title: Dietary soy protein inhibits DNA damage and cell survival of colon epithelial cells through attenuated expression of fatty acid synthase.
abstract: Dietary intake of soy protein decreases tumor incidence in rat models of chemically induced colon cancer. We hypothesized that decreased expression of fatty acid synthase (FASN) underlies, in part, the tumor-preventive effects of soy protein, since FASN overexpression characterizes early tumorigenesis. Here, we show that colonic FASN levels are reduced with dietary intake of soy protein isolate (SPI), compared with a control casein diet, in male Sprague-Dawley rats administered the colon carcinogen azoxymethane. SPI consumption resulted in decreased serum insulin levels and decreased azoxymethane-induced tumor suppressor p53 phosphorylation in colon crypt epithelium. To evaluate potential links between insulin and FASN leading to DNA damage, C2(BBe)1 colon epithelial cells, treated with insulin and/or the carcinogen N-nitroso-N-methylurea (NMU), were evaluated for DNA damage and apoptosis after transfection with control or FASN small interfering RNAs (siRNAs). While the numbers of DNA apurinic/apyrimidinic sites (biomarker of DNA damage) induced by NMU were unaffected by transfection of FASN siRNA, insulin induction of these sites was decreased with FASN knockdown. By contrast, NMU-induced apoptosis of C2(BBe)1, as well as intestinal epithelial cell (IEC)-6, was enhanced by transfected FASN siRNA. Increased FASN expression in IEC-6 cells by addition of liver X receptor agonist T0901317 did not affect apurinic/apyrimidinic site number, but enhanced cell killing by cerulenin, a FASN inhibitor. Moreover, insulin rescued NMU-treated cells from apoptosis in an FASN-dependent manner. Results suggest that dietary SPI, by decreasing circulating insulin levels and colon FASN expression, attenuates insulin-induced DNA damage and FASN-mediated anti-apoptosis during carcinogenesis, resulting in an overall reduced tumorigenic state.
authors.affiliation: Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72202, USA.
authors.forename: Rijin
authors.initials: R
authors.lastname: Xiao
authors.forename: Ying
authors.initials: Y
authors.lastname: Su
authors.forename: Rosalia C M
authors.initials: RC
authors.lastname: Simmen
authors.forename: Frank A
authors.initials: FA
authors.lastname: Simmen
mesh_terms: D000818:Animals; D016588:Anticarcinogenic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001397:Azoxymethane / Q000633:toxicity; D018938:Caco-2 Cells; D002273:Carcinogens / Q000633:toxicity; D002364:Caseins / Q000494:pharmacology; D002471:Cell Transformation, Neoplastic / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002569:Cerulenin / Q000494:pharmacology; D003106:Colon / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D004249:DNA Damage / Q000187:drug effects*; D004044:Dietary Proteins / Q000008:administration & dosage / Q000494:pharmacology*; D015536:Down-Regulation; D004847:Epithelial Cells / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D054890:Fatty Acid Synthase, Type I / Q000378:metabolism; D064429:Fatty Acid Synthases / Q000235:genetics / Q000378:metabolism*; D054872:Fatty Acid Synthesis Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D006845:Hydrocarbons, Fluorinated; D007328:Insulin / Q000097:blood; D008297:Male; D008770:Methylnitrosourea / Q000633:toxicity; D010766:Phosphorylation; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D030262:Soybean Proteins / Q000008:administration & dosage / Q000494:pharmacology*; D013449:Sulfonamides / Q000494:pharmacology; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
chemical_list: D016588:Anticarcinogenic Agents; D001397:Azoxymethane; D002273:Carcinogens; D002364:Caseins; D002569:Cerulenin; D004044:Dietary Proteins; D054890:Fatty Acid Synthase, Type I; D064429:Fatty Acid Synthases; D054872:Fatty Acid Synthesis Inhibitors; D006845:Hydrocarbons, Fluorinated; D007328:Insulin; D008770:Methylnitrosourea; D034741:RNA, Small Interfering; D030262:Soybean Proteins; D013449:Sulfonamides; D016159:Tumor Suppressor Protein p53; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides; C518729:FASN protein, human