c-Myc does not require max for transcriptional activity in PC-12 cells.
The c-Myc proto-oncogene is a basic helix-loop-helix leucine zipper (b/HLH/LZ) protein that participates in cellular growth and differentiation. The expression of c-Myc mRNA is rapidly induced by nerve growth factor (NGF) and epidermal growth factor (EGF) in PC-12 pheochromocytoma cells. In most cell types, c-Myc forms a sequence-specific DNA binding complex with the stable, constitutively expressed Max. This complex can function as a transcriptional regulator. We show here that the expression of Max mRNA or protein was not detected in PC-12 cells. Nevertheless, treatment of PC-12 cells with NGF and serum caused an increase in the expression of the c-Myc protein and the transcription of a reporter gene linked to the Myc/Max DNA binding site. Transcription from the same reporter gene is stimulated by over-expression of c-Myc. These results suggest that c-Myc protein functions as a transcriptional regulator in PC-12 cells despite the lack of Max protein. Therefore, Myc/Max complexes may not be an absolute requirement for Myc-dependent gene expression.
Ribon
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Department of Physiology, University of Michigan School of Medicine, Ann Arbor 48105.
Leff
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Saltiel
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D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D001790:Blood Physiological Phenomena; D002417:Cattle; D003470:Culture Media; D004268:DNA-Binding Proteins / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D018257:Helix-Loop-Helix Motifs; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins; D009414:Nerve Growth Factors / Q000494:pharmacology; D016716:PC12 Cells; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D003470:Culture Media; D004268:DNA-Binding Proteins; C499329:Max protein, rat; C067850:Myc associated factor X; D009363:Neoplasm Proteins; D009414:Nerve Growth Factors; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors