title: Obesity promotes PhIP-induced small intestinal carcinogenesis in hCYP1A-db/db mice: involvement of mutations and DNA hypermethylation of Apc.
abstract: Obesity is associated with an increased risk of cancer. To study the promotion of dietary carcinogen-induced gastrointestinal cancer by obesity, we employed 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) to induce intestinal tumorigenesis in CYP1A-humanized (hCYP1A) mice, in which mouse Cyp1a1/1a2 was replaced with human CYP1A1/1A2 Obesity was introduced in hCYP1A mice by breeding with Lepr(db/+) mice to establish the genetically induced obese hCYP1A-Lepr(db/db) mice or by feeding hCYP1A mice a high-fat diet. PhIP induced the formation of small intestinal tumors at the ages of weeks 28-40 in obese hCYP1A mice, but not in lean hCYP1A mice. No tumors were found in colon and other gastrointestinal organs in the lean or obese mice. Using immunohistochemistry (IHC), we found strong positive staining of NF-κB p65, pSTAT3 and COX2 as well as elevated levels of nuclear β-catenin (Ctnnb1) in small intestinal tumors, but not in normal tissues. By sequencing Apc and Ctnnb1 genes, we found that most PhIP-induced small intestinal tumors in obese mice carried only a single heterozygous mutation in Apc By bisulfite-sequencing of CpG islands of Apc, we found DNA hypermethylation in a CpG cluster located in its transcription initiation site, which most likely caused the inactivation of the wild-type Apc allele. Our findings demonstrate that PhIP-induced small intestinal carcinogenesis in hCYP1A-db/db mice is promoted by obesity and involves Apc mutation and inactivation by DNA hypermethylation. This experimental result is consistent with the association of obesity and the increased incidence of small intestinal cancer in humans in recent decades.
authors.affiliation: Susan L. Cullman Laboratory for Cancer Research, Department of Chemical Biology and Center for Cancer Prevention Research, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, 164 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Wang
authors.affiliation: Susan L. Cullman Laboratory for Cancer Research, Department of Chemical Biology and Center for Cancer Prevention Research, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, 164 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Liu
authors.affiliation: Susan L. Cullman Laboratory for Cancer Research, Department of Chemical Biology and Center for Cancer Prevention Research, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, 164 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Yingyi
authors.initials: Y
authors.lastname: Kuo
authors.affiliation: Susan L. Cullman Laboratory for Cancer Research, Department of Chemical Biology and Center for Cancer Prevention Research, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, 164 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Chi
authors.affiliation: Susan L. Cullman Laboratory for Cancer Research, Department of Chemical Biology and Center for Cancer Prevention Research, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, 164 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Xu
authors.initials: X
authors.lastname: Yang
authors.affiliation: Susan L. Cullman Laboratory for Cancer Research, Department of Chemical Biology and Center for Cancer Prevention Research, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, 164 Frelinghuysen Road, Piscataway, NJ 08854, USA.|Department of Pathology, University Medical Center of Princeton, Plainsboro, NJ 08536, USA and.|Department of Pathology, Robert Wood Johnson Medical School and Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA.
authors.forename: Lanjing
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Susan L. Cullman Laboratory for Cancer Research, Department of Chemical Biology and Center for Cancer Prevention Research, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, 164 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Chung S
authors.initials: CS
authors.lastname: Yang
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics*; D000818:Animals; D063646:Carcinogenesis / Q000187:drug effects / Q000235:genetics*; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation / Q000187:drug effects / Q000235:genetics; D006801:Humans; D007093:Imidazoles / Q000633:toxicity; D007414:Intestinal Neoplasms / Q000139:chemically induced / Q000235:genetics* / Q000473:pathology; D007421:Intestine, Small / Q000187:drug effects / Q000473:pathology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D009363:Neoplasm Proteins / Q000096:biosynthesis; D009765:Obesity / Q000150:complications / Q000235:genetics* / Q000473:pathology; D054411:Receptors, Leptin / Q000235:genetics; D051176:beta Catenin / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D025601:Adenomatous Polyposis Coli Protein; C495267:CTNNB1 protein, mouse; D007093:Imidazoles; D009363:Neoplasm Proteins; D054411:Receptors, Leptin; C000613192:adenomatous polyposis coli protein, mouse; D051176:beta Catenin; C515447:leptin receptor, mouse; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine; D019363:Cytochrome P-450 CYP1A1