LAUSR

IRE1α is a well-characterized stress response signaling protein that adapts the cell to conditions of endoplasmic reticulum (ER) stress. In addition to well-established sources of ER stress such as viral infection, hypoxia and nutrient deprivation, it has recently been proposed that the morphological and epigenetic changes associated with routine cell differentiation are also a source of ER stress for the cell, and that IRE1α has an important role in adapting the cell to its newly differentiated state. Here, we provide evidence that IRE1α is essential for the differentiation of stratified squamous epithelium. We utilized mice expressing K14CreERT2 and floxed IRE1α to enable tamoxifen-inducible deletion of IRE1α targeted to the basal layer and stem cells of stratified squamous epithelium. After tamoxifen injection, IRE1α knockout mice displayed severe weight loss resulting in death within 10 days of treatment. Histological analysis revealed that epithelial homeostasis in the tongue and esophagus was severely disrupted leading to significantly decreased food intake and, as a result, death. The tongue epithelium and esophageal mucosal layer were found to be significantly thinner, and filiform papillae were lost from the tongue. Immunohistochemical staining showed significant downregulation of the proliferative marker Ki67, as well as a marker of differentiation, Sox2, suggesting an almost complete loss of tissue renewal as early as four days after IRE1α deletion. This work highlights the complexity of IRE1α signaling beyond adaptation to external sources of stress and proposes a role of IRE1α in the normal physiology of tissue homeostasis. As inhibition of the IRE1α signaling pathway has been proposed as a therapeutic target in certain cancers, an increased understanding of how broad the scope of IRE1α activity is may provide insight into potential side effects resulting from these treatments. Citation Format: Fiona E. Chalmers, Douglas B. Stairs, Adam B. Glick. The unfolded protein response gene Ire1α is required for tissue renewal and normal differentiation in the mouse tongue and esophagus [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5839.