Mechanism And Contribution Of Caveolin-1 To Radiosensitizing Enhancement Induced By X-ray Irradiation In Human Breast Epithelial Cells

Breast cancer has aroused great social concern as a serious disease threatening wemen's health on both physical and psychology effects. As it is widely known, Radiotherapy after breast-conserving surgery plays a crucial role in local controls. However, during the Radiotherapy, the rays will also damage part of normal tissues while eliminating the cancerous cells. In current molecular biology techniques - "Gene and Radiotherapy", the radiation protection and radiation sensitization strategy has been recognized in many reports.As an important structural protein in caveolae, Caveolin-1(Cav-1) is involved in intracellular and extracellular material exchange, concentration and assembly of lipid/ipid signaling moleculesand several other signaling pathway factors as well. Recent studies have shown that, after exposure to radiation, Cav-1 deficient small intestinal crypt stem cells displayed a decreased survival rate relative to wild-type mice. In three dimensional culture of pancreatic carcinoma, decreased Cav-1 expression has been associated with serious DNA damage after ionizing radiation. These results suggest that Cav-1 may be involved in DNA damage repair after radiation, affecting the radio sensitivity of cells.On the basis of these findings, Cav-1 gene silenced cell line MCF10A^CE and the parent cell line MCF10A were selected and after exposure in X-ray radiation, Cell survival ability, cell cycle variations, and expressions of DNA damage repair factors together with related signaling factors were investigated. The relationship between Cav-1 expression and the radiation sensitivity of mammary epithelial cells is probed, and the possible molecular mechanism of Cav-1 involved in radioactive DNA damage repair is explored. Our data provide experimental evidence for further revealing the function of Cav-1 as tumor suppressor factor in cellular response to radiation injury.The results are as follows:1. MCF10ACE cells displayed a decreased survival rate compared to MCF10A cells after X ray.irradiation. We also showed that ionizing radiation resulted in G1, G2 phase arrested and S phase fraction decreased in both cell lines. The situation was worse in MCF10A^CE cells with high significance (P<0.01). CDK4 and cyclinD1 involved in cell cycle G1 arrest. 2. MCF10A^CE cells were associated with a significant increased number ofγH2AX positive nuclear foci compared to MCF10A cells after X ray.irradiation. There was no significant difference of Cav-1 expression in both cell lines after irradiation. Cav-1 silencing inhibited the activation of DNA damage repair protein ATM,p53 and stress protein p38MAPK than controls, suggests that deficency of Cav-1 may reduce the activation of ATM-mediated DNA damage-responsive signaling pathways.3. Ionizing radiation promoted the interaction between Cav-1 and Mdm2. Obviously, the nteraction after 12hours radiation was significant higher than after 2hours. MCF10A cells displayed more significant variety.Conclusion: Cav-1 plays an important role in radiosensitizing enhancement in human breast epithelial cells. Cav-1 deficiency abates the combination between Cav-1and Mdm2 induced by X-ray, reduces the ATM-mediated activation of DNA damage repair pathways, and subsequently reduces the stability of p53 protein through down regulation of p53, which results in an enhancement of radiosensitizing in mammary cells...