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We have shown that dietary fish oil and pectin (FP) protects against radiation-enhanced colon cancer by upregulating apoptosis in colonic mucosa. To investigate the mechanism of action, we provided rats ( n  = 40) with diets containing the combination of FP or corn oil and cellulose (CC) prior to exposure to 1 Gy, 1 GeV/nucleon Fe-ion. All rats were injected with a colon-specific carcinogen, azoxymethane (AOM; 15 mg/kg), 10 and 17 days after irradiation. Levels of colonocyte apoptosis, prostaglandin E ₂ (PGE ₂ ), PGE ₃ , microsomal prostaglandin E synthase-2 (mPGES-2), total β-catenin, nuclear β-catenin staining (%) and peroxisome proliferator-activated receptor δ (PPARδ) expression were quantified 31 weeks after the last AOM injection. FP induced a higher ( P < 0.01) apoptotic index in both treatment groups, which was associated with suppression ( P < 0.05) of antiapoptotic mediators in the …