Abstract:

Xu Qianqian*, Chen Xu, Li Li, Xu Song, Ding Lan, Zhang Yun, Ju Mei, Li Xinyu, Shi Xin, Chen Kun, Gu Heng. *Department of Dermatology, Second Affiliated Hospital of Soochow University, Suzhou 215004, China Corresponding authors: Chen Xu, Email: doctor_chx@126.com; Shi Xin, Email: shx9@163.com 【Abstract】 Objective To explore the regulatory effects of ultraviolet B （UVB） radiation on the mitogen-activated protein kinase （MAPK） signaling pathway in cultured HaCaT cells in vitro at different post-radiation time points. Methods Some cultured HaCaT cells were classified into several groups to be exposed to UVB of 1.5, 4.5, 7.5,10, 20, 30 and 50 mJ/cm2 for 1, 3, 5, 7, 15, 20 and 34 seconds respectively, or UVB of 50 mJ/cm2 for 34 seconds, or remain untreated （control group）. Western blot was performed to determine the total and phosphorylation levels of ERK1/2, JNK and p38 in HaCaT cells at 8 hours after exposure to 1.5, 4.5, 7.5,10, 20, 30 and 50 mJ/cm2 UVB, as well as at 2, 4, 8 and 12 hours after exposure to 50 mJ/cm2 UVB. Quantity One software was used to measure the absorbance value of protein bands, and protein levels were expressed as the absorbance ratio of target bands to glyceraldehyde-3-phosphate dehydrogenase （GAPDH）. Statistical analysis was carried out by using one-way analysis of variance, least significant difference （LSD）-t test and multivariate analysis of variance. Results Compared with the control group, there was a significant increase at 8 hours in the phosphorylation levels of ERK 1/2 and JNK in HaCaT cells after exposure to 7.5, 10, 20, 30 and 50 mJ/cm2 UVB （all P < 0.05）, and in the phosphorylation level of p38 after exposure to 20, 30 and 50 mJ/cm2 UVB （all P < 0.05）, with the strongest increase in phosphorylation levels of ERK 1/2, JNK and p38 all observed in HaCaT cells exposed to 50 mJ/cm2 UVB （all P < 0.05）. After exposure to 50 mJ/cm2 UVB, the phosphorylation level of ERK1/2 began to increase in HaCaT cells at 8 hours, and significantly increased at 12 hours （44.844 ± 2.023 vs. 10.277 ± 0.320, P < 0.05） compared with the control group; however, the phosphorylation levels of p38 and JNK increased in HaCaT cells as early as 2 hours after exposure （both P < 0.05）, and remained significantly higher compared with the control group at 4, 8 and 12 hours （all P < 0.05）, while the increasing trend in phosphorylated JNK level weakened over time （P < 0.05）. Conclusions The ERK1/2, JNK and p38 MAPK signaling pathways were activated in HaCaT cells after exposure to 50 mJ/cm2 UVB, and the degree of their activation varied over time.