Interactions Between p90 Ribosomal S6 Kinase and Protein Kinase A

描述（由申请人提供）：p90核糖体S6激酶（rsk）是有丝分裂原活化蛋白激酶的直接下游效应物，在细胞增殖和存活的调节中起主要作用。在这四种亚型中，RSK4与其他亚型差异最大，在功能上也存在差异。RSK1和RSK2的上调也使细胞更易转化和肿瘤形成。此外，在心脏中，RSK1参与调节肥大等病理生理过程。这一应用是基于我们最近的发现，失活的RSK1与cAMP依赖性蛋白激酶（PKA）的调控亚基（Rl）相互作用，而磷酸化的活性RSK1与PKA的催化亚基（PKAc）相互作用。无活性RSK1与Rl的关联降低了PKAc与Rl之间的相互作用。相反，磷酸- RSK1与PKAc的结合增加了PKAc和Rl之间的相互作用，降低了cAMP激活PKA全酶的能力。此外，我们已经证明，无活性RSK1和活性RSK1与PKA亚基的相互作用允许RSK1存在于与PKA锚定蛋白（AKAPs）的复合体中，PKA与AKAPs相互作用的破坏显着改变了活性RSK1在细胞中的分布。因此，当PKA与AKAPs的相互作用完整时，活性RSK1主要定位于细胞核中。另一方面，当PKA/AKAP相互作用被消除时，细胞核中活性RSK1的数量减少，细胞质中活性RSK1的数量增加，从而导致细胞质中RSK1底物结节性硬化症复合体2 （TSC2）和BAD的磷酸化增加。RSK1对BAD磷酸化的增加与细胞凋亡保护的增加有关。鉴于这些发现，我们的中心假设是RSK1与PKA和AKAPs的相互作用在调节PKA活性以及调节RSK1的亚细胞定位及其生物学作用方面具有功能意义。为了解决这一假设，并确定调节RSK1和PKA亚基之间相互作用的机制，我们将追求以下具体目标。目的1：确定RSK1和PKA亚基上相互作用的区域。目的2：阐明RSK1调控PKA的机制，确定RSK1/PKA亚基相互作用的调控机制。目的3：确定RSK1/PKA亚基相互作用在RSK1的细胞分布、RSK1的激活及其生物学功能调控中的作用。这些目标将确定调节PKA活性的新机制，并阐明RSK1与PKA亚基或akap之间的相互作用在调节RSK1的生物作用中的作用。这些新颖的见解可能允许开发特定的干预措施来调节这两种激酶的某些功能。

DESCRIPTION (provided by applicant): The p90 Ribosomal S6 kinases (RSKs) are immediately downstream effectors of mitogen activated protein kinases and play a major role in regulation of cell proliferation and survival. Among the four isoforms, RSK4 is the most dissimilar and also functionally different from the other isoforms. The upregulation of RSK1 and RSK2 also predisposes cells to transformation and tumor formation. Moreover, in the heart, RSK1 is involved regulating pathophysiological processes such as hypertrophy. This application is based on our recent findings that inactive RSK1 interacts with the regulatory subunit (Rl) of cAMP dependent protein kinase (PKA) while the phosphorylated, active RSK1 interacts with the catalytic subunit of PKA (PKAc). The association of inactive RSK1 with Rl decreases interactions between PKAc and Rl. In contrast, the association of phospho- RSK1 with PKAc increases interactions between PKAc and Rl and decreases the ability of cAMP to active the PKA holoenzyme. Additionally, we have shown that the interactions of inactive RSK1 and active RSK1 with subunits of PKA permits the RSK1 to exist in a complex with PKA anchoring proteins (AKAPs) and the disruption of PKA interactions with AKAPs dramatically alters the distribution of active RSK1 in cells. Thus, when interactions of PKA with AKAPs are intact, the active RSK1 is localized primarily in the nucleus of cells. On the other hand, when the PKA/AKAP interactions are abolished, the amount of active RSK1 in the nucleus is decreased and its amount in the cytoplasm is increased with a resultant increase in phosphorylation of the cytosolic RSK1 substrates tuberous sclerosis complex 2 (TSC2) and BAD. Increased phosphorylation of BAD by RSK1 is associated with an increase in protection from cellular apoptosis. Given these findings, our central hypothesis is that the interactions of RSK1 with PKA and AKAPs are of functional significance in regulating the activity of PKA as well as modulating the subcellular localization of RSK1 and its biological actions. To address this hypothesis and to identify the mechanisms that regulate interactions between RSK1 and PKA subunits, we will pursue the following specific aims. Aim 1: To identify the regions on RSK1 and the subunits of PKA that interact with each other. Aim 2: To elucidate the mechanisms involved in regulation of PKA by RSK1 and to determine the regulation of RSK1/PKA subunit interactions. Aim 3: To determine the role of RSK1/PKA subunit interactions in the cellular distribution of RSK1, the activation of RSK1, and regulation of its biological functions. These aims will identify novel mechanisms by which PKA activity is regulated and also elucidate of the role of the interactions between RSK1 with PKA subunits or AKAPs in regulating the biological actions of RSK1. These novel insights may then permit the development of specific interventions that regulate certain functions of both these kinases.