Expression, Function of the Human Androgen-Responsive Gene AD11 in Prostate Cancer

We have previously identified an androgen-responsive gene in rat prostate that shares homology with the acireductone dioxygenase (ARD/ARD′) family of metalbinding enzymes involved in methionine salvage. We found that the gene, aci-reductone dioxygenase 1 (ADI1), was downregulated in prostate cancer cells, whereas enforced expression of rat Adi1 in these cells caused apoptosis. Here we report the characterization of human ADI1 in prostate cancer. Androgens induced ADI1 expression in human prostate cancer LNCaP cells, which was not blocked by cycloheximide, indicating that ADI1 is a primary androgen-responsive gene. In human benign prostatic hyperplasia specimens, epithelial cells expressed ADI1. Immunohistochemistry of prostate tumor tissue microarrays showed that benign regions expressed more ADI1 than tumors, suggesting a suppressive role for ADI1 in prostate cancer. Bacterial lysates containing recombinant ADI1 produced a five-fold increase in aci-reductone decay over controls, demonstrating that ADI1 has ARD activity. We generated point mutations at key residues in the metal-binding site of ADI1 to disrupt ARD function, we found that these mutations did not affect intracellular localization, apoptosis, or colony formation suppression in human prostate cancer cells. Collectively, these observations argue that AD11 may check prostate cancer progression through apoptosis, that this activity does not require metal binding.