Mitotic retention of gene expression patterns by the cell fate-determining transcription factor Runx2

Abstract

During cell division, cessation of transcription is coupled with mitotic chromosome condensation. A fundamental biological question is how gene expression patterns are retained during mitosis to ensure the phenotype of progeny cells. We suggest that cell fate-determining transcription factors provide an epigenetic mechanism for the retention of gene expression patterns during cell division. Runx proteins are lineage-specific transcription factors that are essential for hematopoietic, neuronal, gastrointestinal, and osteogenic cell fates. Here we show that Runx2 protein is stable during cell division and remains associated with chromosomes during mitosis through sequence-specific DNA binding. Using siRNA-mediated silencing, mitotic cell synchronization, and expression profiling, we identify Runx2-regulated genes that are modulated postmitotically. Novel target genes involved in cell growth and differentiation were validated by chromatin immunoprecipitation. Importantly, we find that during mitosis, when transcription is shut down, Runx2 selectively occupies target gene promoters, and Runx2 deficiency alters mitotic histone modifications. We conclude that Runx proteins have an active role in retaining phenotype during cell division to support lineage-specific control of gene expression in progeny cells.L ineage commitment and cell proliferation are critical for normal tissue development. Preservation of phenotype during clonal expansion of committed cells necessitates the faithful segregation of chromosomes and the conveyance of lineage-specific gene regulatory machinery to progeny cells. Mitosis involves nuclear reorganization, global chromosome condensation, and transcription silencing and occurs concomitant with protein degradation and/or displacement of many regulatory factors from chromosomes (1-4). One fundamental question is how cells are programmed to sustain phenotypic gene expression patterns after cell division when transcriptional competency is restored in progeny cells.Cell fate is determined in response to extracellular cues by lineage-specific master regulators that include the Runx family of transcription factors. In mammals, these proteins are required for development of hematopoietic (Runx1), osteogenic (Runx2), and gastrointestinal and neuronal (Runx3) cell lineages (5-11). Runx factors integrate cell signaling pathways (e.g., TGF-␤/bone morphogenetic protein and Yes/Src) and recruit chromatin-modifying enzymes (e.g., histone deacetylases, histone acetyltransferases, SWI/SNF, SuVar139) to modulate promoter accessibility within a nucleosomal context (10,(12)(13)(14)(15)(16)(17). Runx proteins function as promoter-bound scaffolds that organize the regulatory machinery for gene expression within punctate subnuclear domains during interphase (18,19). Pathological perturbations in the organization of these domains are linked with altered development and tumorigenesis (10,(20)(21)(22)(23)(24)(25)(26)(27)(28)(29). Temporal and spatial changes of these architecturally organized Runx domains occur during...

Runx2 deficiency and defective subnuclear targeting bypass senescence to promote immortalization and tumorigenic potential

“…Furthermore, Runx2 up-regulation does not impede cell-cycle progression in cancer cells. In contrast, in normal osteoblasts, Runx2 ablation accelerates proliferation and increases ribosomal gene expression (18,19,29,30). Together these observations indicate that Runx2 may function as a tumor suppressor in some cell types and have oncogenic potential in others.…”

“…Runx2, p53, and pRb all control cell proliferation by regulating cell-cycle progression and mediating cell growth through effects on ribosomal biogenesis (18,19,30,37,38). Abrogation of tumor suppressor pathways controlled by p53 and pRb, which are ubiquitously expressed, results in the development of diverse tumors that are confined to specific tissues (7,8), indicating that lineagespecific mechanisms are involved.…”

“…Genetic studies reveal that Runx1 is essential for definitive hematopoiesis, Runx2 is required for osteogenesis, and Runx3 is involved in gut development as well as neurogenesis (12-16). Runx proteins support epigenetic regulation at mitosis and control ribosomal gene expression during the cell cycle (9)(10)(11)(17)(18)(19). Runx transcription factors are nuclear-scaffolding proteins that integrate signaling pathways by organizing macromolecular complexes in nuclear microenvironments and facilitating chromatin remodeling (20).…”

Prevention of Premature Fusion of Calvarial Suture in GLI-Kruppel Family Member 3 (Gli3)-deficient Mice by Removing One Allele of Runt-related Transcription Factor 2 (Runx2)

“…It has been reported that Runx2 controls the cell fate, proliferation, and growth through regulating ribosomal biogenesis (17,35). In Gli3…”

“…In Situ Hybridization-Preparation of 35 S-labeled uridine 5Ј-triphosphate and digoxigenin-UTP-labeled riboprobes, in situ hybridization, and image processing have been described previously (26). The Runx2-I probe used in in situ hybridization was prepared from a 639-bp fragment of murine Runx2 cDNA isolated from C3H10T1/2 cells by RT-PCR with the specific primers: 5Ј-CGGGATCCTCTCAGCTTTAGCGTCGTCA-3Ј for the forward primer and 5Ј-GCTCTAGACCGCAAGGG-ACTTGAAGTT-3Ј for the reverse primer.…”