The researchers then looked at the role that diet plays when expression of two tumor suppressor genes is reduced. The researchers mated mice that had only one APC gene to p27 positive or negative mice, producing variants with no p27 genes or one or two. The APC gene is responsible for an inherited colorectal cancer condition known as FAP (familial adenomatous polyposis), in which patients develop hundreds of potentially precancerous polyps.
They found that on the AIN-76A diet, loss of one APC gene but retention of the "wild-type" (normal) p27 genes was enough to induce tumor formation in 22 percent of the mice, but that number increased to 72 percent when one allele of the p27 gene was lost, and 93 percent when both alleles of the p27 gene were lost. But all of the knock-out mice variants developed tumors in both their small and large intestines when fed a Western-style diet.
"This showed that the diet overwhelmed any protective effect the p27 genes conferred," says Yang. "It not only increased tumor size and number, but also pushed the cancer into an invasive state."
Finally, they examined what happened when the knock-out mice were fed a Western diet enhanced with sulindac, an agent they had previously found help suppress tumor formation. To their surprise, none of the knock-out mice developed cancer.
"To us this means that as long as an animal can activate the p21 gene, this can have an overriding affect on suppressing tumor formation caused by either loss of other tumor suppressor genes or di
Source:American Association for Cancer Research