Speaker
Dr
Odilia Popanda
(German Cancer Research Center (DKFZ))
Description
Several manifestations of the radiation response such as bystander effects, adaptive processes, or transgenerational effects suggest involvement not only of genetic but also of epigenetic mechanisms. These might include transcriptional changes mediated by small RNAs, histone modifications or DNA methylation. Altered methylation of CpG sites can modify gene expression, induce genomic instability and, finally, result in carcinogenesis. How this cascade is driven by radiation is still widely unknown, although there are several reports available on altered methylation patterns following radiation exposure in plants, rodents and human cells. In our analyses we focused on repeated exposure of cell lines to ionizing radiation which can lead to adaptive response. While the importance of epigenetic mechanisms in adaptation to repeated stress exposure is known for a variety of agents (e.g. cisplatin, tobacco smoke), their role in fractioned ionizing radiation needs to be elucidated. We treated MCF7 breast cancer cells with repeated fractions of 2 Gy, resulting in total doses of 10 and 20 Gy. Methylation patterns were determined by methyl-CpG immunoprecipitation (MCIp) followed by global methylation profiling on CpG island microarrays. Cells receiving a total dose of 10 Gy showed a delay in cell division but started regrowing after 14 d, and exhibited similar radioresistance as mock treated cells. MCIp profiling revealed methylation changes in several CpG islands 48 h after fractionated irradiation with 10 and 20 Gy. These methylation differences were quantitatively validated on bisulfite-converted DNA by MassArray technology, a method involving PCR, base-specific cleavage, and MALDI-TOF mass spectrometry. Significant hypomethylation was mainly confirmed in CpG units associated with the transcription factor FOXC1 (P<0.001) and TRAPPC9 (p<0.001) which is involved in NFkB signalling. In summary, we showed differences in epigenetic DNA methylation in cells recovering after fractionated irradiation. Together with published evidence, our data support a role of DNA methylation in the radiation response. Further studies need to clarify the functional impact of these changes
Primary author
Dr
Odilia Popanda
(German Cancer Research Center (DKFZ))
