G-quadruplex formation at the 3' end of telomere DNA inhibits its extension by telomerase, polymerase and unwinding by helicase.

Telomere G-quadruplex is emerging as a promising anti-cancer target due to its inhibition to telomerase, an enzyme expressed in more than 85% tumors. Telomerase-mediated telomere extension and some other reactions require a free 3' telomere end in single-stranded form. G-quadruplex formation near the 3' end of telomere DNA can leave a 3' single-stranded tail of various sizes. How these terminal structures affect reactions at telomere end is not clear. In this work, we studied the 3' tail size-dependence of telomere extension by either telomerase or the alternative lengthening of telomere (ALT) mechanism as well as telomere G-quadruplex unwinding. We show that these reactions require a minimal tail of 8, 12 and 6 nt, respectively. Since we have shown that G-quadruplex tends to form at the farthest 3' distal end of telomere DNA leaving a tail of no more than 5 nt, these results imply that G-quadruplex formation may play a role in regulating reactions at the telomere ends and, as a result, serve as effective drug target for intervening telomere function.

Circulating tumor cell methylation profiles reveal the classification and evolution of non-small cell lung cancer.

Background: The ability of circulating tumor cells (CTCs) to identify lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) could improve pathological diagnosis and the selection of treatments for non-small cell lung cancer (NSCLC). Previous studies have shown that deoxyribonucleic acid (DNA) methylation exhibits cell and tissue specificity. Thus, we aimed to explore the methylation status of CTCs in LUAD and LUSC and identify the potential biomarkers. Methods: We first analyzed Infinium 450K methylation profiles obtained from The Cancer Genome Atlas and Gene Expression Omnibus. We then performed whole-genome sequencing of CTCs in tumor and matched normal lung tissues and white blood cells from 6 NSCLC patients. Results: The bioinformatics analysis revealed a NSCLC-specific DNA methylation marker panel, which could accurately distinguish between LUAD and LUSC with high diagnostic accuracy. The whole-genome sequencing of CTCs in NSCLC patients also showed 100% accuracy for distinguishing between LUAD and LUSC based on the CTC methylation profiles. To investigate the function of CTCs, we further analyzed similar and different methylation profiles between the CTCs and their primary tumors, and found very high similarities between the CTCs and their primary tumor tissues, indicating that these cells inherit information from primary tumors. However, the CTCs also displayed some characteristics that differed to those of primary tumor tissues, which suggest that CTCs acquire some unique characteristics after migrating from the primary tumor; these characteristics may partly explain the ability of tumor cells to evade immune surveillance. Conclusions: Our findings provide insights into the potential use of CTCs in the pathological classification of NSCLC patients. Our findings also show how CTC primary tumor inheritance and CTC evolution affect metastasis and immune escape.

Contribution of telomere G-quadruplex stabilization to the inhibition of telomerase-mediated telomere extension by chemical ligands.

Inhibition of telomerase activity through stabilizing telomere G-quadruplex with small chemical ligands is emerging as a novel strategy for cancer therapy. For the large number of ligands that have been reported to inhibit telomerase activity, it is difficult to validate the contribution of G-quadruplex stabilization to the overall inhibition. Using a modified telomere repeat amplification protocol (TRAP) method to differentiate the telomere G-quadruplex independent effect from dependent ones, we analyzed several ligands that have high affinity and/or selectivity to telomere G-quadruplex. Our results show that these ligands effectively inhibited telomerase activity in the absence of telomere G-quadruplex. The expected G-quadruplex-dependent inhibition was only obvious for the cationic ligands at low K(+) concentration, but it dramatically decreased at physiological concentration of K(+). These observations demonstrate that the ligands are much more than G-quadruplex stabilizers with a strong G-quadruplex-irrelevant off-target effect. They inhibit telomerase via multiple pathways in which stabilization of telomere G-quadruplex may only make a minor or neglectable contribution under physiologically relevant conditions depending on the stability of telomere G-quadruplex under ligand-free conditions.

G-quadruplex hinders translocation of BLM helicase on DNA: a real-time fluorescence spectroscopic unwinding study and comparison with duplex substrates.

Sequences with the potential to form G-quadruplex structures are spread throughout genomic DNA. G-quadruplexes in promoter regions can play regulatory roles in gene expression. Expression of protein-encoding genes involves processing of DNA and RNA molecules at the level of transcription and translation, respectively. In order to examine how the G-quadruplex affects processing of nucleic acids, we established a real-time fluorescent assay and studied the unwinding of intramolecular G-quadruplex formed by the human telomere, ILPR and PSMA4 sequences by the BLM helicase. Through comparison with their corresponding duplex substrates, we found that the unwinding of intramolecular G-quadruplex structures was much less efficient than that of the duplexes. This result is in contrast to previous reports that multistranded intermolecular G-quadruplexes are far better substrates for the BLM and other RecQ family helicases. In addition, the unwinding efficiency varied significantly among the G-quadruplex structures, which correlated with the stability of the structures. These facts suggest that G-quadruplex has the capability to modulate the processing of DNA and RNA molecules in a stability-dependent manner and, as a consequence, may provide a mechanism to play regulatory roles in events such as gene expression.

Aneuploidy of chromosome 8 and mutation of circulating tumor cells predict pathologic complete response in the treatment of locally advanced rectal cancer.

Identifying patients who may or may not achieve pathologic complete response (pathCR) allows for treatment with alternative approaches in the preoperative setting. The aim of the current study was to investigate whether aneuploidy of chromosome 8 and mutations of circulating tumor cells (CTCs) could predict the response of patients with rectal cancer to preoperative chemoradiotherapy. A total of 33 patients with locally advanced rectal cancer (cT3-T4 and/or cN+) treated with neoadjuvant chemoradiotherapy between September 2014 and March 2015 were recruited. Blood samples were collected from 33 patients with pre-chemoradiotherapy rectal cancer. It was demonstrated that ≥5 copies of chromosome 8 was associated with pathCR (univariate logistic regression, P=0.042). Of the 6 patients whose CTCs had <5 copies of chromosome 8, 3 achieved pathCR (3/6, 50%), and of the 27 patients whose CTCs had ≥5 copies of chromosome 8 obtained 3 pathCR (3/27, 11.1%; Chi-square test, P=0.0255). Of the 33 patients with mutations assessed, 8 significant nonsynonymous mutations in CTCs were identified as associated with pathCR (Chi-square test, P-values range, 0.0004-0.0298; mutations in ARID1A, HDAC1, APC, ERBB3, TP53, AMER1 and AR). These results suggest that ≥5 copies of chromosome 8 and 8 nonsynonymous mutations in ARID1A, HDAC1, APC, ERBB3, TP53, AMER1 AR in CTCs were associated with pathCR. This conclusion should be validated further in larger prospective studies and the long-term follow-up survival data of this study will also be reported in the future.