Regulation of cell migration by nucleotide coding sequence and arginylation

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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.