The research, published in Carcinogenesis,used epigenetic analysis to investigate the mechanisms by which the soy isoflavone genistein reduces the risk of colon cancer development - finding that the soy compound regulates the way in which important signalling genes react to cancer onset, by restricting them from sending signals that cause rapid cell growth.
"In our study, we report a change in the expression of three genes that control an important signalling pathway," explained Professor Hong Chen, from the University of Illinois USA - who led the research.
The Professor of food science and human nutrition noted that normally cells in the lining of the human gut turn over and are completely replaced weekly: "However, in 90% of colon cancer patients, an important growth-promoting signal is always on, leading to uncontrolled growth and malignancies," she said.
Chen and her team revealed that chronic exposure to genistein reduced the number of pre-cancerous lesions in the colons of laboratory rats exposed to a carcinogen by 40% and regulated the 'always on' signalling pathway - known as Wnt signalling - so bringing it back to normal levels.
"Our study suggests that the aberrant Wnt signalling during the development of colon cancer can be regulated by soy-rich diets," confirmed Chen.
Chen and her colleagues modelled lifetime exposure to soy by feeding pregnant rats and their offspring a diet containing soy protein isolate and a diet that contained genistein compound. At seven weeks of age, offspring rats were then exposed to a carcinogen, while they continues to consume either the soy protein or the genistein diet until they were 13 weeks old.
The team then analysed the colons of rats in both soy groups and compared them to rats in a control group, noting the number and severity of tiny abnormal growths in each. They also compared Wnt signaling before and after the carcinogen to see whether either diet had any effect on its up-regulation.
The researchers found that in genistein-fed animals, signalling levels were similar to rats that had not received the carcinogen.
"Genistein decreased the expression of three genes and repressed this signalling process that is associated with abnormal cell growth and cancer development," said Chen.
This, she said, shows that colon cancer is an epigenetic disease - meaning that dietary and environmental factors can influence genes to be switched on or off so you have a different pattern of gene expression, leading to a change in disease susceptibility.
"The genetic information you inherit from your parents is not the whole story. Our dietary choices, our exposure to environmental toxins, even our stress levels, affect the expression of those genes," Chen said.
"The good news is that a diet rich in soy genistein represses those signals through epigenetic modifications at the regulatory regions of those genes," added Yukun Zhang - first author of the paper.
Published online ahead of print, doi: 10.1093/carcin/bgt129
DNA methylation and histone modifications of Wnt genes by genistein during colon cancer development
Author: Yukun Zhang, Qian Li, Hong Chen