Differential expression of TP53 associated genes in Fanconi anemia cells after mitomycin C and hydroxyurea treatment

Effects of cyclophosphamide and mitomycin C on radiation-induced transcriptional biomarkers in human lymphoblastoid cells

PURPOSE

Ionizing radiation (IR)-induced transcriptional changes are considered a potential biodosimetry for dose evaluation and health risk monitoring of acute or chronic radiation exposure. It is crucial to understand the impact of confounding factors on the radiation-responsive gene expressions for accurate and reproducible dose assessment. This study aims to explore the potential influence of exposures to chemotherapeutic agents such as cyclophosphamide (CP) and mitomycin C (MMC) on IR-induced transcriptional biomarkers.

METHODS

The human B lymphoblastoid cells (AHH-1) were exposed to 0, 20, 50, 100, 200 and 500 μg/ml CP or 0, 0.025, 0.05, 0.1 and 1 μg/ml MMC, respectively. The appropriate concentrations of CP and MMC were added for 1 h before irradiation with 0, 2, 4 and 6 Gy of 60Co γ-rays at a dose rate of 1 Gy/min. Cell viability was evaluated by CCK-8 assay. The gene expression responses of 18 radiation-induced transcriptional biomarkers were examined at 24 h after exposures to CP and MMC, respectively. The expression levels of five crucial DNA interstrand crosslinks (ICLs) repair genes were also evaluated. The biodosimetry models were established based on the specific radiation-responsive gene combinations.

RESULTS

The baseline transcriptional levels of the 18 selected genes were slightly affected by CP treatment in the absence of IR, while the transcript responses to IR could be inhibited as the concentration of CP up to 50 μg/ml. MMC treatment up-regulated the background levels in most radiation-responsive gene expressions. Of 18 genes, only the relative mRNA expression levels of CDKN1A and BBC3 were repressed after treatment with IR and MMC in combination. The relative mRNA level of RAD51 was significantly up-regulated after exposure to CP, while the expression of FANCD2, RAD51 and BLM showed an overall increase in response to MMC treatment. After irradiation, the relative mRNA expression levels of FANCD2, BRCA2 and RAD51 exhibited dose-dependent increases in IR alone and MMC treatment groups. In addition, the biodosimetry models were established using 2-4 radiation-responsive genes based on different radiation exposure scenarios.

CONCLUSION

Our findings suggested that IR-induced gene expression changes were slightly affected after exposure to a relatively low concentration of CP and MMC. Gene expression combinations might improve the broad applicability of transcriptional biodosimetry across diverse radiation exposures.

A new frontier in Fanconi anemia: From DNA repair to ribosome biogenesis

Described by Guido Fanconi almost 100 years ago, Fanconi anemia (FA) is a rare genetic disease characterized by developmental abnormalities, bone marrow failure (BMF) and cancer predisposition. The proteins encoded by FA-mutated genes (FANC proteins) and assembled in the so-called FANC/BRCA pathway have key functions in DNA repair and replication safeguarding, which loss leads to chromosome structural aberrancies. Therefore, since the 1980s, FA has been considered a genomic instability and chromosome fragility syndrome. However, recent findings have demonstrated new and unexpected roles of FANC proteins in nucleolar homeostasis and ribosome biogenesis, the alteration of which impacts cellular proteostasis. Here, we review the different cellular, biochemical and molecular anomalies associated with the loss of function of FANC proteins and discuss how these anomalies contribute to BMF by comparing FA to other major inherited BMF syndromes. Our aim is to determine the extent to which alterations in the DNA damage response in FA contribute to BMF compared to the consequences of the loss of function of the FANC/BRCA pathway on the other roles of the pathway.

Association of human papillomavirus with Fanconi anemia promotes carcinogenesis in Fanconi anemia patients

Fanconi anemia (FA) is a rare recessive disorder associated with chromosomal fragility. FA patients are at very high risk of cancers, especially head and neck squamous cell carcinomas and squamous cell carcinomas caused by infection of human papillomaviruses (HPVs). By integrating into the host genome, HPV oncogenes E6 and E7 drive the genomic instability to promote DNA damage and gene mutations necessary for carcinogenesis in FA patients. Furthermore, E6 and E7 oncoproteins not only inhibit p53 and retinoblastoma but also impair the FANC/BRCA signaling pathway to prevent DNA damage repair and alter multiple signals including cell-cycle checkpoints, telomere function, cell proliferation, and interference of the host immune system leading to cancer development in FA patients. In this review, we summarize recent advances in unraveling the molecular mechanisms of FA susceptibility to HPV-induced cancers, which facilitate rational preventive and therapeutic strategies.

Increased apoptosis is linked to severe acute GVHD in patients with Fanconi anemia

Fanconi anemia (FA) patients have an increased risk of acute GVHD (aGVHD) after hematopoietic SCT, with hypersensitivity to DNA-cross-linking agents and defective DNA repair. MicroRNA-34 and p53 can induce apoptosis after DNA damage.Here we assessed epithelial cell apoptosis, and studied TP53 and miR-34a expression in the skin and gut biopsies in five non-transplanted FA patients, in 20 FA patients with aGVHD and in 25 acquired aplastic anemia patients (AA). Epithelial apoptosis was higher in FA than in acquired AA patients in both the skin and gut biopsies, though they had a similar preparative regimen. Further study on gut biopsies in FA patients showed that this deleterious effect was not linked to TP53 gene overexpression. As, among p53-independent signaling pathways of apoptosis, the microRNA-34 family mimics p53 apoptotic effects in response to DNA damage, we studied miR-34a expression in the same series of FA patients' gut biopsies. MiR-34a expression level was higher in severe aGVHD compared with non-aGVHD subjects or non-transplanted patients, and significantly related to apoptotic cell numbers across the three groups of FA patients. Thus, in FA patients, increased apoptosis occurs in target epithelial cells of severe aGVHD, and this deleterious effect is linked to overexpression of miR-34a but not TP53.

Hydroxycarbamide: a user's guide for chronic myeloproliferative disorders

Hydroxycarbamide is a nonalkylating antiproliferative and antiviral agent that has been used for over 40 years to treat a variety of neoplastic and non-neoplastic conditions. Hydroxycarbamide is readily absorbed and widely distributed throughout the body. It acts primarily to inhibit DNA synthesis, which underpins its use in solid tumors, viral infections and chronic myeloproliferative disorders. Hydroxycarbamide is an effective treatment for preventing transient ischemic attacks associated with thrombocytosis in chronic myeloproliferative disorders because it is a nitric oxide donor. While its mechanism of action and side-effect profile are well defined, its potential for leukemic transformation as a single agent is still a matter of controversy. Based on a search of the Medline database, this article encompasses the pharmacokinetics, pharmacodynamics, clinical use and tolerability of hydroxycarbamide, plus its potential for mutagenicity with special reference to the chronic myeloproliferative disorders. The toxicity profile of hydroxycarbamide is also discussed to enable clinicians to balance potential risks with therapeutic benefits.

Differential behaviour of normal, transformed and Fanconi's anemia lymphoblastoid cells to modeled microgravity

Background

Whether microgravity might influence tumour growth and carcinogenesis is still an open issue. It is not clear also if and how normal and transformed cells are differently solicited by microgravity. The present study was designed to verify this issue.

Methods

Two normal, LB and HSC93, and two transformed, Jurkat and 1310, lymphoblast cell lines were used as representative for the two conditions. Two lymphoblast lines from Fanconi's anemia patients group A and C (FA-A and FA-C, respectively), along with their isogenic corrected counterparts (FA-A-cor and FA-C-cor) were also used. Cell lines were evaluated for their proliferative ability, vitality and apoptotic susceptibility upon microgravity exposure in comparison with unexposed cells. Different parameters correlated to energy metabolism, glucose consumption, mitochondrial membrane potential (MMP), intracellular ATP content, red-ox balance and ability of the cells to repair the DNA damage product 8-OHdG induced by the treatment of the cells with 20 mM KBrO₃ were also evaluated.

Results

Transformed Jurkat and 1310 cells appear resistant to the microgravitational challenge. On the contrary normal LB and HSC93 cells display increased apoptotic susceptibility, shortage of energy storages and reduced ability to cope with oxidative stress. FA-A and FA-C cells appear resistant to microgravity exposure, analogously to transformed cells. FA corrected cells did shown intermediate sensitivity to microgravity exposure suggesting that genetic correction does not completely reverts cellular phenotype.

Conclusions

In the light of the reported results microgravity should be regarded as an harmful condition either when considering normal as well as transformed cells. Modeled microgravity and space-based technology are interesting tools in the biomedicine laboratory and offer an original, useful and unique approach in the study of cellular biochemistry and in the regulation of metabolic pathways.

Role of Rad51 down-regulation and extracellular signal-regulated kinases 1 and 2 inactivation in emodin and mitomycin C-induced synergistic cytotoxicity in human non-small-cell lung cancer cells

Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone) is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants. It is a tyrosine kinase inhibitor and has anticancer effects on lung cancer. Rad51 plays a central role in homologous recombination, and high levels of Rad51 expression are observed in chemo- or radioresistant carcinomas. Our previous studies have shown that the mitogen-activated protein kinase kinase (MKK) 1/2-extracellular signal-regulated kinase (ERK) 1/2 signal pathway maintains the expression of Rad51. Therefore, in this study, we hypothesized that emodin could enhance the effects of the antitumor antibiotic mitomycin C (MMC)-mediated cytotoxicity by decreasing the expression of Rad51 and the phosphorylation of ERK1/2. Exposure of the human non-small-cell lung cancer H1703 or A549 cell lines to emodin decreased the MMC-elicited phosphorylated ERK1/2 and Rad51 levels. Moreover, emodin significantly decreased the MMC-elicited Rad51 mRNA and protein levels by increasing the instability of Rad51 mRNA and protein. In emodin- and MMC-cotreated cells, ERK1/2 phosphorylation was enhanced by constitutively active MKK1/2 (MKK1/2-CA), thus increasing Rad51 protein levels and protein stability. The synergistic cytotoxic effects induced by emodin combined with MMC were remarkably decreased by MKK1-CA-mediated enhancement of ERK1/2 activation. Depletion of endogenous Rad51 expression by small interfering Rad51 RNA transfection significantly enhanced MMC-induced cell death and cell growth inhibition. In contrast, overexpression of Rad51 protects lung cancer cells from the synergistic cytotoxic effects induced by emodin and MMC. We conclude that suppression of Rad51 expression or a combination of emodin with chemotherapeutic agents may be considered as potential therapeutic modalities for lung cancer.