TJAP1 (tight junction-associated protein 1) is a peripheral membrane protein component of tight junctions in epithelial cells 1. While traditionally associated with tight junction structure, TJAP1 also functions in broader cellular processes. It was identified as a novel interactor of Mint1, a multidomain adaptor protein regulating neuronal membrane trafficking and synaptic vesicle fusion 2, suggesting roles beyond epithelial barriers. TJAP1 is regulated by miR-212/132, which suppress its expression in hypoxic brain microvascular endothelial cells, leading to decreased blood-brain barrier integrity through reduced tight junction protein levels 3. Additionally, TJAP1 functions as an epithelial regulator gene; its transcription is repressed by HMGN3 in a SNAI2-dependent manner in cholangiocarcinoma cells, with repression promoting cell migration and invasion 4. TJAP1 expression is also modulated by miR-132 in adult mouse forebrain 5 and shows differential DNA methylation associated with prenatal PFAS exposure 6. These findings indicate TJAP1 participates in tight junction maintenance, epithelial polarity regulation, and neuronal trafficking, with dysregulation implicated in barrier dysfunction and cancer progression.