YY1 FUNCTIONS IN VASCULAR SMOOTH MUSCLE CELLS

该项目的长期目标是阐明急性动脉损伤导致血管平滑肌细胞异常增殖和迁移并导致再狭窄的分子机制。再狭窄损伤中的细胞与癌细胞在形态上的惊人相似之处表明，许多相同的机制可能是导致两种类型细胞异常生长的原因。我们最近获得的证据表明，转录因子阴阳1(YY1)在G0/G1期停滞的冠状动脉平滑肌细胞(CASMC)中过表达可激活DNA合成。然而，在同时过度表达YY1和RB的细胞中，DNA合成水平下降到正常水平。我们还发现，在生长受阻的CASMC中，很大一部分YY1与Rb形成复合体，而不是在S期培养中，重组Rb与YY1物理上直接相互作用，破坏了YY1‘S与DNA的相互作用。此外，我们在体外发现Rb抑制YY1依赖的转录。初步数据表明，YY1是CASMC中Rb通路的一个重要下游靶点，Rb和YY1的相互作用在体内可能是细胞周期特异性的。这表明，作为Rb复合体的一部分，YY1可能参与了在转录水平上调节从收缩表型到增殖表型的转换的检查点功能。我们推测，炎症细胞因子和生长因子诱导的YY1的过度表达和/或Rb和YY1相互作用的中断可能改变基因表达，甚至可能导致动脉损伤后CASMC的异常生长。这项建议的具体目标是：1.从细胞启动子的角度研究Rb-YY1相互作用以及YY1-Rb相互作用对YY1‘S转录因子功能的影响。2.0研究YY1在人CASMC中表达失控的功能后果。目前，对VSM细胞异常生长和迁移的理解和潜在策略是直接从其他细胞系统获得的知识，特别是从细胞周期检查点被取消和正常细胞周期进程丢失的癌细胞中获得的知识。几乎没有任何实验证据可以用来阐明VSM细胞本身逃脱G0期停滞并开始活跃增殖的机制。因此，在考虑预防再狭窄的具体策略之前，明确VSM细胞增殖的分子机制是至关重要的。

The long term goals of this project are to elucidate the molecular mechanisms underlying the abnormal liferation and migration of vascular smooth muscle (VSM) cells that is induced by acute arterial injury and leads to restenosis. The striking morphological similarities between cells in restenosis injury and cancer cells suggest that many of the same mechanisms may be responsible for abnormal growth of both types of cells. We have recently obtained evidence that overexpression of the transcription factor Yin Yang 1(YY1) in G0/G1-arrested coronary artery smooth muscle cells (CASMC) activates DNA synthesis. In cells that overexpress both YY1 and Rb, however, level of DNA synthesis falls back to normal levels. We also found that in growth arrested CASMC a significant portion of YY1 is in a complex with Rb but not in S-phase cultures and that recombinant Rb physically, directly interacts with YY1, destabilizing YY1's interaction with DNA. Moreover we found that Rb inhibits YY1 dependent transcription in vitro. The preliminary data suggest that YY1 is an important downstream target of the Rb pathway in CASMC and that the interaction of Rb and YY1 is likely to be cell cycle specific in vivo. It suggests that, as part of a complex with Rb, YY1 may participate in checkpoint functions that regulate the transition from a contractile to a "proliferative" phenotype at the level of transcription. We hypothesize that overexpression of YY1 induced by inflammatory cytokines and growth factors and/or disruption of the interaction between Rb and YY1 may alter gene expression and perhaps even cause abnormal CASMC growth after arterial injury. The Specific Aims of this proposal are: 1.0. To characterize the Rb-YY1 interaction and the effect of the YY1-Rb interaction on YY1's transcription factor function in the context of cellular promoters. 2.0 to study the functional consequences of the deregulated expression of YY1 in human CASMC. At present, understanding of and potential strategies to prevent the abnormal growth and migration of VSM cells are directly extrapolated from knowledge obtained from other cell systems, particularly from cancer cells in which cell cycle checkpoints are abrogated and normal cell cycle progression is lost. Little if any experimental evidence is available elucidating the mechanisms by which VSM cells themselves escape from G0 arrest and begin active proliferation. Therefore, it is essential to define the molecular mechanisms of VSM cell proliferation before one can consider specific strategies to prevent restenosis.