Nucleotide excision repair in Human cell lines lacking both XPC and CSB proteins.

Nucleotide excision repair removes UV-induced DNA damage through two distinct sub-pathways, global repair and transcription-coupled repair (TCR). Numerous studies have shown that in human and other mammalian cell lines that the XPC protein is required for repair of DNA damage from nontranscribed DNA via global repair and the CSB protein is required for repair of lesions from transcribed DNA via TCR. Therefore, it is generally assumed that abrogating both sub-pathways with an XPC-/-/CSB-/- double mutant would eliminate all nucleotide excision repair. Here we describe the construction of three different XPC-/-/CSB-/- human cell lines that, contrary to expectations, perform TCR. The XPC and CSB genes were mutated in cell lines derived from Xeroderma Pigmentosum patients as well as from normal human fibroblasts and repair was analyzed at the whole genome level using the very sensitive XR-seq method. As predicted, XPC-/- cells exhibited only TCR and CSB-/- cells exhibited only global repair. However, the XPC-/-/CSB-/- double mutant cell lines, although having greatly reduced repair, exhibited TCR. Mutating the CSA gene to generate a triple mutant XPC-/-/CSB-/-/CSA-/- cell line eliminated all residual TCR activity. Together, these findings provide new insights into the mechanistic features of mammalian nucleotide excision repair.

Investigation of the DNMT3B -579 G>T Promoter Polymorphism in Patients with Colorectal Cancer in an Azerbaijani Population.

OBJECTIVE: The main aim of the present study was to determine the clinical significance of the DNA methyltransferase 3B (DNMT3B) gene -579 G>T polymorphism in colorectal cancer (CRC) patients. METHODS: A total of 140 patients with CRC and 164 healthy individuals were included in the study. According to the manufacturer's instructions, DNA was isolated from blood, and genotypes were determined on agarose gel by the PCR-RFLP method. Genotype confirmation was performed using Sanger sequencing in randomly selected samples. RESULTS: When comparing the case and control groups, heterozygous GT (OR=0.53; 95% CI=0.32-0.88), under the dominant model (OR=0.53; 95% CI=0.33-0.87), and the mutant T allele (OR=0.71; 95% CI=0.51-0.98) were statistically associated with a reduced risk of CRC. However, when the age, pathological tumor grade and stage, smoking habit, and alcohol consumption were compared, no significant relationship was determined (P>0.05). Furthermore, among males, heterozygous GT was associated with a reduced risk of CRC (OR=0.40; 95% CI=0.19-0.84). CONCLUSION: Our study highlighted that the -579 G>T polymorphism of the DNMT3B gene plays a protective role against CRC development.

Circadian regulation of c-MYC in mice.

The circadian clock is a global regulatory mechanism that controls the expression of 50 to 80% of transcripts in mammals. Some of the genes controlled by the circadian clock are oncogenes or tumor suppressors. Among these Myc has been the focus of several studies which have investigated the effect of clock genes and proteins on Myc transcription and MYC protein stability. Other studies have focused on effects of Myc mutation or overproduction on the circadian clock in comparison to their effects on cell cycle progression and tumorigenesis. Here we have used mice with mutations in the essential clock genes Bmal1, Cry1, and Cry2 to gain further insight into the effect of the circadian clock on this important oncogene/oncoprotein and tumorigenesis. We find that mutation of both Cry1 and Cry2, which abolishes the negative arm of the clock transcription-translation feedback loop (TTFL), causes down-regulation of c-MYC, and mutation of Bmal1, which abolishes the positive arm of TTFL, causes up-regulation of the c-MYC protein level in mouse spleen. These findings must be taken into account in models of the clock disruption-cancer connection.