Bypass of a psoralen DNA interstrand cross-link by DNA polymerases ß, ι, and κ in vitro.

Repair of DNA interstrand cross-links in mammalian cells involves several biochemically distinctive processes, including the release of one of the cross-linked strands and translesion DNA synthesis (TLS). In this report, we investigated the in vitro TLS activity of a psoralen DNA interstrand cross-link by three DNA repair polymerases, DNA polymerases ß, κ, and ι. DNA polymerase ß is capable of bypassing a psoralen cross-link with a low efficiency. Cell extracts prepared from DNA polymerase ß knockout mouse embryonic fibroblasts showed a reduced bypass activity of the psoralen cross-link, and purified DNA polymerase ß restored the bypass activity. In addition, DNA polymerase ι misincorporated thymine across the psoralen cross-link and DNA polymerase κ extended these mispaired primer ends, suggesting that DNA polymerase ι may serve as an inserter and DNA polymerase κ may play a role as an extender in the repair of psoralen DNA interstrand cross-links. The results demonstrated here indicate that multiple DNA polymerases could participate in TLS steps in mammalian DNA interstrand cross-link repair.

Multiple spontaneous cerebrospinal fluid leaks: a rare case report and review of literature.

While a spontaneous cerebrospinal fluid leak (sCSFL) is a rare phenomenon, patients who present with multiple cerebrospinal fluid leaks (mCSFLs) are an even rarer entity. There have been documented cases reported over the last decades, but many with only limited descriptions of each patient. We present a mCSFL patient as a case report and demonstrate the need for future prospective studies to improve further understanding and management of the condition. This is explored through summarizing the literature on mCSFLs to the present time. A 45-year-old obese female presented with a 5-week history of bilateral clear nasal discharge with no previous surgery or trauma. Initially misdiagnosed as allergic rhinitis, nasal discharge was later confirmed positive for beta-2-transferrin and a CT scan revealed multiple bony areas of skull base erosion. The patient underwent image guided endoscopic sinus surgery with multilayer skull base defect repair of three active CSFLs. Three months post-operatively the patient had no evidence of a recurrence. As mCSFL tend to be sporadic and asymptomatic in nature, it is likely they are underreported. Future prospective studies in the area of mCSFLs that take into consideration demographic and geographical information are needed for more accurate interpretation and better recruitment. Additionally, studies need to ensure longer follow-up time due to the underlying chronicity of increased intracranial pressure (ICP) and investigate whether or not a non-active leak site should be repaired or left alone.

Removal of reactive oxygen species-induced 3'-blocked ends by XPF-ERCC1.

XPF-ERCC1 is a structure-specific endonuclease that is essential for nucleotide excision repair and DNA interstrand cross-link repair in mammalian cells. The yeast counterpart of XPF-ERCC1, Rad1-Rad10, plays multiple roles in DNA repair. Rad1-Rad10 is implicated to be involved in the repair of oxidative DNA damage. To explore the role(s) of XPF-ERCC1 in the repair of DNA damage induced by reactive oxygen species (ROS), cellular sensitivity of the XPF-deficient Chinese hamster ovary cell line UV41 to ROS was investigated. The XPF-deficient UV41 showed sensitivity to hydrogen peroxide, bleomycin, and paraquat. Furthermore, XPF-ERCC1 showed an ability to remove 3'-blocked ends such as 3'-phosphoglycolate from the 3'-end of DNA in vitro. These data suggest that XPF-ERCC1 plays a role in the repair of ROS-induced DNA damage by trimming 3'-blocked ends. The accumulation of various types of DNA damage, including ROS-induced DNA damage due to defects in multiple XPF-ERCC1-mediated DNA repair pathways, could contribute to the accelerated aging phenotypes observed in an XPF-ERCC1-deficient patient.