The Xpc gene markedly affects cell survival in mouse bone marrow
ABSTRACT The XPC protein (encoded by the xeroderma pigmentosum Xpc gene) is a key DNA damage recognition factor that is required for global genomic nucleotide excision repair (G-NER). In contrast to transcription-coupled nucleotide excision repair (TC-NER), XPC and G-NER have been reported to contribute only modestly to cell survival after DNA damage. Previous studies were conducted using fibroblasts of human or mouse origin. Since the advent of Xpc-/- mice, no study has focused on the bone marrow of these mice. We used carboplatin to induce DNA damage in Xpc-/- and strain-matched wild-type mice. Using several independent methods, Xpc-/- bone marrow was approximately 10-fold more sensitive to carboplatin than the wild type. Importantly, 12/20 Xpc-/- mice died while 0/20 wild-type mice died. We conclude that G-NER, and XPC specifically, can contribute substantially to cell survival. The data are important in the context of cancer chemotherapy, where Xpc gene status and G-NER may be determinants of response to DNA-damaging agents including carboplatin. Additionally, altered cell cycles and altered DNA damage signalling may contribute to the cell survival end point.
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ABSTRACT: DNA is subject to various types of damage that can impair cellular function or cause cell death. DNA damage blocks normal cellular processes such as replication and transcription and can have catastrophic consequences for the cell and for the organism. It has long been thought that the G1/S cell cycle checkpoint allows time for DNA repair by delaying S-phase entry. The p53 tumor suppressor pathway regulates the G1/S checkpoint by regulating the cyclin-dependent kinase inhibitor p21Waf1/Cip1, but p53 also regulates the nucleotide excision DNA repair protein XPC. Here, using p53-null cell lines we show that additional mechanisms stabilize XPC protein and promote NER in concert with the G1/S checkpoint. At least one mechanism to stabilize and destabilize XPC involves ubiquitin-mediated degradation of XPC, as the ubiquitin ligase inhibitor MG-132 blocked XPC degradation. The retinoblastoma protein, RB, in its unphosphorylated form actually stabilized XPC and promoted NER as measured by host-cell reactivation experiments. The data suggest that XPC protein and XPC-mediated NER is tightly linked to the G1/S checkpoint even in cells lacking functional p53. Indiana University-Purdue University Indianapolis (IUPUI)
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ABSTRACT: Reactive oxygen species (ROS) can be generated by defective endogenous reduction of oxygen by cellular enzymes or in the mitochondrial respiratory pathway, as well as by exogenous exposure to UV or environmental damaging agents. Regulation of intracellular ROS levels is critical since increases above normal concentrations lead to oxidative stress and DNA damage. A growing body of evidence indicates that the inability to regulate high levels of ROS leading to alteration of cellular homeostasis or defective repair of ROS-induced damage lies at the root of diseases characterized by both neurodegeneration and bone marrow failure as well as cancer. That these diseases may be reflective of the dynamic ability of cells to respond to ROS through developmental stages and aging lies in the similarities between phenotypes at the cellular level. This review summarizes work linking the ability to regulate intracellular ROS to the hematopoietic stem cell phenotype, aging, and disease.International Journal of Molecular Sciences 01/2015; 16(2):2366-2385. DOI:10.3390/ijms16022366 · 2.34 Impact Factor
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ABSTRACT: About 15 years ago, several groups including ours had used matched pairs of cell lines carrying wild type or mutant p53 genes to ascertain a role for p53 in cell survival. These were isogenic cell lines differing only by p53 status. The trend at that time was to support p53-mediated apoptosis. Accordingly, p53-wildtype cells were sensitive to DNA damage compared to p53-mutant cells which were thought to evade apoptosis. However, this finding was not universal. In particular, after UV-radiation, p53-mutant cells were more sensitive than their wild type p53 counterparts in several studies. The finding that p53 controlled a major DNA repair pathway, nucleotide excision repair (NER) which repairs UV-damage, provided a mechanism for the observations. We coined the term "the two faces of tumor suppressor p53" to illustrate that p53 can on one hand induce apoptosis leading to cell sensitivity, but p53 can also enhance the rate of DNA repair thereby protecting cells from DNA damage. This concept has gained acceptance and has been expanded to other DNA-damaging agents. New insights into how p53 is "switched" from a protective function to an apoptotic function are reviewed.Molecular and Cellular Pharmacology 01/2010; 2(3):117-119.