Involvement of Serum and Glucocorticoid Inducible Kinase 1 (SGK1) in VSMC Profile

描述(申请人提供)：SGK1是一种可诱导的丝氨酸/苏氨酸激酶，参与上皮细胞的膜转运过程。研究表明，SGK1在转录水平上被诱导，并受到刺激依赖的翻译后磷酸化的影响。SGK1的过度磷酸化导致其激酶活性的激活，并与细胞增殖、存活以及细胞内离子和运输过程的变化有关。磷酸化也控制着SGK1的核/胞质穿梭，从而丝氨酸/苏氨酸残基上的过度磷酸化导致胞浆中的核转移。尽管SGK1在上皮细胞生物学中的作用已经取得了很大的进展，但它在血管平滑肌细胞功能中的作用，特别是在病变形成过程中的作用，仍然是完全未知的。因此，该应用试图确定SGK1在调节血管平滑肌细胞命运中的作用，特别是它与生长相关的作用。在初步研究中，我们发现强有力的有丝分裂原PDGF显著且短暂地增加血管平滑肌细胞SGK1mRNA的表达，暗示该激酶在血管平滑肌细胞生长中发挥作用。我们还发现，PDGF的刺激与SGK1的磷酸化增加有关，提示PDGF可能介导了SGK1激酶活性的激活。有趣的是，损伤颈动脉的免疫组织化学染色显示SGK1在新生内膜血管病变中表达上调。 根据这些发现，我们假设SGK1是血管平滑肌细胞增殖的重要介质，其表达和/或活性的改变导致随后血管内膜病变的形成。我们将从以下几个方面对这一假说进行验证：(1)研究促有丝分裂刺激对体外培养的VSMC SGK1表达、活性和室区化的影响；(2)研究结构性SGK1基因敲除和过度表达对体外培养的VSMC生长的调节作用；(3)探讨机械血管损伤对大鼠颈动脉球囊损伤模型SGK1表达和活性的影响。总之，这一系列实验将为深入了解SGK1在血管平滑肌细胞增殖中的作用提供依据，并为进一步研究SGK1在病理性血管重塑中的作用提供基础。最终，这些研究确定SGK1是治疗动脉粥样硬化、再狭窄或高血压引起的闭塞性血管疾病的新靶点。

DESCRIPTION (provided by applicant): SGK1 is an inducible serine/threonine kinase that has been implicated in membrane transport processes in epithelial cell. Studies have shown that SGK1 is transcriptionally induced and subject to stimulus-dependent post-translational phosphorylation. Hyperphosphorylation of SGK1 leads to activation of its kinase activity and has been linked to changes in cellular proliferation, survival and intracellular ion and transport processes. Phosphorylation also controls nuclear/cytoplasmic shuttling of SGK1 such that hyperphosphorylation on serine/threonine residues leads to nuclear translocation from the cytosol. Although much progress has been made regarding the role of SGK1 in epithelial cell biology, its role in vascular smooth muscle cell function and in the development of lesion formation in particular is completely unknown. Therefore, this application seeks to define the role of SGK1 in regulation of vascular smooth muscle cell fate, specifically as it relates to growth. In preliminary studies we found that the potent mitogen, PDGF, dramatically and transiently increases SGK1 mRNA expression in vascular smooth muscle cells implicating a role for this kinase in vascular smooth muscle cell growth. We also found that PDGF stimulation is associated with increased phosphorylation of SGK1, suggesting that PDGF may mediate activation of SGK1 kinase activity. Interestingly, immunohistological staining of injured carotid artery revealed that SGK1 is up-regulated in neointimal vascular lesions. In light of these findings, we hypothesize that SGK1 is an important mediator of vascular smooth muscle cell proliferation and that alterations in its expression and/or activity leads to the subsequent development of vascular neointimal lesion formation. We will test this hypothesis in the following aims: (1) to investigate the effects of mitogenic stimuli on SGK1 expression, activity and compartmentalization in VSMC in vitro; (2) to investigate the effect of constitutive SGK1 knockdown and over-expression on regulation of VSMC growth in vitro; (3) to investigate the effect of mechanical vascular injury on SGK1 expression and activity in a rat carotid artery balloon-injury model in vivo. Overall, this series of experiments will provide insight into the role of SGK1 in vascular smooth muscle cell proliferation and provide the basis for future studies to define the role of SGK1 in pathological vascular remodeling. Ultimately, these studies identify SGK1 as a novel therapeutic target for occlusive vascular diseases that occur as a consequence of atherosclerosis, restenosis or hypertension.