To further understand the molecular mechanism of DCPA in decreasing HIF-1α expression in these cells, we found that 1) DCPA specifically inhibits the induction of HIF-1α expression by serum, 2) expression of HIF-1β is not altered by the addition of serum or DCPA, 3) the effect of DCPA on HIF-1α is not due to the non-specific effect in the cells, 4) DCPA treatment decreased HIF-1α expression by affecting its stability through the proteasomal degradation pathway, and 5) DCPA also inhibited hypoxia-induced HIF-1α expression in human prostate cancer cells. This evidence concerns the gene ARNT and prostate cancer.