MAPT and neuroblastoma: In response to the p-tau or P301L p-tau challenge, expression levels of the ER chaperone BiP/GRP78, a master regulator of the ER stress response [28], in the neuroblastoma cells were significantly increased compared to those of the cells treated with vehicle (Figure 6A), demonstrating that p-tau or P301L p-tau is a potent trigger for ER stress.