Threonine 788 in integrin subunit beta1 regulates integrin activation.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Integrins are critical cell surface receptors mediating cell adhesion and migration.
• Phosphorylation of integrin cytoplasmic tails is a key regulatory mechanism for integrin function.
• The functional significance of conserved threonine phosphorylation in integrin beta1 remains incompletely understood.

Purpose of the Study:

• To investigate the functional role of conserved threonine phosphorylation in the cytoplasmic domain of integrin subunit beta1.
• To determine the specific contribution of threonine 788 (T788) and threonine 789 (T789) phosphorylation to integrin beta1 function.

Main Methods:

• Site-directed mutagenesis was used to create beta1 mutants mimicking phosphorylated (T788D) and unphosphorylated (T788A) forms.
• These mutants were expressed in beta1-deficient GD25 cells.
• Cell attachment assays, epitope exposure measurements (9EG7), talin head domain binding assays, and focal contact analysis were performed.

Main Results:

• Mutation of T788 to alanine (T788A) significantly reduced beta1-dependent cell attachment and 9EG7 epitope exposure.
• Mutation of T789 to alanine did not affect ligand-binding ability.
• The T788A mutation impaired integrin activation through a mechanism distinct from talin binding.
• The phosphorylation-mimicking mutation T788D restored cell adhesion and increased focal contact accumulation, albeit with slower cell migration.
• Neither T788D nor T788A mutations affected focal adhesion kinase (FAK) tyrosine phosphorylation.

Conclusions:

• Phosphorylation of T788 in integrin beta1 is essential for promoting inside-out receptor activation and cell adhesion.
• T788 phosphorylation influences focal contact accumulation and cell migration.
• The T788 site regulates integrin activation independently of direct talin interaction and FAK phosphorylation.