The Polarity Protein Scrib is Essential for Directed Endothelial Cell Migration
Rationale: Polarity proteins are involved in the apico-basal orientation of epithelial cells but relatively little is known regarding their function in mesenchymal cells.
Objective: We hypothesized that polarity proteins also contribute to endothelial processes like angiogenesis.
Methods and Results: Screening of endothelial cells revealed high expression of the polarity protein Scrib. On fibronectin-coated carriers Scrib siRNA (siScrib) blocked directed but not random migration of human umbilical vein endothelial cells (HUVECs) and lead to an increased number and disturbed orientation of cellular lamellipodia. Co-immunoprecipitation/mass spectrometry and GST pulldown assays identified integrin α5 as a novel Scrib interacting protein. By TIRF microscopy, Scrib and integrin α5 colocalize at the basal plasma membrane of HUVEC. Western blot and FACS analysis revealed that silencing of Scrib reduced the protein amount and surface expression of integrin α5 subunit whereas surface expression of integrin αV subunit was unaffected. Moreover, in contrast to fibronectin, the ligand of integrin α5, directional migration on collagen mediated by collagen-binding integrins was unaffected by siScrib. Mechanistically, Scrib supported integrin α5 recycling and protein stability by blocking its interaction with Rab7a, translocation into lysosomes and its subsequent degradation by pepstatin-sensitive proteases. In siScrib-treated cells, reinduction of the wildtype protein but not of PDZ- or LRR-domain mutants restored integrin α5 abundance and directional cell migration. The downregulation of Scrib function in Tg(kdrl:EGFP)s843 transgenic zebrafish embryos delayed the angiogenesis of intersegmental vessels.
Conclusions: Scrib is a novel regulator of integrin α5 turnover and sorting, which is required for oriented cell migration and sprouting angiogenesis.
- Received November 21, 2012.
- Revision received December 27, 2012.
- Accepted January 29, 2013.
- Copyright © 2013, Circulation Research