Case-control analysis of truncating mutations in DNA damage response genes connects TEX15 and FANCD2 with hereditary breast cancer susceptibility.

Several known breast cancer susceptibility genes encode proteins involved in DNA damage response (DDR) and are characterized by rare loss-of-function mutations. However, these explain less than half of the familial cases. To identify novel susceptibility factors, 39 rare truncating mutations, identified in 189 Northern Finnish hereditary breast cancer patients in parallel sequencing of 796 DDR genes, were studied for disease association.

Acetylation limits 53BP1 association with damaged chromatin to promote homologous recombination.

The pathogenic sequelae of BRCA1 mutation in human and mouse cells are mitigated by concomitant deletion of 53BP1, which binds histone H4 dimethylated at Lys20 (H4K20me2) to promote nonhomologous end joining, suggesting that a balance between BRCA1 and 53BP1 regulates DNA double strand-break (DSB) repair mechanism choice. Here we document that acetylation is a key determinant of this balance. TIP60 acetyltransferase deficiency reduced BRCA1 at DSB chromatin with commensurate increases in 53BP1, whereas HDAC inhibition yielded the opposite effect.

Biallelic deleterious BRCA1 mutations in a woman with early-onset ovarian cancer.

Unlabelled: BRCA1 and BRCA2 are the most important breast and ovarian cancer susceptibility genes. Biallelic mutations in BRCA2 can lead to Fanconi anemia and predisposition to cancers, whereas biallelic BRCA1 mutations have not been confirmed, presumably because one wild-type BRCA1 allele is required during embryogenesis. This study describes an individual who was diagnosed with ovarian carcinoma at age 28 and found to have one allele with a deleterious mutation in BRCA1, c.

Alkylation sensitivity screens reveal a conserved cross-species functionome.

To identify genes that contribute to chemotherapy resistance in glioblastoma, we conducted a synthetic lethal screen in a chemotherapy-resistant glioblastoma-derived cell line with the clinical alkylator temozolomide (TMZ) and an siRNA library tailored toward "druggable" targets. Select DNA repair genes in the screen were validated independently, confirming the DNA glycosylases uracil-DNA glycosylase (UNG) and A/G-specific adenine DNA glycosylase (MYH) as well as methylpurine-DNA glycosylase (MPG) to be involved in the response to high dose TMZ. The involvement of UNG and MYH is likely the result of a TMZ-induced burst of reactive oxygen species.

Overcoming temozolomide resistance in glioblastoma via dual inhibition of NAD+ biosynthesis and base excision repair.

Glioblastoma multiforme (GBM) is a devastating brain tumor with poor prognosis and low median survival time. Standard treatment includes radiation and chemotherapy with the DNA alkylating agent temozolomide (TMZ). However, a large percentage of tumors are resistant to the cytotoxic effects of the TMZ-induced DNA lesion O(6)-methylguanine due to elevated expression of the repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) or a defect in the mismatch repair (MMR) pathway.

N-methylpurine DNA glycosylase and DNA polymerase beta modulate BER inhibitor potentiation of glioma cells to temozolomide.

Temozolomide (TMZ) is the preferred chemotherapeutic agent in the treatment of glioma following surgical resection and/or radiation. Resistance to TMZ is attributed to efficient repair and/or tolerance of TMZ-induced DNA lesions. The majority of the TMZ-induced DNA base adducts are repaired by the base excision repair (BER) pathway and therefore modulation of this pathway can enhance drug sensitivity.

Connecting the Dots: Interplay between Ubiquitylation and SUMOylation at DNA Double-Strand Breaks.

Protein modifications, including phosphorylation, ubiquitylation, and SUMOylation, have emerged as essential components of the response to DNA double-strand breaks (DSBs). Mutations within the genes encoding effectors of these components lead to genomic instability and in selected cases, human radiosensitivity and cancer susceptibility syndromes. In this review, we highlight recent advances in the study of DSB-associated signaling events by ubiquitylation and SUMOylation and discuss how coordination among protein modification systems integrates components of the DNA damage response into a network that regulates DNA repair and transcriptional processes on contiguous stretches of chromatin.

Parp1 activation in mouse embryonic fibroblasts promotes Pol beta-dependent cellular hypersensitivity to alkylation damage.

Alkylating agents induce cell death in wild-type (WT) mouse embryonic fibroblasts (MEFs) by multiple mechanisms, including apoptosis, autophagy and necrosis. DNA polymerase beta (Pol beta) knockout (KO) MEFs are hypersensitive to the cytotoxic effect of alkylating agents, as compared to WT MEFs. To test the hypothesis that Parp1 is preferentially activated by methyl methanesulfonate (MMS) exposure of Pol beta KO MEFs, we have examined the relationship between Pol beta expression, Parp1 activation and cell survival following MMS exposure in a series of WT and Pol beta deficient MEF cell lines.

Bioenergetic metabolites regulate base excision repair-dependent cell death in response to DNA damage.

Base excision repair (BER) protein expression is important for resistance to DNA damage-induced cytotoxicity. Conversely, BER imbalance [DNA polymerase beta (Polbeta) deficiency or repair inhibition] enhances cytotoxicity of radiation and chemotherapeutic DNA-damaging agents. Whereas inhibition of critical steps in the BER pathway result in the accumulation of cytotoxic DNA double-strand breaks, we report that DNA damage-induced cytotoxicity due to deficiency in the BER protein Polbeta triggers cell death dependent on poly(ADP-ribose) (PAR) polymerase activation yet independent of PAR-mediated apoptosis-inducing factor nuclear translocation or PAR glycohydrolase, suggesting that cytotoxicity is not from PAR or PAR catabolite signaling.

Human methyl purine DNA glycosylase and DNA polymerase beta expression collectively predict sensitivity to temozolomide.

Overexpression of N-methylpurine DNA glycosylase (MPG) has been suggested as a possible gene therapy approach to sensitize tumor cells to the cell-killing effects of temozolomide, an imidazotetrazine-class chemotherapeutic alkylating agent. In the present study, we show that both elevated MPG expression and short hairpin RNA-mediated loss of DNA polymerase beta (Pol beta) expression in human breast cancer cells increases cellular sensitivity to temozolomide. Resistance to temozolomide is restored by complementation of either wild-type human Pol beta or human Pol beta with an inactivating mutation specific to the polymerase active site yet functional for 5'-deoxyribose-phosphate (5'dRP) lyase activity.

Expression of cyclooxygenase-2 in human esophageal squamous cell carcinomas.

Aim: To determine whether cyclooxygenase-2 (COX-2) was expressed in human esophageal squamous cell carcinoma.

Methods: Quantitative reverse transcription-polymerase chain reaction (RT-PCR), western blotting, immunohistoc-hemistry and immunofluorescence were used to assess the expression level of COX-2 in esophageal tissue.

Results: COX-2 mRNA levels were increased by >80-fold in esophageal squamous cell carcinoma when compared to adjacent noncancerous tissue.