DBC1 Regulates p53 Stability via Inhibition of CBP-Dependent p53 Polyubiquitination

Summary: The control of p53 protein stability is critical to its tumor suppressor functions. The CREB binding protein (CBP) transcriptional co-activator co-operates with MDM2 to maintain normally low physiological p53 levels in cells via exclusively cytoplasmic E4 polyubiquitination activity. Using mass spectrometry to identify nuclear and cytoplasmic CBP-interacting proteins that regulate compartmentalized CBP E4 activity, we identified deleted in breast cancer 1 (DBC1) as a stoichiometric CBP-interacting protein that negatively regulates CBP-dependent p53 polyubiquitination, stabilizes p53, and augments p53-dependent apoptosis. TCGA analysis demonstrated that solid tumors often retain wild-type p53 alleles in conjunction with DBC1 loss, supporting the hypothesis that DBC1 is selected for disruption during carcinogenesis as a surrogate for p53 functional loss. Because DBC1 maintains p53 stability in the nucleus, where p53 exerts its tumor-suppressive transcriptional function, replacement of DBC1 functionality in DBC1-deleted tumors might enhance p53 function and chemosensitivity for therapeutic benefit. : Akande et al. describe DBC1 as a negative regulator of CBP p53-directed ubiquitin ligase activity that maintains nuclear p53 stability. DBC1 loss may be selected in tumors to inactivate the p53 pathway. Because expression of DBC1 enhances p53-dependent apoptosis, restoration of DBC1 in null tumors may be of therapeutic value. Keywords: apoptosis, CBP, DBC1, p53, ubiquiti