PCDH1 (protocadherin 1) is a non-clustered protocadherin belonging to the cadherin superfamily that functions primarily in cell-cell adhesion and epithelial barrier integrity 1. The protein localizes to cell-cell contact sites and colocalizes with E-cadherin at apical regions of airway epithelial cells, where it maintains both tight and adhesion junctions 2. PCDH1 expression is upregulated during epithelial barrier development and is glucocorticoid-responsive, with dexamethasone enhancing barrier function through PCDH1 induction 2. Beyond adhesion, PCDH1 serves as a viral entry receptor: New World hantavirus surface glycoproteins directly recognize PCDH1's extracellular repeat domain to facilitate cellular entry in pulmonary endothelial cells, and genetic ablation of PCDH1 renders animals highly resistant to lethal hantavirus challenge 3. Genetic variants in PCDH1 are associated with increased risk of transient early asthma and atopic dermatitis in early childhood 4, and cigarette smoke exposure reduces PCDH1 expression in lung tissue, correlating with airway hyperresponsiveness 5. Impaired PCDH1 expression in inflamed tissues from asthma and chr5 rhinosinusitis patients suggests dysfunction contributes to allergic airway inflammation 2. In pancreatic adenocarcinoma, PCDH1 is significantly upregulated and promotes metastasis and chemoresistance through NF-κB pathway activation via KPNB1 interaction, serving as a poor prognostic biomarker 67.