The antiestrogen ICI 182780 disrupts estrogen receptor nucleocytoplasmic shuttling.

The mouse estrogen receptor was shown to be constantly shuttling between the nucleus and cytoplasm although under steady-state conditions it is detected predominantly in the cell nucleus in both the absence and presence of estradiol. Shuttling was demonstrated by monitoring the transfer of protein between nuclei in heterokaryons and by examining the subcellular distribution of mutant receptors. In the presence of the partial antiestrogen 4-hydroxytamoxifen the receptor was retained in the nucleus whereas it accumulated in the cytoplasm when cells were treated with the pure antiestrogen ICI 182780. The effect of the pure antiestrogen was to inhibit nucleocytoplasmic shuttling of the receptor by blocking its nuclear uptake. Thus although ligand binding is not required by the estrogen receptor to undergo nucleocytoplasmic shuttling, this process can be disrupted by the binding of a pure antiestrogen.