DNA damage response and repair in lymphocyte development and cancer
DNA is the ultimate carrier for genetic information. Cancer is a genetic disease driven by changes in DNA. We are interested in how cells sense DNA damage and mount efficient and precise repair pathways to fix the damages. Lymphocytes face a daunting task to rearrange their genome to generate diverse antigen receptor genes all while maintaining genomic instability. We use lymphocyte development as a model system to understand the DNA repair pathway and the lens of DNA repair to understand the mechanism of immunodeficiency and lymphomagenesis. We use mouse models, as well as cell biology and genomic tools.
DNA Damage response
DNA double-strand break activates a cascade of signaling events led by three PI3 kinase-like protein kinases: ATM, ATR, and DNA-PK, along with the help of PARP1 and PARP2. We generated and characterized mouse models expressing catalytic inactivated forms of ATM, ATR, DNA-PKcs as well as PARP1 and PARP2. Characterization of these animal models revealed that the catalysis is coupled with the recruitment and releases of the kinases and PARP. This revealed a structural function of the kinases/PARPs at the DNA damage sites that shows that kinase/PARP inhibition is not the same as loss of kinases and PARP. This has implications in specific inhibitors used for cancer therapy.
Non-homologous end joining
The non-homologous end-joining (NHEJ) pathway is one of the two main DNA double-strand break repair pathways in mammalian cells and is the main pathway responsible for lymphocyte-specific gene-rearrangements during both V(D)J recombination and Ig class switch recombination. Using lymphocyte development as a model system, we have characterized novel NHEJ factors and illustrated the functional interaction between different NHEJ factors.
V(D)J recombination and Class switch recombination
Developing lymphocytes somatically assemble into functional TCR and Ig genes through V(D)J recombination. B cells further modify the IgH locus through Ig Class switch recombination (CSR). Both V(D)J recombination and CSR are initiated by lymphocyte-specific mechanisms, but the resulted DNA double-strand breaks activate DNA damage response and require the NHEJ pathway for repair. Mis-repair of DNA double-strand breaks during V(D)J or CSR leads to chromosomal translocations that are characteristic for human lymphomas and leukemia.
rDNA instability and rRNA processing
The ribosomal DNA loci encode the 5.8s, 18s, and 28s rRNA and are responsible for >70% of cellular transcription. We use cytogenetics and genomic tools to understand rDNA repair and rDNA instability upon DNA damage. We are interested in how rDNA responds to genotoxic anti-cancer therapy and how rDNA instability contributes to aging and myeloid dysplasia.
Mechanism of chromosomal translocations
Structural variation in the genome drives malignant transformation. We are interested in the mechanism of chromosomal translocations and the factors that influence the frequency and the types of chromosomal translocations in human cancers.
Techniques and Tools
We generated over 30 novel genetically engineered mouse models and have over 65 active alleles in breeding covering a broad range of DNA repair deficiencies
We developed novel cytogenetic tools to analyze chromosomal rearrangements including the repetitive elements - telomere and rDNA. We provided them as a service through the HICCC molecular cytogenetic shared resource.
We are always looking forward to developing new tools and techniques to address pending questions. If you have an idea, let us talk about it!! Maybe we could help.