The research interests in my laboratory are in the field of DNA damage and repair, particularly the repair of novel and/or biologically important DNA adducts by the base excision repair (BER) pathway, and the implications in environmental carcinogenesis and epigenetic mechanisms.
Our primary research over more than a decade, including the long-term collaboration with Dr. B. Singer at LBNL, has been focused on combining chemical, biochemical and biological approaches to understand the key questions in environmental mutagenesis and carcinogenesis. The chemical compounds selected for such purposes are all able to react with DNA to modify bases. The focus of our studies is on testing new bulky DNA base lesions, particularly the exocyclic DNA adducts that are a group of base modifications with similar chemical structures, for their effects on DNA local structure as well as cellular processes, mainly DNA repair and translesion synthesis (TLS). We have developed in vitro assay systems based on chemical synthesis of many defined oligonucleotides containing a site-directed adduct, combined with the use of gene knockout cells/animals, site-directed mutagenesis and molecular modeling. These studies have led to mutagenic/structural characterization of selected adducts and identification of novel substrates/mechanisms for various repair enzymes. These findings enhance our understanding of how specific DNA adducts would be repaired in vitro (immediate goals) and in vivo (long-term goals) and how repair enzymes and DNA polymerases would interact with adducted DNA at the molecular level.
One of our new projects is on the genotoxicity of chemical compounds identified from thirdhand smoke (THS), a new type of cigarette hazard that has received public attention recently (New York Times 2009, JNCI 2010 see here). THS contains residual tobacco smoke compounds that remain on surfaces and in dust after tobacco has been smoked; or are re-emitted back into the gas phase; or react with oxidants and other compounds in the environment to produce secondary toxicants (Matt et al., EHP, 2011). THS may adversely affect human health; a particularly vulnerable population could be small children who may get exposed to THS toxicants through inhalation, ingestion and dermal contact. Our primary task is to investigate the formation of DNA adducts using HPLC/MS/MS following in vitro and in vivo experiments with THS samples or individual chemical compounds identified from THS. This project is being supported by UC/TRDRP through an Innovative Developmental and Exploratory Award and the Consortium of Thirdhand Tobacco Smoke Exposure and Public Health Risk Assessment (see here).
A new direction in my laboratory is exploring the involvement of the BER pathway in epigenetic regulatory mechanisms, specifically the active DNA demethylation in mammalian cells. This is an exciting time for research in this area, since there are many unsolved and crucial questions related to this process that could well be linked to pathogenesis of known human diseases. Through studies on gene/protein expression and protein-protein interactions, we are interested in determining whether TDG-mediated BER is an important mechanism in active demethylation at promoters of certain human genes, such as the FMR1 gene, through its interaction with specific protein(s) that can target or stimulate TDG to the site. Ultimately we hope to understand how its activity and targeting are regulated normally and how they become dysfunctional in those “epigenetic diseases” associated with aberrant gene silencing by DNA methylation, such as the Fragile X syndrome and in cancer.
Matt, GE, Quintana, PJE, Destaillats, H, Gundel, LA, Mohamad, S, Singer, BC, Jacob III, J, Benowitz, N, Winickoff, JP, Rehan, V, Talbot, P, Schick, S, Samet, J, Wang, Y, Hang, B, Martins-Green, M, and Hovell, MF. Thirdhand tobacco smoke: Emerging evidence and arguments for a multidisciplinary research agenda. Environ Health Perspect., May 31 (2011). In the News (sign in required).
Hang, B. Formation and Repair of tobacco carcinogen-derived bulky DNA adducts. J. of Nucleic Acids, Special issue: DNA Damage, Mutagenesis, and DNA Repair, Editors: Basu, A., Broyde, S., Iwai, S., and Kisker, C, Dec. 20 (2010).
Rodriguez, B, Yang, Y, Guliaev, AB, Chenna, A. and Hang, B. Benzene-derived N2-(4-hydroxyphenyl)-deoxyguanosine adduct: UvrABC nuclease incision and its conformation in DNA. Toxicol Lett. 193, 26-32 (2010).
Chenna, A., Gupta, R., Bonala, R., Johnson, F. and Hang, B. Synthesis of the fully protected phosphoramidite of the benzene-DNA adduct, N2-(4-hydroxyphenyl)-2'-doxyguanosine and incorporation of the later into DNA oligomers. Nucleosides, Nucleotides & Nucleic Acids, 27, 979-91 (2008).
Hang, B. and Guliaev, AB. Substrate specificity of human thymine-DNA glycosylase on exocyclic cytosine adducts. Chem Biol Interact., 165, 230-8 (2007).
Wang, P., Guliaev, AB. and Hang, B. Metal inhibition of human N-methylpurine-DNA glycosylase activity in base excision repair. Toxicol Lett., 166, 237-47 (2006).
Wang, P., Guliaev, AB., Elder, RH. and Hang, B. Alkylpurine-DNA-N-glycosylase excision of 7-(hydroxymethyl)-1,N6-ethenoadenine, a glycidaldehyde-derived DNA adduct. DNA Repair, 5, 23-31 (2006).
Xie, Z., Zhang, Y., Guliaev, AB., Shen, H., Hang, B., Singer, B. and Wang, Z. The p-benzoquinone DNA adducts derived from benzene are highly mutagenic. DNA Repair, 8, 1399-409 (2005).
Hang, B. Repair of exocyclic DNA adducts: rings of complexity. BioEssays, 26, 1195-208 (2004).
Guliaev, AB., Singer, B. and Hang, B. Chloroethylnitrosoureas-derived ethano adenine and cytosine adducts are substrates for E. coli glycosylases excising analogous etheno adducts. DNA Repair, 3, 1195-208 (2004).
Guliaev, AB., Hang, B. and Singer, B. Structural insights by molecular dynamics simulations into specificity of the major human AP endonuclease toward the benzene-derived DNA adduct, pBQ-C. Nucleic Acids Res., 32, 2844-52 (2004).
Hang, B, Chenna, A, Guliaev, AB, and Singer, B. Miscoding properties of 1,N6-ethanoadenine, a DNA adduct derived from reaction with the antitumor agent 1,3-bis(2-chloroethyl)-1-nitrosourea. Mutat Res., 531(1-2),191-203 (2003).
Hang, B., Downing, G., Guliaev, AB. and Singer, B. Novel activity of Escherichia coli mismatch uracil glycosylase (MUG) excising 8-(hydroxymethyl)-3,N4-ethenocytosine, a potential product resulting from glycidaldehyde reaction. Biochemistry, 41, 2158-65 (2002).
Singer, B., Medina, M., Wang, Z., Guliaev, AB. and Hang, B. 8-(hydroxymethyl) 3,N4-etheno-dC, a potential carcinogenic glycidaldehyde product, miscodes in vitro using mammalian polymerases. Biochemistry, 41, 1778-85 (2002).
Guliaev, AB., Hang, B. and Singer, B. Structural insights by molecular dynamics simulations into differential repair efficiency for ethano-A vs. etheno-A adducts by the human alkylpurine-DNA-N-glycosylase (APNG). Nucleic Acids Res., 30, 3778-87 (2002).
Singer, B. and Hang, B. Commentary: Nucleic acid sequence and repair: role of adduct, neighbor bases and enzyme specificity. Carcinogenesis, 21, 1071-8 (2000).
Hang, B., Medina, M., Fraenkel-Conrat, H. and Singer, B. A 55-kDa protein isolated from human cells shows DNA glycosylase activity toward 3,N4-ethenocytosine and the G/T mismatch. Proc. Natl. Acad. Sci. USA, 95, 13561-6 (1998).
Hang, B., Singer, B., Margison, GP. and Elder, RH. Targeted deletion of alkylpurine-DNA-N-glycosylase in mice eliminate repair of 1,N6-ethenoadenine and hypoxanthine but not of 3,N4-ethenocytosine or 8-oxoguanine. Proc. Natl. Acad. Sci. USA, 94, 12869-74 (1997).
Singer, B. and Hang, B. Perspective: What structural features determine repair enzyme specificity and mechanism in chemically modified DNA? Chem. Res. Toxicol., 10, 713-32 (1997).
Hang, B., Chenna, A., Fraenkel-Conrat, H. and Singer, B. An unusual mechanism for the major human AP endonuclease involving 5' cleavage of DNA containing a benzene-derived exocyclic adduct in the absence of an AP site. Proc. Natl. Acad. Sci. USA, 93, 13737-41 (1996).