Tyrosine kinase Etk/BMX protects nasopharyngeal carcinoma cells from apoptosis induced by radiation

Abstract

Etk (Epithelial and endothelial tyrosine kinase), also known as Bmx (bone marrow X kinase) plays an important role in apoptosis of cancer cells. The purpose of this study was to investigate whether Etk/Bmx is involved in the apoptosis induced by irradiation in NPC cells and correlated with the apoptosis associated proteins such as p53, Bcl-2, Bcl-XL and Bak. To this end, we first developed a NPC subline (SUNE1-Etk) by transfection. The SUNE1-Etk that over-expresses Etk/BMX and its parental SUNE1 cell line were used to confirm whether Etk/BMX can protect NPC cells from apoptosis induced by radiation. The proliferation rates or the level of cell survival following irradiation were assessed by MTT and flow cytometry. Tumorigenecity study was done to substantiate the results in vitro. The results showed that the cell viability was significantly higher in SUNE1-Etk cells than that in parental SUNE1 cells in vitro, and tumors inoculated with SUNE1-Etk cells grew rapidly than those with SUNE1 after irradiation treatment. Our data also demonstrated that the up-expression of Etk/BMX increased G2/M arrest in response to irradiation. The protein level of p53 was greatly down-regulated whereas Bcl-2 was up-regulated, after irradiation treatment of SUNE1-Etk cells. Our results suggested that Etk/BMX may play a role in protection of NPC cells from apoptosis, and both p53 and Bcl-2 may be involved in radiation-induced apoptosis through Etk/Bmx pathway in NPC cells.