DNA damage checkpoint, damage repair, and genome stability

Long non-coding RNA SPRY4-IT1 promotes proliferation and metastasis in nasopharyngeal carcinoma cell

Background

Long non-coding RNA SPRY4 intronic transcript 1 (Lnc RNA SPRY4-IT1) was aberrant-expressed in various kinds of cancer. Increasing evidence demonstrated that lnc RNAs involved in tumorigenesis and metastasis. In this study, we aimed to explore the biological role of SPRY4-IT1 on the phenotype of nasopharyngeal carcinoma (NPC) in vitro and in vivo.

Methods

The expression level of SPRY4-IT1 in NPC cell lines were measured by quantitative real-time polymerase chain reaction (qRT-PCR). Cell Counting Kit-8 (CCK-8) and colony formation assay were used to detect cell proliferation. Wound-healing assay, transwell assay and animal experiment were performed to evaluate the ability of cell migration and metastasis. Cell cycle distribution and apoptosis were determined by flow cytometry. Western blotting and immunofluorescence were employed to identify protein expression.

Results

SPRY4-IT1 was significantly up-regulated in several NPC cell lines (6-10B, CNE-2, and HONE-1) compared with human immortalized nasopharyngeal epithelial cell (NP69). Silencing of SPRY4-IT1 inhibited proliferation, migration, and metastasis, and induced significant G2/M phase arrest and apoptosis. Western blotting showed that the expression levels of cell cycle-related proteins (cyclin B1, cdc2 and p-cdc2) were down-regulated and apoptosis-associated proteins (PARP, cleaved PARP and cleaved caspase-3) were up-regulated after knockdown of SPRY4-IT1. The expression level of E-cadherin was increased and the expression of Vimentin, Snail and Twist1 were decreased after the SPRY4-IT1 knockdown.

Conclusion

lncRNA SPRY4-IT1 played a significant role in NPC proliferation, migration and metastasis, suggesting that SPRY4-IT1 might be a potential therapeutic target for the treatment of NPC.

Programmed Cell Death Alterations Mediated by Synthetic Indole Chalcone Resulted in Cell Cycle Arrest, DNA Damage, Apoptosis and Signaling Pathway Modulations in Breast Cancer Model

Although new chemotherapy significantly increased the survival of breast cancer (BC) patients, the use of these drugs is often associated with serious toxicity. The discovery of novel anticancer agents for BC therapy is expected. This study was conducted to explore the antiproliferative effect of newly synthesized indole chalcone derivative ZK-CH-11d on human BC cell lines. MTT screening, flow cytometry, Western blot, and fluorescence microscopy were used to evaluate the mode of cell death. ZK-CH-11d significantly suppressed the proliferation of BC cells with minimal effect against non-cancer cells. This effect was associated with cell cycle arrest at the G2/M phase and apoptosis induction. Apoptosis was associated with cytochrome c release, increased activity of caspase 3 and caspase 7, PARP cleavage, reduced mitochondrial membrane potential, and activation of the DNA damage response system. Furthermore, our study demonstrated that ZK-CH-11d increased the AMPK phosphorylation with simultaneous inhibition of the PI3K/Akt/mTOR pathway indicating autophagy initiation. However, chloroquine, an autophagy inhibitor, significantly potentiated the cytotoxic effect of ZK-CH-11d in MDA-MB-231 cells indicating that autophagy is not principally involved in the antiproliferative effect of ZK-CH-11d. Taking together the results from our experiments, we assume that autophagy was activated as a defense mechanism in treated cells trying to escape from chalcone-induced harmful effects.

Expression and Clinical Significance of ERCC1 and XPF in Human Hepatocellular Carcinoma

Objective

To investigate the correlation between the ERCC1 and XPF expression and the clinicopathological parameters of hepatocellular carcinoma (HCC) patients through assessment of the expression of the DNA repair genes ERCC1 and XPF.

Methods

ERCC1 and XPF mRNA expression in HCC (n= 177) and adjacent para-cancer tissues (n=21) were assessed by RT-PCR. The correlation between ERCC1 and XPF expression, clinicopathological features and HCC prognosis were compared.

Results

ERCC1 expression in liver cancer tissues was significantly lower than that of adjacent tissues (9.5% (2/21) vs 38.1% (8/21); P<0.05). The positive expression rates of XPF in liver cancer tissues was lower than that of adjacent tissues (14.3% (3/21) vs 71.4% (15/21); P<0.05). ERCC1 and XPF expression were associated with hepatic capsular invasion and microvascular invasion. HCC patients with hepatic capsular invasion and microvascular tumor embolus formation had significantly lower levels of ERCC1 and XPF mRNA than those without hepatic capsular invasion and microvascular tumor embolus formation (P<0.05). In addition, ERCC1 expression was associated with TNM staging of HCC. The expression of ERCC1 mRNA in patients with stage II and III HCC were lower than that of patients with stage I HCC (P<0.05). The low levels of ERCC1 and XPF mRNA significantly correlated with relapse-free survival times (RFS) in HCC patients. The median RFS of the low ERCC1 expression group and low XPF expression group were shorter than those of the high expression group (15.0 months vs 32.0 months, P<0.05) and (19.0 months vs 33.0 months, P<0.05). The decrease in XPF mRNA expression was significantly associated with the overall survival (OS) of HCC patients. The median OS in the low XPF expression group was shorter than that of the high expression group (46.0 months vs 78.0 months, P<0.05). However, no significant difference in OS between the low ERCC1 expression group and the high ERCC1 expression groups were observed (63.0 months vs 64.0 months, P>0.05). Multivariate analysis showed that tumor size and the extent of differentiation were independent factors affecting the RFS in HCC patients (P<0.05). The extent of differentiation and XPF were independent factors affecting the OS in HCC (P<0.05).

Conclusion

The expression in ERCC1 and XPF were low in HCC and associated with early relapse after HCC surgery. Low XPF expression may be a potential indicator of a high risk of death.

The Emerging Role of DNA Damage in the Pathogenesis of the C9orf72 Repeat Expansion in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal, rapidly progressing neurodegenerative disease affecting motor neurons, and frontotemporal dementia (FTD) is a behavioural disorder resulting in early-onset dementia. Hexanucleotide (G4C2) repeat expansions in the gene encoding chromosome 9 open reading frame 72 (C9orf72) are the major cause of familial forms of both ALS (~40%) and FTD (~20%) worldwide. The C9orf72 repeat expansion is known to form abnormal nuclei acid structures, such as hairpins, G-quadruplexes, and R-loops, which are increasingly associated with human diseases involving microsatellite repeats. These configurations form during normal cellular processes, but if they persist they also damage DNA, and hence are a serious threat to genome integrity. It is unclear how the repeat expansion in C9orf72 causes ALS, but recent evidence implicates DNA damage in neurodegeneration. This may arise from abnormal nucleic acid structures, the greatly expanded C9orf72 RNA, or by repeat-associated non-ATG (RAN) translation, which generates toxic dipeptide repeat proteins. In this review, we detail recent advances implicating DNA damage in C9orf72-ALS. Furthermore, we also discuss increasing evidence that targeting these aberrant C9orf72 confirmations may have therapeutic value for ALS, thus revealing new avenues for drug discovery for this disorder.

Association between Genomic Instability and Evolutionary Chromosomal Rearrangements in Neotropical Primates

During the last decades, the mammalian genome has been proposed to have regions prone to breakage and reorganization concentrated in certain chromosomal bands that seem to correspond to evolutionary breakpoints. These bands are likely to be involved in chromosome fragility or instability. In Primates, some biomarkers of genetic damage may be associated with various degrees of genomic instability. Here, we investigated the usefulness of Sister Chromatid Exchange as a biomarker of potential sites of frequent chromosome breakage and rearrangement in Alouatta caraya, Ateles chamek, Ateles paniscus, and Cebus cay. These Neotropical species have particular genomic and chromosomal features allowing the analysis of genomic instability for comparative purposes. We determined the frequency of spontaneous induction of Sister Chromatid Exchanges and assessed the relationship between these and structural rearrangements implicated in the evolution of the primates of interest. Overall, A. caraya and C. cay presented a low proportion of statistically significant unstable bands, suggesting fairly stable genomes and the existence of some kind of protection against endogenous damage. In contrast, Ateles showed a highly significant proportion of unstable bands; these were mainly found in the rearranged regions, which is consistent with the numerous genomic reorganizations that might have occurred during the evolution of this genus.

Spatial positioning of all 24 chromosomes in the lymphocytes of six subjects: evidence of reproducible positioning and spatial repositioning following DNA damage with hydrogen peroxide and ultraviolet B

The higher-order organization of chromatin is well-established, with chromosomes occupying distinct positions within the interphase nucleus. Chromatin is susceptible to, and constantly assaulted by both endogenous and exogenous threats. However, the effects of DNA damage on the spatial topology of chromosomes are hitherto, poorly understood. This study investigates the organization of all 24 human chromosomes in lymphocytes from six individuals prior to- and following in-vitro exposure to genotoxic agents: hydrogen peroxide and ultraviolet B. This study is the first to report reproducible distinct hierarchical radial organization of chromosomes with little inter-individual differences between subjects. Perturbed nuclear organization was observed following genotoxic exposure for both agents; however a greater effect was observed for hydrogen peroxide including: 1) More peripheral radial organization; 2) Alterations in the global distribution of chromosomes; and 3) More events of chromosome repositioning (18 events involving 10 chromosomes vs. 11 events involving 9 chromosomes for hydrogen peroxide and ultraviolet B respectively). Evidence is provided of chromosome repositioning and altered nuclear organization following in-vitro exposure to genotoxic agents, with notable differences observed between the two investigated agents. Repositioning of chromosomes following genotoxicity involved recurrent chromosomes and is most likely part of the genomes inherent response to DNA damage. The variances in nuclear organization observed between the two agents likely reflects differences in mobility and/or decondensation of chromatin as a result of differences in the type of DNA damage induced, chromatin regions targeted, and DNA repair mechanisms.

Differential S-phase progression after irradiation of p53 functional versus non-functional tumour cells

Background

Many pathways seem to be involved in the regulation of the intra-S-phase checkpoint after exposure to ionizing radiation, but the role of p53 has proven to be rather elusive. Here we have a closer look at the progression of irradiated cells through S-phase in dependence of their p53 status.

Materials and methods.

Three pairs of tumour cell lines were used, each consisting of one p53 functional and one p53 non-functional line. Cells were labelled with bromodeoxyuridine(BrdU) immediately after irradiation, they were then incubated in label-free medium, and at different times afterwards their position within the S-phase was determined by means of flow cytometry.

Results

While in the p53 deficient cells progression through S-phase was slowed significantly over at least a few hours, it was halted for just about an hour in the p53 proficient cells and then proceeded without further delay or even at a slightly accelerated pace.

Conclusions

It is clear from the experiments presented here that p53 does play a role for the progress of cells through the S-phase after X-ray exposure, but the exact mechanisms by which replicon initiation and elongation is controlled in irradiated cells remain to be elucidated.

Blocking Hedgehog survival signaling at the level of the GLI genes induces DNA damage and extensive cell death in human colon carcinoma cells

Canonical Hedgehog (HH) signaling is characterized by Smoothened (Smo)-dependent activation of the transcription factors Gli1 and Gli2, which regulate HH target genes. In human colon carcinoma cells, treatment with the Gli small-molecule inhibitor GANT61 induces extensive cell death in contrast to the Smo inhibitor cyclopamine. Here we elucidate cellular events upstream of cell death elicited by GANT61, which reveal the basis for its unique cytotoxic activity in colon carcinoma cells. Unlike cyclopamine, GANT61 induced transient cellular accumulation at G(1)-S (24 hours) and in early S-phase (32 hours), with elevated p21(Cip1), cyclin E, and cyclin A in HT29 cells. GANT61 induced DNA damage within 24 hours, with the appearance of p-ATM and p-Chk2. Pharmacologic inhibition of Gli1 and Gli2 by GANT61 or genetic inhibition by transient transfection of the Gli3 repressor (Gli3R) downregulated Gli1 and Gli2 expression and induced γH2AX, PARP cleavage, caspase-3 activation, and cell death. GANT61 induced γH2AX nuclear foci, while transient transfection of Gli3R showed expression of Gli3R and γH2AX foci within the same nuclei in HT29, SW480, and HCT116. GANT61 specifically targeted Gli1 and Gli2 substantiated by specific inhibition of (i) direct binding of Gli1 and Gli2 to the promoters of target genes HIP1 and BCL-2, (ii) Gli-luciferase activity, and (iii) transcriptional activation of BCL-2. Taken together, these findings establish that inhibition of HH signaling at the level of the GLI genes downstream of Smo is critical in the induction of DNA damage in early S-phase, leading to cell death in human colon carcinoma cells.