Mechanisms for glucocorticoid vs. progesterone receptor-specific gene regulation

比较GR与PR调节的基因转录的机制细节的任务随着我们开发类固醇受体作用的理论模型而获得了额外的标准（Ong等人，2010，Proc Natl Acad Sci U S A，107，7107-7112）。 该模型的三个新特征及其相关的图形分析，允许类固醇受体调节的基因反式激活的机制信息的前所未有的水平。 首先，现在可以确定因子所显示的动力学定义的作用类型（竞争性抑制剂、非竞争性抑制剂、共激活剂等）。 其次，通常可以定义因子相对于称为浓度限制步骤（CLS）的参考点的作用位置，浓度限制步骤是酶动力学速率限制步骤的稳态模拟。 第三，该模型及其图形分析最近已扩展到同一测定中两个竞争因子的分析（Doughnesset al.，2012，PLoS ONE，7，e30225）。 与使情况更加模糊相反，这种竞争测定实际上产生了更多的机理信息。 这种竞争测定不仅可以确定每个因子相对于CLS如何和在何处起作用，而且通常还可以揭示两个因子相对于彼此的作用位点。 因此，人们现在可以根据辅因子的生物学功能组装有序的反应序列，就像上位性分析一样，即使辅因子的生物化学性质是未知的。 用几种辅因子进行的初步实验没有发现GR和PR作用之间的任何重大差异。 我们与大卫莱文斯博士（NCI，NIH）合作的最新研究发现了一种以细胞特异性方式差异影响GR的辅因子。 与检查的其他因素一样，GR和PR之间没有显著差异。 然而，杂交转录因子GAL/VP 16也对GR有类似的反应，因此我们似乎还没有发现区分不同转录因子的因子。 尽管如此，这些研究大大有助于我们的长期目标，即在分子水平上定义GR与PR的作用，并了解它们在人体生理学中的作用。

The task of comparing the mechanistic details of GR- vs. PR-regulated gene transcription gained additional criteria with our development of a theoretical model of steroid receptor action (Ong et al., 2010, Proc Natl Acad Sci U S A, 107, 7107-7112). Three novel features of this model, and its associated graphical analysis, permit an unprecedented level of mechanistic information regarding steroid receptor-regulated gene transactivation. First, it is now possible to determine the kinetically-defined type of action being displayed by the factor (competitive inhibitor, uncompetitive inhibitor, coactivator, etc.). Second, it is usually possible to define where the factor acts relative to a reference point called the concentration limiting step (CLS), which is the steady state analog of the rate limiting step of enzyme kinetics. Third, the model and its graphical analysis have recently been extended to the analysis of two competing factors in the same assay (Dougherty et al., 2012, PLoS ONE, 7, e30225). As opposed to making the situation more obscure, this competition assay actually yields greater mechanistic information. Not only can such competition assays determine how and where each factor acts, relative to the CLS, but the site of action of the two factors relative to each other is usually revealed. Thus, one can now assemble an ordered sequence of reactions based on the biological function of cofactors, much as in epistasis analysis, even when the biochemical properties of the cofactors are not known. Initial experiments with a several cofactors have not exposed any major differences between GR and PR action. Recent studies in our collaboration with Dr. David Levens (NCI, NIH) have uncovered one cofactor that differentially affects GR in a cell-specific manner. As with the other factors examined, no significant differences between GR and PR are seen with this new factor. However, the hybrid transcription factor GAL/VP16 also responds similarly to GR so we do not appear to have yet found a factor that discriminates between different transcription factors. Nonetheless, these studies greatly contribute to our long-term goal of defining the action of GRs vs. PRs at a molecular level and of understanding their role in human physiology.