Specific association of estrogen receptor β with the cell cycle spindle assembly checkpoint protein, MAD2

Estrogen receptors (ERs) are ligand-activated transcription factors that regulate gene expression and cell growth. Two ERs now have been identified: ERα and the more recently discovered ERβ. The physiological function of ERβ remains unclear, but evidence from vascular injury studies and from ERβ knockout mice suggests that ERβ may be involved in the regulation of cellular proliferation. Here we show a direct and specific interaction between ERβ and the cell cycle mitotic spindle assembly checkpoint protein, MAD2 (mitosis arrest-deficient 2). The ERβ-MAD2 interaction was identified by screening of a yeast two-hybrid system vascular endothelial cell library with ERβ and confirmed with glutathione S-transferase-fusion protein interaction studies. In contrast, ERα did not interact with MAD2 in either the two-hybrid system or in the protein–protein interaction experiments. Amino acids 173–208 in the hinge region of ERβ were sufficient to mediate the interaction with MAD2 in the two-hybrid system and in glutathione S-transferase-fusion protein studies. These data identify a link between ERβ and MAD2 of potential importance to regulation of the cell cycle and support a function of ERβ distinct from the established role of ERs as transcription factors.