Distinct ligand binding sites in integrin alpha3beta1 regulate matrix adhesion and cell-cell contact

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Integrin alpha3beta1 is crucial for cell adhesion to laminin-5.
• The urokinase receptor (uPAR) binds integrin alpha3beta1 at a distinct site from laminin-5.
• uPAR-integrin interactions may signal differently than matrix binding.

Purpose of the Study:

• To investigate the distinct signaling roles of integrin alpha3beta1 when binding to laminin-5 versus uPAR.
• To determine the specific residues in integrin alpha3beta1 involved in uPAR interaction and downstream signaling.

Main Methods:

• Reconstitution of alpha3-/- epithelial cells with wild-type or mutant alpha3 integrins.
• Analysis of cell adhesion, Src kinase activity, and expression of epithelial-mesenchymal transition markers (SLUG, E-cadherin, gamma-catenin).
• Assessment of the effects of Src kinase inhibition and expression of truncated Src.

Main Results:

• Wild-type alpha3beta1 co-expression with uPAR induced cell dissociation, increased Src activity, SLUG upregulation, and E-cadherin/gamma-catenin downregulation.
• Src kinase inhibition or expression of a dominant-negative Src construct restored epithelial phenotype.
• Mutations in the uPAR-interacting loop (H245A, R244A) abrogated uPAR-induced cell dissociation and downstream signaling.

Conclusions:

• Integrin alpha3beta1 regulates both cell-matrix adhesion and cell-cell contact through distinct interaction sites.
• A novel integrin alpha3beta1- and Src-dependent pathway regulates SLUG expression and mesenchymal transition.
• The beta-propeller domain of alpha3beta1 contains distinct sites for matrix and uPAR engagement, mediating differential signaling.