Myc and Miz-1 have coordinate genomic functions including targeting Hox genes in human embryonic stem cells

To test the hypothesis that the zinc finger protein Miz-1 plays a central role, in the present work we conducted chromatin immunoprecipitation/microarray (ChIP-chip) analysis of Myc and Miz-1 in human ES cells, finding homeobox (Hox) genes as the most significant functional class of Miz-1 direct targets. Miz-1 differentiation-associated target genes specifically lack acetylated lysine 9 and trimethylated lysine 4 of histone H3 (AcH3K9 and H3K4me3) 9 histone marks, consistent with a repressed transcriptional state. Almost 30% of Miz-1 targets are also bound by Myc and these cobound genes are mostly factors that promote differentiation including Hox genes. Knockdown of Myc increased expression of differentiation genes directly bound by Myc and Miz-1, while a subset of the same genes is downregulated by Miz-1 loss-of-function. Myc and Miz-1 proteins interact with each other and associate with several corepressor factors in ES cells, suggesting a mechanism of repression of differentiation genes.Taken together our data indicate that Miz-1 and Myc maintain human ES cell pluripotency by coordinately suppressing differentiation genes, particularly Hox genes. These data also support a new model of how Myc and Miz-1 function on chromatin.Miz-1 is a member of the POZ domain/zinc finger transcription factor family. It contains 13 zinc fingers and a POZ/BTB (BTB for BR-C, ttk and bab, POZ for Pox virus and zinc finger) domain at its N-terminus [1]. In cancer cell lines, Miz-1 binds to specific sequences termed initiator elements (INR) in the core promoters of its target genes and activates their transcription through recruitment of coactivators including the histone acetyltransferase (HAT) p300 and nucleophosmin [2-4]. Among previously identified Miz-1 regulated targets are negative regulators of cell cycle control and cell growth, including p15Ink4b, p21Cip1, and c/EBPα [3,5,6]. By activating negative regulators of cell cycle, Miz-1 has a growth arrest function. In addition, Mi