Brosens J J, Hayashi N, White J O
Department of Reproductive Sciences and Medicine, Imperial College of Science, Technology, and Medicine, Hammersmith Hospital, London, United Kingdom.
Endocrinology. 1999 Oct;140(10):4809-20. doi: 10.1210/endo.140.10.7070.
Human endometrial stromal (ES) cells in culture express PRL, a marker of decidualization, in response to sustained activation of protein kinase A (PKA). Cotreatment with the progestin medroxyprogesterone acetate (MPA) enhanced decidual PRL gene activation in the presence of elevated intracellular cAMP levels. This synergy became apparent, at protein and promoter level, after a lag period of 2 days and increased in a time-dependent manner thereafter. Pretreatment with cAMP advanced the time at which synergy between cAMP and MPA was apparent, suggesting that PKA activation sensitized ES cells to the effects of progestins. Analysis of the progesterone receptor (PR) indicated that PR-A was the predominant form in differentiating ES cells, but its abundance decreased markedly during the course of the decidualization response. The decline in PR levels was of functional relevance, as expression of PR-B or PR-A, by transient transfection, dramatically inhibited the activity of a decidual PRL promoter-reporter construct in response to cAMP. Furthermore, the expression of endogenous PRL protein in response to cAMP or cAMP plus MPA was substantially decreased by constitutive expression of green fluorescence protein-tagged PR, which was localized in the nucleus even in the absence of added ligand. Ligand-independent PR inhibition of the decidual PRL promoter was receptor specific, independent of known PR phosphorylation sites, and required minimally a functional DNA-binding domain. Transient expression of steroid receptor coactivator-1e (SRC-1e), but not SRC-1a, allowed synergy between cAMP and MPA without the requirement of sensitization by pretreatment with cAMP. This raised the possibility that SRC-1e was a component of cAMP-dependent sensitization of ES cells, but there was no evidence of altered messenger RNA expression of either SRC-1 isoform during decidualization. In conclusion, cellular PR levels determine the onset of the decidualization response. Initiation of this process requires elevated intracellular cAMP levels that sensitize ES cells to the actions of progestins through down-regulation of cellular PR levels and possibly via modulation of function of an intermediate factor(s) such as SRC-1e.
培养的人子宫内膜基质（ES）细胞在蛋白激酶A（PKA）持续激活时会表达催乳素（PRL），这是蜕膜化的一个标志物。在细胞内cAMP水平升高的情况下，与孕激素醋酸甲羟孕酮（MPA）共同处理可增强蜕膜PRL基因的激活。这种协同作用在蛋白和启动子水平上，经过2天的延迟期后变得明显，此后以时间依赖的方式增加。用cAMP预处理提前了cAMP与MPA之间协同作用明显的时间，这表明PKA激活使ES细胞对孕激素的作用敏感。对孕激素受体（PR）的分析表明，PR-A是分化中的ES细胞中的主要形式，但其丰度在蜕膜化反应过程中显著下降。PR水平的下降具有功能相关性，因为通过瞬时转染表达PR-B或PR-A会显著抑制蜕膜PRL启动子-报告基因构建体对cAMP的反应活性。此外，绿色荧光蛋白标记的PR的组成性表达会使内源性PRL蛋白对cAMP或cAMP加MPA的反应表达大幅降低，即使在没有添加配体的情况下，该标记的PR也定位于细胞核中。PR对蜕膜PRL启动子的非配体依赖性抑制是受体特异性的，独立于已知的PR磷酸化位点，并且至少需要一个功能性的DNA结合结构域。类固醇受体辅激活因子-1e（SRC-1e）而非SRC-1a的瞬时表达使得cAMP与MPA之间产生协同作用，而无需用cAMP预处理来致敏。这增加了SRC-1e是ES细胞cAMP依赖性致敏成分的可能性，但没有证据表明在蜕膜化过程中两种SRC-1同工型的信使RNA表达发生改变。总之，细胞PR水平决定了蜕膜化反应的起始。这个过程的启动需要细胞内cAMP水平升高，通过下调细胞PR水平并可能通过调节诸如SRC-1e等中间因子的功能，使ES细胞对孕激素的作用敏感。
