Kindlin-1 Is Required for RhoGTPase-Mediated Lamellipodia Formation in Keratinocytes

Kindlin-1 is an epithelial-specific member of the novel kindlin protein family, which are regulators of integrin functions. Mutations in the gene that encodes Kindlin-1, FERMT1 (KIND1), cause the Kindler syndrome (KS), a human disorder characterized by mucocutaneous fragility, progressive skin atrophy, ulcerative colitis, photosensitivity, and propensity to skin cancer. Our previous studies indicated that loss of kindlin-1 resulted in abnormalities associated with integrin functions, such as adhesion, proliferation, polarization, and motility of epidermal cells. Here, we disclosed novel FERMT1 mutations in KS and used them, in combination with small-interfering RNA, protein, and imaging studies, to uncover new functions for kindlin-1 in keratinocytes and to discern the molecular pathology of KS. We show that kindlin-1 forms molecular complexes with β1 integrin, α-actinin, migfilin, and focal adhesion kinase and regulates cell shape and migration by controlling lamellipodia formation. Kindlin-1 governs these processes by signaling via Rho family GTPases, and it is required to maintain the pool of GTP-bound, active Rac1, RhoA and Cdc42, and the phosphorylation of their downstream effectors p21-activated kinase 1, LIM kinase, and cofilin. Loss of these kindlin-1 functions forms the biological basis for the epithelial cell fragility and atrophy in the pathology of KS.