Xu Wu, Kasper Lawryn H, Lerach Stephanie, Jeevan Trushar, Brindle Paul K
Department of Biochemistry, St Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38105, USA.
EMBO J. 2007 Jun 20;26(12):2890-903. doi: 10.1038/sj.emboj.7601734. Epub 2007 May 24.
CREB is a key mediator of cAMP- and calcium-inducible transcription, where phosphorylation of serine 133 in its Kinase-Inducible Domain (KID) is often equated with transactivation. Phospho-Ser133 is required for CREB to bind the KIX domain of the coactivators CBP and p300 (CBP/p300) in vitro, although the importance of this archetype coactivator interaction for endogenous gene expression is unclear. Here, we show that the CREB interaction with KIX is necessary for only a part of cAMP-inducible transcription and CBP/p300 recruitment. Surprisingly, individual cAMP-inducible genes with CREB bound at their promoters differed in their reliance on KIX and none examined showed complete dependence. Alternatively, we found that arginine 314 (Arg314) in the CREB basic-leucine zipper (bZIP) domain contributed to CBP/p300 recruitment and KIX-independent CREB transactivation function. This implicates Transducer Of Regulated CREB (TORC), an unrelated cAMP-responsive coactivator that binds via Arg314, and which can bind CBP/p300, in these functions. Interestingly, KIX was also required for the full cAMP induction of a gene that did not require CREB. Thus, individual CREB-target gene context dictates the relative contribution of at least two different cAMP-responsive coactivation mechanisms.
CREB是cAMP和钙诱导转录的关键调节因子，其激酶诱导结构域（KID）中丝氨酸133的磷酸化通常等同于反式激活。在体外，磷酸化的丝氨酸133是CREB结合共激活因子CBP和p300（CBP/p300）的KIX结构域所必需的，尽管这种典型的共激活因子相互作用对内源基因表达的重要性尚不清楚。在此，我们表明，CREB与KIX的相互作用仅对部分cAMP诱导转录和CBP/p300募集是必需的。令人惊讶的是，启动子上结合有CREB的各个cAMP诱导基因对KIX的依赖程度不同，且所检测的基因均未表现出完全依赖。另外，我们发现CREB碱性亮氨酸拉链（bZIP）结构域中的精氨酸314（Arg314）有助于CBP/p300募集和不依赖KIX的CREB反式激活功能。这表明在这些功能中，受调控的CREB转导子（TORC）参与其中，TORC是一种不相关的cAMP反应性共激活因子，通过Arg314结合，且能结合CBP/p300。有趣的是，对于一个不需要CREB的基因，其cAMP的完全诱导也需要KIX。因此，单个CREB靶基因的背景决定了至少两种不同的cAMP反应性共激活机制的相对贡献。
