: Seong-Ho
authors.initials: SH
authors.lastname: Lee
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Yamaguchi
authors.forename: Jong-Sik
authors.initials: JS
authors.lastname: Kim
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Eling
authors.forename: Stephen
authors.initials: S
authors.lastname: Safe
authors.forename: Yeonhwa
authors.initials: Y
authors.lastname: Park
authors.forename: Seung Joon
authors.initials: SJ
authors.lastname: Baek
mesh_terms: D051700:Activating Transcription Factor 3 / Q000378:metabolism; D016588:Anticarcinogenic Agents / Q000737:chemistry; D017209:Apoptosis; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D015179:Colorectal Neoplasms / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism*; D005434:Flow Cytometry; D055436:Growth Differentiation Factor 15; D006801:Humans; D044243:Linoleic Acids, Conjugated / Q000494:pharmacology*; D020033:Protein Isoforms; D034741:RNA, Small Interfering / Q000378:metabolism; D014162:Transfection
chemical_list: C490449:ATF3 protein, human; D051700:Activating Transcription Factor 3; D016588:Anticarcinogenic Agents; D016207:Cytokines; C526140:GDF15 protein, human; D055436:Growth Differentiation Factor 15; D044243:Linoleic Acids, Conjugated; D020033:Protein Isoforms; D034741:RNA, Small Interfering