Alternative titles; symbols
HGNC Approved Gene Symbol: CCAR2
Cytogenetic location: 8p21.3 Genomic coordinates (GRCh38) : 8:22,604,757-22,621,514 (from NCBI)
CCAR2, or DBC1, regulates the deacetylase SIRT1 (604479) (Kim et al., 2008; Zhao et al., 2008). It is also a subunit of a protein complex that regulates alternative mRNA splicing (Close et al., 2012).
By randomly sequencing clones obtained from a fetal brain cDNA library, Nagase et al. (2001) cloned CCAR2, which they called KIAA1967. The deduced protein contains 818 amino acids. RT-PCR followed by ELISA revealed moderate expression in all tissues and brain regions tested, with highest expression in liver.
Hamaguchi et al. (2002) identified DBC1 near a region of chromosome 8p21 that is deleted in breast cancers (114480). RT-PCR revealed expression of DBC1 in all normal breast, lung, placenta, and brain tissue samples tested, and in 84 to 100% of neoplastic breast, lung, colon, and other tissues tested.
By genomic sequence analysis, Hamaguchi et al. (2002) mapped the CCAR2 gene to chromosome 8p21.
Kim et al. (2008) demonstrated that DBC1, initially cloned from a region on chromosome 8p21 homozygously deleted in breast cancers, forms a stable complex with SIRT1 (604479). DBC1 directly interacted with SIRT1 and inhibited SIRT1 activity in vitro and in vivo. Downregulation of DBC1 expression potentiated SIRT1-dependent inhibition of apoptosis induced by genotoxic stress.
Zhao et al. (2008) independently showed that DBC1 acts as a native inhibitor of SIRT1 in human cells. DCB1-mediated repression of SIRT1 led to increasing levels of p53 (191170) acetylation and upregulation of p53-mediated function. In contrast, depletion of endogenous DBC1 by RNA interference (RNAi) stimulated SIRT1-mediated deacetylation of p53 and inhibited p53-dependent apoptosis. Notably, these effects could be reversed in cells by concomitant knockdown of endogenous SIRT1. Zhao et al. (2008) concluded that DBC1 promotes p53-mediated apoptosis through specific inhibition of SIRT1.
Close et al. (2012) identified ZIRD (ZNF326; 614601) and DBC1 as subunits of an approximately 800-kD protein complex that they named the ZIRD-DBC1 (DBIRD) complex. Coimmunoprecipitation analysis of transfected HEK293 cells revealed that ZIRD and DBC1 interacted directly. The 2 proteins also interacted directly with RNA polymerase II (see POLR2A; 180660) and with mRNPs, although the interaction with mRNPs depended upon the presence of RNA. Depletion of ZIRD via RNAi led to increased exon inclusion in more than 2,800 cases, whereas exon exclusion was observed in only 390 cases. Depletion of DBC1 led to exon inclusion in 796 cases, most of which were also observed following ZIRD depletion. The effect of ZIRD or DBC1 depletion occurred at the level of alternative splicing. RNA immunoprecipitation analysis confirmed that the DBIRD complex bound to relevant exons in mRNAs from 7 tested genes. The exons affected by DBIRD tended to be AT rich. Depletion of either DBC1 or ZIRD slowed the rate of transcript elongation and RNA polymerase II density. Close et al. (2012) concluded that the DBIRD complex affects the efficiency of splicing, possibly by facilitating transcript elongation across AT-rich regions and favoring exon inclusion.
The DBC1 protein contains a Nudix hydrolase (600312) homology domain (NHD) that lacks catalytic activity due to the absence of key catalytic residues (Anantharaman and Aravind, 2008). Li et al. (2017) showed that NHDs are NAD+ (oxidized nicotinamide adenine dinucleotide)-binding domains that regulate protein-protein interactions. Immunoprecipitation assays in HEK293T cells demonstrated binding of DBC1 and PARP1 (173870), a critical DNA repair protein, that was independent of PARP1 catalytic activity. PARP1 activity was inhibited by DBC1 in vitro. Binding of NAD+ to the NHD domain of DBC1 prevented it from inhibiting PARP1. Li et al. (2017) found that as mice aged and NAD+ concentrations declined, DBC1 was increasingly bound to PARP1, causing DNA damage to accumulate, a process rapidly reversed by restoring the abundance of NAD+. The authors concluded that NAD+ directly regulates protein-protein interactions, the modulation of which may protect against cancer, radiation, and aging.
Anantharaman, V., Aravind, L. Analysis of DBC1 and its homologs suggests a potential mechanism for regulation of sirtuin domain deacetylases by NAD metabolites. Cell Cycle 7: 1467-1472, 2008. [PubMed: 18418069] [Full Text: https://doi.org/10.4161/cc.7.10.5883]
Close, P., East, P., Dirac-Svejstrup, A. B., Hartmann, H., Heron, M., Maslen, S., Chariot, A., Soding, J., Skehel, M., Svejstrup, J. Q. DBIRD complex integrates alternative mRNA splicing with RNA polymerase II transcript elongation. Nature 484: 386-389, 2012. [PubMed: 22446626] [Full Text: https://doi.org/10.1038/nature10925]
Hamaguchi, M., Meth, J. L., von Klitzing, C., Wei, W., Esposito, D., Rodgers, L., Walsh, T., Welcsh, P., King, M.-C., Wigler, M. H. DBC2, a candidate for a tumor suppressor gene involved in breast cancer. Proc. Nat. Acad. Sci. 99: 13647-13652, 2002. [PubMed: 12370419] [Full Text: https://doi.org/10.1073/pnas.212516099]
Kim, J.-E., Chen, J., Lou, Z. DBC1 is a negative regulator of SIRT1. Nature 451: 583-586, 2008. [PubMed: 18235501] [Full Text: https://doi.org/10.1038/nature06500]
Li, J., Bonkowski, M. S., Moniot, S., Zhang, D., Hubbard, B. P., Ling, A. J. Y., Rajman, L. A., Qin, B., Lou, Z., Gorbunova, V., Aravind, L., Steegborn, C., Sinclair, D. A. A conserved NAD+ binding pocket that regulates protein-protein interactions during aging. Science 355: 1312-1317, 2017. [PubMed: 28336669] [Full Text: https://doi.org/10.1126/science.aad8242]
Nagase, T., Kikuno, R., Ohara, O. Prediction of the coding sequences of unidentified human genes. XXII. The complete sequences of 50 new cDNA clones which code for large proteins. DNA Res. 8: 319-327, 2001. [PubMed: 11853319] [Full Text: https://doi.org/10.1093/dnares/8.6.319]
Zhao, W., Kruse, J.-P., Tang, Y., Jung, S. Y., Qin, J., Gu, W. Negative regulation of the deacetylase SIRT1 by DBC1. Nature 451: 587-590, 2008. [PubMed: 18235502] [Full Text: https://doi.org/10.1038/nature06515]