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: ER alpha and the more recently discovered ER beta, The physiological function of ER beta remains unclear, but evidence from vascular injury studies and from ER beta knockout mice suggests that ER beta may be involved in the regulation of cellular proliferation. Here we show a direct and specific interaction between ER beta and the cell cycle mitotic spindle assembly checkpoint protein, MAD2 (mitosis arrest-deficient 2). The ER beta-MAD2 interaction was identified by screening of a yeast two-hybrid system vascular endothelial cell library with ER beta and confirmed with glutathione S-transferase-fusion protein interaction studies. In contrast, ER alpha 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 ER beta 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 ER beta and MADZ of potential importance to regulation of the cell cycle and support a function of ER beta distinct from the established role of ERs as transcription factors.