Carcinogenesis Advance Access originally published online on February 1, 2007
Carcinogenesis 2007 28(7):1589-1598; doi:10.1093/carcin/bgm017
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Gene expression analysis during tumor enhancement by the dietary phytochemical, 3,3'-diindolylmethane, in rainbow trout
1 Department of Environmental and Molecular Toxicology
2 Marine and Freshwater Biomedical Sciences Center
3 Linus Pauling Institute
4 Environmental Health Sciences Center
5 Department of Statistics, Oregon State University, Corvallis, OR 97331, USA
6 Present address: Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, Seattle, WA 98105, USA
* To whom correspondence should be addressed. Tel: +1 541 737 3277; Fax: +1 541 737 7966; Email: david.williams{at}oregonstate.edu
Indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM), a primary I3C derivative, are known dietary chemopreventive agents also available as supplements. However, I3C has been found to act as a tumor promoter in rat (multi-organ) and trout (liver) models. I3C and DIM were previously found to be estrogenic in trout liver based on toxicogenomic profiles. In this study, we compare the post-initiation effects of DIM and 17ß-estradiol (E2) on aflatoxin B1 (AFB1)-induced hepatocarcinogenesis in trout. Trout were initiated as embryos with AFB1 and juvenile fish were fed diets containing 0, 120 or 400 p.p.m. DIM or 5 p.p.m. E2 for 18 weeks. Tumor incidence was determined at 13 months and found to be significantly elevated in AFB1-initiated trout fed either 400 p.p.m. DIM or 5 p.p.m. E2 compared with control animals. To evaluate the mechanism of tumor enhancement, hepatic gene expression profiles were examined in animals fed promotional diets during the course of tumorigenesis and in hepatocellular carcinomas (HCCs) of initiated animals. We demonstrate that DIM alters gene expression profiles similar to E2 in liver samples during tumorigenesis and in HCC tumors. Further, HCCs from animals on DIM and E2 promotional diets had a transcriptional signature indicating decreased invasive or metastatic potential compared with HCCs from control animals. Overall, these findings are the first to demonstrate tumor promotion by DIM. They confirm the importance of estrogenic signaling in the mechanism of promotion by dietary indoles in trout liver and indicate a possible dual effect that enhances tumor incidence and decreases potential for metastasis.
Abbreviations: AFB1, aflatoxin B1; AhR, aryl hydrocarbon receptor; DIM, 3,3'-diindolylmethane; EST, expressed sequence tag; ER, estrogen receptor; E2, 17ß-estradiol; HCC, hepatocellular carcinoma; IFN, interferon; I3C, indole-3-carbinol; JAK, Janus kinase; MHC-I, histocompatability complex class-I; PCA, principal component analysis; PCR, polymerase chain reaction; PER, perforin; RAG2, recombination-activating gene 2; SDS, sodium dodecylsulphate; SSC, standard saline citrate
Received October 19, 2006; revised January 1, 2007; accepted January 13, 2007.