Conjugated linoleic acid stimulates an anti-tumorigenic protein NAG-1 in an isomer specific manner.
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.
Lee
Seong-Ho
SH
Department of Pathobiology, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.
Yamaguchi
Kiyoshi
K
Kim
Jong-Sik
JS
Eling
Thomas E
TE
Safe
Stephen
S
Park
Yeonhwa
Y
Baek
Seung Joon
SJ
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
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