The putative cofactor TIF1α is a protein kinase that is hyperphosphorylated upon interaction with liganded nuclear receptors
The putative cofactor TIF1α is a protein kinase that is hyperphosphorylated upon interaction with liganded nuclear receptors
复制标题
DOI：
10.1074/jbc.273.26.16199
复制
发表时间：
1998-06-26
影响因子：
4.8
通讯作者：
Chambon, P
中科院分区：
文献类型：
--
作者：
Fraser, RA;Heard, DJ;Chambon, P
配体诱导的核受体（NR）基因激活是一个复杂的过程，需要解离的辅阻遏物和募集的辅激活。假定的转录中介因子TIF 1 α先前已被表征为与AF-2配体依赖性激活结构域直接相互作用的核蛋白，所述AF-2配体依赖性激活结构域存在于许多类固醇和非类固醇受体的配体结合结构域中，包括雌激素（ER α）和类维生素A X（RXR α）受体。我们在这里报告，TIF 1 α是一个磷蛋白和蛋白激酶。在COS-1细胞中与RXRa或ER α共表达的TIF 1 α！被磷酸化并在配体处理后变得过度磷酸化。这种过度磷酸化需要TIF 1 α与转录活性NR结合，因为它被RXR α和ER α的AF-2激活结构域的核心（配体结合结构域的α-螺旋12）或TIF 1 α的NR盒中的突变所阻止，已知这些突变会阻止TIF 1 α-NR相互作用。因此，TIF 1 α是一种磷蛋白，其由于核受体结合而经历配体依赖性过度磷酸化。我们进一步表明，纯化的重组TIF 1 α具有内在的激酶活性，并且除了自磷酸化，TIF 1 α在体外选择性磷酸化转录因子TFIIE α、TAF（II）28和TAF（II）55。这些后者的结果提出的可能性，TIF 1 α可能会采取行动，至少部分，通过磷酸化和修改的转录机制的组件的活动。
Ligand-induced gene activation by nuclear receptors (NRs) is a complex process requiring dissociation of corepressors and recruitment of coactivators. The putative transcriptional intermediary factor TIF1 alpha has been previously characterized as a nuclear protein that interacts directly with the AF-2 ligand-dependent activating domain present in the ligand-binding domain of numerous steroid and nonsteroid receptors, including the estrogen (ER alpha) and retinoid X (RXR alpha) receptors. We report here that TIF1 alpha is both a phosphoprotein and a protein kinase. TIF1 alpha coexpressed in COS-l cells with RXRa or ERa! is phosphorylated and becomes hyperphosphorylated upon ligand treatment. This hyperphosphorylation requires the binding of TIF1 alpha to transcriptionally active NRs since it is prevented by mutations either in the core (alpha-helix 12 of the ligand-binding domain) of the AF-2 activating domains of RXR alpha and ER alpha or in the NR box of TIF1 alpha that are known to prevent TIF1 alpha-NR interactions. Thus, TIF1 alpha is a phosphoprotein that undergoes ligand-dependent hyperphosphorylation as a consequence of nuclear receptor binding. We further show that purified recombinant TIF1 alpha possesses intrinsic kinase activity and that, in addition to autophosphorylation, TIF1 alpha selectively phosphorylates the transcription factors TFIIE alpha, TAF(II)28, and TAF(II)55 in vitro. These latter results raise the possibility that TIF1 alpha may act, at least in part, by phosphorylating and modifying the activity of components of the transcriptional machinery.