A switch from Myc:Max to Mad:Max heterocomplexes accompanies monocyte/macrophage differentiation.
Mad is a basic-helix-loop-helix-zipper protein that heterodimerizes with Max in vitro. Mad:Max heterodimers recognize the same E-box-related DNA-binding sites as Myc:Max heterodimers. However, in transient transfection assays Myc and Mad influence transcription in opposite ways through interaction with Max; Myc activates while Mad represses transcription. Here, we demonstrate that Mad protein is induced rapidly upon differentiation of cells of the myeloid lineage. The Mad protein is synthesized in human cells as a 35-kD nuclear phosphoprotein with an extremely short half-life (t1/2 = 15-30 min) and can be detected in vivo in a complex with Max. In the undifferentiated U937 monocyte cell line Max was found complexed with Myc but not Mad. However, Mad:Max complexes began to accumulate as early as 2 hr after induction of macrophage differentiation with TPA. By 48 hr following TPA treatment only Mad:Max complexes were detectable. These data show that differentiation is accompanied by a change in the composition of Max heterocomplexes. We speculate that this switch in heterocomplexes results in a change in the transcriptional regulation of Myc:Max target genes required for cell proliferation.
Ayer
D E
DE
Division of Basic Sciences A2-025, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104.
Eisenman
R N
RN
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000302:isolation & purification; D004591:Electrophoresis, Polyacrylamide Gel; D015972:Gene Expression Regulation, Neoplastic; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D008970:Molecular Weight; D014176:Protein Biosynthesis; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis* / Q000302:isolation & purification; D012333:RNA, Messenger / Q000096:biosynthesis; D012097:Repressor Proteins; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C499330:MAX protein, human; C079439:MXD1 protein, human; D046911:Macromolecular Substances; C067850:Myc associated factor X; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D012097:Repressor Proteins; D014157:Transcription Factors; D013755:Tetradecanoylphorbol Acetate