Nagano Kohji, Bornhauser Beat C, Warnasuriya Gayathri, Entwistle Alan, Cramer Rainer, Lindholm Dan, Naaby-Hansen Soren
Ludwig Institute for Cancer Research, Royal Free and University College London, Medical School, UK.
EMBO J. 2006 May 3;25(9):1871-82. doi: 10.1038/sj.emboj.7601059. Epub 2006 Apr 13.
PDGF is a potent chemotactic mitogen and a strong inductor of fibroblast motility. In Swiss 3T3 fibroblasts, exposure to PDGF but not EGF or IGF-1 causes a rapid loss of actin stress fibers (SFs) and focal adhesions (FAs), which is followed by the development of retractile dendritic protrusions and induction of motility. The PDGF-specific actin reorganization was blocked by inhibition of Src-kinase and the 26S proteasome. PDGF induced Src-dependent association between the multifunctional transcription/translation regulator hnRNP-K and the mRNA-encoding myosin regulatory light-chain (MRLC)-interacting protein (MIR), a E(3)-ubiquitin ligase that is MRLC specific. This in turn rapidly increased MIR expression, and led to ubiquitination and proteasome-mediated degradation of MRLC. Downregulation of MIR by RNA muting prevented the reorganization of actin structures and severely reduced the migratory and wound-healing potential of PDGF-treated cells. The results show that activation of MIR and the resulting removal of diphosphorylated MRLC are essential for PDGF to instigate and maintain control over the actin-myosin-based contractile system in Swiss 3T3 fibroblasts. The PDGF induced protein destabilization through the regulation of hnRNP-K controlled ubiquitin -ligase translation identifies a novel pathway by which external stimuli can regulate phenotypic development through rapid, organelle-specific changes in the activity and stability of cytoskeletal regulators.
血小板衍生生长因子（PDGF）是一种强效的趋化性有丝分裂原，也是成纤维细胞运动的强力诱导剂。在瑞士3T3成纤维细胞中，暴露于PDGF而非表皮生长因子（EGF）或胰岛素样生长因子-1（IGF-1）会导致肌动蛋白应力纤维（SFs）和粘着斑（FAs）迅速丧失，随后出现可收缩的树突状突起并诱导细胞运动。PDGF特异性的肌动蛋白重组被Src激酶和26S蛋白酶体的抑制所阻断。PDGF诱导多功能转录/翻译调节因子异质性核糖核蛋白K（hnRNP-K）与编码肌球蛋白调节轻链（MRLC）相互作用蛋白（MIR）的mRNA之间发生Src依赖性结合，MIR是一种MRLC特异性的E（3）泛素连接酶。这反过来又迅速增加了MIR的表达，并导致MRLC的泛素化和蛋白酶体介导的降解。通过RNA沉默下调MIR可防止肌动蛋白结构的重组，并严重降低PDGF处理细胞的迁移和伤口愈合能力。结果表明，MIR的激活以及由此导致的双磷酸化MRLC的去除对于PDGF在瑞士3T3成纤维细胞中激发和维持对基于肌动蛋白-肌球蛋白的收缩系统的控制至关重要。PDGF通过对hnRNP-K控制的泛素连接酶翻译的调节诱导蛋白质不稳定，这确定了一条新的途径，通过该途径外部刺激可以通过细胞骨架调节因子的活性和稳定性的快速、细胞器特异性变化来调节表型发育。
