Breast cancer in two sisters with Friedreich's ataxia

Iron-Sulfur Cluster Biogenesis as a Critical Target in Cancer

Cancer cells preferentially accumulate iron (Fe) relative to non-malignant cells; however, the underlying rationale remains elusive. Iron-sulfur (Fe-S) clusters are critical cofactors that aid in a wide variety of cellular functions (e.g., DNA metabolism and electron transport). In this article, we theorize that a differential need for Fe-S biogenesis in tumor versus non-malignant cells underlies the Fe-dependent cell growth demand of cancer cells to promote cell division and survival by promoting genomic stability via Fe-S containing DNA metabolic enzymes. In this review, we outline the complex Fe-S biogenesis process and its potential upregulation in cancer. We also discuss three therapeutic strategies to target Fe-S biogenesis: (i) redox manipulation, (ii) Fe chelation, and (iii) Fe mimicry.

Characterization of human frataxin missense variants in cancer tissues

Human frataxin is an iron-binding protein involved in the mitochondrial iron-sulfur (Fe-S) clusters assembly, a process fundamental for the functional activity of mitochondrial proteins. Decreased level of frataxin expression is associated with the neurodegenerative disease Friedreich ataxia. Defective function of frataxin may cause defects in mitochondria, leading to increased tumorigenesis. Tumor-initiating cells show higher iron uptake, a decrease in iron storage and a reduced Fe-S clusters synthesis and utilization. In this study, we selected, from COSMIC database, the somatic human frataxin missense variants found in cancer tissues p.D104G, p.A107V, p.F109L, p.Y123S, p.S161I, p.W173C, p.S181F, and p.S202F to analyze the effect of the single amino acid substitutions on frataxin structure, function, and stability. The spectral properties, the thermodynamic and the kinetic stability, as well as the molecular dynamics of the frataxin missense variants found in cancer tissues point to local changes confined to the environment of the mutated residues. The global fold of the variants is not altered by the amino acid substitutions; however, some of the variants show a decreased stability and a decreased functional activity in comparison with that of the wild-type protein.

Five markers useful for the distinction of canine mammary malignancy

Background

Spontaneous canine mammary tumors constitute a serious clinical problem. There are significant differences in survival between cases with different tumor grades. Unfortunately, the distinction between various grades is not clear. A major problem in evaluating canine mammary cancer is identifying those, that are “truly” malignant. That is why the aim of our study was to find the new markers of canine malignancy, which could help to diagnose the most malignant tumors.

Results

Analysis of gene expression profiles of canine mammary carcinoma of various grade of malignancy followed by the boosted tree analysis distinguished a `gene set`. The expression of this gene set (sehrl, zfp37, mipep, relaxin, and magi3) differs significantly in the most malignant tumors at mRNA level as well as at protein level. Despite this `gene set` is very interesting as an additional tool to estimate canine mammary malignancy, it should be validated using higher number of samples.

Conclusions

The proposed gene set can constitute a `malignancy marker` that could help to distinguish the most malignant canine mammary carcinomas. These genes are also interesting as targets for further investigations and therapy. So far, only two of them were linked with the cancer development.

Iron and cancer: more ore to be mined

Iron is an essential nutrient that facilitates cell proliferation and growth. However, iron also has the capacity to engage in redox cycling and free radical formation. Therefore, iron can contribute to both tumour initiation and tumour growth; recent work has also shown that iron has a role in the tumour microenvironment and in metastasis. Pathways of iron acquisition, efflux, storage and regulation are all perturbed in cancer, suggesting that reprogramming of iron metabolism is a central aspect of tumour cell survival. Signalling through hypoxia-inducible factor (HIF) and WNT pathways may contribute to altered iron metabolism in cancer. Targeting iron metabolic pathways may provide new tools for cancer prognosis and therapy.

Clinical data and characterization of the liver conditional mouse model exclude neoplasia as a non-neurological manifestation associated with Friedreich's ataxia

Friedreich's ataxia (FRDA) is the most common hereditary ataxia in the caucasian population and is characterized by a mixed spinocerebellar and sensory ataxia, hypertrophic cardiomyopathy and increased incidence of diabetes. FRDA is caused by impaired expression of the FXN gene coding for the mitochondrial protein frataxin. During the past ten years, the development of mouse models of FRDA has allowed better understanding of the pathophysiology of the disease. Among the mouse models of FRDA, the liver conditional mouse model pointed to a tumor suppressor activity of frataxin leading to the hypothesis that individuals with FRDA might be predisposed to cancer. In the present work, we investigated the presence and the incidence of neoplasia in the largest FRDA patient cohorts from the USA, Australia and Europe. As no predisposition to cancer could be observed in both cohorts, we revisited the phenotype of the liver conditional mouse model. Our results show that frataxin-deficient livers developed early mitochondriopathy, iron-sulfur cluster deficits and intramitochondrial dense deposits, classical hallmarks observed in frataxin-deficient tissues and cells. With age, a minority of mice developed structures similar to the ones previously associated with tumor formation. However, these peripheral structures contained dying, frataxin-deficient hepatocytes, whereas the inner liver structure was composed of a pool of frataxin-positive cells, due to inefficient Cre-mediated recombination of the Fxn gene, that contributed to regeneration of a functional liver. Together, our data demonstrate that frataxin deficiency and tumorigenesis are not associated.

Massive Uterine Leiomyoma in a Patient with Friedreich's Ataxia: Is There a Possible Association?

A possible association between Friedreich's ataxia (FA) and neoplastic development has been recognized. FA patients have low frataxin levels and insufficient response to oxidative stress. In these patients fibroblasts are characterized by a high rate of mutations. Herein, a case of a 39-year-old woman with FA tetraplegia, who was admitted in our department with intestinal obstruction due to a huge uterine tumor, is described. An abdominal CT revealed a huge intra-abdominal mass originating from the right cornu of the uterus. Tumor excision and adhesionlysis were performed. The histological examination of the tumor revealed a leiomyoma. FA patients seem to present with a variety of neoplasms uncommon for their young age. This is the first report of a leiomyoma originating from the genital system in a female patient with FA tetraplegia. Therefore it is important to identify neoplasms at an early stage in patients with FA and start immediate therapy.

The Friedreich's ataxia protein frataxin modulates DNA base excision repair in prokaryotes and mammals

DNA-repair mechanisms enable cells to maintain their genetic information by protecting it from mutations that may cause malignant growth. Recent evidence suggests that specific DNA-repair enzymes contain ISCs (iron-sulfur clusters). The nuclearencoded protein frataxin is essential for the mitochondrial biosynthesis of ISCs. Frataxin deficiency causes a neurodegenerative disorder named Friedreich's ataxia in humans. Various types of cancer occurring at young age are associated with this disease, and hence with frataxin deficiency. Mice carrying a hepatocyte-specific disruption of the frataxin gene develop multiple liver tumours for unresolved reasons. In the present study, we show that frataxin deficiency in murine liver is associated with increased basal levels of oxidative DNA base damage. Accordingly, eukaryotic V79 fibroblasts overexpressing human frataxin show decreased basal levels of these modifications, while prokaryotic Salmonella enterica serotype Typhimurium TA104 strains transformed with human frataxin show decreased mutation rates. The repair rates of oxidative DNA base modifications in V79 cells overexpressing frataxin were significantly higher than in control cells. Lastly, cleavage activity related to the ISC-independent repair enzyme 8-oxoguanine glycosylase was found to be unaltered by frataxin overexpression. These findings indicate that frataxin modulates DNA-repair mechanisms probably due to its impact on ISC-dependent repair proteins, linking mitochondrial dysfunction to DNA repair and tumour initiation.

Altered gene expression and DNA damage in peripheral blood cells from Friedreich's ataxia patients: cellular model of pathology

The neurodegenerative disease Friedreich's ataxia (FRDA) is the most common autosomal-recessively inherited ataxia and is caused by a GAA triplet repeat expansion in the first intron of the frataxin gene. In this disease, transcription of frataxin, a mitochondrial protein involved in iron homeostasis, is impaired, resulting in a significant reduction in mRNA and protein levels. Global gene expression analysis was performed in peripheral blood samples from FRDA patients as compared to controls, which suggested altered expression patterns pertaining to genotoxic stress. We then confirmed the presence of genotoxic DNA damage by using a gene-specific quantitative PCR assay and discovered an increase in both mitochondrial and nuclear DNA damage in the blood of these patients (p<0.0001, respectively). Additionally, frataxin mRNA levels correlated with age of onset of disease and displayed unique sets of gene alterations involved in immune response, oxidative phosphorylation, and protein synthesis. Many of the key pathways observed by transcription profiling were downregulated, and we believe these data suggest that patients with prolonged frataxin deficiency undergo a systemic survival response to chronic genotoxic stress and consequent DNA damage detectable in blood. In conclusion, our results yield insight into the nature and progression of FRDA, as well as possible therapeutic approaches. Furthermore, the identification of potential biomarkers, including the DNA damage found in peripheral blood, may have predictive value in future clinical trials.

Targeted disruption of hepatic frataxin expression causes impaired mitochondrial function, decreased life span and tumor growth in mice

We have disrupted expression of the mitochondrial Friedreich ataxia protein frataxin specifically in murine hepatocytes to generate mice with impaired mitochondrial function and decreased oxidative phosphorylation. These animals have a reduced life span and develop multiple hepatic tumors. Livers also show increased oxidative stress, impaired respiration and reduced ATP levels paralleled by reduced activity of iron-sulfur cluster (Fe/S) containing proteins (ISP), which all leads to increased hepatocyte turnover by promoting both apoptosis and proliferation. Accordingly, phosphorylation of the stress-inducible p38 MAP kinase was found to be specifically impaired following disruption of frataxin. Taken together, these findings indicate that frataxin may act as a mitochondrial tumor suppressor protein in mammals.

Neurodegenerative disorders associated with diabetes mellitus

More than 20 syndromes among the significant and increasing number of degenerative diseases of neuronal tissues are known to be associated with diabetes mellitus, increased insulin resistance and obesity, disturbed insulin sensitivity, and excessive or impaired insulin secretion. This review briefly presents such syndromes, including Alzheimer disease, ataxia-telangiectasia, Down syndrome/trisomy 21, Friedreich ataxia, Huntington disease, several disorders of mitochondria, myotonic dystrophy, Parkinson disease, Prader-Willi syndrome, Werner syndrome, Wolfram syndrome, mitochondrial disorders affecting oxidative phosphorylation, and vitamin B(1) deficiency/inherited thiamine-responsive megaloblastic anemia syndrome as well as their respective relationship to malignancies, cancer, and aging and the nature of their inheritance (including triplet repeat expansions), genetic loci, and corresponding functional biochemistry. Discussed in further detail are disturbances of glucose metabolism including impaired glucose tolerance and both insulin-dependent and non-insulin-dependent diabetes caused by neurodegeneration in humans and mice, sometimes accompanied by degeneration of pancreatic beta-cells. Concordant mouse models obtained by targeted disruption (knock-out), knock-in, or transgenic overexpression of the respective transgene are also described. Preliminary conclusions suggest that many of the diabetogenic neurodegenerative disorders are related to alterations in oxidative phosphorylation (OXPHOS) and mitochondrial nutrient metabolism, which coincide with aberrant protein precipitation in the majority of affected individuals.