McKay Melissa M, Ritt Daniel A, Morrison Deborah K
Laboratory of Cell and Developmental Signaling, Center for Cancer Research, National Cancer Institute-Frederick, P. O. Box B, Frederick, MD 21702, USA.
Proc Natl Acad Sci U S A. 2009 Jul 7;106(27):11022-7. doi: 10.1073/pnas.0901590106. Epub 2009 Jun 18.
Scaffold proteins contribute to the spatiotemporal control of MAPK signaling and KSR1 is an ERK cascade scaffold that localizes to the plasma membrane in response to growth factor treatment. To better understand the molecular mechanisms of KSR1 function, we examined the interaction of KSR1 with each of the ERK cascade components, Raf, MEK, and ERK. Here, we identify a hydrophobic motif within the proline-rich sequence (PRS) of MEK1 and MEK2 that is required for constitutive binding to KSR1 and find that MEK binding and residues in the KSR1 CA1 region enable KSR1 to form a ternary complex with B-Raf and MEK following growth factor treatment that enhances MEK activation. We also find that docking of active ERK to the KSR1 scaffold allows ERK to phosphorylate KSR1 and B-Raf on feedback S/TP sites. Strikingly, feedback phosphorylation of KSR1 and B-Raf promote their dissociation and result in the release of KSR1 from the plasma membrane. Together, these findings provide unique insight into the signaling dynamics of the KSR1 scaffold and reveal that through regulated interactions with Raf and ERK, KSR1 acts to both potentiate and attenuate ERK cascade activation, thus regulating the intensity and duration of ERK cascade signaling emanating from the plasma membrane during growth factor signaling.
支架蛋白有助于丝裂原活化蛋白激酶(MAPK)信号传导的时空控制,而KSR1是一种ERK级联支架,在生长因子处理后定位于质膜。为了更好地理解KSR1功能的分子机制,我们研究了KSR1与ERK级联反应的各个组分Raf、MEK和ERK之间的相互作用。在此,我们在MEK1和MEK2的富含脯氨酸序列(PRS)中鉴定出一个疏水基序,该基序是与KSR1组成性结合所必需的,并发现MEK结合以及KSR1 CA1区域中的残基使KSR1在生长因子处理后能够与B-Raf和MEK形成三元复合物,从而增强MEK的激活。我们还发现,活性ERK与KSR1支架的对接使ERK能够在反馈性S/TP位点上磷酸化KSR1和B-Raf。引人注目的是,KSR1和B-Raf的反馈性磷酸化促进了它们的解离,并导致KSR1从质膜释放。总之,这些发现为KSR1支架的信号动力学提供了独特的见解,并揭示了通过与Raf和ERK的调节性相互作用,KSR1既增强又减弱ERK级联激活,从而在生长因子信号传导过程中调节源自质膜的ERK级联信号的强度和持续时间。