Significant Impact of let-7d MicroRNA on Breast Cancer Cell Lines Post-Radiation Treatment

Abstract

Introduction: Radiotherapy is a common treatment for breast cancer treatment, that induces DNA damage. These DNA damages are addressed through various repair pathways, which regulate the DNA repair systems and confer radio-resistance. Non-coding RNAs are a big proportion of genome transcripts without the potential to encode proteins. Related studies demonstrated that radiation affects the expression of non-coding RNAs. Let-7d, a tumor suppressor in numerous cancers, has some target genes that play a role in the DNA repair system.

Materials and Methods: Human breast cancer cell lines MDA-MB-231 and MCF-7 were cultured in a Dulbecco's Modified Eagle Medium. The exponentially growing cells were treated with some doses of X-rays. After radiation treatment and cell harvesting, RNA was extracted, and cDNA synthesis was done. The let-7d miRNA expression changes were calculated with real-time quantitative reverse transcription polymerase chain reaction.

Results: The results implied that radiation caused increased let-7d expression in breast cancer cell lines after radiation treatment. In addition, the results showed that 24 h after radiation, the expression of let-7d in the radioresistant cell line was higher than the radiosensitive one; 48 h after radiation, the expression of let-7d in the radiosensitive cell line was higher than the other one.

Conclusions: The results demonstrated that radiation treatment increased let-7d miRNA expression in both radiosensitive and radio-resistant breast cancer cell lines. Therefore, let-7d might be involved in the radiosensitivity of breast cancer.