ERs are classified as a group of nuclear receptors super family also called nuclear ERs that function as transcription factors when they interact with their responsive ligand, estrogen. Estrogen exerts this action by passive diffusion into target cells (van Landeghem et al. 1985). Normally, ERs associate with the chaperone proteins and locate in cytoplasm (Jensen et al. 1968; van Landeghem et al. 1985).