APBB1 is a multifunctional transcriptional coregulator and adapter protein with dual roles in development and disease. As a coactivator/corepressor, APBB1 forms transcriptionally active complexes with the amyloid precursor protein intracellular domain (AICD) 1234. In DNA damage response, APBB1 translocates to the nucleus and induces apoptosis by recognizing phosphorylated histone H2AX at double-strand breaks, recruiting pro-apoptotic factors like JNK1 and facilitating histone H4 acetylation 5. APBB1 exerts transcriptional repression via association with TSHZ3, SET, and HDAC factors to inhibit CASP4 expression 6. The protein functions in neurite outgrowth by activating the RAC1-ARF6 axis during insulin signaling 7. Clinically, APBB1 regulates spermatogonial stem cell fate through KAT5/GDF15 interaction, with deleterious mutations associated with male infertility and non-obstructive azoospermia 8. In cancer, APBB1 promotes cancer stem cell properties and epithelial-to-mesenchymal transition via IGF1R/PI3K/AKT signaling in lung cancer 9. APBB1 also serves as an anaplastic lymphoma kinase substrate in neuroblastoma 10. Additionally, APBB1 autoantibodies represent diagnostic markers in anticitrullination protein antibody-negative rheumatoid arthritis 11.