CRB3 is a cell polarity protein essential for establishing and maintaining epithelial cell architecture. It localizes to apical junctions and regulates tight junction morphogenesis, while also suppressing transforming growth factor-beta signaling through phosphorylation and cytoplasmic retention of the transcriptional coactivators YAP1 and TAZ. During ciliogenesis, CRB3 navigates Rab11-positive trafficking vesicles to facilitate γ-tubulin ring complex assembly at the basal body 1. In the developing neocortex, dynein-mediated apical transport of CRB3 is critical for maintaining radial glial cell integrity; loss of this transport induces delamination and ectopic cell division 2. CRB3 has bidirectional roles in cancer: reduced expression promotes breast cancer stemness and tamoxifen resistance through elevated β-catenin signaling 3, while CRB3 expression suppresses bladder cancer cell proliferation, migration, and invasion 4. In a therapeutic context, recombinant oncolytic adenovirus expressing CRB3, combined with PD-L1 inhibitors, enhances immune infiltration and tumor control in bladder cancer models. At the molecular level, a Golgi-resident size filter restricts apical sorting to proteins with small cytoplasmic domains; CRB3's compact tail and timely dissociation from its binding partner PALS1 enable normal apical localization 5.