last updated April 2013
Revealing dioxin’s cellular sabotage
New research reveals how certain environmental toxins exert their effects by tagging specific target proteins for destruction
Although most signaling factors require physical transportation across the cellular plasma membrane, some — including sex hormones and certain environmental contaminants — are fat-soluble and can readily penetrate the membrane.
These compounds subsequently interact with receptors present within the cell, forming complexes that can modulate gene activity. This is mediated in part by direct regulation of gene transcription, but recent work from
The researchers focused their study on the arylhydrocarbon receptor (AhR), which binds dioxin — a highly toxic industrial pollutant known to influence sex hormone signaling. Surprisingly, they found that dioxin lowers levels of estrogen receptor protein without affecting gene activity; instead, the dioxin-AhR complex appears to directly induce degradation of the protein itself.
Closer analysis revealed that AhR acts as an ubiquitin ligase, a class of enzymes that physically marks specific proteins for destruction — in this case, steroid sex hormone receptors. In addition to providing a new perspective on the effects of dioxin exposure, these findings may reveal an additional means by which fat-soluble signaling factors can affect protein levels beyond merely switching genes on or off.