In our cells there are thousands of receptors which act as our messenger system. These receptors bind to key chemical molecules, typically proteins with certain structures that enable chemical bonding on its surfaces in a manner often described as “a lock and a key.”
Once a receptor is paired with its “protein key,” it can influence the expression of DNA within a cell. This organizes useful chemicals to enable healthy cell functioning. In the case of 2,3,7,8-TCDD, scientists are the most concerned with Ahr, or the Aryl hydrocarbon receptor. The Ah receptor is a relic of from our evolutionary history, with its “key” being a growth-regulating hormone which we no longer use.
Dioxins are only toxic when the Ah receptor is involved! After exposure and uptake, the 2,3,7,8-TCDD-Ahr complex is then transported to the DNA in the cell nucleus, where activated genes will result in (1) production of the P450 enzymes; and (2) regulatory chemicals important for growth and division of cells. Due to the high affinity of 2,3,7,8-TCDD for the Ah receptor the dioxin is not broken down. The P-450 enzymes, which breakdown contaminants, are produced in the cell and remain there for extended periods. All those extra enzymes can lead to the breakdown of other beneficial hormones. The breakdown of regulatory hormones can lead to dysfunctional cells and promote cancer.
The Ah receptor has other functions besides enzyme induction. It controls certain genes and cell functions particularly those governing growth and differentiation. 2,3,7,8-TCDD is somewhat similar in structure to an important thyroid hormone, thryoxine. As hormones do not act alone, this interaction of 'dioxin hormone' complex mimics other hormones that can result in a cascade of effects throughout the body.