Effects of inhibiting the proteasomal degradation of estrogen receptor alpha on estrogen receptor alpha activation under hypoxic conditions.

Hypoxia, which is intimately associated with the biology of breast carcinomas, modulates the level of estrogen receptor (ER) alpha expression and transactivation. We investigated the effect of blocking ER degradation on ERalpha-mediated transactivation under hypoxic conditions using the proteasome inhibitor MG132. Pretreatment with MG132 blocked hypoxia-induced degradation of ERalpha protein. Our data imply that ERalpha proteasomal inhibition is linked to receptor transactivation under hypoxia.