ABSTRACT
The Myc oncoprotein forms a binary activating complex with its partner protein, Max, and a ternary repressive complex that, in addition to Max, contains the zinc finger protein Miz1. Here we show that the E3 ubiquitin ligase HectH9 ubiquitinates Myc in vivo and in vitro, forming a lysine 63-linked polyubiquitin chain. Miz1 inhibits this ubiquitination. HectH9-mediated ubiquitination of Myc is required for transactivation of multiple target genes, recruitment of the coactivator p300, and induction of cell proliferation by Myc. HectH9 is overexpressed in multiple human tumors and is essential for proliferation of a subset of tumor cells. Our results suggest that site-specific ubiquitination regulates the switch between an activating and a repressive state of the Myc protein, and they suggest a strategy to interfere with Myc function in vivo.
Subject(s)
Neoplasms/pathology , Proto-Oncogene Proteins c-myc/physiology , Transcriptional Activation , Ubiquitin-Protein Ligases/physiology , Amino Acid Sequence , Animals , Cell Line, Tumor , Cell Proliferation , DNA-Binding Proteins/metabolism , Genes, myc , Humans , Kruppel-Like Transcription Factors , Mice , Molecular Sequence Data , Neoplasms/metabolism , Polyubiquitin/metabolism , Proto-Oncogene Proteins c-myc/genetics , Transcription Factors/metabolism , Tumor Suppressor Proteins , Ubiquitin-Protein Ligases/genetics , p300-CBP Transcription Factors/metabolismABSTRACT
Myc genes are key regulators of cell proliferation, and their deregulation contributes to the genesis of most human tumours. Recently, a wealth of data has shed new light on the biochemical functions of Myc proteins and on the mechanisms through which they function in cellular transformation.
Subject(s)
Cell Transformation, Neoplastic/genetics , Gene Expression Regulation, Neoplastic , Proto-Oncogene Proteins c-myc/metabolism , Binding Sites , DNA-Binding Proteins/metabolism , Humans , Repressor Proteins/metabolism , Transcription, GeneticABSTRACT
Miz1 is a member of the POZ domain/zinc finger transcription factor family. In vivo, Miz1 forms a complex with the Myc oncoprotein and recruits Myc to core promoter elements. Myc represses transcription through Miz1 binding sites. We now show that the Miz1 gene is ubiquitously expressed during mouse embryogenesis. In order to elucidate the physiological function of Miz1, we have deleted the mouse Miz1 gene by homologous recombination. Miz1(+/-) mice are indistinguishable from wild-type animals; in contrast, Miz1(-/-) embryos are not viable. They are severely retarded in early embryonic development and do not undergo normal gastrulation. Expression of Goosecoid and Brachyury is detectable in Miz1(-/-) embryos, suggesting that Miz1 is not required for signal transduction by Nodal. Expression of p21Cip1, a target gene of Miz1 is unaltered; in contrast, expression of p57Kip2, another target gene of Miz1 is absent in Miz1(-/-) embryos. Miz1(-/-) embryos succumb to massive apoptosis of ectodermal cells around day 7.5 of embryonic development. Our results show that Miz1 is required for early embryonic development during gastrulation.
