ATF4 and plasma cell myeloma: While we did not observe increased eIF2α phosphorylation [33], the absence of eIF2α phosphorylation upon arginine starvation has also been observed for multiple myeloma and breast cancer cells [35, 50], possible through the phosphatase GADD34, a downstream target of ATF4 that restores protein synthesis by dephosphorylating eIF2α in a feedback mechanism [51].