Bai W, Tullos S, Weigel N L
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
Mol Endocrinol. 1994 Nov;8(11):1465-73. doi: 10.1210/mend.8.11.7877616.
Phosphorylation regulates the activities of many proteins, including transcription factors. However, the evidence for the significance of phosphorylation in steroid hormone receptor action is mainly indirect. In this study, one of the hormone-induced phosphorylation sites of chicken progesterone receptor, Ser530, was mutated to alanine, a nonphosphorylatable amino acid, and the transcriptional activity of the mutant receptor was compared with that of wild type in a transient cotransfection assay. The results showed that this mutation resulted in reduced transcriptional activity of chicken progesterone receptor at low hormone concentrations but did not affect the maximal activity of the receptor at saturating levels of hormone, suggesting that the phosphorylation at Ser530 influences the response of the receptor to its ligand. The decreased sensitivity of the mutant receptor is not due to a decrease in hormone-binding affinity, leading to our hypothesis that Ser530 phosphorylation stabilizes the receptor in its active state, perhaps by preventing its reassociation with heat shock proteins or by maintaining a conformation suitable for interaction with other transcription factors.
磷酸化作用可调节包括转录因子在内的多种蛋白质的活性。然而，磷酸化在类固醇激素受体作用中的重要性证据主要是间接的。在本研究中，鸡孕酮受体的激素诱导磷酸化位点之一Ser530被突变为丙氨酸（一种不可磷酸化的氨基酸），并在瞬时共转染实验中将突变受体的转录活性与野生型受体的转录活性进行比较。结果表明，这种突变导致鸡孕酮受体在低激素浓度下的转录活性降低，但在激素饱和水平时不影响受体的最大活性，这表明Ser530处的磷酸化影响受体对其配体的反应。突变受体敏感性降低并非由于激素结合亲和力下降，由此我们提出假说：Ser530磷酸化可能通过阻止其与热休克蛋白重新结合或维持适合与其他转录因子相互作用的构象，从而使受体稳定于其活性状态。
