ABSTRACT
In response to stimuli that activate p53, cells can undergo either apoptosis or cell cycle arrest, depending on the precise pattern of p53 target genes that is activated. We show here that Zbtb4, a transcriptional repressor protein, associates with the Sin3/histone deacetylase co-repressor and represses expression of P21CIP1 as part of a heterodimeric complex with Miz1. In vivo, expression of ZBTB4 is downregulated in advanced stages of multiple human tumours. In cell culture, depletion of ZBTB4 promotes cell cycle arrest in response to activation of p53 and suppresses apoptosis through regulation of P21CIP1, thereby promoting long-term cell survival. Our data suggest that Zbtb4 is a critical determinant of the cellular response to p53 activation and reinforce the notion that p21Cip1 can provide an essential survival signal in cells with activated p53.
Subject(s)
Cyclin-Dependent Kinase Inhibitor p21/genetics , DNA-Binding Proteins/metabolism , Gene Expression Regulation , Repressor Proteins/metabolism , Tumor Suppressor Protein p53/metabolism , Apoptosis , Cell Cycle , Child , DNA-Binding Proteins/genetics , Down-Regulation , Humans , Kruppel-Like Transcription Factors/metabolism , Neoplasms/genetics , Neoplasms/metabolism , Promoter Regions, Genetic , Repressor Proteins/genetics , Sin3 Histone Deacetylase and Corepressor Complex , Transcription Factors/metabolism , Transcription, Genetic , Tumor Cells, CulturedABSTRACT
Myc synergizes with Ras and PI3-kinase in cell transformation, yet the molecular basis for this behavior is poorly understood. We now show that Myc recruits TFIIH, P-TEFb and Mediator to the cyclin D2 and other target promoters, while the PI3-kinase pathway controls formation of the pre-initiation complex and loading of RNA polymerase II. The PI3-kinase pathway involves Akt-mediated phosphorylation of FoxO transcription factors. In a nonphosphorylated state, FoxO factors inhibit induction of multiple Myc target genes, Myc-induced cell proliferation and transformation by Myc and Ras. Abrogation of FoxO function enables Myc to activate target genes in the absence of PI3-kinase activity and to induce foci formation in primary cells in the absence of oncogenic Ras. We suggest that the cooperativity between Myc and Ras is at least in part due to the fact that Myc and FoxO proteins control distinct steps in the activation of an overlapping set of critical target genes.
