Department of Biochemistry and Molecular Biology, College of Medicine, University of South Alabama, 5851 USA Drive North, Room 2366, Mobile, AL 36688, USA.
Department of Pathology, O'Neal Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Cardiovasc Res. 2022 Mar 16;118(4):1150-1163. doi: 10.1093/cvr/cvab132.
Vascular smooth muscle cells (VSMCs) normally exhibit a very low proliferative rate. Vessel injury triggers VSMC proliferation, in part, through focal adhesion kinase (FAK) activation, which increases transcription of cyclin D1, a key activator for cell cycle-dependent kinases (CDKs). At the same time, we also observe that FAK regulates the expression of the CDK inhibitors (CDKIs) p27 and p21. However, the mechanism of how FAK controls CDKIs in cell cycle progression is not fully understood.
We found that pharmacological and genetic FAK inhibition increased p27 and p21 by reducing stability of S-phase kinase-associated protein 2 (Skp2), which targets theCDKIs for degradation. FAK N-terminal domain interacts with Skp2 and an APC/C E3 ligase activator fizzy-related 1 (Fzr1) in the nucleus, which promote ubiquitination and degradation of both Skp2 and Fzr1. Notably, overexpression of cyclin D1 alone failed to promote proliferation of genetic FAK kinase-dead (KD) VSMCs, suggesting that the FAK-Skp2-CDKI signalling axis is distinct from the FAK-cyclin D1 pathway. However, overexpression of both cyclin D1 and Skp2 enabled proliferation of FAK-KD VSMCs, implicating that FAK ought to control both activating and inhibitory switches for CDKs. In vivo, wire injury activated FAK in the cytosol, which increased Skp2 and decreased p27 and p21 levels.
Both pharmacological FAK and genetic FAK inhibition reduced Skp2 expression in VSMCs upon injury, which significantly reduced intimal hyperplasia through elevated expression of p27 and p21. This study revealed that nuclear FAK-Skp2-CDKI signalling negatively regulates CDK activity in VSMC proliferation.
血管平滑肌细胞（VSMCs）通常表现出非常低的增殖率。血管损伤通过局灶黏附激酶（FAK）的激活触发 VSMC 增殖，这增加了细胞周期依赖性激酶（CDKs）的关键激活剂细胞周期蛋白 D1（cyclin D1）的转录。同时，我们还观察到 FAK 调节 CDK 抑制剂（CDKIs）p27 和 p21 的表达。然而，FAK 如何控制细胞周期进程中的 CDKIs 的机制尚不完全清楚。
我们发现，通过降低 S 期激酶相关蛋白 2（Skp2）的稳定性，药理学和遗传 FAK 抑制增加了 p27 和 p21，Skp2 靶向 CDKIs 进行降解。FAK N 端结构域在核内与 Skp2 和 APC/C E3 连接酶激活因子 fizzy-related 1（Fzr1）相互作用，促进 Skp2 和 Fzr1 的泛素化和降解。值得注意的是，cyclin D1 的过表达本身并不能促进遗传 FAK 激酶失活（KD）VSMCs 的增殖，这表明 FAK-Skp2-CDKI 信号轴与 FAK-cyclin D1 途径不同。然而，cyclin D1 和 Skp2 的过表达使 FAK-KD VSMCs 增殖，这表明 FAK 应该控制 CDK 的激活和抑制开关。在体内，导线损伤使细胞质中的 FAK 激活，增加了 Skp2 并降低了 p27 和 p21 的水平。
FAK 的药理学和遗传学抑制在损伤后降低了 VSMCs 中的 Skp2 表达，这通过提高 p27 和 p21 的表达显著减少了内膜增生。这项研究揭示了核 FAK-Skp2-CDKI 信号负调节 VSMC 增殖中的 CDK 活性。
