MUC12 is a transmembrane mucin that functions in epithelial cell protection and barrier maintenance. In normal intestinal epithelium, MUC12 forms part of the enterocyte glycocalyx, contributing to the gastrointestinal tract's defense against pathogens by limiting bacterial access to the epithelium 1. The protein is localized to the apical membrane of normal epithelial cells in the colon and small intestine 2. MUC12 expression is dysregulated in disease states. Patients with active ulcerative colitis show significantly reduced MUC12 gene expression compared to those in remission and healthy controls, indicating impaired mucosal barrier function 3. Conversely, MUC12 is aberrantly overexpressed in renal cell carcinoma (RCC) and colorectal tumors, where it exhibits depolarized membrane localization rather than apical restriction 2. In RCC, MUC12 overexpression promotes cell growth and invasion through c-Jun-mediated transactivation of TGF-β1 signaling 4. MUC12 stability is regulated by ubiquitination mechanisms involving the piRNA-1742/hnRNPU/USP8 axis in RCC 5. MUC12's differential expression patterns between normal and tumor cells, combined with its role in both barrier function and oncogenic signaling, make it a candidate biomarker for disease severity and a potential therapeutic target for both inflammatory bowel disease and cancer.