The Journal of biological chemistry
Nov 27, 2019
Epithelial-specific isoforms of protein 4.1R promote adherens junction assembly in maturing epithelia.
Epithelial adherens junctions (AJs) and tight junctions (TJs) undergo disassembly and reassembly during morphogenesis and pathologic states. The membrane-cytoskeleton interface plays a crucial role in junctional reorganization. Protein 4.1R (4.1R), expressed as a diverse array of spliceoforms, has been implicated in linking the AJs and TJs complex to the cytoskeleton. However, which specific 4.1 isoform(s) participate, and the mechanisms involved in junctional stability or remodeling remain unclear. We now describe a role for epithelial-specific isoforms containing exon 17b and excluding exon 16 4.1R (4.1R+17b) in AJs. 4.1R+17b is exclusively co-localized with the AJs. 4.1R+17b binds to the armadillo repeats 1-2 of β-catenin via its membrane binding domain. This complex is linked to the actin cytoskeleton via a bispecific interaction with an exon 17b encoded peptide. Exon 17b peptides also promote fodrin-actin complex formation. Expression of 4.1R+17b forms does not disrupt junctional cytoskeleton and AJs during the steady-state or calcium-dependent AJ reassembly. Over expression of 4.1R-17b forms, which displace the endogenous 4.1R+17b forms at the AJs, as well as depletion of 4.1R+17b forms both decrease junctional actin and attenuate the recruitment of spectrin to the AJs and also reduce E-cadherin during the initial junctional formation of the AJ reassembly process. Expressing 4.1R+17b forms in depleted cells rescues junctional localization of actin, spectrin, and E-cadherin assembly at the AJs. Together, our results identify a critical role for 4.1R+17b forms in AJ assembly and offer additional insights into the spectrin-actin-4.1R-based membrane skeleton as an emerging regulator of epithelial integrity and remodeling.