Identification of DBC1 as a transcriptional repressor for BRCA1

Background: DBC1/KIAA1967 (deleted in breast Cancer 1) is a putative tumour-suppressor gene cloned from a heterozygously deleted region in breast Cancer specimens. Caspase-dependent processing of DBC1 promotes Apoptosis, and depletion of endogenous DBC1 negatively regulates p53-dependent Apoptosis through its specific inhibition of SIRT1. Hereditary breast and ovarian Cancer susceptibility gene product BRCA1, by binding to the promoter region of SIRT1, is a positive regulator of SIRT1 expression.

Methods: A physical interaction between DBC1 and BRCA1 was investigated both in vivo and in vitro. To determine the pathophysiological significance of DBC1, its role as a transcriptional factor was studied.

Results: We found a physical interaction between the amino terminus of DBC1 and the carboxyl terminus of BRCA1, also known as the BRCT domain. Endogenous DBC1 and BRCA1 form a complex in the nucleus of intact cells, which is exported to the cytoplasm during ultraviolet-induced Apoptosis. We also showed that the expression of DBC1 represses the transcriptional activation function of BRCT by a transient expression assay. The expression of DBC1 also inhibits the transactivation of the SIRT1 promoter mediated by full-length BRCA1.

Conclusion: These results revealed that DBC1 may modulate the cellular functions of BRCA1 and have important implications in the understanding of carcinogenesis in breast tissue.