Ionizing Radiation deregulates the microRNA expression profile in differentiated thyroid cells.

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Ionizing Radiation deregulates the microRNA expression profile in differentiated thyroid cells.

Thyroid. 2018 Feb 03;:

Authors: Penha RCC, Pellecchia S, Pacelli R, Pinto LFR, Fusco A

Abstract
BACKGROUND: Ionizing Radiation (IR) is a well-known risk factor for papillary thyroid cancer, and it has been reported to deregulate microRNA expression, which is important to thyroid carcinogenesis. Therefore, we have investigated the impact of IR on microRNA expression profile of the normal thyroid cell line (FRTL-5 CL2) and as well as its effect on radiosensitivity of thyroid cancer cell lines, especially the human anaplastic thyroid carcinoma cell line (8505c).
METHODS: The global microRNA expression profile of irradiated FRTL-5 CL2 cells (5 Gy X-ray) was characterized and data were confirmed by qRT-PCR evaluating the expression of rno-miR-10b-5p, rno-miR-33-5p, rno-miR-128-1-5p, rno-miR-199a-3p, rno-miR-296-5p, rno-miR-328a-3p and rno-miR-541-5p in irradiated cells. The miR-199a-3p and miR-10b-5p targets were validated by qRT-PCR, western blot and luciferase target assays. The effects of miR-199a-3p and miR-10b-5p on DNA repair were determined by evaluating the activation of the protein kinases ataxia-telangiectasia mutated (ATM), ataxia telangiectasia and Rad3-related (ATR) and the serine 39 phosphorylation of variant histone H2AX (γH2AX) as indirect measure of double-strand DNA breaks (DSB) in irradiated FRTL-5 CL2 cells. The impact of miR-10b-5p on radiosensitivity was analyzed by cell counting and MTT assays in FRTL-5 CL2, Kras-transformed FRTL-5 CL2 (FRTL KiKi) and 8505c cell lines.
RESULTS: Our results reveal that miR-10b-5p and miR-199a-3p display the most pronounced alterations in expression in irradiated FRTL-5 CL2 cells. We validated Dicer1 and Lin28b as targets of miR-10b-5p and miR-199a-3p, respectively. Functional studies demonstrate that miR-10b-5p increases the growth rate of FRTL-5 CL2 cells, while miR-199a-3p inhibits their proliferation. Moreover, both of these microRNAs negatively affect homologous recombination repair, reducing activated ATM and ATR protein levels and, consequently, leading to an accumulation of γH2AX. Interestingly, the overexpression of miR-10b-5p decreases the viability of the irradiated FRTL5-CL2 and 8505c cell lines. Consistent with this observation, its inhibition in FRTL KiKi cells, which display high basal expression levels of miR-10b-5p, leads to the opposite effect.
CONCLUSIONS: These results demonstrate that IR deregulates microRNA expression, affecting the DSB repair efficiency of irradiated thyroid cells, and suggest that miR-10b-5p overexpression may be an innovative approach for anaplastic thyroid cancer therapy by increasing cancer cell radiosensitivity.

PMID: 29397781 [PubMed - as supplied by publisher]

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