Differential requirements for Runx proteins in CD4 repression and epigenetic silencing during T lymphocyte development.
(9/202)
T lymphocytes differentiate in discrete stages within the thymus. Immature thymocytes lacking CD4 and CD8 coreceptors differentiate into double-positive cells (CD4(+)CD8(+)), which are selected to become either CD4(+)CD8(-)helper cells or CD4(-)CD8(+) cytotoxic cells. A stage-specific transcriptional silencer regulates expression of CD4 in both immature and CD4(-)CD8(+) thymocytes. We show here that binding sites for Runt domain transcription factors are essential for CD4 silencer function at both stages, and that different Runx family members are required to fulfill unique functions at each stage. Runx1 is required for active repression in CD4(-)CD8(-) thymocytes whereas Runx3 is required for establishing epigenetic silencing in cytotoxic lineage thymocytes. Runx3-deficient cytotoxic T cells, but not helper cells, have defective responses to antigen, suggesting that Runx proteins have critical functions in lineage specification and homeostasis of CD8-lineage T lymphocytes. (+info)
Expression of galectin-3 in skeletal tissues is controlled by Runx2.
(10/202)
The beta-galatoside-specific lectin galectin-3 is expressed in vivo in osteoblasts as well as in epiphyseal cartilage. Here we show that in vitro, galectin-3 expression is up-regulated in the preosteoblastic cell line MC3T3-E1 during the matrix maturation stage of the osteoblast developmental sequence. Expression persists into late differentiation stages when the mature osteoblastic phenotype is established. The skeletal expression pattern of galectin-3 overlaps at many sites with that of the transcription factor Runx2. Runx2 is a key regulator of osteoblast development and necessary for chondrocyte differentiation in the growth plate. Both human and mouse galectin-3 promoters contain putative Runx-binding sites. The constitutive or inducible forced expression of Runx2 is sufficient for the onset of galectin-3 transcription in the mesenchymal precursor cell line C3H10T1/2. Moreover, Runx2 is able to bind to at least two sites in the galectin-3 promoter region. The crucial role of Runx2 was confirmed in Runx2-deficient mice, which are devoid of galectin-3 expression in skeletal cells. The overlapping expression pattern of galectin-3 with the other two members of the Runt family of transcription factors (Runx1 and Runx3) points to a potential regulation of the galectin-3 gene (LGALS3) by these factors in hematopoietic, skin, and dorsal root ganglial cells. (+info)
T-cell differentiation: chromatin remodelling in CD4/CD8 regulation.
(11/202)
CD4 and CD8 genes are integral indicators of T-cell lineage commitment. New insights into the control of expression of these genes have come from recent reports implicating chromatin-remodelling factors in their regulation. (+info)
The evolution of Runx genes I. A comparative study of sequences from phylogenetically diverse model organisms.
(12/202)
BACKGROUND: Runx genes encode proteins defined by the highly conserved Runt DNA-binding domain. Studies of Runx genes and proteins in model organisms indicate that they are key transcriptional regulators of animal development. However, little is known about Runx gene evolution. RESULTS: A phylogenetically broad sampling of publicly available Runx gene sequences was collected. In addition to the published sequences from mouse, sea urchin, Drosophila melanogaster and Caenorhabditis elegans, we collected several previously uncharacterised Runx sequences from public genome sequence databases. Among deuterostomes, mouse and pufferfish each contain three Runx genes, while the tunicate Ciona intestinalis and the sea urchin Strongylocentrotus purpuratus were each found to have only one Runx gene. Among protostomes, C. elegans has a single Runx gene, while Anopheles gambiae has three and D. melanogaster has four, including two genes that have not been previously described. Comparative sequence analysis reveals two highly conserved introns, one within and one just downstream of the Runt domain. All vertebrate Runx genes utilize two alternative promoters. CONCLUSIONS: In the current public sequence database, the Runt domain is found only in bilaterians, suggesting that it may be a metazoan invention. Bilaterians appear to ancestrally contain a single Runx gene, suggesting that the multiple Runx genes in vertebrates and insects arose by independent duplication events within those respective lineages. At least two introns were present in the primordial bilaterian Runx gene. Alternative promoter usage arose prior to the duplication events that gave rise to three Runx genes in vertebrates. (+info)
Runx3 knockouts and stomach cancer.
(13/202)
Gene targeting often results in knockout mice that show several phenotypes, some of which may not directly relate to the intrinsic function of the disrupted gene. Hence, to study the biological function of genes using knockout mice, one must identify the defects that are directly due to the loss of the targeted gene. Runx3 is a transcription factor that regulates lineage-specific gene expression in developmental processes. Recently, two groups produced Runx3 knockout mice. Two comparable defects were identified in both knockout strains, one involved neurogenesis and the other thymopoiesis. In addition, a stomach defect pertaining to gastric cancer was observed in one of the mutant strains, but not in the other. Here, we assess the differences between the two Runx3 mutant strains and discuss further studies that could reconcile these discrepancies. This article highlights the difficulties of inferring gene function through the interpretation of knockout phenotypes. (+info)
Runx3 and Runx1 are required for CD8 T cell development during thymopoiesis.
(14/202)
The RUNX transcription factors are important regulators of lineage-specific gene expression. RUNX are bifunctional, acting both as activators and repressors of tissue-specific target genes. Recently, we have demonstrated that Runx3 is a neurogenic transcription factor, which regulates development and survival of proprioceptive neurons in dorsal root ganglia. Here we report that Runx3 and Runx1 are highly expressed in thymic medulla and cortex, respectively, and function in development of CD8 T cells during thymopoiesis. Runx3-deficient (Runx3 KO) mice display abnormalities in CD4 expression during lineage decisions and impairment of CD8 T cell maturation in the thymus. A large proportion of Runx3 KO peripheral CD8 T cells also expressed CD4, and in contrast to wild-type, their proliferation ability was largely reduced. In addition, the in vitro cytotoxic activity of alloimmunized peritoneal exudate lymphocytes was significantly lower in Runx3 KO compared with WT mice. In a compound mutant mouse, null for Runx3 and heterozygous for Runx1 (Runx3-/-;Runx1+/-), all peripheral CD8 T cells also expressed CD4, resulting in a complete lack of single-positive CD8+ T cells in the spleen. The results provide information on the role of Runx3 and Runx1 in thymopoiesis and suggest that both act as transcriptional repressors of CD4 expression during T cell lineage decisions. (+info)
Hypermethylation of the RUNX3 gene promoter in testicular yolk sac tumor of infants.
(15/202)
Testicular yolk sac tumor (YST) of infants is biologically distinct from its adult counterpart. Cytogenetically, YSTs in infants generally lack i(12p), which is highly characteristic of adult germ cell tumors (GCTs), whereas they frequently show a deletion of 1p36, indicating that the loss of a certain gene(s) in this region is an important event in the pathogenesis of infantile YSTs. In the present study, we examined 10 testicular YSTs from infants for promoter methylation status of the RUNX3 gene, localizing in 1p36.1, and loss of heterozygosity (LOH) in this region, on the presumption that RUNX3 acts as a tumor suppressor. Methylation of RUNX3 and LOH at 1p36.1 were detected in 8 of 10 (80%) and 6 of 8 (75%) infantile YSTs examined, respectively. All six cases harboring LOH showed RUNX3 methylation. In contrast, 0 of 12 adult GCTs showed RUNX3 methylation, and LOH at 1p36.1 was less frequent (1 of 6 cases: 16%) in adult GCTs. There is a significant difference in RUNX3 methylation between these 2 groups (P < 0.001). In normal testes of the young group, RUNX3 methylation was not detected. These results strongly suggest that RUNX3 is one of the tumor suppressors involved in the pathogenesis of testicular YSTs in infants. (+info)
An important role for RUNX3 in human L1 transcription and retrotransposition.
(16/202)
LINE-1s (long interspersed nuclear elements-1) are abundant non-LTR retrotransposons that comprise 17% of the human genome. The 5' untranslated region (5'UTR) of human L1 (L1Hs) houses a poorly understood internal promoter. Here we report that mutations at a putative runt-domain transcription factor (RUNX) site (+83 to +101) in the 5'UTR decreased L1Hs transcription and retrotransposition in cell culture-based assays. Exogenous expression of RUNX3, but not the other two RUNX family members, RUNX1 and RUNX2, increased L1Hs transcription and retrotransposition, which were otherwise decreased by siRNAs targeting RUNX3 and a dominant negative RUNX. Further more, the specific interaction between RUNX3 and its binding site was demonstrated by an electrophoretic mobility shift assay (EMSA) using an anti-RUNX3 antibody. Interestingly, RUNX3 may also regulate the antisense promoter activity of L1Hs 5'UTR via another putative RUNX site (+526 to +508), as revealed by site-directed mutations and exogenous expression of RUNX factors. Our results indicate an important role for RUNX3 in L1Hs retrotransposition as well as transcription from its 5'UTR in both sense and antisense directions, and they should contribute to our understanding of the mechanism underlying L1Hs retrotransposition and its impact on the expression of adjacent cellular genes. (+info)