Distinct recognition of collagen subtypes by alpha(1)beta(1) and alpha(2)beta(1) integrins - alpha(1)beta(1) mediates cell adhesion to type XIII collagen

Two integrin-type collagen receptors, alpha(1)beta(1) and alpha(2)beta(1), are structurally very similar. However, cells can concomitantly express the both receptors and they might have independent functions. Here, Chinese ha mster ovary (CHO) cells, which lack endogenous collagen receptors, were tra nsfected with either alpha(1) or alpha(2) 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 alpha( 1)beta(1) integrin could spread on collagen types I, III, IV, and V but not on type II, while alpha(2)beta(1) integrin could mediate cell spreading on collagen types I-V. Type XIII is a transmembrane collagen and its interact ion with the integrins has not been previously studied. CHO-alpha 1 beta 1 cells could spread on human recombinant type XIII collagen, unlike CHO-alph a 2 beta 1 cells. Integrins alpha(1)beta(1) and alpha(2)beta(1) recognize c ollagens with the specific alpha I domains. The alpha(1)I and alpha(2)I dom ains were produced as recombinant proteins, labeled with europium and used in a sensitive solid-phase binding assay based on time-resolved fluorescenc e. alpha(1)I domain, unlike the alpha(2)I domain, could attach to type XIII collagen. The results indicate, that alpha(1)beta(1) and alpha(2)beta(1) h ave different ligand binding specificity. Distinct recognition of different collagen subtypes by the aI domains can partially explain the differences seen in cell spreading. However, despite the fact that CHO-alpha 1 beta 1 c ells could not spread on type II collagen alpha(1)I domain could bind to th is collagen type. Thus, the cell spreading on collagens may also be regulat ed by factors other than the integrins.