Disease relevance of Runx2

• Thus, Runx2 joins a small group of transcription factors that can interfere with early T cell development, cause an expansion of a specific subset, and predispose to lymphoma [1].
• Ets-1 and Runx2 are critical transcriptional regulators of OPN expression in CT26 colorectal cancer cells [2].
• RESULTS: Immunohistochemistry showed that Runx1 and Runx2 are co-expressed in undifferentiated mesenchyme, had similar levels in chondrocytes undergoing transition from proliferation to hypertrophy, and that there was primarily Runx2 expression in hypertrophic chondrocytes [3].
• Cell growth regulation of Runx2 is also observed in primary calvarial osteoblasts and other osteoblastic cells with relatively normal cell growth characteristics, but not in osteosarcoma cells (e.g. SAOS-2 and ROS17/2.8) [4].
• Subsequent analysis revealed not only a short-term differential regulation of Runx2 and its targets by anoxia and hypoxia, but a long-term inhibition of Runx2 transcriptional and protein levels after only 12-24 h of anoxic insult [5].

High impact information on Runx2

• HDAC4-null mice display premature ossification of developing bones due to ectopic and early onset chondrocyte hypertrophy, mimicking the phenotype that results from constitutive Runx2 expression in chondrocytes [6].
• Here we report that HDAC4, which is expressed in prehypertrophic chondrocytes, regulates chondrocyte hypertrophy and endochondral bone formation by interacting with and inhibiting the activity of Runx2, a transcription factor necessary for chondrocyte hypertrophy [6].
• TSH also inhibits osteoblast differentiation and type 1 collagen expression in a Runx-2- and osterix-independent manner by downregulating Wnt (LRP-5) and VEGF (Flk) signaling [7].
• These cells do, however, express Runx2/Cbfa1, another transcription factor required for bone formation [8].
• Targeted disruption of Cbfa1 results in a complete lack of bone formation owing to maturational arrest of osteoblasts [9].

Biological context of Runx2

• Moreover, Runx2 directly bound to the promoter region of the Ihh gene and strongly induced expression of the reporter gene driven by the Ihh promoter [10].
• Further, the length of the limbs was reduced depending on the dosages of Runx2 and Runx3, due to reduced and disorganized chondrocyte proliferation and reduced cell size in the diaphyses [10].
• Our results indicate that Runx2 is a major target gene shared by TGF-beta and BMP signaling pathways and that the coordinated action of Runx2 and BMP-activated Smads leads to the induction of osteoblast-specific gene expression in C2C12 cells [11].
• This stimulation required Runx2 and its DNA binding site in the osteocalcin promoter [12].
• Thus, this study demonstrates that the activation of PPARgamma inhibits osteocalcin expression both by suppressing the expression of Runx2 and by interfering with the transactivation ability of Runx2 [13].

Anatomical context of Runx2

• Because Osx null preosteoblasts express typical chondrocyte marker genes, we propose that Runx2/Cbfa1-expressing preosteoblasts are still bipotential cells [8].
• Moreover, expression of Runx2, a transcription factor needed for osteoblast differentiation, was also abolished [14].
• Enforced expression of Runx2 perturbs T cell development at a stage coincident with beta-selection [1].
• Here we show that the Runx2 protein is expressed in several mammary epithelial cell lines and in primary mammary epithelial cells [15].
• Runx2 expression was localized to the critical area of cranial suture closure, being found in parietal bones, osteogenic fronts, and sutural mesenchyme [16].

Associations of Runx2 with chemical compounds

• Treatment of MC3T3-E1 osteoblasts and ROS 17/2.8 cells stably transfected with PPARgamma2 with the PPARgamma activator 15-deoxy-Delta12,14-prostaglandin J2 inhibited the mRNA expression of osteocalcin and Runx2, the latter of which is a key transcription factor in osteoblast differentiation [13].
• Deletion analysis showed that the leucine zipper domain of ATF4 is critical for Runx2 activation [17].
• In contrast, pull-down assays using purified glutathione S-transferase fusion proteins were unable to demonstrate a direct physical interaction between ATF4 and Runx2 [17].
• Consistent with these cell type-specific effects, expression of the adipocyte-specific gene marker FABP4/aP2 was increased, whereas the expression of osteoblast-specific gene markers, Runx2, Dlx5, osteocalcin, and collagen were not affected by netoglitazone [18].
• Forced expression of Runx2 enhanced osteoblastic differentiation of C3H10T1/2 and MC3T3-E1 cells and enhanced chondrogenic differentiation of ATDC5 cells, whereas these effects were blocked by treatment with IGF-I antibody or LY294002 or adenoviral introduction of dominant-negative (dn)-Akt [19].

Physical interactions of Runx2

• E3 ubiquitin ligase Smurf1 mediates core-binding factor alpha1/Runx2 degradation and plays a specific role in osteoblast differentiation [20].
• Functional relevance was demonstrated through mutations in the Ets-1 and Runx2 consensus binding sites resulting in >60% decrease in OPN transcription [2].
• Groucho homologue Grg5 interacts with the transcription factor Runx2-Cbfa1 and modulates its activity during postnatal growth in mice [21].
• Actually, Stat1 interacts with Runx2 in its latent form in the cytoplasm, thereby inhibiting the nuclear localization of Runx2, an essential transcription factor for osteoblast differentiation [22].
• Treatment with LY294002 or introduction of dn-Akt severely diminished DNA binding of Runx2 and Runx2-dependent transcription, whereas forced expression of myrAkt enhanced them [19].
• Notwithstanding its growth-suppressive potential, our results surprisingly indicate that Runx2 may sensitize cAMP-related G protein-coupled receptor signaling by activating Gpr30 and repressing Rgs2 gene expression in osteoblasts to increase responsiveness to mitogenic signals [23].

Co-localisations of Runx2

• Dach1 colocalized with Runx2/Cbfa1 in chondrocytes but not in the forming bone collar or primary spongiosa [24].

Regulatory relationships of Runx2

• 1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) or Runx2 stimulated OPN transcription (mouse OPN promoter -777/+79) 2-3-fold [25].
• In chromatin immunoprecipitation assays, Msx2 selectively inhibits Runx2 binding to OC chromatin [26].
• Runx1 is highly expressed during chondrogenesis in comparison with Runx2, and Runx1 gain of functions stimulated this process [3].
• The expression of Fgf3 was downregulated in the mesenchyme of Runx2 mutant teeth [27].
• Runx2 regulates FGF2-induced Bmp2 expression during cranial bone development [28].

Other interactions of Runx2

• Both a Runx2 site (-136/-130) and the vitamin D response element (-757/-743) in the OPN promoter are needed for cooperative activation [25].
• To better understand Msx2 regulation of the OCFRE, we have studied functional interactions between MINT and Runx2, a master regulator of osteoblast differentiation [26].
• Recently we have found that Smurf1 mediates the protein degradation of the osteoblast-specific transcription factor Runx2/Cbfa1 [29].
• Overall, the expression of Runx1 remained significantly higher than Runx2 mRNA levels during early limb bud cell maturation [3].
• We have recently shown that over-expression of the full-length, most highly expressed Runx2 isoform in the thymus perturbs T-cell development, leads to development of spontaneous lymphomas at low frequency and is strongly synergistic with Myc [30].

Analytical, diagnostic and therapeutic context of Runx2

• Subsequent supershift and chromatin immunoprecipitation assays confirmed the corresponding nuclear proteins to be Ets-1 and Runx2 [2].
• Immunoprecipitation assays indicated that Hes-1 and Runx2 interact and that 1,25(OH)(2)D(3) can enhance this interaction [25].
• MATERIALS AND METHODS: Wildtype and Runx2-/- tissue was collected from mouse embryos, and gene expression was compared by Affymetrix microarray analysis and radioactive in situ hybridization of embryonic tissue sections (E12-E14) [31].
• On luciferase and electrophoretic mobility shift assays, Runx2-I was less active than Runx2-II in the absence of Cbfb, but the two Runx2 isoforms had similar activity levels in the presence of Cbfb [32].
• Coimmunoprecipitation and mammalian two-hybrid assay revealed a physical interaction between Runx2 and Nrf2, whereas cellular distribution of endogenous Runx2 was not apparently changed by nrf2 overexpression in MC3T3-E1 cells [33].

References