ATF4 and Parkinson disease: Another study showed that the DA neurotoxin mimicking PD, 1-methyl-4-phenylpyridinium ion (MPP+) and the neurotoxin 6-hydroxydopamine (6-OHDA) widely used to induce models of PD upregulate the expression of UPR proteins such as BIP, CHOP, ATF4, P-PERK, and P-eIF2α [182].