BCAS3 (BCAS3 microtubule associated cell migration factor) is a multifunctional protein with roles in cell migration, transcriptional regulation, and autophagy. Primary function: BCAS3 regulates endothelial cell migration and angiogenesis by mediating CDC42 activation and actin cytoskeleton reorganization at the cell leading edge 1. Mechanism: BCAS3 functions as a transcriptional coactivator of estrogen receptor-responsive genes with histone acetyltransferase activity [UniProt]. Critically, BCAS3 associates with the phagophore assembly site during autophagy through its WD40 repeat domain, which directly binds phosphatidylinositol-3-phosphate, and forms a complex with C16orf70 to regulate autophagosome formation 2. BCAS3 is required for autophagy as a scaffold protein that recruits core autophagy machinery 3. Disease relevance: Mutations in BCAS3 cause neurodevelopmental deficits including microcephaly, developmental delay, and motor dysfunction, with increased neuronal apoptosis as a pathological mechanism 4. BCAS3 is amplified in breast cancer at 17q23 5 and overexpressed in glioblastoma, where it restrains p53/GADD45α signaling to promote tumorigenesis 6. Rare coding variants in BCAS3 are associated with cognitive function variation in adults 7. Clinical significance: BCAS3 serves as both a potential therapeutic target and biomarker in malignancies and neurodevelopmental disorders.