title: Reversible differentiation of human monoblastic leukemia U937 cells by ML-9, an inhibitor of myosin light chain kinase.
abstract: Human monoblastic leukemia U937 cells are induced to differentiate into monocytes and macrophages by various agents. We have shown that 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-9), an inhibitor of myosin light chain kinase, induces differentiation of monocytoid leukemia cell lines U937 and THP-1 but not of myeloblastic leukemic ML-1 cell or erythroleukemia K562 cells. In the present study, we further analyzed the effect of ML-9 in comparison with that of 1 alpha, 25-dihydroxyvitamin D3 (VD3) a typical inducer of monocytic differentiation. ML-9 induced nitroblue tetrazolium (NBT)-reducing activity of U937 cell more rapidly than VD3: This differentiation marker was induced significantly after incubation with ML-9 and VD3 for 4 hours and 1 day, respectively. ML-9 also induced alpha-naphthyl acetate esterase (ANAE) activity, another monocytic differentiation marker, more rapidly than VD3. The maximum levels of these markers induced by ML-9 were comparable to those induced by VD3, but after removal of ML-9 from the medium by washing the cells, the expressions of theses markers decreased within 4 hours and reached basal levels in 1 day, indicating that ML-9's induction of expression of differentiation-associated phenotypes was reversible. The growth inhibition of U937 cells by ML-9 was also reversible. Similar effects were observed in another line of human monoblastic cells, THP-1. ML-9 had little or no effect on the morphology of U937 cells but increased the expression of monocyte-macrophage lineage-associated surface antigen, CD14, to some extent. Irreversible terminal differentiation induced by VD3 is associated with down regulation of the expression of c-myc and upregulation of the expression of c-fos and c-jun, but ML-9 did not affect the expression of these oncogenes appreciably. ML-9-induced differentiation was also reversible when the cells were cultured with cultured with ML-9 plus an anti-cancer drug such as 1-beta-D-arabino-furanosylcytosine or daunomycin. it became irreversible, however, upon simultaneous treatment with dexamethasone and transforming growth factor-beta 1 (TGF-beta 1), which did not induce differentiation of U937 cells but caused growth arrest of the cells in the G0/G1 phase of the cell cycle. These results suggest that ML-9 should be useful for studying the mechanisms of monocytic differentiation.
authors.affiliation: Department of Chemotherapy, Saitama Cancer Center Research Institute, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto-Yamaguchi
authors.forename: M
authors.initials: M
authors.lastname: Makishima
authors.forename: Y
authors.initials: Y
authors.lastname: Kanatani
authors.forename: T
authors.initials: T
authors.lastname: Kasukabe
authors.forename: Y
authors.initials: Y
authors.lastname: Honma
mesh_terms: D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology; D001381:Azepines / Q000494:pharmacology*; D001483:Base Sequence; D002117:Calcitriol / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D003561:Cytarabine / Q000494:pharmacology; D017931:DNA Primers / Q000737:chemistry; D003630:Daunorubicin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D016758:Genes, jun; D016259:Genes, myc; D005938:Glucocorticoids / Q000494:pharmacology; D006801:Humans; D007948:Leukemia, Monocytic, Acute / Q000473:pathology*; D008969:Molecular Sequence Data; D009000:Monocytes / Q000166:cytology*; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors*; D012333:RNA, Messenger / Q000235:genetics; D013997:Time Factors; D018808:Transcription Factor AP-1 / Q000235:genetics; D014407:Tumor Cells, Cultured
chemical_list: D015214:Antigens, Differentiation, Myelomonocytic; D000970:Antineoplastic Agents; D001381:Azepines; D017931:DNA Primers; D004791:Enzyme Inhibitors; D005938:Glucocorticoids; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D003561:Cytarabine; C056218:ML 9; D003907:Dexamethasone; D009219:Myosin-Light-Chain Kinase; D002117:Calcitriol; D003630:Daunorubicin