A post-irradiation-induced replication stress promotes RET proto-oncogene breakage

Area of Science:

• Genomics
• Radiation Oncology
• Molecular Biology

Background:

• Ionizing radiation induces genomic instability and chromosomal rearrangements.
• The RET/PTC1 translocation is a hallmark of radiation-induced thyroid cancers.
• Both RET and CCDC6 genes are located in common fragile sites, prone to breakage during replication stress.

Purpose of the Study:

• To investigate DNA breakage in RET and CCDC6 genes under replicative stress in thyroid cells several days post-irradiation.
• To understand the molecular mechanisms underlying radiation-induced genomic instability in thyroid cancer.

Main Methods:

• Human thyroid epithelial cells (HThy-ori-3.1) were exposed to 5-Gy radiation.
• Molecular DNA combing and replication-timing experiments were used to analyze DNA replication dynamics.
• Chromatin immunoprecipitation followed by quantitative PCR (ChIP-qPCR) assessed DNA breakage in RET and CCDC6 genes.

Main Results:

• Replicative stress several days post-irradiation primarily caused double-strand breaks (DSBs) in the RET gene.
• Both RET and CCDC6 genes exhibited late replication timing in thyroid cells.
• Irradiation notably delayed the replication rate of the RET gene.

Conclusions:

• Post-irradiation, the RET gene experiences replication fork breakage under replicative stress.
• This breakage may lead to genomic rearrangements, potentially involving the CCDC6 gene.
• These findings contribute to understanding the high prevalence of RET/PTC rearrangements in radiation-exposed individuals.