Human Fibroblasts with Mutations in COL5A1 and COL3A1 Genes Do Not Organize Collagens and Fibronectin in the Extracellular Matrix, Down-regulate α₂β₁ Integrin, and Recruit α_vβ₃ Instead of α₅β₁ Integrin*

Dermal fibroblasts derived from types I and IV Ehlers-Danlos syndrome (EDS) patients, carrying mutations in COL5A1 and COL3A1 genes, respectively, synthesize aberrant types V and III collagen (COLL) and show defective organization of these proteins into the extracellular matrix (ECM) and high reduction of their functional receptor, the α₂β₁ integrin, compared with control fibroblasts. EDS cells also show reduced levels of fibronectin (FN) in the culture medium and lack an FN fibrillar network. Finally, EDS cells prevalently organize α_vβ₃ integrin instead of α₅β₁ integrin. The α_vβ₃ integrin, distributed on the whole EDS cell surface, shows FN binding and assembly properties when the cells are treated with purified FN. Treatment of EDS cells with purified COLLV or COLLIII, but not with FN, restores the control phenotype (COLL⁺, FN⁺, α_vβ₃^–, α₅β₁⁺, α₂β₁⁺). Function-blocking antibodies to COLLV, COLLIII, or α₂β₁ integrin induce in control fibroblasts an EDS-like phenotype (COLL^–, FN^–, α_vβ₃⁺, α₅β₁^–, α₂β₁^–). These results show that in human fibroblasts α₂β₁ integrin organization and function are controlled by its ligand, and that the α₂β₁-COLL interaction, in turn, regulates FN integrin receptor recruitment: high α₂β₁ integrin levels induce α₅β₁ integrin organization, while low α₂β₁ integrin levels lead to α_vβ₃ integrin organization.