Inhibition of Neu-induced mammary carcinogenesis in transgenic mice expressing ERΔ3, a dominant negative estrogen receptor α variant.

The estrogen receptor α (ERα) splicing variant with an in-frame deletion of exon 3 (ERΔ3) is frequently expressed in the normal breast, but its influence on tumorigenesis has not been explored. In vitro, ERΔ3 has dominant negative activity, suggesting it may suppress estrogen stimulation in the breast. ERΔ3 may inhibit classical signaling on estrogen response element (ERE)-regulated genes as well as activate non-classical pathways at Sp1 and AP-1 sites.