MAPK3 and infection: While infection of Atf6−/− MEFs, PERK−/− MEFs, and wild-type MEFs with V. parahaemolyticus T3SS1+ resulted in robust ERK1/2 phosphorylation 45 and 60 min postinfection, phosphorylated ERK1/2 was not detected in IRE1−/− MEFs infected with V. parahaemolyticus T3SS1+ (Fig. 3A and B).