Double-Strand Break Repair

DNA double strand breaks (DSBs) are one of the most dangerous forms of DNA lesions that a cell can encounter. One unrepaired DSB can be lethal. The formation of DSBs has inherently high oncogenic potential because of potential recombination of free DNA ends. These ends, if left un-repaired, can invade surrounding genomic material resulting in chromosomal translocations and eventually genetic rearrangements, leading to cancer. DSBs can be introduced into the genetic material by various means, including  exposure from exogenous agents and chemotherapeutic drugs, such as ionizing radiation and Cisplatin.

Altered metabolism, or loss of specific DNA repair functions, such as found in pre-cancerous cells, can also lead to elevated DSBs. DSBs are also introduced in the cell naturally during the S phase of the cell cycle when DNA synthesis has stalled, and/or by reactions involving reactive oxygen species that are produced during normal cellular metabolism. In special cases, such as in the developing B and T cells in the immune system, DSBs are introduce into the genome as part of normal development. This occurs during V(D)J and Class switch recombination. In general, DSBs are repaired by two separable process: a) non-homologous end joining (NHEJ), or b) homologous recombination (HR).

Relatively recent DNA lesions created after loss of specific factors and formed after DNA damage are DNA:RNA:DNA hybrids, known as R-loops. The carcinogenic effects of persistent R-loops due to loss of specific RNA termination and/or DNA damaging agents have not been realized. We are currently focused on studying the interface of RNA termination factors (Kub5-Hera/RPRD1B, p15RS and XRN2) in both resolving R-loops and mediating HR as well as NHEJ pathways of repairing DSBs. Key factors involved in these pathways include the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), Artemis, XRCC4, DNA Ligase 4, Ku70, and Ku80. We are investigating a novel DNA repair factor, which has been termed Ku70 binding protein 5 (Kub5-Hera) by its intrinsic ability to bind Ku70. We are employing a variety of approaches to study the cellular function of Kub5-Hera in vitro, and we have developed conditional knock-out, and heterozygote (+/-) mouse model systems to study Kub5-Hera (K-H) function in vivo.

 Kub5-Hera is important in cellular processes such as DNA repair, transcription termination, telomere maintenance, cellular senescence, immunological development, and tumor suppression.

Lab members involved in this project include postdoctoral fellows Drs. Edward A. Motea and Praveen Patidar, and former postdoctoral fellows Drs. Julio C. Morales, Farjana Fattah, and Ling Xiao. Dr. Amy Rommel, a former graduate student of this group, is now a senior postdoctoral fellow in Dr. Inder Verma’s lab at Salk Institute of Biological Sciences, La Jolla.

Stained Cells
Immunofluorescence using Kub5 specific antibody reveals a discrete nuclear staining pattern.
L-R: DAPI, FITC, and merged image.