Radiobiological Characterization of Tuberous Sclerosis: a Delay in the Nucleo-Shuttling of ATM May Be Responsible for Radiosensitivity

Abstract

The tuberous sclerosis complex (TSC) syndrome is associated with numerous cutaneous pathologies (notably on the face), epilepsy, intellectual disability and developmental retardation and, overall, high occurrence of benign tumors in several organs, like angiofibromas, giant cell astrocytomas, renal angiomyolipomas, and pulmonary lymphangioleiomyomatosis. TSC is caused by mutations of either of the hamartin or tuberin proteins that are mainly cytoplasmic. Some studies published in the 1980s reported that TSC is associated with radiosensitivity. However, its molecular basis in TSC cells is not documented enough. Here, we examined the functionality of the repair and signaling of radiation-induced DNA double-strand breaks (DSB) in fibroblasts derived from TSC patients. Quiescent TSC fibroblast cells elicited abnormally low rate of recognized DSB reflected by a low yield of nuclear foci formed by phosphorylated H2AX histones. Irradiated TSC cells also presented a delay in the nucleo-shuttling of the ATM kinase, potentially due to a specific binding of ATM to mutated TSC protein in cytoplasm. Lastly, TSC fibroblasts showed abnormally high MRE11 nuclease activity suggesting genomic instability. A combination of biphosphonates and statins complemented these impairments by facilitating the nucleoshuttling of ATM and increasing the yield of recognized DSB. Our results showed that TSC belongs to the group of syndromes associated with low but significant defect of DSB signaling and delay in the ATM nucleo-shuttling associated with radiosensitivity.

The Phosphorylated ATM Immunofluorescence Assay: A High-performance Radiosensitivity Assay to Predict Postradiation Therapy Overreactions

“…This quantitative correlation was found to be independent of tumor location, cell type and of early or late occurrence of the toxicity (9). Unlike other assays reporting molecular or cellular endpoints like polymorphisms or apoptosis, our assay provides: 1) a reliable prediction of radiosensitivity by considering CTCAE grades separately -and in a binarized way (9); 2) a relevant biological interpretation of the linear-quadratic model (16)(17)(18); 3) a relevant mechanistic model to explain major iRS in genetic diseases associated with mutations of cytoplasm proteins interacting with pATM nucleoshuttling (11,19,20). Patients are currently enrolled prior RT in confirmatory prospective studies in pediatrics (NCT02827552) and sarcomas/GI malignancies (NCT02797405).…”

The Nucleoshuttling of the ATM Protein: A Unified Model to Describe the Individual Response to High- and Low-Dose of Radiation?

“…Interestingly, some of the syndromes that are associated with a moderate radiosensitivity [39] are caused by mutations of cytoplasmic proteins, like Huntington’s disease [34], neurofibromatosis type I [44], tuberous sclerosis [45], and Bruton’s [46] and Usher’s syndromes [47]. This is also the case of the progeroid Hutchinson–Gilford syndrome, caused by mutations of lamina A, that is not directly involved in DNA damage signaling and repair [33].…”

“…Indeed, for the homozygous mutations or some neo (mosaicism) mutations of proteins essential for the vital cellular functions, a significant dysfunction is observed (group III cases), but such gene mutations remain very rare. For the heterozygous gene mutations that are more frequent, a paradoxical overexpression of the mutated protein may contribute to delaying the RIANS by a more probable binding to ATM in the cytoplasm (group II cases) [2,34,45].…”

“…In the case of heterozygous mutations of the TSC2 protein, the TSC1 and TSC2 proteins separate, which contributes to activating the mTOR pathway. In parallel, the over-expression of the TSC2 protein contributes to sequestrating ATM in the cytoplasm [45]. In addition, neurofibromatosis type 1 (NF1) is also affected by these characteristics.…”

Modulation of DNA Damage Response by Sphingolipid Signaling: An Interplay that Shapes Cell Fate

“…The maximal number of nuclear p-ATM foci is usually reached within 10 min to 1 h post-injury [ 50 ]. However, certain cytoplasmic proteins like mutated huntingtin or tuberous sclerosis complex can bind activated ATM monomers and impede their shuttling towards the nucleus [ 49 , 51 ]. Therefore, DSBs recognition and repair may be influenced by the diffusion of p-ATM monomers as well as ATM re-dimerization or re-association with certain cytoplasmic proteins [ 14 , 47 , 49 ].…”