Critical amino acid residues of the α4 subunit for α4β7 integrin function

Abstract

AbstractA characteristic feature of integrin–ligand interactions is the requirement for divalent cations. Putative cation binding sites have been identified in the α and β subunit of the α4 integrins, α4β1 and α4β7, and within their ligands which display the tripeptide LDV in fibronectin and homologous motifs in VCAM‐1 and MAdCAM‐1. The extracellular domain of the murine and human α4‐subunit contains three conserved LDV motifs, designated LDV‐1 to ‐3. Using site directed mutagenesis and transfection studies, we now examined the functional relevance of the LDV motifs for α4β7 integrins. We present evidence that LDV‐1 mutants (D489N) behave like α4 wt cells, but LDV‐3 mutants (D811N) are impaired in α4β7 integrin‐triggered homotypic cell aggregation and in adhesion and spreading on α4 specific ligands. Further characterization of LDV‐3 mutants revealed a defect in mAb‐induced α4β7‐cell surface cluster formation. Mutation of the LDV‐2 motif (D698N) caused loss of α4β7 integrin cell surface expression. Our results indicate: (i) that LDV‐3, located proximal to the cell membrane, is important for α4β7 integrin‐triggered functions and for lateral clustering and (ii) that LDV‐2 affects α4β7 heterodimer stability. J. Cell. Biochem. 83: 304–319, 2001. © 2001 Wiley‐Liss, Inc.