A novel noncanonical function for IRF6 in the recycling of E-cadherin.

Interferon Regulatory Factor 6 (IRF6) is a transcription factor essential for keratinocyte cell-cell adhesions. Previously, we found that recycling of E-cadherin was defective in the absence of IRF6, yet total E-cadherin levels were not altered, suggesting a previously unknown, nontranscriptional function for IRF6. IRF6 protein contains a DNA binding domain (DBD) and a protein binding domain (PBD). The transcriptional function of IRF6 depends on its DBD and PBD, however, whether the PBD is necessary for the interaction with cytoplasmic proteins has yet to be demonstrated. Here, we show that an intact PBD is required for recruitment of cell-cell adhesion proteins at the plasma membrane, including the recycling of E-cadherin. Colocalizations and coimmunoprecipitations reveal that IRF6 forms a complex in recycling endosomes with Rab11, Myosin Vb, and E-cadherin, and that the PBD is required for this interaction. These data indicate that IRF6 is a novel effector of the endosomal recycling of E-cadherin and demonstrate a non-transcriptional function for IRF6 in regulating cell-cell adhesions.

To Stick or Not to Stick: Adhesions in Orofacial Clefts.

Morphogenesis requires a tight coordination between mechanical forces and biochemical signals to inform individual cellular behavior. For these developmental processes to happen correctly the organism requires precise spatial and temporal coordination of the adhesion, migration, growth, differentiation, and apoptosis of cells originating from the three key embryonic layers, namely the ectoderm, mesoderm, and endoderm. The cytoskeleton and its remodeling are essential to organize and amplify many of the signaling pathways required for proper morphogenesis. In particular, the interaction of the cell junctions with the cytoskeleton functions to amplify the behavior of individual cells into collective events that are critical for development. In this review we summarize the key morphogenic events that occur during the formation of the face and the palate, as well as the protein complexes required for cell-to-cell adhesions. We then integrate the current knowledge into a comprehensive review of how mutations in cell-to-cell adhesion genes lead to abnormal craniofacial development, with a particular focus on cleft lip with or without cleft palate.

IRF6 Regulates the Delivery of E-Cadherin to the Plasma Membrane.

IRF6 is a transcription factor that is required for craniofacial development and epidermal morphogenesis. Specifically, Irf6-deficient mice lack the terminally differentiated epidermal layers, leading to an absence of barrier function. This phenotype also includes intraoral adhesions due to the absence of the oral periderm, leading to the mislocalization of E-cadherin and other cell‒cell adhesion proteins of the oral epithelium. However, the mechanisms by which IRF6 controls the localization of cell adhesion proteins are not understood. In this study, we show that in human and murine keratinocytes, loss of IRF6 leads to a breakdown of epidermal sheets after mechanical stress. This defect is due to a reduction of adhesion proteins at the plasma membrane. Dynamin inhibitors rescued the IRF6-dependent resistance of epidermal sheets to mechanical stress, but only inhibition of clathrin-mediated endocytosis rescued the localization of junctional proteins at the membrane. Our data show that E-cadherin recycling but not its endocytosis is affected by loss of IRF6. Overall, we demonstrate a role for IRF6 in the delivery of adhesion proteins to the cell membrane.