Heme synthesis inhibition induces the intrinsic apoptosis pathway in leukemia with OSGIN1 upregulation

Acute myeloid leukemia (AML) is one of the hematologic malignancies with a poor outcome. AML has a unique metabolic status, and identifying its metabolic vulnerabilities is warranted. Recent genome-wide screenings suggest that heme synthesis might be such a vulnerability. Heme is required not only for hemoglobin synthesis but also for the proper function of hemoproteins. Cytochromes are such hemoproteins and are necessary for mitochondrial respiration. Therefore, heme synthesis inhibition can diminish AML by altering mitochondrial status and function. However, still little is known about the importance of heme synthesis in leukemia cells. To reveal the roles of heme synthesis in leukemia, we treated human leukemia cell lines with heme synthesis inhibitors, succinylacetone (SA) or N-methyl protoporphyrin IX (NMPP). Heme synthesis inhibition induced cell growth inhibition and cell death in a concentration-dependent manner. Therefore, heme synthesis is required for leukemia cell proliferation and survival. Increased proapoptotic factors (cleaved caspase 3 and cleaved PARP) and decreased antiapoptotic factor (XIAP) were observed following heme synthesis inhibition. Cytochrome c and Smac were released into the cytoplasm by heme synthesis inhibition, suggesting that heme synthesis inhibition led to mitochondrial outer membrane permeabilization and activation of the intrinsic pathway of apoptosis. Comprehensive transcriptomic analysis revealed that heme synthesis inhibition induced OSGIN1 expression, leading to the release of cytochrome c and Smac from mitochondria into the cytoplasm. Therefore, heme synthesis inhibition induced leukemia apoptosis by activating the intrinsic apoptosis pathway.