Padron Adrian, Li Li, Kofoed Eric M, Schaufele Fred
Diabetes Center, University of California San Francisco, San Francisco, California 94143-0540, USA.
Mol Endocrinol. 2007 Jan;21(1):49-61. doi: 10.1210/me.2006-0075. Epub 2006 Sep 28.
Selective estrogen receptor modulators (SERMs) inhibit estrogen activation of the estrogen receptor (ER) in some tissues but activate ER in other tissues. These tissue-selective actions suggest that SERMs may be identified with tissue specificities that would improve the safety of breast cancer and hormone replacement therapies. The identification of an improved SERM would be aided by understanding the effects of each SERM on the structure and interactions of ER. To date, the inability to obtain structures of the full-length ER has limited our structural characterization of SERM action to their antiestrogenic effects on the isolated ER ligand binding domain. We studied the effects of estradiol and the clinically useful SERMs 4-hydroxytamoxifen and fulvestrant on the conformation of the full-length ERalpha dimer complex by comparing, in living human breast cancer cells, the amounts of energy transfer between fluorophores attached to different domains of ERalpha. Estradiol, 4-hydroxytamoxifen, and fulvestrant all promoted the rapid formation of ERalpha dimers with equivalent interaction kinetics. The amino- and carboxyl-terminal ERalpha domains both contain activation functions differentially affected by these ligands, but the positions of only the carboxyl termini differed upon binding with estradiol, 4-hydroxytamoxifen, or fulvestrant. The association of a specific ERalpha dimer conformation with the binding of ligands of different clinical effect will assist the identification of a SERM with optimal tissue-selective estrogenic and antiestrogenic activities. These studies also provide a roadmap for dissecting important structural and kinetic details for any protein complex from the quantitative analysis of energy transfer.
选择性雌激素受体调节剂（SERM）在某些组织中抑制雌激素对雌激素受体（ER）的激活作用，但在其他组织中却能激活ER。这些组织选择性作用表明，SERM可能具有组织特异性，从而可提高乳腺癌和激素替代疗法的安全性。了解每种SERM对ER结构和相互作用的影响，将有助于鉴定出改良的SERM。迄今为止，由于无法获得全长ER的结构，我们对SERM作用的结构表征仅限于它们对分离的ER配体结合域的抗雌激素作用。我们通过比较在活的人乳腺癌细胞中，连接到ERα不同结构域的荧光团之间的能量转移量，研究了雌二醇以及临床上常用的SERM 4-羟基他莫昔芬和氟维司群对全长ERα二聚体复合物构象的影响。雌二醇、4-羟基他莫昔芬和氟维司群均能促进ERα二聚体的快速形成，且具有相同的相互作用动力学。ERα的氨基末端和羧基末端结构域均含有受这些配体不同影响的激活功能，但只有羧基末端在与雌二醇、4-羟基他莫昔芬或氟维司群结合时位置不同。特定的ERα二聚体构象与具有不同临床效应的配体结合之间的关联，将有助于鉴定出具有最佳组织选择性雌激素和抗雌激素活性的SERM。这些研究还为通过能量转移的定量分析来剖析任何蛋白质复合物的重要结构和动力学细节提供了路线图。
