Regulation of cell migration by nucleotide coding sequence and arginylation

细胞迁移是组织形态发生、免疫反应和肿瘤转移等关键生物学事件的重要过程。多种细胞类型的定向迁移依赖于密集的肌动蛋白网络，该网络在细胞前缘迅速形成，并通过肌动蛋白丝的极化伸长促进其突出。我们发表的研究揭示了肌动蛋白在细胞前沿功能的两个新的相互关联的决定因素：肌动蛋白的核苷酸编码序列和肌动蛋白精氨酸化。利用蛋白质生物化学、细胞生物学和小鼠转基因相结合的综合方法，我的实验室的工作证明了精氨酸转移酶（ATE1），即精氨酸化蛋白质的酶，在细胞迁移过程中特异性地调节肌动蛋白的功能，并有助于几乎所有的生理过程，包括小鼠的远程迁移和组织重塑。这些研究推动了我的研究计划，旨在通过核苷酸编码序列和精氨酸化来描述肌动蛋白调节的新机制。我们最近的数据表明，前沿肌动蛋白的n端精氨酸化是一个动态事件，对细胞外刺激表现出快速反应，对维持细胞迁移速度至关重要。此外，精氨酸化对普遍存在且必需的β-肌动蛋白异构体具有高度特异性，而对相同细胞类型中密切相关的γ-肌动蛋白则没有特异性。值得注意的是，这种特异性是由mRNA编码序列在核苷酸水平上决定的，mRNA编码序列负责不同肌动蛋白同种异构体的差异翻译速率，对其折叠速率和共翻译泛素化产生下游影响。这种新的肌动蛋白调节机制针对不正确的精氨酸化肌动蛋白异构体进行降解，并确保只有快速积累的β-肌动蛋白在细胞中被精氨酸化。因此，细胞前沿的肌动蛋白精氨酸化是一个受到严格调控的过程，其核苷酸序列是遗传编码的，这表明精氨酸化是肌动蛋白调控的初级水平，发生在任何其他肌动蛋白依赖事件之前。揭示这种调节肌动蛋白功能和体内细胞迁移协调的基本步骤是我的长期研究目标。

Cell migration is a critically important process in key biological events such as tissue morphogenesis, immune response, and cancer metastasis. Directional migration of multiple cell types depends on the dense actin network that rapidly forms at the cell leading edge and facilitates its protrusion via polarized elongation of the actin filaments. Our published studies revealed two novel interconnected determinants of the function of actin at the cell leading edge: actin's nucleotide coding sequence and actin arginylation. Using integrated approaches that combine protein biochemistry, cell biology, and mouse transgenesis, work from my lab demonstrated that arginyltransferase (ATE1), the enzyme that arginylates proteins, specifically regulates the function of actin during cell migration and contributes to virtually every physiologic process involving long-range migration and tissue remodeling in mice. These studies drive my research program, which aims to characterize the novel mechanisms of actin regulation by nucleotide coding sequence and arginylation. Our recent data show that N-terminal arginylation of the leading edge actin is a dynamic event that exhibits a rapid response to extracellular stimuli and is essential for maintaining cell migration speed. Moreover, arginylation is highly specific to the ubiquitous and essential β-actin isoform but not to the closely homologous γ-actin in the same cell types. Remarkably, this specificity is determined at the nucleotide level by the mRNA coding sequence, which is responsible for the differential translation rates of different actin isoforms, exerting downstream effects on their folding rates and co-translational ubiquitination. This novel actin regulatory mechanism targets incorrectly arginylated actin isoforms for degradation and ensures that only the fast­ accumulating β-actin becomes arginylated in cells. Thus, actin arginylation at the cell leading edge is a tightly regulated process that is genetically encoded in its nucleotide sequence, suggesting that arginylation is the primary level of actin regulation that occurs prior to any other actin-dependent event. Uncovering the essential steps of this regulation in actin function and coordination of cell migration in vivo constitutes my long-term research goal.