Phytoestrogens are assumed to affect the endocrine system of animal species similarly to other man-made endocrine disrupters and to exert their effects through estrogen receptors, specifically ERalpha and ERbeta. However, these molecular mechanisms are not fully understood. In this study, 19 phytochemicals were surveyed for agonist and antagonist activities of ERalpha and ERbeta using an ERE-luciferase reporter assay. The results showed that ferutinine is an agonist for ERalpha and an agonist/antagonist for ERbeta, tschimgine is an agonist for both ERalpha and ERbeta, and tschimganidine is an agonist for only ERalpha. Ferutinine and tschimganidine are sesquiterpenoids, and tschimgine is a monoterpenoid derived from the Umbelliferae family. A competitive binding assay showed that ferutinine has higher binding affinities than tamoxifen for both ERs. Co-transfections of coactivators such as SRC-1, TIF2, AIB1, and TRAP220 in 293T cells and use of the luciferase assay revealed that TRAP220 failed to enhance the transcription mediated by ERbeta in the presence of ferutinine. Moreover, a GST pull-down assay showed that TRAP220 marginally bound to ERbeta ligand binding domain in the presence of ferutinine. These results suggest that the conformation of ferutinine-liganded ERbeta is difficult for TRAP220 to recognize. Taken together, this suggests that some terpenoids can modulate estrogen signaling as ER subtype-selective phytoestrogens similar to SERMs (selective estrogen receptor modulators). (C) 2002 Elsevier Science (USA).