title: Rapid transcriptional down-regulation of c-myc expression during cyclic adenosine monophosphate-promoted differentiation of leukemic cells.
abstract: Pharmacologic elevation of cyclic AMP (cAMP) promotes growth arrest and differentiation in a variety of transformed mammalian cells, including the HL-60 human promyelocytic leukemia cell line. However, mechanisms underlying this phenomenon are poorly understood. Because cellular oncogenes play a pivotal role in regulating proliferation and differentiation, we examined whether cAMP-promoted differentiation of HL-60 was preceded by a decrease in the expression of c-myc, a cellular oncogene both amplified and constitutively expressed in HL-60. We find that cyclic AMP elevation in HL-60 caused by three different pharmacologic regimens is followed by an abrupt, greater than 90% decrease in steady state c-myc mRNA levels within 3 h, well before detectable changes in proliferation and differentiation. This decrease, which occurs despite protein synthetic blockade, is attributable to transcriptional down-regulation of c-myc and is accompanied by changes in chromatin structure near c-myc promoter sites. Our findings establish that cAMP, a ubiquitous intracellular regulatory messenger previously known only to enhance gene transcriptional activity in higher eukaryotic cells, can also suppress transcription of a cellular oncogene, thereby suggesting a potential mechanism for cAMP-promoted differentiation.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D003994:Bucladesine / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D003609:Dactinomycin / Q000494:pharmacology; D003850:Deoxyribonuclease I / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism*; D009857:Oncogenes; D012313:RNA / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D003609:Dactinomycin; D012313:RNA; D003994:Bucladesine; D002772:Cholera Toxin; D000242:Cyclic AMP; D003850:Deoxyribonuclease I; D015056:1-Methyl-3-isobutylxanthine