The tetraspanin CD151 and integrin α3β1 signaling complex in basement membrane adhesion - Project Summary The structural integrity of the skin is dependent on appropriate cell attachment to the basement membrane, which forms the foundation of the epidermis and separates it from the dermis. Laminins are the major component of the basement membrane, where integrin receptors form adhesive contacts and connect the intracellular cytoskeleton to the extracellular matrix. Integrins are heterodimeric adhesion receptors that link cells to components of the extracellular matrix and to other cells, and they are essential for cell adhesion, migration, and multicellularity. Laminin binding integrins are fundamental in attaching epithelial cells to the basement membrane. In humans, a well conserved family of proteins, the tetraspanins, have been shown to bind and form signaling complexes with laminin-binding integrins. Tetraspanins are a class of four-pass transmembrane domain proteins with diverse biological roles involving modulation of the trafficking, membrane localization, and signaling of their various partners. The interaction between tetraspanins and integrins remains an exciting area of research as in vivo evidence suggests the interaction is necessary for normal integrin function. The tetraspanin CD151 binds all laminin binding integrins but associates most stably with the laminin-binding integrin α3β1 (ITGα3β1). Silencing mutations in either CD151 and ITGα3β1 both result in epidermolysis bullosa (EB), a disease phenotype consistent with impaired laminin binding and basement membrane attachment. However, why integrin function is diminished in this disease remains unclear, and whether CD151 affects ITGα3β1conformation or affects its activity through other signaling mechanisms is unresolved. Integrins characteristically exist in three conformations which each conferring different ligand affinity. CD151 may bind to and stabilize a specific ITGα3β1 conformation. This proposal will use structural approaches to determine if ITGα3β1 signaling is CD151 dependent due to conformation regulation. Additionally, signaling may be dependent on other downstream signaling mechanisms. I will use a proximity labeling time course approach to define the dynamic response to integrin activation and the influence of CD151 on ITGα3β1 signaling. These approaches will determine how CD151 modulates ITGα3β1, which can be applied to understand general tetraspanin and laminin binding integrin signaling biology. Although tetraspanins have many interaction partners and are implicated in various biological processes, the mechanism by which they engage and modulate their binding partners remains understudied. Specifically, understanding the CD151-ITGα3β1 signaling complex and its role in epidermal adhesion could be exploited therapeutically to strengthen epidermis attachment in EB and potentially other diseases of the skin.
