Distinct Recognition of Collagen Subtypes by α₁β₁ and α₂β₁Integrins

Two integrin-type collagen receptors, α₁β₁ and α₂β₁, are structurally very similar. However, cells can concomitantly express the both receptors and they might have independent functions. Here, Chinese hamster ovary (CHO) cells, which lack endogenous collagen receptors, were transfected with either α₁ or α₂ integrin cDNA. Cells were allowed to adhere to various collagen types and their integrin function was tested by observing the progression of cell spreading. The cells expressing α₁β₁ integrin could spread on collagen types I, III, IV, and V but not on type II, while α₂β₁ integrin could mediate cell spreading on collagen types I-V. Type XIII is a transmembrane collagen and its interaction with the integrins has not been previously studied. CHO-α1β1 cells could spread on human recombinant type XIII collagen, unlike CHO-α2β1 cells. Integrins α₁β₁ and α₂β₁recognize collagens with the specific αI domains. The α₁I and α₂I domains were produced as recombinant proteins, labeled with europium and used in a sensitive solid-phase binding assay based on time-resolved fluorescence. α₁I domain, unlike the α₂I domain, could attach to type XIII collagen. The results indicate, that α₁β₁ and α₂β₁have different ligand binding specificity. Distinct recognition of different collagen subtypes by the αI domains can partially explain the differences seen in cell spreading. However, despite the fact that CHO-α1β1 cells could not spread on type II collagen α₁I domain could bind to this collagen type. Thus, the cell spreading on collagens may also be regulated by factors other than the integrins.