ATF6 and glioma: The p-PERK levels in RG-2, U87-MG, U251, and LN-428 cells were 46.4%, 23.7%, 18.8%, and 24.7%, respectively, higher than those in normal glioma cells (P < 0.01; Figure 3(b)), and the levels of cleaved ATF6 increased by 89.3%, 78.6%, 92.4%, and 29.1% (P < 0.01) in RG-2, U87-MG, U251, and LN-428 cells, respectively, when treated with 15 μM SSD for 48 h compared with those in the corresponding control cells.