title: Puromycin-elicited c-myc mRNA superinduction precedes apoptosis in HL-60 leukaemic cells.
abstract: The phenomenon of superinduction refers to the process by which high concentrations of protein synthesis inhibitors augment and stabilize mRNA transcript levels, e.g. 36-180 microM of Puromycin (PM) has been found to elicit c-myc mRNA superinduction. The expression of the proto-oncogene c-myc has been strongly variously implicated in the regulation of the apoptotic cascade. Since we recently found that a low dose of the protein synthesis inhibitor PM activated the apoptotic cascade in HL-60 leukaemic cells, the current study was undertaken to examine c-myc mRNA transcript levels in such cells, and to assess the relationship, if any, between PM-elicited c-myc mRNA superinduction and subsequent activation of the apoptotic cascade. PM was employed in vitro at doses of 0.9 microM and 2 microM. Dose-dependent c-myc mRNA superinduction was present at 1 hour of PM-exposure, and was associated with subsequent activation of the apoptotic cascade at 24 hours of exposure. Apoptosis was confirmed morphologically as evidenced by chromatin condensation, nuclear fragmentation and the formation of apoptotic bodies, and by DNA agarose gel electrophoresis which showed the pattern of double-stranded DNA fragments that result from the activation of an endogenous endonuclease. [C14]Leucine incorporation studies at 1 hour demonstrated minimal protein synthesis inhibition at doses used, suggesting that c-myc mRNA superinduction in this context may have been the result of mechanisms which were independent of the inhibition of synthesis of new proteins, such as interruptions in signal transduction.
authors.affiliation: Department of Haematology, School of Pathology, University of the Witwatersrand, Johannesburg, South Africa.
authors.forename: A N
authors.initials: AN
authors.lastname: Davidoff
authors.forename: B V
authors.initials: BV
authors.lastname: Mendelow
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002460:Cell Line; D004249:DNA Damage / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects*; D016259:Genes, myc / Q000187:drug effects*; D006801:Humans; D007930:Leucine / Q000378:metabolism; D015473:Leukemia, Promyelocytic, Acute; D009363:Neoplasm Proteins / Q000096:biosynthesis; D000090063:Proto-Oncogene Mas; D011519:Proto-Oncogenes / Q000187:drug effects; D011691:Puromycin / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis*; D015398:Signal Transduction / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: C000715470:MAS1 protein, human; D009363:Neoplasm Proteins; D000090063:Proto-Oncogene Mas; D012333:RNA, Messenger; D011691:Puromycin; D007930:Leucine