Down-regulates ESR1 protein levels through the ubiquitination-proteasome pathway, regardless of the presence of 17 beta-estradiol. Also involved in 17 beta-estradiol-induced ESR1 degradation. Controls PGR protein levels through a similar mechanism. Interacts with PGR. Interacts with ESR1 in the presence or absence of 17 beta-estradiol. Significantly up-regulated in breast tumor tissues compared with matched adjacent normal tissues (at protein level). Levels inversely correlate with ESR1 in breast cancers and are lower in low-grade tumors compared to high-grade tumors. The CUE domain mediates interaction with PGR and ESR1. May predict the clinical outcome of tamoxifen therapy of breast cancer patients. Patients with tumors that highly express CUEDC2 do not respond to tamoxifen treatment as effectively as those with tumors with low expression. Belongs to the CUEDC2 family. Truncated C-terminus.