Interactions Between p90 Ribosomal S6 Kinase and Protein Kinase A

描述(申请人提供)：P90核糖体S6激酶(RSK)是丝裂原激活蛋白激酶的直接下游效应因子，在调节细胞增殖和存活方面发挥重要作用。在四种异构体中，RSK4与其他异构体最为不同，在功能上也不同。RSK1和RSK2的上调也使细胞易于转化和肿瘤形成。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，即无活性的RSK1与cAMP依赖的蛋白激酶(PKA)的调节亚单位(RL)相互作用，而磷酸化的、有活性的RSK1与PKA的催化亚单位(PKAc)相互作用。非活性RSK1与RL的结合减少了PKAc与RL之间的相互作用。相反，磷酸化的RSK1与PKAc的结合增加了PKAc与RL之间的相互作用，降低了cAMP激活PKA全酶的能力。此外，我们还发现，非活性RSK1和活性RSK1与PKA亚单位的相互作用允许RSK1与PKA锚定蛋白(AKAP)形成复合体，而PKA与AKAP相互作用的中断显著改变了活性RSK1在细胞中的分布。因此，当PKA与AKAPs相互作用完整时，活性RSK1主要定位于细胞的细胞核。另一方面，当PKA/AKAP相互作用被取消时，胞核中活性RSK1的数量减少，胞浆中的活性RSK1数量增加，从而导致胞浆RSK1底物结节性硬化症复合体2(TSC2)和BAD的磷酸化增加。RSK1增加BAD的磷酸化与增强对细胞凋亡的保护有关。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的活性以及调节RSK1的亚细胞定位和生物学作用方面具有功能意义。为了解决这一假说，并确定调节RSK1和PKA亚单位之间相互作用的机制，我们将追求以下特定目标。目的1：确定RSK1上与PKA亚基相互作用的区域。目的：阐明RSK1调控PKA的机制，确定RSK1/PKA亚单位相互作用的调控机制。目的：研究RSK1/PKA亚基相互作用在RSK1的细胞分布、激活及其生物学功能调控中的作用。这些目的将确定调控PKA活性的新机制，并阐明RSK1与PKA亚单位或AKAP之间的相互作用在调控RSK1生物学行为中的作用。然后，这些新的见解可能会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.