Effect of Bmal1 expression on radiotherapy sensitivity of nasopharyngeal carcinoma xenograft / 中国肿瘤临床

ABSTRACT

Objective: To explore the effects of up- and down-regulation of circadian clock gene Bmal1 on the growth and radiation sensitivity of nasopharyngeal carcinoma after CNE1 xenograft in nude mice. Methods: We produced four groups of cells using lentiviral transfection: cells overexpressing CNE1 (CNE1OE), negative control in which there was no overexpression of CNE1 (OENC), cells with short hairpin RNAi (CNE1sh3), and RNAi negative cells (CNE1shNC). We investigated the expression of Bmal1 protein in the aforementioned groups with Western blot. After subcutaneously injecting the four groups of cells in nude mice, the size of the xenograft was measured. Subsequently, the xenografts were irradiated with 15 Gy at 6 MeV, and variation in the xenograft volume was recorded. mRNA and protein expression levels of Bmal1, p53, and p21 in the xenograft were measured with RT-PCR and Western blot, respectively. Results: The CNE1OE group highly expressed Bmal1 protein whereas the CNE1sh3 group was silenced by RNAi as shown with the Western blot, indicating successful transfection. The xenograft in the nude mice developed well. The CNE1OE xenograft volume was lower than that of the CNE1OENC xenograft, whereas the CNE1sh3 xenograft was larger than the CNE1shNC xenograft (P<0.05). CNE1OE, CNE1OENC, and CNE1shNC xenograft volumes shrank after being irradiated (t=4.32, 5.38, 5.16, respectively; P<0.05) and the effect was the highest in the CNE1OE group. However, there was almost no variation in xenograft volume in the CNE1sh3 group. The relative amounts of mRNA and protein of Bmal1, P53, and P21 were higher in the CNE1OE group than in the CNE1OENC group,while they were lower in the CNE1sh3 group compared to the CNE1shNC group (P<0.05). Conclusions: Overexpression of Bmal1 inhibited the growth of the CNE1 xenograft in nude mice and enhanced its radiation sensitivity whereas silencing the Bmal1 gene by RNAi promoted the growth of the xenograft and led to radiation resistance. We believe that Bmal1 overexpression leads to P53 and P21 overexpression, thereby inhibiting the growth of the xenograft.