Reduced PaxillinB localization to cell-substrate adhesions promotes cell migration in Dictyostelium
Many cells adhere to the extracellular matrix for efficient cell migration. This adhesion is mediated by focal adhesions, a protein complex linking the extracellular matrix to the intracellular cytoskeleton. Focal adhesions have been studied extensively in Metazoan mesenchymal cells, but recent research in physiological contexts and amoeboid cells suggest that focal adhesion regulation differs from the mesenchymal focal adhesion paradigm. While focal adhesion machinery predates the origin of Metazoans, focal adhesion formation and regulation during non-Metazoan cell migration is largely unexplored. We used Dictyostelium discoideum to investigate novel mechanisms and the evolution of focal adhesion regulation, as Dictyostelium are non-Metazoans that form cell-substrate adhesion structures for migration. We show that PaxillinB, the Dictyostelium homologue of Paxillin, localizes to dynamic cell-substrate adhesions. As expected, PaxillinB mutations decreased the number of cell-substrate adhesions. Unexpectedly, however, decreased cell-substrate adhesion number led to an increase in cell migration speed. These findings are in direct contrast to Paxillin function at focal adhesions and regulation of cell migration in mammalian cells, challenging the established focal adhesion model and providing insight into the evolution of cell-substrate adhesions and Paxillin function during cell migration. Significance StatementO_LIFocal adhesions are understudied in non-mesenchymal, non-Metazoan systems. C_LIO_LIThe authors characterize PaxillinB, the Dictyostelium homologue of Paxillin, during Dictyostelium cell migration. Reducing cell-substrate adhesion number via PaxillinB mutations lead to decreased cell adhesion and, surprisingly, increased cell migration speeds. C_LIO_LIThese findings suggest Dictyostelium cells form cell-substrate adhesions that act as molecular "brakes" during cell migration and provides unique insight into the evolution of Paxillin as a regulator of cell-substrate adhesion function and formation during cell migration. C_LI