The polarity protein Scrib is essential for directed endothelial cell migration

The role of polarity proteins in mesenchymal cells remains poorly understood, despite their well-established function in epithelial cell orientation. Prior research has shown that proteins like Scribble (Scrib) are critical for apical-basal polarity in epithelia. However, no prior work had resolved their role in endothelial cell behavior. Established knowledge includes the involvement of integrins in cell adhesion and migration, but the specific contribution of polarity proteins to these processes is unclear. This gap motivated further investigation into how Scrib might influence endothelial cell migration. The current literature lacks detailed mechanisms linking Scrib to integrin function during angiogenesis. No prior studies have demonstrated a direct interaction between Scrib and integrin α5. The need for clarity on how Scrib modulates integrin activity remains unmet in the field. This uncertainty drives the exploration of Scrib’s role in directional cell migration.

This study aims to determine whether the polarity protein Scrib contributes to directed endothelial cell migration. The specific problem addressed is the lack of understanding about how Scrib influences integrin function during angiogenesis. The motivation stems from the observation that Scrib is highly expressed in endothelial cells. The authors sought to investigate whether Scrib regulates integrin α5, a key adhesion receptor. The study also aimed to uncover how Scrib affects lamellipodia formation and cell migration. The authors hypothesized that Scrib supports directional migration by modulating integrin α5. The goal was to test whether Scrib’s role is essential for integrin α5 stability and trafficking. The study’s findings could clarify the molecular basis of endothelial cell orientation during angiogenesis.

The researchers used siRNA to silence Scrib in human umbilical vein endothelial cells. They assessed cell migration on fibronectin-coated surfaces using migration assays. Lamellipodia formation was analyzed using time-lapse microscopy. Integrin α5 interactions were identified via coimmunoprecipitation and mass spectrometry. GST pulldown assays confirmed the direct interaction between Scrib and integrin α5. TIRF microscopy was used to observe the colocalization of Scrib and integrin α5 at the plasma membrane. Western blot and FACS analysis measured integrin α5 protein levels and surface expression. The study also tested whether reexpression of wild-type Scrib could restore integrin α5 abundance and migration.

Silencing Scrib blocked directed but not random migration of endothelial cells on fibronectin. The number and orientation of lamellipodia were increased and disorganized in siScrib-treated cells. Integrin α5 was identified as a novel binding partner of Scrib through coimmunoprecipitation and mass spectrometry. TIRF microscopy showed colocalization of Scrib and integrin α5 at the basal membrane. Silencing Scrib reduced integrin α5 protein levels and surface expression. Integrin αV surface expression remained unaffected by Scrib silencing. Directional migration on collagen was not impacted by siScrib, suggesting integrin α5 specificity. Scrib blocked integrin α5 interaction with Rab7a, preventing lysosomal degradation and supporting its recycling.

The authors concluded that Scrib is essential for directed endothelial cell migration. Their findings suggest that Scrib regulates integrin α5 stability and trafficking. The study supports the role of Scrib in integrin α5 recycling and protein protection from degradation. The authors propose that Scrib prevents integrin α5 from entering lysosomes via Rab7a. Reexpression of wild-type Scrib, but not PDZ or leucine-rich mutants, restored integrin α5 and migration. The study also showed that Scrib knockdown in zebrafish embryos delayed angiogenesis. The results indicate that Scrib functions as a novel regulator of integrin α5 turnover. The authors suggest that Scrib’s role is specific to integrin α5 and fibronectin-dependent migration.