Conservation and expression of an alternative 3' exon of Runx2 encoding a novel proline-rich C-terminal domain

RUNX transcription factors: orchestrators of development

RUNX transcription factors orchestrate many different aspects of biology, including basic cellular and developmental processes, stem cell biology and tumorigenesis. In this Primer, we introduce the molecular hallmarks of the three mammalian RUNX genes, RUNX1, RUNX2 and RUNX3, and discuss the regulation of their activities and their mechanisms of action. We then review their crucial roles in the specification and maintenance of a wide array of tissues during embryonic development and adult homeostasis.

RUNX family: Oncogenes or tumor suppressors (Review)

Runt-related transcription factor (RUNX) proteins belong to a transcription factors family known as master regulators of important embryonic developmental programs. In the last decade, the whole family has been implicated in the regulation of different oncogenic processes and signaling pathways associated with cancer. Furthermore, a suppressor tumor function has been also reported, suggesting the RUNX family serves key role in all different types of cancer. In this review, the known biological characteristics, specific regulatory abilities and experimental evidence of RUNX proteins will be analyzed to demonstrate their oncogenic potential and tumor suppressor abilities during oncogenic processes, suggesting their importance as biomarkers of cancer. Additionally, the importance of continuing with the molecular studies of RUNX proteins' and its dual functions in cancer will be underlined in order to apply it in the future development of specific diagnostic methods and therapies against different types of cancer.

Molecular bases of the crosstalk between bone and muscle

Exercise is an evolutionary conserved survival function that nowadays has beneficial health effects. The increased metabolic activity of contracting skeletal muscle affects the biology of many organs involved in regulating muscle functions. The discovery of hormones and cytokines secreted by bone and skeletal muscle during exercise, has recently added experimental credence to the notion that a crosstalk exists between these organs. Bone through the hormone osteocalcin, promotes exercise capacity in the mouse. After binding to a G-coupled protein receptor, Gprc6a, osteocalcin increases nutrients uptake and catabolism in myofibers during exercise. The catabolic aspect of osteocalcin distinguishes it from insulin signaling. In addition, osteocalcin regulates the endocrine function of skeletal muscle because it enhances the expression of interleukin-6 (IL-6). IL-6 is produced and secreted by contracting skeletal muscle and exerts autocrine, paracrine and systemic effects. One of the systemic functions of IL-6 is to drive the generation of bioactive osteocalcin. Altogether, these studies have revealed a feed-forward loop between bone and skeletal muscle that are necessary and sufficient for optimum exercise capacity. This endocrine regulation of exercise biology, suggest novel and adapted strategies for the prevention or treatment of age related muscle loss.

Characterization of CADD522, a small molecule that inhibits RUNX2-DNA binding and exhibits antitumor activity

The RUNX2 transcription factor promotes breast cancer growth and metastasis through interactions with a variety of cofactors that activate or repress target genes. Using a direct drug discovery approach we identified CADD522 as a small molecule that inhibits the DNA binding of the runt box domain protein, RUNX2. The current study defines the effect of CADD522 on breast cancer growth and metastasis, and addresses the mechanisms by which it exerts its anti-tumor activity.

CADD522 treatment resulted in significant growth inhibition, clonogenic survival, tumorsphere formation, and invasion of breast cancer cells. CADD522 negatively regulated transcription of RUNX2 target genes such as matrix metalloproteinase-13, vascular endothelial growth factor and glucose transporter-1, but upregulated RUNX2 expression by increasing RUNX2 stability. CADD522 reduced RUNX2-mediated increases in glucose uptake and decreased the level of CBF-β and RUNX2 phosphorylation at the S451 residue. These results suggest several potential mechanisms by which CADD522 exerts an inhibitory function on RUNX2-DNA binding; interference with RUNX2 for the DNA binding pocket, inhibition of glucose uptake leading to cell cycle arrest, down-regulation of CBF-β, and reduction of S451-RUNX2 phosphorylation.

The administration of CADD522 into MMTV-PyMT mice resulted in significant delay in tumor incidence and reduction in tumor burden. A significant decrease of tumor volume was also observed in a CADD522-treated human triple-negative breast cancer-patient derived xenograft model. CADD522 impaired the lung retention and outgrowth of breast cancer cells in vivo with no apparent toxicity to the mice. Therefore, by inhibiting RUNX2-DNA binding, CADD522 may represent a potential antitumor drug.

Runx2-I is an Early Regulator of Epithelial-Mesenchymal Cell Transition in the Chick Embryo

BACKGROUND

Although normally linked to bone and cartilage development, the Runt-related transcription factor, RUNX2, was reported in the mouse heart during development of the valves. We examined RUNX2 expression and function in the developing avian heart as it related to the epithelial-mesenchymal transition (EMT) in the atrioventricular canal. EMT can be separated into an activation stage involving hypertrophy and cell separation and an invasion stage where cells invade the extracellular matrix. The localization and activity of RUNX2 was explored in relation to these steps in the heart. As RUNX2 was also reported in cancer tissues, we examined its expression in the progression of esophageal cancer in staged tissues.

RESULTS

A specific isoform, RUNX2-I, is present and required for EMT by endothelia of the atrioventricular canal. Knockdown of RUNX2-I inhibits the cell-cell separation that is characteristic of initial activation of EMT. Loss of RUNX2-I altered expression of EMT markers to a greater extent during activation than during subsequent cell invasion. Transforming growth factor beta 2 (TGFβ2) mediates activation during cardiac endothelial EMT. Consistent with a role in activation, RUNX2-I is regulated by TGFβ2 and its activity is independent of similarly expressed Snai2 in regulation of EMT. Examination of RUNX2 expression in esophageal cancer showed its upregulation concomitant with the development of dysplasia and continued expression in adenocarcinoma.

CONCLUSIONS

These data introduce the RUNX2-I isoform as a critical early transcription factor mediating EMT in the developing heart after induction by TGFβ2. Its expression in tumor tissue suggests a similar role for RUNX2 in the EMT of metastasis. Developmental Dynamics 247:542-554, 2018. © 2017 Wiley Periodicals, Inc.

Runx transcription factors in the development and function of the definitive hematopoietic system

The Runx family of transcription factors (Runx1, Runx2, and Runx3) are highly conserved and encode proteins involved in a variety of cell lineages, including blood and blood-related cell lineages, during developmental and adult stages of life. They perform activation and repressive functions in the regulation of gene expression. The requirement for Runx1 in the normal hematopoietic development and its dysregulation through chromosomal translocations and loss-of-function mutations as found in acute myeloid leukemias highlight the importance of this transcription factor in the healthy blood system. Whereas another review will focus on the role of Runx factors in leukemias, this review will provide an overview of the normal regulation and function of Runx factors in hematopoiesis and focus particularly on the biological effects of Runx1 in the generation of hematopoietic stem cells. We will present the current knowledge of the structure and regulatory features directing lineage-specific expression of Runx genes, the models of embryonic and adult hematopoietic development that provide information on their function, and some of the mechanisms by which they affect hematopoietic function.

Role of RUNX2 in Breast Carcinogenesis

RUNX2 is a transcription factor playing the major role in osteogenesis, but it can be involved in DNA damage response, which is crucial for cancer transformation. RUNX2 can interact with cell cycle regulators: cyclin-dependent kinases, pRB and p21Cip1 proteins, as well as the master regulator of the cell cycle, the p53 tumor suppressor. RUNX2 is involved in many signaling pathways, including those important for estrogen signaling, which, in turn, are significant for breast carcinogenesis. RUNX2 can promote breast cancer development through Wnt and Tgfβ signaling pathways, especially in estrogen receptor (ER)-negative cases. ERα interacts directly with RUNX2 and regulates its activity. Moreover, the ERα gene has a RUNX2 binding site within its promoter. RUNX2 stimulates the expression of aromatase, an estrogen producing enzyme, increasing the level of estrogens, which in turn stimulate cell proliferation and replication errors, which can be turned into carcinogenic mutations. Exploring the role of RUNX2 in the pathogenesis of breast cancer can lead to revealing new therapeutic targets.

Digital expression profiling identifies RUNX2, CDC5L, MDM2, RECQL4, and CDK4 as potential predictive biomarkers for neo-adjuvant chemotherapy response in paediatric osteosarcoma

Osteosarcoma is the most common malignancy of bone, and occurs most frequently in children and adolescents. Currently, the most reliable technique for determining a patients’ prognosis is measurement of histopathologic tumor necrosis following pre-operative neo-adjuvant chemotherapy. Unfavourable prognosis is indicated by less than 90% estimated necrosis of the tumor. Neither genetic testing nor molecular biomarkers for diagnosis and prognosis have been described for osteosarcomas. We used the novel nanoString mRNA digital expression analysis system to analyse gene expression in 32 patients with sporadic paediatric osteosarcoma. This system used specific molecular barcodes to quantify expression of a set of 17 genes associated with osteosarcoma tumorigenesis. Five genes, from this panel, which encoded the bone differentiation regulator RUNX2, the cell cycle regulator CDC5L, the TP53 transcriptional inactivator MDM2, the DNA helicase RECQL4, and the cyclin-dependent kinase gene CDK4, were differentially expressed in tumors that responded poorly to neo-adjuvant chemotherapy. Analysis of the signalling relationships of these genes, as well as other expression markers of osteosarcoma, indicated that gene networks linked to RB1, TP53, PI3K, PTEN/Akt, myc and RECQL4 are associated with osteosarcoma. The discovery of these networks provides a basis for further experimental studies of role of the five genes (RUNX2, CDC5L, MDM2, RECQL4, and CDK4) in differential response to chemotherapy.

Runx family genes in a cartilaginous fish, the elephant shark (Callorhinchus milii)

The Runx family genes encode transcription factors that play key roles in hematopoiesis, skeletogenesis and neurogenesis and are often implicated in diseases. We describe here the cloning and characterization of Runx1, Runx2, Runx3 and Runxb genes in the elephant shark (Callorhinchus milii), a member of Chondrichthyes, the oldest living group of jawed vertebrates. Through the use of alternative promoters and/or alternative splicing, each of the elephant shark Runx genes expresses multiple isoforms similar to their orthologs in human and other bony vertebrates. The expression profiles of elephant shark Runx genes are similar to those of mammalian Runx genes. The syntenic blocks of genes at the elephant shark Runx gene loci are highly conserved in human, but represented by shorter conserved blocks in zebrafish indicating a higher degree of rearrangements in this teleost fish. Analysis of promoter regions revealed conservation of binding sites for transcription factors, including two tandem binding sites for Runx that are totally conserved in the distal promoter regions of elephant shark Runx1-3. Several conserved noncoding elements (CNEs), which are putative cis-regulatory elements, and miRNA binding sites were identified in the elephant shark and human Runx gene loci. Some of these CNEs and miRNA binding sites are absent in teleost fishes such as zebrafish and fugu. In summary, our analysis reveals that the genomic organization and expression profiles of Runx genes were already complex in the common ancestor of jawed vertebrates.

Investigation of Parental Transmission of RUNX2 Single Nucleotide Polymorphism and Its Association with Nonsyndromic Cleft Lip with or Without Palate

Objective

To investigate the association and parental transmission of RUNX2 single nucleotide polymorphisms (SNPs) with risk of nonsyndromic cleft lip with or without cleft palate (NS-CL±P).

Design

Four RUNX2 SNPs in 142 Korean NS-CL±P families (nine cleft lip, 26 cleft lip and alveolus, and 107 cleft lip and palate; 76 trios and 66 dyads) were genotyped. The minor allele frequency, heterozygosity, and chi-square test for Hardy-Weinberg equilibrium at each SNP were computed between parents. Pairwise linkage disequilibrium was computed as D′ and r2 for all SNPs. Both allelic and genotypic transmission disequilibrium tests (TDTs) were performed for individual SNPs using a family-based association test program. Sliding windows of haplotypes consisting of two to four SNPs were tested using a haplotype-based association test program. Genotypic odds ratios (GORs) were calculated from conditional logistic regression models. Parent-of-origin effects were assessed using transmission asymmetry test and parent-of-origin likelihood ratio test.

Results

The family-based TDT showed significant evidence of linkage and association at rs1934328 ( P = .001). In the haplotype analysis, two, three, and four haplotypes containing rs1934328 revealed significant associations ( P = .0017, P = .0022, and P = .0020, respectively). The genotypes A/T and T/T at rs1934328 were significantly associated with NS-CL±P compared with the genotype A/A (GOR = 2.75, 95% confidence interval [CI] = 1.39–5.45, P =0.0019 in the dominant model; GOR = 5.38, 95% CI = 1.34–21.68, P = .0046 in the additive model). However, no parent-of origin effect was observed.

Conclusion

These findings suggest possible involvement of RUNX2-rs 194328 in the etiology of NS-CL±P in Korean cleft-parent trios without excess parental transmission.

Runx2 protein expression utilizes the Runx2 P1 promoter to establish osteoprogenitor cell number for normal bone formation

The Runt-related transcription factor, Runx2, is essential for osteogenesis and is controlled by both distal (P1) and proximal (P2) promoters. To understand Runx2 function requires determination of the spatiotemporal activity of P1 and P2 to Runx2 protein production. We generated a mouse model in which the P1-derived transcript was replaced with a lacZ reporter allele, resulting in loss of P1-derived protein while simultaneously allowing discrimination between the activities of the two promoters. Loss of P1-driven expression causes developmental defects with cleidocranial dysplasia-like syndromes that persist in the postnatal skeleton. P1 activity is robust in preosteogenic mesenchyme and at the onset of bone formation but decreases as bone matures. Homozygous Runx2-P1(lacZ/lacZ) mice have a normal life span but exhibit severe osteopenia and compromised bone repair in adult mice because of osteoblastic defects and not increased osteoclastic resorption. Gene expression profiles of bone, immunohistochemical studies, and ex vivo differentiation using calvarial osteoblasts and marrow stromal cells identified mechanisms for the skeletal phenotype. The findings indicate that P1 promoter activity is necessary for generating a threshold level of Runx2 protein to commit sufficient osteoprogenitor numbers for normal bone formation. P1 promoter function is not compensated via the P2 promoter. However, the P2 transcript with compensatory mechanisms from bone morphogenetic protein (BMP) and Wnt signaling is adequate for mineralization of the bone tissue that does form. We conclude that selective utilization of the P1 and P2 promoters enables the precise spatiotemporal expression of Runx2 necessary for normal skeletogenesis and the maintenance of bone mass in the adult.

The Role of RUNX2 in Osteosarcoma Oncogenesis

Osteosarcoma is an aggressive but ill-understood cancer of bone that predominantly affects adolescents. Its rarity and biological heterogeneity have limited studies of its molecular basis. In recent years, an important role has emerged for the RUNX2 "platform protein" in osteosarcoma oncogenesis. RUNX proteins are DNA-binding transcription factors that regulate the expression of multiple genes involved in cellular differentiation and cell-cycle progression. RUNX2 is genetically essential for developing bone and osteoblast maturation. Studies of osteosarcoma tumours have revealed that the RUNX2 DNA copy number together with RNA and protein levels are highly elevated in osteosarcoma tumors. The protein is also important for metastatic bone disease of prostate and breast cancers, while RUNX2 may have both tumor suppressive and oncogenic roles in bone morphogenesis. This paper provides a synopsis of the current understanding of the functions of RUNX2 and its potential role in osteosarcoma and suggests directions for future study.

Expression of master regulatory genes controlling skeletal development in benign cartilage and bone forming tumors

Recent progress in skeletal molecular biology has led to the clarification of the transcriptional mechanisms of chondroblastic and osteoblastic lineage differentiation. Three master transcription factors-Sox9, Runx2, and Osterix-were shown to play an essential role in determining the skeletal progenitor cells' fate. The present study evaluates the expression of these factors in 4 types of benign bone tumors-chondromyxoid fibroma, chondroblastoma, osteoid osteoma, and osteoblastoma-using immunohistochemistry and tissue microarrays. Osteoid osteoma and osteoblastoma showed strong nuclear expression of Osterix and Runx2. In contrast, only a few chondroblastomas showed positive nuclear expression of Osterix. Strong nuclear expression of Sox9 was detected in all chondroblastomas, whereas nearly half of the osteoblastomas showed focal weak cytoplasmic expression of Sox9.

Dual transcriptional regulation by runx2 of matrix Gla protein in Xenopus laevis

Matrix Gla protein (MGP) is an extracellular mineral-binding protein expressed in several tissues but it only accumulates in bone and calcified cartilage under physiological conditions. Available evidence indicates that it acts as a physiological inhibitor of mineralization. Runx2 is a transcription factor essential for bone formation in mammals, affecting osteoblast and chondrocyte differentiation by regulating key genes crucial for bone and cartilage development. Being an important cartilage-associated gene, MGP is a potential target for Runx2, and thus we have investigated the possible functional interactions between them. In A6 cells, Runx2 was found to modulate MGP transcription and deletion analysis of MGP distal and proximal promoter-luciferase constructs identified cis-regulatory regions. Interestingly, we have also identified a runx2-binding site that mediates transcriptional repression of XlMGP. Mutation of this element, located between -54 and +33 bp, results in 18-fold up-regulation of transcription. Furthermore, and in addition to the previously reported Xlrunx2 types I and II, we have identified three transcripts encoding novel, truncated Xlrunx2 isoforms. Although only type I and type II could transactivate XlMGP, the truncated isoforms identified in this study, which result from alternative splicing, could be involved in negative regulation of MGP expression, as described for other RUNX2 truncated isoforms acting in other target genes. In vivo microinjection of XlMGP promoter constructs and runx2 mRNA confirmed that those promoters are targets for this transcription factor. These data also indicate that MGP is under dual regulation by runx2 through the use of various isoforms and context-dependent formation of transcriptional complexes.

Post-translational Regulation of Runx2 in Bone and Cartilage

The Runx2 gene product is essential for mammalian bone development. In humans, Runx2 haploinsufficiency results in cleidocranial dysplasia, a skeletal disorder characterized by bone and dental abnormalities. At the molecular level, Runx2 acts as a transcription factor for genes expressed in hypertrophic chondrocytes and osteoblasts. Runx2 gene expression and protein function are regulated on multiple levels, including transcription, translation, and post-translational modification. Furthermore, Runx2 is involved in numerous protein-protein interactions, most of which either activate or repress transcription of target genes. In this review, we discuss expression of Runx2 during development as well as the post-translational regulation of Runx2 through modification by phosphorylation, ubiquitination, and acetylation.

Differential parental transmission of markers in RUNX2 among cleft case-parent trios from four populations

Isolated cleft lip with or without cleft palate (CL/P) is among the most common human birth defects, with a prevalence around 1 in 700 live births. The Runt-related transcription factor 2 (RUNX2) gene has been suggested as a candidate gene for CL/P based largely on mouse models; however, no human studies have focused on RUNX2 as a risk factor for CL/P. This study examines the association between markers in RUNX2 and isolated, nonsyndromic CL/P using a case-parent trio design, while considering parent-of-origin effects. Case-parent trios from four populations (77 from Maryland, 146 from Taiwan, 35 from Singapore, and 40 from Korea) were genotyped for 24 single nucleotide polymorphisms (SNPs) in the RUNX2 gene. We performed the transmission disequilibrium test on individual SNPs. Parent-of-origin effects were assessed using the transmission asymmetry test and the parent-of-origin likelihood ratio test (PO-LRT). When all trios were combined, the transmission asymmetry test revealed a block of 11 SNPs showing excess maternal transmission significant at the P<0.01 level, plus one SNP (rs1934328) showing excess paternal transmission (P=0.002). For the 11 SNPs showing excess maternal transmission, odds ratios of being transmitted to the case from the mother ranged between 3.00 and 4.00. The parent-of-origin likelihood ratio tests for equality of maternal and paternal transmission were significant for three individual SNPs (rs910586, rs2819861, and rs1934328). Thus, RUNX2 appears to influence risk of CL/P through a parent-of-origin effect with excess maternal transmission.

Dialysis Accelerates Medial Vascular Calcification in Part by Triggering Smooth Muscle Cell Apoptosis

Background— Vascular calcification is associated with increased morbidity and mortality in stage V chronic kidney disease, yet its early pathogenesis and initiating mechanisms in vivo remain poorly understood. To address this, we quantified the calcium (Ca) load in arteries from children (10 predialysis, 24 dialysis) and correlated it with clinical, biochemical, and vascular measures.

Methods and Results— Vessel Ca load was significantly elevated in both predialysis and dialysis and was correlated with the patients’ mean serum Ca×phosphate product. However, only dialysis patients showed increased carotid intima-media thickness and increased aortic stiffness, and calcification on computed tomography was present in only the 2 patients with the highest Ca loads. Importantly, predialysis vessels appeared histologically intact, whereas dialysis vessels exhibited evidence of extensive vascular smooth muscle cell (VSMC) loss owing to apoptosis. Dialysis vessels also showed increased alkaline phosphatase activity and Runx2 and osterix expression, indicative of VSMC osteogenic transformation. Deposition of the vesicle membrane marker annexin VI and vesicle component mineralization inhibitors fetuin-A and matrix Gla-protein increased in dialysis vessels and preceded von Kossa positive overt calcification. Electron microscopy showed hydroxyapatite nanocrystals within vesicles released from damaged/dead VSMCs, indicative of their role in initiating calcification.

Conclusions— Taken together, this study shows that Ca accumulation begins predialysis, but it is the induction of VSMC apoptosis in dialysis that is the key event in disabling VSMC defense mechanisms and leading to overt calcification, eventually with clinically detectable vascular damage. Thus the identification of factors that lead to VSMC death in dialysis will be of prime importance in preventing vascular calcification.

Expression of Runx2 transcription factor in non-skeletal tissues, sperm and brain

Runx2 is a master transcription factor for chondrocyte and osteoblast differentiation and bone formation. However expression of Runx2 (by RT-PCR), has been reported in non-skeletal tissues such as breast, T cells and testis. To better define Runx2 activity in non-skeletal tissues, we examined transgenic (Tg) mice expressing LacZ gene under control of 3.0 kb (3 kb Tg) or 1.0 kb (1 kb Tg) of the Runx2 distal (P1) promoter, Runx2 LacZ knock-in (Runx2(+/LacZ)) and Runx2/P1 LacZ knock-in (Runx2/P1(+/LacZ)). In the Runx2 3 kb Tg mouse, beta-galactosidase (beta-gal) expression appeared in various non-skeletal tissues including testis, skin, adrenal gland and brain. beta-gal expression from both 3 kb and 1 kb Tg, reflecting activity of the Runx2 promoter, was readily detectable in seminiferous tubules of the testis and the epididymis. At the single cell level, beta-gal was detected in spermatids and mature sperms not in sertoli or Leydig cells. We also detected a positive signal from the Runx2(+/LacZ) and Runx2/P1(+/LacZ) mice. Indeed, Runx2 expression was observed in isolated mature sperms, which was confirmed by RT-PCR and Western blot analysis. Runx2, however, was not related to sex determination and sperm motility. Runx2 mediated beta-gal activity is also found robustly in the hippocampus and frontal lobe of the brain in Runx2(+/LacZ). Collectively, these results indicate that Runx2 is expressed in several non-skeletal tissues particularly sperms of testis and hippocampus of brain. It suggests that Runx2 may play an important role in male reproductive organ testis and brain.

Gene array analysis reveals a common Runx transcriptional programme controlling cell adhesion and survival

The Runx genes are important in development and cancer, where they can act either as oncogenes or tumour suppressors. We compared the effects of ectopic Runx expression in established fibroblasts, where all three genes produce an indistinguishable phenotype entailing epithelioid morphology and increased cell survival under stress conditions. Gene array analysis revealed a strongly overlapping transcriptional signature, with no examples of opposing regulation of the same target gene. A common set of 50 highly regulated genes was identified after further filtering on regulation by inducible RUNX1-ER. This set revealed a strong bias toward genes with annotated roles in cancer and development, and a preponderance of targets encoding extracellular or surface proteins, reflecting the marked effects of Runx on cell adhesion. Furthermore, in silico prediction of resistance to glucocorticoid growth inhibition was confirmed in fibroblasts and lymphoid cells expressing ectopic Runx. The effects of fibroblast expression of common RUNX1 fusion oncoproteins (RUNX1-ETO, TEL-RUNX1 and CBFB-MYH11) were also tested. Although two direct Runx activation target genes were repressed (Ncam1 and Rgc32), the fusion proteins appeared to disrupt the regulation of downregulated targets (Cebpd, Id2 and Rgs2) rather than impose constitutive repression. These results elucidate the oncogenic potential of the Runx family and reveal novel targets for therapeutic inhibition.

RUNX genes in development and cancer: regulation of viral gene expression and the discovery of RUNX family genes

Mouse embryonal carcinoma (EC) cells, also called teratocarcinoma stem cells, are nonpermissive for polyomavirus growth, whereas differentiated derivatives of the cells are permissive. Mutant viruses capable of growing in EC cells can be isolated. They have genomic alterations within the viral enhancer, which is required for viral gene expression and DNA replication. This viral regulatory region was considered as a potential probe for mouse cell differentiation. The 24-bp-long A element within the enhancer was identified as a minimum element, which also shows a lower activity in EC cells compared with the differentiated cells. Transcription factors PEA1/AP1, PEA2/PEBP2, and PEA3/ETS were identified as A element-binding proteins. All of them are absent in EC cells and induced to be expressed when the cells are differentiated. Although PEBP2 has a weaker transactivation activity compared with other two, it is essential for the enhancer function of the A element. Purification and cDNA cloning revealed that PEBP2 has two subunits, DNA-binding alpha (PEBP2alpha) and non-DNA-binding beta (PEBP2beta). PEBP2alpha was found to be highly homologous to a Drosophila segmentation gene, runt, and a human gene AML1 that was identified as a part of the fusion gene, AML1/ETO (MTG8) generated by t(8;21) chromosome translocation associated with acute myelogenous leukemia (AML). Core-binding factor (CBF), which interacts with a murine retrovirus enhancer, was found to be identical to PEBP2. runt, PEBP2alpha and AML1 are now termed RUNX family, which are involved in cell specification during development. There are three mammalian RUNX genes, RUNX1, RUNX2, and RUNX3. RUNX1 is essential for generation of hematopoietic stem cells and is involved in human leukemia. RUNX2 is essential for skeletal development and has an oncogenic potential. RUNX3 is expressed in wider ranges of tissues and has multiple roles. Among others, RUNX3 is a major tumor suppressor of gastric and many other solid tumors.

Two of four alternatively spliced isoforms of RUNX2 control osteocalcin gene expression in human osteoblast cells

Runx2 is a Runt domain transcription factor that transcriptionally regulates osteoblast differentiation and bone formation. In this study, we show that human chondro- and osteosarcoma cell lines, human mesenchymal stem cells (hMSC) and a human primary chondrocytes (HC), osteoblst cells (HOb) express an intact isoform (RUNX2wt) and 3 alternatively spliced isoforms (RUNX2Delta5, Delta7, and Delta5Delta7) that are generated by skipping exon 5 and/or exon 7. Two of the truncated forms of RUNX2 (RUNX2Delta5 and RUNX2Delta5Delta7) did not localize in the nucleus and had lost their DNA binding activity. In cotransfection experiments with an osteocalcin (OC) promoter construct, we confirmed that only RUNX2wt and RUNX2Delta7 could upregulate the OC promoter activity in the osteosarcoma cell line. In addition, the coactivator CBP/p300 enhanced the transcriptional activity of the OC promoter when coexpressed with RUNX2wt or RUNX2Delta7, but not when coexpressed with RUNX2Delta5 or RUNX2Delta5Delta7. In contrast, the corepressor HDAC3 only repressed the activation from the OC promoter when coexpressed with RUNX2wt. These results support the hypothesis that RUNX2 both up- and downregulates its target gene promoters, as exemplified by the OC gene, using various isoforms and context-dependent formation of transcriptional complexes.

Promoter 2 -1025 T/C polymorphism in the RUNX2 gene is associated with femoral neck bmd in Spanish postmenopausal women

Stimulation of bone formation is a key therapeutic target in osteoporosis. Runx2 is a runt domain transcription factor essential to osteoblast differentiation, bone remodeling, and fracture healing. Runx2 knockout mice exhibit a complete lack of ossification, while overexpression of this gene in transgenic mice results in an osteoporotic phenotype. Thus, RUNX2 is a good candidate for the genetic determination of osteoporosis. In this association study, the effects of the -330 G/T polymorphism in promoter 1 and the -1025 T/C polymorphism (rs7771980) in promoter 2 of RUNX2 were tested in relation to lumbar spine (LS) and femoral neck (FN) bone mineral density (BMD) in a cohort of 821 Spanish postmenopausal women. The minor allele frequencies for the two polymorphisms were 0.15 and 0.07, respectively. The two polymorphisms, located more than 90 kb apart, were not in linkage disequilibrium (D' = 0.27, r (2) = 0.028). In an ANCOVA test adjusting by weight, height, age, and years since menopause, the -330 G/T polymorphism was not associated with any of the phenotypes analyzed, while we found the -1025 T/C polymorphism to be associated with FN BMD (p = 0.001). In particular, individuals carrying the TC genotype had higher mean adjusted FN BMD values than those bearing the TT genotype. Our results highlight the importance of this RUNX2 promoter 2 polymorphism in FN BMD determination.

Expression of AML/Runx and ETO/MTG family members during hematopoietic differentiation of embryonic stem cells

Runx1/AML1 plays important roles in hematopoiesis, including the commitment of cells to hematopoiesis during embryonic development, and in the maintenance of hematopoietic cell populations. It is also one of the most common genes involved in chromosomal translocations related to leukemia. One such translocation is t(8;21), which fuses the Runx1 gene to the MTG8/ETO gene and generates the Runx1-MTG8 (AML1-ETO) fusion gene. Both Runx1 and MTG8 have two additional family members that are much less studied in hematopoiesis. Here we report the expression of every member of the Runx and MTG families as well as the Runx heterodimerization partner CBFbeta during hematopoietic differentiation of murine embryonic stem cells. We observed substantially increased expression of Runx1, Runx2, and MTG16 during hematopoietic differentiation. Furthermore, the increase in Runx2 expression is delayed relative to Runx1 expression, suggesting their possible sequential contribution to hematopoiesis.

Runx2 and dental development

The Runx2 gene is a master transcription factor of bone and plays a role in all stages of bone formation. It is essential for the initial commitment of mesenchymal cells to the osteoblastic lineage and also controls the proliferation, differentiation, and maintenance of these cells. Control is complex, with involvement of a multitude of factors, thereby regulating the expression and activity of this gene both temporally and spatially. The use of multiple promoters and alternative splicing of exons further extends its diversity of actions. RUNX2 is also essential for the later stages of tooth formation, is intimately involved in the development of calcified tooth tissue, and exerts an influence on proliferation of the dental lamina. Furthermore, RUNX2 regulates the alveolar remodelling process essential for tooth eruption and may play a role in the maintenance of the periodontal ligament. In this article, the structure of Runx2 is described. The control and function of the gene and its product are discussed, with special reference to developing tooth tissues, in an attempt to elucidate the role of this gene in the development of the teeth and supporting structures.

Association of functionally different RUNX2 P2 promoter alleles with BMD

RUNX2 gene SNPs were genotyped in subjects from the upper and lower deciles of age- and weight-adjusted femoral neck BMD. Of 16 SNPs in RUNX2 and its two promoters (P1 and P2), only SNPs in the P2 promoter were significantly associated with BMD. These P2 promoter SNPs were functionally different in gel-shift and promoter activity assays.

INTRODUCTION

Specific osteoblast genes are induced by Runx2, a cell-specific transcription factor that is a candidate gene for controlling BMD. We tested the hypothesis that RUNX2 genetic variation is associated with BMD.

MATERIALS AND METHODS

From a population repository of normal subjects, the age- and weight-adjusted femoral neck BMD was ranked, and the upper and lower deciles (n = 132 each) were taken to represent the adjusted extremes of the population distribution. In these 264 subjects, we identified 16 allelic variations within the RUNX2 gene and promoters (P1 and P2) through DNA sequencing and denaturing high-performance liquid chromatography. Characterization of these alleles was performed through allele-specific cloning, transfection into ROS 17/2.8 cells, luciferase reporter analysis, and electrophoretic mobility shift assays.

RESULTS

Within the P2 promoter were three polymorphic nucleotides for which the minor alleles were over-represented in the upper decile of BMD (0.117 and 0.064 in the upper and lower deciles, respectively). These alleles are in near complete linkage disequilibrium with each other and represent a haplotype block that is significantly associated with increased BMD. The common and rare P2 promoter alleles were cloned upstream of luciferase, and when transfected into osteoblast-like cells, the construct representing the rare haplotype showed significantly greater P2 promoter activity than the common haplotype.

CONCLUSIONS

Because the high BMD allele had higher P2 promoter activity, the data suggest that greater RUNX2 P2 promoter activity is associated with higher BMD.

Identification and characterisation of two runx2 homologues in zebrafish with different expression patterns

Genome and gene duplications are considered to be the impetus to generate new genes, as the presence of multiple copies of a gene allows for paralogues to adopt novel function. After at least two rounds of genome/gene duplication, the Runt gene family consists of three members in vertebrates, instead of one in invertebrates. One of the family members, Runx2, plays a key role in the development of bone, a tissue that first occurs in vertebrates. The family has thus gained new gene function in the course of evolution. Two Runx2 genes were cloned in the vertebrate model system the zebrafish (Danio rerio). The expression patterns of the two genes differ and their kinetics differ up to four fold. In addition, splice forms exist that are novel when compared with mammals. Together, these findings comprise opportunities for selection and retention of the paralogues towards divergent and possibly new function.

The RUNX genes: gain or loss of function in cancer

The RUNX genes have come to prominence recently because of their roles as essential regulators of cell fate in development and their paradoxical effects in cancer, in which they can function either as tumour-suppressor genes or dominant oncogenes according to context. How can this family of transcription factors have such an ambiguous role in cancer? How and where do these genes impinge on the pathways that regulate growth control and differentiation? And what is the evidence for a wider role for the RUNX genes in non-haematopoietic cancers?

Runx2: A master organizer of gene transcription in developing and maturing osteoblasts

Runx2 is essential for osteoblast development and proper bone formation. A member of the Runt domain family of transcription factors, Runx2 binds specific DNA sequences to regulate transcription of numerous genes and thereby control osteoblast development from mesenchymal stem cells and maturation into osteocytes. Although necessary for gene transcription and osteoblast development, Runx2 is not sufficient for optimal gene expression or bone formation. Runx2 cooperates with numerous proteins, including transcription factors and cofactors, is posttranslationally modified, and associates with the nuclear matrix to integrate a variety of signals and organize crucial events during osteoblast development and maturation. Consistent with its role as a master organizer, alterations in Runx2 expression levels are associated with skeletal diseases. Runx2 haploinsufficiency causes cleidocranial dysplasia, while Runx2 overexpression is common in many bone-metastatic cancers. In this review, we summarize the molecular mechanisms by which Runx2 integrates signals through coregulatory interactions, and discuss how its role as a master organizer may shift depending on promoter structure, developmental cues, and cellular context.