Cancer is a DNA disease. DNA can become damaged during DNA replication resulting in the formation of mutations. When these mutations accumulate they can cause diseases, most notably--cancer. Cells have a variety of proteins whose job is to safeguard the genome by finding DNA damage and repairing it. Generally, when these proteins themselves have defects, mutations accumulate in the genome, resulting in cancer. Our work aims to uncover the mechanisms of action for DNA repair proteins. We use combinations of biochemistry, chemistry, molecular biology, and genetics to understand this diverse family of proteins and to uncover new diagnostic approaches and therapeutic targets. Our work also aims to develop new technologies to improve DNA repair proteins used in clinical and biotech applications.
DNA mismatch repair
DNA mismatch repair is a spellchecking mechanism that scans DNA searching for typos which can become mutations. Failures in the mismatch repair proteins are associated with Lynch syndrome. Lynch syndrome is a hereditary cancer syndrome that affects approximately 1 in every 300 individuals although ~95% of people with Lynch syndrome are unaware of their diagnosis. Lynch syndrome results in increased lifetime risk and the potential for early onset of a variety of cancers, including colorectal and endometrial cancer (Lynch, et al., 2015, Nat. Rev. Cancer. 15, 181–194).
Our lab works to understand how the mismatch repair proteins detect and remove DNA typos efficiently and how defects in their mechanisms result in human cancers (Manhart, 2021, Encyclopedia of Biological Chemistry, 3rd edition) (Figure 1). Such a mechanistic understanding paves the way for improved diagnosis and the elucidation of therapeutic targets.
In addition to being critical for DNA spellchecking, mismatch repair is also involved in expanding trinucleotide repeats found in the genome. These expansions are linked to over 30 neurological disorders, including Huntington's disease, in addition to human cancers, and other diseases associated with genome instability. Our work probing the mechanisms of DNA mismatch repair proteins also strives to address their actions in promoting diseases associated with trinucleotide repeat expansions.
Our lab works to understand how the mismatch repair proteins detect and remove DNA typos efficiently and how defects in their mechanisms result in human cancers (Manhart, 2021, Encyclopedia of Biological Chemistry, 3rd edition) (Figure 1). Such a mechanistic understanding paves the way for improved diagnosis and the elucidation of therapeutic targets.
In addition to being critical for DNA spellchecking, mismatch repair is also involved in expanding trinucleotide repeats found in the genome. These expansions are linked to over 30 neurological disorders, including Huntington's disease, in addition to human cancers, and other diseases associated with genome instability. Our work probing the mechanisms of DNA mismatch repair proteins also strives to address their actions in promoting diseases associated with trinucleotide repeat expansions.
Figure 1: (A) Increased lifetime risks for select cancers in individuals with Lynch Syndrome relative to the average population. (B) Overview of the mismatch repair pathway and the functions of the repair proteins. (C) Structure of a DNA mismatch. (D) Structure of the MutL𝛼 heterodimeric protein and the number (N) and positions of missense mutations in human (Hs) MLH1, one of two MutL𝛼 subunits. Adapted from London, et al., PNAS, 2021. The distribution of Lynch syndrome mutations among mismatch repair proteins can be found at: InSIGHT variant database http://www.insight-database.org/.
DNA Recombination
DNA recombination is a specialized form of DNA double strand break repair where the DNA break is repaired using sequence information from homologous DNA (e.g.--the sister chromosome or exogenous DNA). All organisms use DNA recombination as a mechanism of DNA repair. The result of repair by this mechanism can result in the exchange of DNA between DNA fragments. This can be a source of genetic diversity (bacteria can acquire antibiotic resistance by this mechanism) and also a method for genetic engineering.
Most organisms use DNA mismatch repair proteins to mediate DNA recombination. How these proteins function in this pathway using properties and mechanisms that are also used in DNA mismatch is unknown (Manhart and Alani, 2016, DNA Repair. 38, 84-93). Our lab uses biochemistry, chemistry, biophysics, molecular biology, and genetics to understand how DNA recombination works. Our work uncovering these mechanisms can aid in the diagnosis of diseases associated with mis-regulation genetic recombination. Our work also aims to understand an origin of antibiotic resistance in bacteria along with therapeutic targets. We also are interested in adapting DNA repair proteins to improve genetic engineering approaches.
Most organisms use DNA mismatch repair proteins to mediate DNA recombination. How these proteins function in this pathway using properties and mechanisms that are also used in DNA mismatch is unknown (Manhart and Alani, 2016, DNA Repair. 38, 84-93). Our lab uses biochemistry, chemistry, biophysics, molecular biology, and genetics to understand how DNA recombination works. Our work uncovering these mechanisms can aid in the diagnosis of diseases associated with mis-regulation genetic recombination. Our work also aims to understand an origin of antibiotic resistance in bacteria along with therapeutic targets. We also are interested in adapting DNA repair proteins to improve genetic engineering approaches.
Figure 2: Pathways for recombination in eukaryotes and bacteria. (A) Model for Holliday junction DNA intermediate that is recognized by DNA mismatch repair proteins. (B) Pathway for eukaryotic recombination that forms crossover products (genetic exchange). (C) Pathway for prokaryotic recombination to acquire antibiotic resistance.