Subcellular and extracellular localization of specific binding sites for triphenylethylene antiestrogens in human breast cancer

Membrane associated estrogen receptors and related proteins: localization at the plasma membrane and the endoplasmic reticulum

The female sex steroid, estradiol 17beta, mediates its effect through its association with estrogen receptor present in the target cell. So far the major emphasis has been given to the genomic actions of the hormone mediated by the nuclear estrogen receptors. Recent years have seen a shift in the ideas revealing the existence of estradiol binding entities both in the plasma membrane and the endoplasmic reticulum. Though the true identity of this membrane associated receptors is far from being known, a functional role for the same have been implicated both at the genomic as well as the non-genomic level. The major focus of the review is to highlight the existence of membrane associated estrogen receptors and receptor-related proteins and the functional roles played by some of them. The signalling events exerted by this class of membrane associated estrogen receptor could partly explain the physiological significance of estrogen in cardiovascular disease, osteoporosis and breast cancer as well as the molecular mechanism associated with xenoestrogen action.

Antiestrogen(4-hydroxytamoxifen)-charged estrogen receptor binding to nuclei from normal and neoplastic rat mammary tissues is not affected by host hormonal status

Interaction of [3H]4-hydroxytamoxifen-charged estrogen receptor [( 3H]AER) with nuclei was compared to that of [3H]17 beta-estradiol-charged estrogen receptor [( 3H]ER) in vitro. Specificity of [3H]AER binding was demonstrated since more than 90% of [3H]AER binding was displaced by ten-fold excess estradiol-charged ER. For R3230AC tumors, the number of [3H]AER binding sites was approximately 40% lower than the number of [3H]ER binding sites. There were no differences in affinity of binding of these receptors complexes (Kd range 0.7-1.6 nM). In contrast 0.7-1.6 nM). In contrast to a reduction of [3H]ER binding after ovariectomy, no difference in the number of [3H]AER binding sites was seen among tumors from intact, ovex, or estrogen-treated ovex rats. These results suggest that [3H]AER bind to 60% of the sites that bind [3H]ER, and that neither tissue type nor host ovarian status affects the number of nuclear [3H]AER binding sites.