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

描述（由申请人提供）：SGK1是一种诱导型丝氨酸/苏氨酸激酶，参与上皮细胞的膜转运过程。研究表明，SGK1是转录诱导的，并受到刺激依赖性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、存活和细胞内离子和运输过程的变化有关。磷酸化还控制SGK1的核/细胞质穿梭，因此丝氨酸/苏氨酸残基上的过度磷酸化导致核从细胞质转运。尽管SGK1在上皮细胞生物学中的作用已经取得了很多进展，但它在血管平滑肌细胞功能中的作用，特别是在病变形成的发展中是完全未知的。因此，本应用旨在确定SGK1在调节血管平滑肌细胞命运中的作用，特别是它与生长有关。在初步研究中，我们发现强效的丝裂原PDGF显著且短暂地增加血管平滑肌细胞中SGK1 mRNA的表达，这暗示了该激酶在血管平滑肌细胞生长中的作用。我们还发现PDGF刺激与SGK1磷酸化增加相关，这表明PDGF可能介导SGK1激酶活性的激活。有趣的是，受损颈动脉的免疫组织学染色显示，SGK1在新内膜血管病变中表达上调。

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.