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Conjugated linoleic acid stimulates an anti-tumorigenic protein NAG-1 in an isomer specific manner.

Department of Pathobiology, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.
Carcinogenesis (Impact Factor: 5.27). 06/2006; 27(5):972-81. DOI: 10.1093/carcin/bgi268
Source: PubMed

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.

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The significance of this study is that CLA might be used as a dietary supplement in prevention and/or treatment of osteosarcoma. Journal of Nature and Science, 1(4):e67, 2015 Conjugated linoleic acid | CLA | osteosarcoma | NAG-1 Introduction Osteosarcoma is one of the most aggressive types of cancer in children and adolescents (1). Overall, it comprises approximately 20% of all bone tumors including about 5 % of pediatric tumors. On average, approximately 400 children and adolescents are diagnosed with osteosarcoma in the US each year, where the majority of them are in their early adolescence (1-3). It was suggested that osteosarcoma may be a disease of differentiation, particularly associated with impairment of osteoblastic differentiation, however, the current understanding of osteosarcoma etiology is relatively limited (2). To date, the survival rate for osteosarcoma patients is 70 %, but 20 % of all diagnosed osteosarcoma patients experience severe side effects from chemotherapy (2). Thus, there is a great need for understanding osteosarcoma to develop treatment as well as prevention strategies for osteosarcoma. Conjugated linoleic acid (CLA) is a type of dietary fatty acid, which has been shown to have an anti-cancer effect in a number of studies (4). CLA is a geometric and positional isomer of linoleic acid, and was originally identified as an anti-cancer component from ground beef (5). Since then, CLA has drawn considerable attention due to its other biologically beneficial effects, such as immune modulation, reduction of atherosclerosis, and reduction of body fat while enhancing lean body mass (6, 7). The anticancer properties of CLA have been reported in animal models, and it is suggested that CLA acts on all stages of cancer; initiation, promotion, progression, and metastasis by modulating eicosanoids production, interfering with cell signaling pathways, inhibiting DNA synthesis, promoting apoptosis, and modulating angiogenesis (8-17). Currently the bioactivities of two isomers of CLA, the cis-9,trans-11 and the trans-10,cis-12, are the focus of much study. The cis-9,trans-11 CLA isomer, the major isomer present in food sources, derives naturally from rumen bacteria via biohydrogenation (18), or alternatively by Δ9 desaturation of trans-11 vaccenic acid in mammalian tissues (19, 20). On the other hand, the trans-10,cis-12 CLA isomer is present in relatively low amounts in natural sources. However, when CLA is prepared by chemical isomerization of linoleic acid from either pure or vegetable oils, it consists of approximately 40-45% trans-10,cis-12 CLA along with a similar amount of the cis-9,trans-11 CLA (21). It has been reported that these CLA as a mixture of these two isomers can have various biological effects, including effects on cancer suppression in a number of human cancer cell lines and animal models (6, 7, 22-26). There are studies using two separate CLA isomers in cancer studies; the trans-10,cis-12 CLA isomer is more effective than the cis-9,trans-11 isomer with regard to its anti-cancer effect, while others reported no differences between these two isomers or greater effects of the cis-9,trans-11 isomer (25, 27-32). Thus, the two CLA isomers may exert anti-cancer effects through different and/or independent mechanism(s) or depending on cell context, and understanding their exact roles in cancer prevention is necessary in order to determine the proper application of CLA. Previously, it has been suggested that one of the main anti-cancer mediators of CLA is non-steroidal anti-inflammatory drug-activated gene-1 (NAG-1) (12). Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used in the treatment of inflammatory disease. NAG-1 (also known as Growth Differentiation Factor-15, GDF-15) has been suggested as one of the main targets of NSAIDs and is a member of the transforming growth factor-β (TGF-β) super family, which plays a role in apoptosis, reduction of cell proliferation, and inhibition of cell cycle progression (33). 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