Study On The Role Of YAP Protein In Radiosensitivity Of Breast Cancer Cells

Radiotherapy is one of the important methods in the treatment of breast cancer. It can not only improve the local tumor control rate, but also improve the long-term survival rate of patients. However, radioresistance occurrence results in limitation of actual application of radiotherapy. The Hippo pathway plays a key role in the growth of tumors in Drosophila and mammals. One of downstream factors involved in this pathway is YAP (protein Yes-associated, the Drosophila Yki), which functions as a cofactor through binding with the transcription factor TEADs and regulates the expression of downstream target genes in the Hippo pathway. This study focuses on the effect of radiation on YAP protein and YAP phosphorylation, and potential role of Hippo-YAP signaling pathway in the radiosensitivity in breast cancer cells. The findings in the study are summarized as follows:Part 1. The effect of YAP protein on the radiosensitisation of breast cancer cellsBy using a transient transfection assay, a dose-dependent down-regulation of YAP expression was obtained in MDA-MB-231 cells transfected with si-YAP. Furthermore, a significant increase of radiosenstivity was observed in the cells transfected with si-YAP as determined by MTT assay and colony formation assay. An inhibition of migration and invasion capacity in si-YAP transfected MDA-MB-231 cells was also observed. Decreased expression of YAP down-regulated the expression of Bcl-2 protein, which is a key protein in apoptosis-mediated pathway. These preliminary results indicate that YAP might be an important mediator in radiosensitivity of breast cancer via regulating apoptosis.Part 2. Effect on radiation on YAP expression in breast cancer cellsBreast cancer cell lines, MDA-MB-231 and MCF-7, were used as the research objects. After gamma-ray radiation (0-10 Gy), the cell survival significantly decreased in a dose-depedent manner, MCF-7 cells were more sensitive to radiation compared with MDA-MB-231 cells. Total Yap protein level was not changed, the phosphorylated Yap (p-YAP) protein increased in a dose-dependent manner. As shown by Western blot, the p-YAP protein appeared to significantly be elevated in both of two cell lines at 16 h following irradiation with 6 Gy. Futhermore, this increase of p-YAP protein was still observable until 24 h following irradiation. By western blot, a significant increase of the phosphate YAP on Serl27 was seen in irradiated MDA-MB-231 cells. From the above experiments, we can infer that there is no significant change in the total YAP, but p-YAP on the site of Ser127 was significantly increased in breast cancer cells after irradiation.