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Marfan syndrome (MFS) is an autosomal dominant connective-tissue disorder affecting multiple systems, such as skeletal, cardiovascular, and ocular systems. MFS is predominantly caused by mutations in the FBN1 gene, which encodes the fibrillin-1 protein, crucial for connective-tissue integrity. FBN1 mutations lead to defective fibrillin, resulting in structurally compromised connective tissues. Additionally, these mutations cause aberrant TGF-β expression, contributing to vascular issues and increased susceptibility to radiation-induced fibrosis. Studies about the potential radiosensitivity of MFS are rare and generally limited to case reports. Here, we aimed to investigate the radiation-induced ATM nucleo-shuttling (RIANS) model to explore the molecular and cellular radiation response in fibroblasts from MFS patients. The results showed that the MFS fibroblast cell lines tested are associated with moderate but significant radiosensitivity, high yield of micronuclei, and impaired recognition of DNA double-strand breaks (DSBs) caused by a diminished RIANS. The diminished RIANS is supported by the sequestration of ATM protein in the cytoplasm not only by mutated FBN1 protein but also by overexpressed TGF-β. This report is the first molecular and cellular characterization of the radiation response of MFS fibroblasts and highlights the importance of the FBN1-TGF-β complex after irradiation. [ABSTRACT FROM AUTHOR]

Simple Summary: By hypothesizing that molecular hyper-recombination and cellular proliferation are among the major features of multi-factorial cancer proneness, by using skin fibroblasts derived from eight major cancer syndromes, a significant correlation was found between the hyper-recombination rate quantified by plasmid assay, proliferation capacity assessed by flow cytometry, and excess of relative cancer risk (ERR). The product of the hyper-recombination rate and capacity of proliferation described a linear function of ERR. Context: Although carcinogenesis is a multi-factorial process, the mutability and the capacity of cells to proliferate are among the major features of the cells that contribute together to the initiation and promotion steps of cancer formation. Particularly, mutability can be quantified by hyper-recombination rate assessed with specific plasmid assay, hypoxanthine-guanine phosphoribosyltransferase (HPRT) mutations frequency rate, or MRE11 nuclease activities. Cell proliferation can be assessed by flow cytometry by quantifying G2/M, G1 arrests, or global cellular evasion. Methods: All these assays were applied to skin untransformed fibroblasts derived from eight major cancer syndromes characterized by their excess of relative cancer risk (ERR). Results: Significant correlations with ERR were found between hyper-recombination assessed by the plasmid assay and G2/M arrest and described a third-degree polynomial ERR function and a sigmoidal ERR function, respectively. The product of the hyper-recombination rate and capacity of proliferation described a linear ERR function that permits one to better discriminate each cancer syndrome. Conclusions: Hyper-recombination and cell proliferation were found to obey differential equations that better highlight the intrinsic bases of cancer formation. Further investigations to verify their relevance for cancer proneness induced by exogenous agents are in progress. [ABSTRACT FROM AUTHOR]

Immunofluorescence with antibodies against phosphorylated forms of H2AX (γH2AX) is revolutionizing our understanding of repair and signaling of DNA double-strand breaks (DSBs). Unfortunately, the pattern of γH2AX foci depends upon a number of parameters (nature of stress, number of foci, radiation dose, repair time, cell cycle phase, gene mutations, etc...) whose one of the common points is chromatin condensation/decondensation. Here, we endeavored to demonstrate how chromatin conformation affects γH2AX foci pattern and influences immunofluorescence signal. DSBs induced in non-transformed human fibroblasts were analyzed by γH2AX immunofluorescence with sodium butyrate treatment of chromatin applied after the irradiation that decondenses chromatin but does not induce DNA breaks. Our data showed that the pattern of γH2AX foci may drastically change with the experimental protocols in terms of size and brightness. Notably, some γH2AX minifoci resulting from the dispersion of the main signal due to chromatin decondensation may bias the quantification of the number of DSBs. We proposed a model called "Christmas light models" to tentatively explain this diversity of γH2AX foci pattern that may also be considered for any DNA damage marker that relocalizes as nuclear foci. [ABSTRACT FROM AUTHOR]

Retinoblastoma (Rb) is a rare form of pediatric cancer that develops from retina cells. Bilateral and some unilateral forms of Rb are associated with heterozygous germline mutations of the (retinoblastoma 1) RB1 gene. RB1 mutations are also associated with a significant risk of secondary malignancy like head and neck tumors. Hence, to date, even if Rb patients are less subjected to radiotherapy to treat their primary ocular tumors, their healthy tissues may be exposed to significant doses of ionizing radiation during the treatment against their secondary malignancies with a significant risk of adverse tissue reactions (radiosensitivity) and/or radiation-induced cancer (radiosusceptibility). However, the biological role of the Rb protein in response to radiation remains misunderstood. Since the ataxia telangiectasia mutated (ATM) protein is a key protein of radiation response and since untransformed skin fibroblasts are a current model to quantify cellular radiosensitivity, we investigated here for the first time the functionality of the ATM-dependent signaling and repair pathway of the radiation-induced DNA double-strand breaks (DSB) in irradiated skin fibroblasts derived from Rb patients The major biomarkers of the DSB repair and signaling, namely clonogenic cell survival, micronuclei, nuclear foci of the phosphorylated forms of the X variant of the H2A histone (γH2AX), the phosphorylated forms of the ATM protein (pATM) and the meiotic recombination 11 nuclease (MRE11) were assessed in untransformed skin fibroblasts derived from three Rb patients. Skin fibroblasts from Rb patients showed significant cellular radiosensitivity, incomplete DSB recognition, delay in the ATM nucleo-shuttling and exacerbated MRE11 nuclease activity. Treatment with statin and bisphosphonates led to significant complementation of these impairments. Our findings strongly suggest the involvement of the ATM kinase in the radiosensitivity/radiosusceptibility phenotype observed in Rb cases. [ABSTRACT FROM AUTHOR]

Purpose: Xeroderma Pigmentosum (XP) is a rare, recessive genetic disease associated with photosensitivity, skin cancer proneness, neurological abnormalities and impaired nucleotide excision repair of the UV-induced DNA damage. Less frequently, XP can be associated with sensitivity to ionizing radiation (IR). Here, a complete radiobiological characterization was performed on a panel of fibroblasts derived from XP-group D patients (XPD). Materials and methods: Cellular radiosensitivity and the functionality of the recognition and repair of chromosome breaks and DNA double-strand breaks (DSB) was evaluated by different techniques including clonogenic cell survival, micronuclei, premature chromosome condensation, pulsed-field gel electrophoresis, chromatin decondensation and immunofluorescence assays. Quantitative correlations between each endpoint were analyzed systematically. Results: Among the seven fibroblast cell lines tested, those derived from three non-relative patients holding the p.[Arg683Trp];[Arg616Pro] XPD mutations showed significant cellular radiosensitivity, high yield of residual micronuclei, incomplete DSB recognition, DSB and chromosome repair defects, impaired ATM, MRE11 relocalization, significant chromatin decondensation. Interestingly, XPD transduction and treatment with statins and bisphosphonates known to accelerate the radiation-induced ATM nucleoshuttling led to significant complementation of these impairments. Conclusions: Our findings suggest that some subsets of XPD patients may be at risk of radiosensitivity reactions and treatment with statins and bisphosphonates may be an interesting approach of radioprotection countermeasure. Different mechanistic models were discussed to better understand the potential specificity of the p.[Arg683Trp];[Arg616Pro] XPD mutations. [ABSTRACT FROM AUTHOR]