Vegeto E, Allan G F, Schrader W T, Tsai M J, McDonnell D P, O'Malley B W
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
Cell. 1992 May 15;69(4):703-13. doi: 10.1016/0092-8674(92)90234-4.
The human progesterone receptor form B (hPR-B) was expressed in Saccharomyces cerevisiae together with a specific reporter plasmid. To understand the mechanism underlying antagonist ligand activity, libraries of hormone binding domain (HBD)-mutated hPR-B molecules were prepared. A mutant receptor was identified that had lost the ability to bind either progesterone or R5020; it could still bind RU486 and, surprisingly, fully activated transcription in the presence of this "antagonist" and other antiprogestins. When this receptor mutant was assayed in mammalian cells, RU486 again demonstrated agonistic activity. Sequence analysis indicated that the mutant phenotype was due to truncation of the carboxy (C)-terminal 42 aa. We conclude that amino acids in the extreme C-terminal region are required for the receptor to bind progesterone, while antagonists bind to a site located more N-terminal of the HBD. Our results suggest that the extreme C-terminal region of the receptor contains an inhibitory function that silences receptor transactivation in the absence of agonist and in the presence of antagonist.
人孕激素受体B型（hPR - B）与一种特定的报告质粒一起在酿酒酵母中表达。为了解拮抗剂配体活性的潜在机制，制备了激素结合域（HBD）突变的hPR - B分子文库。鉴定出一种突变受体，它失去了结合孕酮或R5020的能力；它仍能结合RU486，令人惊讶的是，在这种“拮抗剂”和其他抗孕激素存在的情况下能完全激活转录。当在哺乳动物细胞中检测这种受体突变体时，RU486再次表现出激动活性。序列分析表明，突变表型是由于羧基（C）末端42个氨基酸的截短所致。我们得出结论，受体极端C末端区域的氨基酸是受体结合孕酮所必需的，而拮抗剂结合到HBD更靠近N末端的位点。我们的结果表明，受体的极端C末端区域具有一种抑制功能，在没有激动剂和存在拮抗剂的情况下使受体反式激活沉默。
