EFFECTS OF BRAF ON GROWTH AND PROLIFERATION OF THYROID CANCER CELLS BY REGULATING THE RAS-BRAF-MEK-ERK SIGNALING PATHWAY

Hong Chai¹, Qin Huang², Zequan Chen¹, Jiahuan Yang¹, Yongli Yu^{3, *}

¹Department of Nuclear Medicine, Shanghai Sixth People's Hospital East Affiliated with Shanghai University of Medicine & Health Sciences, Shanghai, 201306, China - ²Department of Pathology, Shanghai Sixth People's Hospital East Affiliated with Shanghai University of Medicine & Health Sciences, Shanghai, 201306, China - ³Department of Nuclear Medicine, Shanghai Jiao Tong University Affiliated with Sixth People’s Hospital, Shanghai 200233, China

Objective: To analyze the effects of BRAF on growth and proliferation of thyroid cancer cells by regulating the RAS-BRAF-MEK-ERK signaling pathway.

Methods: Thyroid cancer SW579 cell line and thyroid tumor cells were cultured in vitro, and mRNA expression of BRAF in thyroid cancer cells was detected by real-time quantitative PCR assay. Thyroid cancer SW579 cells were randomly divided into control group, down-regulated BRAF 1 group and down-regulated BRAF 2 group, and transfected with control interference fragment, BRAF interference fragment 1 and BRAF interference fragment 2, respectively. An MTT assay was used to detect the effect of down-regulated BRAF expression on the proliferation of thyroid cancer cells, and a western blot was used to measure the effect of down-regulated BRAF expression on the protein expressions of RAS, BRAF, p-MEK, MEK, p-ERK and ERK.

Results: The expression level of BRAF mRNA in thyroid cancer cells was significantly higher than that in thyroid tumors, and the difference was statistically significant (P < 0.05). After 25 nmol siRNA was used to interfere with BRAF, the cell growth ability was detected. Compared with the control group, the down-regulated BRAF 1 group and the down-regulated BRAF 2 group could significantly inhibit the growth of thyroid cancer cells after 7 days of interference. The cell proliferation rate was detected at 12, 24 and 36 h and it was found that compared with the control group, the proliferation of thyroid cancer cells in the down-regulated BRAF 1 group and the down-regulated BRAF 2 group was remarkably inhibited at each time point (P<0.05). Compared with the control group, BRAF and RAS protein levels and MEK and ERK phosphorylation levels were obviously reduced in the down-regulated BRAF 1 group and the down-regulated BRAF 2 group, with statistically significant differences (P<0.05).

Conclusion: The BRAF gene is highly expressed in thyroid cancer cells, and down-regulation of its level can significantly inhibit the growth and proliferation of thyroid cancer cells, and its mechanism may be related to the inhibition of the expression of the RAS-BRAF-MEK-ERK signaling pathway.