Human EH3 is a recently characterized protein with epoxy hydrolase activity for metabolizing epoxyeicosatrienoic acids (EETs) and vernolic acids (leukotoxins) to their corresponding diols; in these capacities they may thereby limit the cell signaling activity of the EETs and contribute to the toxicity of the leukotoxins. mRNA for EH3 is most strongly expressed in the lung, skin, and upper gastrointestinal tract tissues of mice. The function of EH3 in humans, mice, or other mammals has not yet been determined although the gene for EH3 has been validated as being hypermethylated on CpG sites in its promoter region in human prostate cancer tissue, particularly in the tissues of more advanced or morphologically-based (i.e. Gleason score) more aggressive cancers; this suggests that the gene silencing of EH3 due to this hypermethylation may contribute to the onset and/or progression of prostate cancer.  Similar CpG site hypermethylations in the promoter of for the EH3 gene have been validated for other cancers.  This promoter methylation pattern, although not yet validated, was also found in human malignant melanoma.