title: Absence of phorbol ester-induced down-regulation of myc protein in the phorbol ester-tolerant mutant of HL-60 promyelocytes.
abstract: The human promyelocytic leukemia cell line HL-60 has an amplified number of copies of the protooncogene c-myc. It is induced to differentiate by exposure to the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA). We have developed a mutant phorbol ester-tolerant (PET) line of HL-60 which undergoes a transient growth arrest but does not differentiate when exposed to TPA (Macfarlane et al., Br. J. Haematol., 68: 291-302, 1988). The defect is not due to a general failure of TPA-induced phosphorylation. In this paper, we show that exposing phorbol ester-sensitive (S) HL-60 cells to TPA caused the disappearance of the c-myc protein antigen (detected on Western blots) in 4 h, whereas TPA had no effect on the c-myc protein content of PET cells. Dimethyl sulfoxide caused the rapid disappearance of the myc antigen in both cells. PET cells had slightly more copies of the c-myc gene detected on Southern blots than S cells. c-myc mRNA was equally unstable in both cells, as determined by Northern blots following actinomycin D. TPA induced the down-regulation of c-myc mRNA in S cells to a greater extent than in PET cells. Dimethyl sulfoxide caused a rapid down-regulation of c-myc mRNA in both cell lines. This shows that PET cells have a defect in the mechanism by which protein kinase C regulates c-myc transcription. Our results provide further evidence that reduction in c-myc expression is necessary for differentiation to occur in HL-60 cells.
authors.affiliation: Department of Internal Medicine, Iowa City Veterans Administration Medical Center, Iowa.
authors.forename: D
authors.initials: D
authors.lastname: Gailani
authors.forename: F J
authors.initials: FJ
authors.lastname: Cadwell
authors.forename: P S
authors.initials: PS
authors.lastname: O'Donnell
authors.forename: R A
authors.initials: RA
authors.lastname: Hromas
authors.forename: D E
authors.initials: DE
authors.lastname: Macfarlane
mesh_terms: D015139:Blotting, Southern; D002454:Cell Differentiation / Q000187:drug effects; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D005784:Gene Amplification / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000235:genetics* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger / Q000032:analysis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000378:metabolism
chemical_list: D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D013755:Tetradecanoylphorbol Acetate; D004121:Dimethyl Sulfoxide