Cortactin controls cell motility and lamellipodial dynamics by regulating ECM secretion

Cell movement relies on dynamic actin structures like lamellipodia, which are shaped by regulators such as cortactin. While cortactin is known to influence lamellipodia and cell migration, recent findings suggest that lamellipodia may not be essential for motility. This raises questions about alternative mechanisms by which cortactin might regulate movement. Established research has shown that cortactin also affects membrane trafficking and adhesion processes. However, the role of cortactin in extracellular matrix (ECM) secretion and its impact on cell motility remains unclear. No prior work had resolved how cortactin might coordinate ECM secretion and actin regulation to influence migration. This gap motivated an investigation into whether cortactin's effects on motility are linked to altered ECM secretion and trafficking. The study aimed to clarify the interplay between cortactin, ECM dynamics, and cell movement. Prior research has shown that ECM components like fibronectin are internalized and resecreted during migration. Yet, the specific role of cortactin in this process had not been fully explored. This uncertainty drove the need to examine cortactin’s role in ECM secretion and its effect on cell motility.

The study aimed to investigate whether cortactin’s regulation of cell motility is linked to its role in extracellular matrix (ECM) secretion and trafficking. The researchers sought to determine if defects in ECM secretion could explain the reduced motility observed in cortactin-knockdown cells. They hypothesized that altered ECM secretion or integrin trafficking might underlie the migration defects in these cells. To test this, the team examined whether restoring ECM availability could rescue the motility defects. They also explored whether cortactin’s interaction with actin and the Arp2/3 complex was necessary for this rescue. The study aimed to clarify the relationship between cortactin, ECM secretion, and cell movement. By comparing ECM produced by control and cortactin-knockdown cells, the researchers sought to determine if the quality of the ECM influenced motility. The goal was to identify the specific mechanisms by which cortactin affects ECM processing and secretion. Ultimately, the study aimed to reveal how cortactin regulates motility through ECM dynamics.

The researchers used cortactin-knockdown (KD) cells to study motility and ECM secretion. They tested whether adding exogenous extracellular matrix (ECM) could rescue motility defects in these cells. They also compared ECM produced by control and cortactin-KD cells to assess its effect on cell movement. To investigate ECM trafficking, they tracked fibronectin (FN) localization in control and KD cells using endocytic markers. They examined whether FN was retained in late endocytic or lysosomal compartments in KD cells. To determine the role of lysosomal fusion, they knocked down synaptotagmin-7 in control cells and observed the effects on motility and ECM deposition. The team used cortactin-binding domain mutants to assess which interactions are essential for rescuing motility and ECM secretion defects. By expressing these mutants in KD cells, they evaluated the importance of Arp2/3 complex and actin filament interactions. The study combined biochemical assays, live-cell imaging, and functional rescue experiments to dissect cortactin’s role in ECM secretion and cell motility.

Cortactin-knockdown (KD) cells showed reduced motility and lamellipodial defects. These defects were fully rescued when the cells were plated on increasing concentrations of exogenous extracellular matrix (ECM). Motility was also restored when cells were placed on autocrine ECM produced by control cells, but not on ECM from KD cells. Investigation revealed that fibronectin (FN) was retained in late endocytic/lysosomal compartments in KD cells. Control cells, in contrast, redeposited endocytosed FN at the cell surface. Knockdown of synaptotagmin-7 in control cells phenocopied the motility and FN deposition defects of KD cells. Expression of cortactin-binding domain mutants rescued both motility and ECM secretion defects. Only mutants interacting with the Arp2/3 complex and actin filaments were effective in this rescue. These findings indicate that cortactin’s regulation of branched actin is essential for ECM secretion and cell motility.

The authors propose that cortactin regulates cell motility by controlling extracellular matrix (ECM) secretion and trafficking. Their findings suggest that motility defects in cortactin-knockdown cells are due to impaired ECM secretion and abnormal fibronectin (FN) retention in lysosomal compartments. The study shows that exogenous ECM can fully rescue these defects, indicating that ECM availability is a key factor. The researchers also found that synaptotagmin-7, a lysosomal fusion regulator, is involved in ECM secretion and motility. Expression of cortactin-binding domain mutants revealed that interactions with the Arp2/3 complex and actin filaments are essential for rescuing motility and ECM secretion defects. These results suggest that cortactin’s role in actin regulation is critical for ECM processing and resecretion. The authors conclude that efficient cell motility depends on cortactin’s ability to regulate both branched actin networks and ECM dynamics. Their work supports the idea that ECM secretion from late endosomal/lysosomal compartments is necessary for normal cell movement.