HF treatment markedly increased activating transcription factor 4 (ATF4), CHOP (encoded by DNA damage inducible transcript 3), and p-eIF2α protein levels compared with control treatment (Fig. 4A–D), confirming that HF activates AAR mediated by p-eIF2α-ATF4-CHOP signaling in AML cells. Here, ATF4 is linked to hydrops fetalis.