Purpose <p>Junction plakoglobin (JUP/γ-catenin) is a dual-component cell adhesion molecule of adherens junctions and desmosomes, maintaining epithelial homeostasis while paradoxically involving oncogenic transformation. In pancreatic ductal adenocarcinoma (PDAC), the mechanistic role and clinical implications of JUP signaling in oncogenic reprogramming remains undefined.</p> Experimental design <p>Gene expression and its association with clinicopathologic characteristics and therapeutic resistance of patients with PDAC were analyzed using IHC and bioinformatics and functionally validated by using mouse models. Protein expression and their regulation were measured by using gain- and loss-of-function assays and molecular biology methods.</p> Results <p>Our immunostaining results and bioinformatics reveals JUP overexpression in pancreatic intraepithelial neoplasia (PanIN) and primary tumors, correlating with advanced TNM staging and diminished survival. Enforced JUP expression promoted PDAC proliferation, migration and invasion in vitro and PDAC growth and metastasis in vivo, whereas decreased expression of JUP exerted opposing effects. JUP expression was positively correlated with FOXM1 expression in PDAC tissues. Mechanistically, FOXM1 transcriptionally activated JUP expression by directly binding to the promoter region of JUP. Moreover, treatment of gemcitabine and oxaliplatin induced JUP expression and subsequently rendered PDAC cells therapeutic resistance, which was reversed by deletion of JUP, whereas knockdown of JUP also attenuated FOXM1-driven therapeutic resistance.</p> Conclusions <p>Therefore, our findings suggest that JUP promotes PDAC tumorigenesis and progression through FOXM1-JUP transcriptional axis and the combination of FOXM1 and JUP be a more precise biomarker for targeted therapy and prognostic prediction, nominating this dyad as an actionable vulnerability for molecularly targeted interventions in PDAC.</p>