RESUMEN
Protein networks asymetrically distributed to basolateral and apical epithelial membranes maintain cell polarity and homeostasis of epithelial tissues. Genetic studies in non-vertebrates assigned two families of basolateral proteins, MAGUK (membrane-associated and guanylate kinase) and LAP (leucine-rich repeats and PDZ) proteins, to a common pathway crucial for the epithelial architecture and acting as a gatekeeper to malignancy. In mammals, three LAP proteins have been described, Densin-180, Erbin, and hScribble. Here, we identify a protein called Lano (LAP and no PDZ) only present in vertebrates and presenting strong identities with LAP proteins. Despite the lack of PDZ domain, Lano is located at the basolateral side of epithelial cells in a similar manner to Erbin and hScribble. Using in vitro and in vivo experiments, we demonstrate that Lano directly interacts with the PDZ domains of MAGUK proteins, including hDLG (human disc large), in epithelial cells. A second pool of Lano is complexed to Erbin. These LAP-MAGUK protein complexes coexist at the basolateral side of epithelial cells. We provide evidence for a direct interaction between LAP and MAGUK proteins, and we propose that various LAP-MAGUK networks targeted to the basolateral side of epithelial cells participate to homeostasis of epithelial tissues and tumor growth.
Asunto(s)
Proteínas Portadoras/metabolismo , Proteínas de la Membrana , Nucleósido-Fosfato Quinasa/metabolismo , Secuencia de Aminoácidos , Animales , Células COS , Células CACO-2 , Proteínas Portadoras/química , ADN Complementario , Células Epiteliales/enzimología , Células Epiteliales/metabolismo , Guanilato-Quinasas , Humanos , Datos de Secuencia Molecular , Unión Proteica , Homología de Secuencia de AminoácidoRESUMEN
Identification of protein complexes associated with the ERBB2/HER2 receptor may help unravel the mechanisms of its activation and regulation in normal and pathological situations. Interactions between ERBB2/HER2 and Src homology 2 or phosphotyrosine binding domain signaling proteins have been extensively studied. We have identified ERBIN and PICK1 as new binding partners for ERBB2/HER2 that associate with its carboxyl-terminal sequence through a PDZ (PSD-95/DLG/ZO-1) domain. This peptide sequence acts as a dominant retention or targeting basolateral signal for receptors in epithelial cells. ERBIN belongs to the newly described LAP (LRR and PDZ) protein family, whose function is crucial in non vertebrates for epithelial homeostasis. Whereas ERBIN appears to locate ERBB2/HER2 to the basolateral epithelium, PICK1 is thought to be involved in the clustering of receptors. We show here that ERBIN and PICK1 bind to ERBB2/HER2 with different mechanisms, and we propose that these interactions are regulated in cells. Since ERBIN and PICK1 tend to oligomerize, further complexity of protein networks may participate in ERBB2/HER2 functions and specificity.
Asunto(s)
Proteínas Portadoras/metabolismo , Proteínas de la Membrana/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Proteínas Nucleares/metabolismo , Fosfoproteínas/metabolismo , Proteínas/metabolismo , Receptor ErbB-2/metabolismo , Proteínas Adaptadoras Transductoras de Señales , Secuencia de Aminoácidos , Animales , Sitios de Unión , Proteínas Portadoras/química , Línea Celular , Homólogo 1 de la Proteína Discs Large , Homólogo 4 de la Proteína Discs Large , Guanilato-Quinasas , Humanos , Péptidos y Proteínas de Señalización Intracelular , Datos de Secuencia Molecular , Unión Proteica , Homología de Secuencia de Aminoácido , Técnicas del Sistema de Dos Híbridos , Proteína de la Zonula Occludens-1RESUMEN
The ERBB receptors have a crucial role in morphogenesis and oncogenesis. We have identified a new PDZ protein we named ERBIN (ERBB2 interacting protein) that acts as an adaptor for the receptor ERBB2/HER2 in epithelia. ERBIN contains 16 leucine-rich repeats (LRRs) in its amino terminus and a PDZ (PSD-95/DLG/ZO-1) domain at its carboxy terminus, and belongs to a new PDZ protein family. The PDZ domain directly and specifically interacts with ERBB2/HER2. ERBIN and ERBB2/HER2 colocalize to the lateral membrane of human intestinal epithelial cells. The ERBIN-binding site in ERBB2/HER2 has a critical role in restricting this receptor to the basolateral membrane of epithelial cells, as mutation of the ERBIN-binding site leads to the mislocalization of the receptor in these cells. We suggest that ERBIN acts in the localization and signalling of ERBB2/HER2 in epithelia.