title: Enhanced autophagy in cytarabine arabinoside-resistant U937 leukemia cells and its potential as a target for overcoming resistance.
abstract: Autophagy is a lysosomal degradation mechanism that is essential for cell survival, differentiation, development, and homeostasis. Autophagy protects cells from various stresses, including protecting normal cells from harmful metabolic conditions, and cancer cells from chemotherapeutics. In the current study, a cytarabine arabinoside (Ara‑C)‑sensitive U937 leukemia cell line and an Ara‑C‑resistant U937 (U937/AR) cell line were assessed for baseline autophagy activity by investigating the LC3‑I conversion to LC3‑II, performing EGFP‑LC3 puncta, an acidic autophagolysosome assay, and measuring the expression of various autophagy‑related genes. The results demonstrated significantly higher autophagic activity in the U937/AR cells compared with the U937 cells, when the cells were cultured with or without serum. Furthermore, an increase in the autophagic activity in starved U937/AR cells was demonstrated, compared with that in the starved U937 cells. Administration of an autophagy inhibitor demonstrated no change in cell death in the two cell lines when cultured with serum, however, it induced cell death regardless of the Ara‑C sensitivity when the cell lines were cultured without serum. In addition, the U937 cells demonstrated an Ara‑C resistance when cultured without serum. Co‑treatment with Ara‑C and the autophagy inhibitor significantly induced cell death in the U937/AR and Ara‑C‑sensitive U937 cells. In conclusion, autophagy serves an important role in protecting U937 cells from Ara‑C and in the development of Ara‑C resistance. Inhibition of autophagy combined with the Ara‑C treatment in the U937 cells augmented the anti‑leukemic effect of Ara‑C and overcame Ara‑C resistance, suggesting that autophagy may be an important therapeutic target to further improve the treatment outcome in patients with acute myeloid leukemia.
authors.affiliation: Department of Internal Medicine, Yonsei University College of Medicine, Seoul 120‑752, Republic of Korea.
authors.forename: June-Won
authors.initials: JW
authors.lastname: Cheong
authors.affiliation: Department of Internal Medicine, Yonsei University College of Medicine, Seoul 120‑752, Republic of Korea.
authors.forename: Yundeok
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Medical Research Center, Yonsei University College of Medicine, Seoul 120‑752, Republic of Korea.
authors.forename: Ju In
authors.initials: JI
authors.lastname: Eom
authors.affiliation: Medical Research Center, Yonsei University College of Medicine, Seoul 120‑752, Republic of Korea.
authors.forename: Hoi-Kyung
authors.initials: HK
authors.lastname: Jeung
authors.affiliation: Department of Internal Medicine, Yonsei University College of Medicine, Seoul 120‑752, Republic of Korea.
authors.forename: Yoo Hong
authors.initials: YH
authors.lastname: Min
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D001343:Autophagy / Q000187:drug effects*; D015153:Blotting, Western; D003561:Cytarabine / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D006886:Hydroxychloroquine / Q000633:toxicity; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism / Q000473:pathology; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D020298:U937 Cells
chemical_list: D000964:Antimetabolites, Antineoplastic; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; C485184:enhanced green fluorescent protein; D003561:Cytarabine; D049452:Green Fluorescent Proteins; D006886:Hydroxychloroquine