Macrophage growth arrest by cyclic AMP defines a distinct checkpoint in the mid-G1 stage of the cell cycle and overrides constitutive c-myc expression.
Proliferation of a murine macrophage cell line (BAC1.2F5) in response to colony-stimulating factor 1 (CSF-1) is inhibited by prostaglandin E2 (PGE2)-mediated elevation of intracellular cyclic AMP (cAMP). When BAC1.2F5 cells were growth arrested in early G1 by CSF-1 starvation and stimulated to synchronously enter the cell cycle by readdition of growth factor, PGE2 inhibited [3H]thymidine incorporation when added before mid-G1, but its addition at later times did not block the onset of S phase. Reversible cell cycle arrest mediated by a cAMP analog required the presence of CSF-1 for cells to initiate DNA synthesis, whereas cells released from an aphidicolin block at the G1/S boundary entered S phase in the absence of CSF-1. PGE2 or cAMP analogs did not block the initial induction of c-myc mRNA by CSF-1 but abolished the CSF-1-dependent expression of c-myc mRNA in the mid-G1 stage of the cell cycle. The cAMP-mediated reduction in c-myc RNA levels was due to decreased c-myc transcription. However, CSF-1-dependent BAC1.2F5 clones infected with a c-myc retrovirus were growth arrested by cAMP analogs despite constitutive c-myc expression. Therefore, the reduction of endogenous c-myc expression by cAMP is neither necessary nor sufficient for growth inhibition.
Rock
C O
CO
Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38101.
Cleveland
J L
JL
Jackowski
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D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D004261:DNA Replication / Q000187:drug effects; D015232:Dinoprostone / Q000494:pharmacology*; D005091:Exons; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology*; D015870:Gene Expression; D016259:Genes, myc; D007438:Introns; D007700:Kinetics; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D008264:Macrophages / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D051379:Mice; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects*
D012333:RNA, Messenger; D011994:Recombinant Proteins; D012313:RNA; D003994:Bucladesine; D016173:Macrophage Colony-Stimulating Factor; D003513:Cycloheximide; D000242:Cyclic AMP; D015232:Dinoprostone