Antiestrogen binding site complex (AEBS)

The Antiestrogen Binding Site (AEBS) complex is a microsomal protein assembly that binds selective estrogen receptor modulators (SERMs) such as tamoxifen with high affinity, but does not bind estrogens (Silvente-Poirot & Poirot, 2012, PMID: 22564308). It is primarily composed of two subunits: the 3β-hydroxysteroid-Δ8,Δ7-isomerase (also known as the emopamil-binding protein or EBP) and the 3β-hydroxysteroid dehydrogenase (de Medina et al., 2010, PMID: 20154298). Biologically, the AEBS is an integral part of the cholesterol biosynthetic pathway, catalyzing the conversion of zymostenol to lathosterol (Moebius et al., 1998, PMID: 9461604). In the context of oncology, the binding of antiestrogens to the AEBS inhibits its enzymatic activity, resulting in the accumulation of sterol precursors that induce cell differentiation, growth arrest, and apoptosis in breast cancer cells (Silvente-Poirot et al., 2003, PMID: 12810713). This mechanism represents an important estrogen receptor-independent pathway for the therapeutic action of tamoxifen and related compounds (Payre et al., 2008, PMID: 18448480). Additionally, the AEBS has been investigated for its role in neuroprotection and as a target for chemopotentiating agents like tesmilifene (Kedjouar et al., 2004, PMID: 15155836).

Other names

Microsomal antiestrogen binding siteEBP3-beta-hydroxysteroid-Delta(8),Delta(7)-isomeraseSterol Delta(8)-Delta(7) isomeraseEmopamil-binding protein

Inhibition of 3-beta-hydroxysteroid-Delta(8),Delta(7)-isomerase activity within the complex, leading to the accumulation of sterol intermediates that trigger cell differentiation and apoptosis.