In vitro cultured cells as probes for space radiation effects on biological systems

Mutant MYO1F alters the mitochondrial network and induces tumor proliferation in thyroid cancer

Familial aggregation is a significant risk factor for the development of thyroid cancer and familial non-medullary thyroid cancer (FNMTC) accounts for 5-7% of all NMTC. Whole exome sequencing analysis in the family affected by FNMTC with oncocytic features where our group previously identified a predisposing locus on chromosome 19p13.2, revealed a novel heterozygous mutation (c.400G > A, NM_012335; p.Gly134Ser) in exon 5 of MYO1F, mapping to the linkage locus. In the thyroid FRTL-5 cell model stably expressing the mutant MYO1F p.Gly134Ser protein, we observed an altered mitochondrial network, with increased mitochondrial mass and a significant increase in both intracellular and extracellular reactive oxygen species, compared to cells expressing the wild-type (wt) protein or carrying the empty vector. The mutation conferred a significant advantage in colony formation, invasion and anchorage-independent growth. These data were corroborated by in vivo studies in zebrafish, since we demonstrated that the mutant MYO1F p.Gly134Ser, when overexpressed, can induce proliferation in whole vertebrate embryos, compared to the wt one. MYO1F screening in additional 192 FNMTC families identified another variant in exon 7, which leads to exon skipping, and is predicted to alter the ATP-binding domain in MYO1F. Our study identified for the first time a role for MYO1F in NMTC.

Effects of ultraviolet radiation on FRTL-5 cell growth and thyroid-specific gene expression

During space missions, radiation represents a major hazard for human health and involves all body organs and tissues. Regarding thyroid function, it has been shown that ultraviolet radiation (UVC) has dose-dependent apoptotic effects on FRTL-5 cells, a normal strain of rat thyrocytes. We examined the effects of a sublethal dose of UVC on FRTL-5 cell growth and gene expression. Cells exposed to 10 J/m(2) UVC showed no differences in viability compared to control cells after 24 h, but the BrdU incorporation was reduced, indicating a cytostatic effect. Quantitative RT-PCR carried out at 24 and 48 h after irradiation demonstrated that the mRNA levels of thyroglobulin (Tg), thyroperoxidase (Tpo), and sodium/iodide symporter (Nis) were transiently decreased at 24 h in treated cells, while the mRNAs of the thyroid transcription factors TTF1, Foxe1, and Pax8 were not affected. In cells cultured with TSH-free medium, the basal transcription of Tg, Tpo, and Nis genes was equally impaired by radiation and no longer stimulated by TSH. Overall, the results demonstrate that a sub-apoptotic dose of UVC compromises not only thyrocyte proliferation but also the expression of genes involved in thyroid hormone production. These findings might contribute to explaining the histological, biochemical, and clinical features of hypothyroidism observed in both animals and humans during spaceflight, and suggest that free thyroxine levels of astronauts during prolonged space missions should be monitored.

Thyrotropin effects on ultraviolet radiation-dependent apoptosis in FRTL-5 cells

Apoptosis plays an important role within the endocrine system, particularly in the thyroid gland, although little is known about its regulation in normal thyroids. Because thyrotropin (TSH) regulates many thyroid-specific functions and cell proliferation, we investigated whether TSH can influence such mechanisms. To induce apoptosis we used UV-C radiation. The FRTL-5 rat thyroid cell strain, a cloned strain of differentiated and untransformed cells that reproduces many of the characteristics of the normal thyroid was chosen for this study. The FRTL-5 cells are a particularly suitable model because they actively proliferate when cultured in the presence of TSH (6H medium), while in TSH-free medium (5H medium) cells remain in a physiologic quiescent state for a long period of time. FRTL-5 cells in both culture conditions were irradiated with UV-C radiation (254 nm wavelength). At 48 hours after radiation, 6H cultured cells showed the characteristic signs of apoptosis. However, 5H cultured cells did not present macroscopic signs of damage, DNA fragmentation, or detectable apoptosis. Furthermore, the expression of 23 apoptosis-related genes was compared. Results indicate that Bcl2 and caspase-2 expression is enhanced, while bax, GADD45 and mdm-2 expression is reduced in irradiated cells. These data confirm that TSH plays a major role in regulating UV-induced apoptosis in FRTL-5 cells.