Corticosteroids bind to the glucocorticoid receptor NR3C1 (Rupprecht et al. 1993, Lind et al. 2000), inhibiting pro-inflammatory NF-Kappa B and other inflammatory transcription factors, and promoting anti-inflammatory genes like interleukin-10. The short term effects of corticosteroids are decreased vasodilation and permeability of capillaries, as well as decreased leukocyte migration to sites of inflammation. From the Randomized Evaluation of COVID-19 Therapy (RECOVERY) trial in June 2020, dexamethasone was recommended for use in COVID-19 patients with severe respiratory symptoms. In the trial, dexamethasone reduced deaths by approximately one third in patients requiring ventilation and by one fifth in those requiring oxygen.

NR3C1 (Glucocorticoid receptor, GR) is SUMOylated at lysine-277 and lysine-293 with SUMO1 (Tian et al. 2002, Impens et al. 2014). SUMOylation is enhanced when NR3C1 binds ligand (dexamethasone). SUMOylation reduces transcription activation by NR3C1.

Steroid hormones receptors (SHRs) are intracellular transcription factors that can be activated by binding specific ligands (i.e., steroid hormones (SH)) to the ligand-binding domain (LBD) (Ray DW et AL. 1999; Pike AC et al. 1999; Bledsoe RK et al. 2002; Li Y et al. 2005; Kumar R and McEwan IJ 2012; Kumar R et al. 2011; Williams SP & Sigler PB 1998; Tanenbaum DM et al. 1998; Lusher SJ et al. 2012). LBD (E-region) resides in the C-terminal half of the receptor and in addition to ligand binding function contains a transcriptional activation function (AF2), sequences for dimerization, heat shock protein association, intermolecular silencing and intramolecular repression (Kumar R and McEwan IJ 2012). The binding of hormone acts as an allosteric switch to regulate SHR-DNA and SHR-protein interactions, including interdomain interactions and/or dimerization (Kumar R and McEwan IJ 2012).

SHs are synthesized from cholesterol in the adrenal cortex (glucocorticoids, mineralocorticoids, and adrenal androgens), the testes (testicular androgens, estrogen), and the ovary and placenta (estrogen and progestogen or progestins) (Payne AH & Hales DB 2004; Hu J et al. 2010;). SHs reach their target cells via the blood, where they are bound to specific carrier proteins (Grishkovskaya I et al. 2000; Hammond GL 2016). SHs detach from the carrier proteins and because of their lipophilic nature readily diffuse through the plasma membrane of cells (Oren I et al. 2004). Within the target cells SHs bind to steroid hormone receptors (SHRs) which are present in a heterocomplex with heat shock protein HSP90 and co-chaperones (e.g., immunophilins p23) (Echeverria PC & Picard D 2010). The ATP-bound form of HSP90 and chaperone-mediated conformational changes are required to keep SHRs in a ligand binding-competent state (McLaughlin SH et al. 2002; Pratt WB et al. 2008; Krukenberg KA et al. 2011).

Glucocorticoid receptor elements (GREs) and forkhead box elements are conserved in the promoter of the mouse, rat and human TRIM63 gene, encoding an E3 ubiquitin ligase TRIM63 (MuRF1) (Waddell et al. 2008).

EPAS1 (HIF2A) and dexamethasone-activated glucocorticoid receptor NR3C1 (GCR or GR), in the presence of the NR3C1 co-factor PELP1, cooperatively bind to adjacent hypoxia response and glucocorticoid response elements in the PTK6 gene promoter. The cooperative binding of EPAS1 and NR3C1 to the PTK6 gene promoter may be facilitated by p38 MAPK-mediated phosphorylation of NR3C1 on serine residue S134. EPAS1 expression can also be stimulated by the activated NR3C1. EPAS1 and NR3C1-mediated activation of PTK6 expression may play an important role in the progression of the triple negative breast cancer (Regan Anderson et al. 2016).

Based on studies in mice, glucocorticoid receptor (NR3C1) activated by dexamethasone (DEXA) binds to glucocorticoid receptor response element (GRE) in the proximal (P2) promoter of the RUNX2 gene. NR3C1 may also recruit histone deacetylase HDAC1 to the RUNX2 promoter (Zhang et al. 2012). Similar to the mouse promoter, human RUNX2 P2 promoter also contains GREs.

Activation of liver X receptor α (LXRα, NR1H3) alters the expression of genes in liver and adipose tissue that collectively may limit hepatic glucose output and improve peripheral glucose uptake (Laffitte BA et al. 2003). In the liver, activation of NR1H3 led to the suppression of the expression of genes involved in gluconeogenesis including glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PCK1 or PEPCK) (Laffitte BA et al. 2003; Dalen KT et al. 2003; Herzog B et al. 2007; Commerford et al. 2007). In adipose tissue, activation of NR1H3 led to the transcriptional induction of the insulin-sensitive glucose transporter, GLUT4 (Laffitte BA et al. 2003; Dalen KT et al. 2003). In contrast, basal expression of LXRβ (NR1H2) has been shown to be essential for the regulation of PCK1 by another nuclear receptor, the glucocorticoid receptor GR (NR3C1) (Patel et al. 2011; Patel et. al. 2017). The LXRs appear to have somewhat opposing roles in the regulation of PCK1 in the liver since NR1H3 (LXRα) activation represses PCK1 mRNA expression induced by glucocorticoids (Nader et al. 2012) and NR1H2 (LXRβ) antagonism reduces glucocorticoid-induced PCK1 mRNA expression (Patel et al. 2017).

Several transcription factors have been implicated in regulation of the RUNX2 gene transcription. Similar to the RUNX1 gene, the RUNX2 gene expression can be regulated from the proximal P2 promoter or the distal P1 promoter (reviewed in Li and Xiao 2007).
Activated estrogen receptor alpha (ESR1) binds estrogen response elements (EREs) in the P2 promoter and stimulates RUNX2 transcription (Kammerer et al. 2013). Estrogen-related receptor alpha (ERRA) binds EREs or estrogen-related response elements (ERREs) in the P2 promoter of RUNX2. When ERRA is bound to its co-factor PPARG1CA (PGC1A), it stimulates RUNX2 transcription. When bound to its co-factor PPARG1CB (PGC1B), ERRA represses RUNX2 transcription (Kammerer et al. 2013).
TWIST1, a basic helix-loop-helix (bHLH) transcription factor, stimulates RUNX2 transcription by binding to the E1-box in the P2 promoter (Yang, Yang et al. 2011). TWIST proteins also interact with the DNA-binding domain of RUNX2 to modulate its activity during skeletogenesis (Bialek et al. 2004). Schnurri-3 (SHN3) is another protein that interacts with RUNX2 to decrease its availability in the nucleus and therefore its activity (Jones et al. 2006). In contrast, RUNX2 and SATB2 interact to enhance the expression of osteoblast-specific genes (Dobreva et al. 2006). Formation of the heterodimer with CBFB (CBF-beta) also enhances the transcriptional activity of RUNX2 (Kundu et al. 2002, Yoshida et al. 2002, Otto et al. 2002).
Transcription of RUNX2 from the proximal promoter is inhibited by binding of the glucocorticoid receptor (NR3C1) activated by dexamethasone (DEXA) to a glucocorticoid receptor response element (GRE), which is also present in the human promoter (Zhang et al. 2012).
NKX3-2 (BAPX1), required for embryonic development of the axial skeleton (Tribioli and Lufkin 1999), binds the distal (P1) promoter of the RUNX2 gene and inhibits its transcription (Lengner et al. 2005). RUNX2-P1 transcription is also autoinhibited by RUNX2-P1, which binds to RUNX2 response elements in the P1 promoter of RUNX2 (Drissi et al. 2000). In contrast, binding of RUNX2-P2 to the proximal P2 promoter autoactivates transcription of RUNX2-P2 (Ducy et al. 1999). Binding of a homeodomain transcription factor DLX5, and possibly DLX6, to the RUNX2 P1 promoter stimulates RUNX2 transcription (Robledo et al. 2002, Lee et al. 2005). The homeobox transcription factor MSX2 can bind to DLX5 sites in the promoter of RUNX2 and inhibit transcription of RUNX2-P1 (Lee et al. 2005).
Translocation of RUNX2 protein to the nucleus is inhibited by binding to non-activated STAT1 (Kim et al. 2003).
Several E3 ubiquitin ligases were shown to polyubiquitinate RUNX2, targeting it for proteasome-mediated degradation: FBXW7a (Kumar et al. 2015), STUB1 (CHIP) (Li et al. 2008), SMURF1 (Zhao et al. 2003, Yang et al. 2014), WWP1 (Jones et al. 2006), and SKP2 (Thacker et al. 2016).

RUNX2 (CBFA1 or AML3) transcription factor, similar to other RUNX family members, RUNX1 and RUNX3, can function in complex with CBFB (CBF-beta) (Kundu et al. 2002, Yoshida et al. 2002, Otto et al. 2002). RUNX2 mainly regulates transcription of genes involved in skeletal development (reviewed in Karsenty 2008). RUNX2 is involved in development of both intramembraneous and endochondral bones through regulation of osteoblast differentiation and chondrocyte maturation, respectively. RUNX2 stimulates transcription of the BGLAP gene (Ducy and Karsenty 1995, Ducy et al. 1997), which encodes Osteocalcin, a bone-derived hormone which is one of the most abundant non-collagenous proteins of the bone extracellular matrix (reviewed in Karsenty and Olson 2016). RUNX2 directly controls the expression of most genes associated with osteoblast differentiation and function (Sato et al. 1998, Ducy et al. 1999, Roce et al. 2005). RUNX2-mediated transcriptional regulation of several genes involved in GPCR (G protein coupled receptor) signaling is implicated in the control of growth of osteoblast progenitors (Teplyuk et al. 2009). RUNX2 promotes chondrocyte maturation by stimulating transcription of the IHH gene, encoding Indian hedgehog (Takeda et al. 2001, Yoshida et al. 2004). Germline loss-of-function mutations of the RUNX2 gene are associated with cleidocranial dysplasia syndrome (CCD), an autosomal skeletal disorder (reviewed in Jaruga et al. 2016). The function of RUNX2 is frequently disrupted in osteosarcoma (reviewed in Mortus et al. 2014). Vitamin D3 is implicated in regulation of transcriptional activity of the RUNX2:CBFB complex (Underwood et al. 2012).

RUNX2 expression is regulated by estrogen signaling, and RUNX2 is implicated in breast cancer development and metastasis (reviewed in Wysokinski et al. 2014). Besides estrogen receptor alpha (ESR1) and estrogen-related receptor alpha (ERRA) (Kammerer et al. 2013), RUNX2 transcription is also regulated by TWIST1 (Yang, Yang et al. 2011), glucocorticoid receptor (NR3C1) (Zhang et al. 2012), NKX3-2 (BAPX1) (Tribioli and Lufkin 1999, Lengner et al. 2005), DLX5 (Robledo et al. 2002, Lee et al. 2005) and MSX2 (Lee et al. 2005). RUNX2 can autoregulate, by directly inhibiting its own transcription (Drissi et al. 2000). Several E3 ubiquitin ligases target RUNX2 for proteasome-mediated degradation: FBXW7a (Kumar et al. 2015), STUB1 (CHIP) (Li et al. 2008), SMURF1 (Zhao et al. 2003, Yang et al. 2014), WWP1 (Jones et al. 2006), and SKP2 (Thacker et al. 2016). Besides formation of RUNX2:CBFB heterodimers, transcriptional activity of RUNX2 is regulated by binding to a number of other transcription factors, for example SOX9 (Zhou et al. 2006, TWIST1 (Bialek et al. 2004) and RB1 (Thomas et al. 2001).

RUNX2 regulates expression of several genes implicated in cell migration during normal development and bone metastasis of breast cancer cells. RUNX2 stimulates transcription of the ITGA5 gene, encoding Integrin alpha 5 (Li et al. 2016) and the ITGBL1 gene, encoding Integrin beta like protein 1 (Li et al. 2015). RUNX2 mediated transcription of the MMP13 gene, encoding Colagenase 3 (Matrix metalloproteinase 13), is stimulated by AKT mediated phosphorylation of RUNX2 (Pande et al. 2013). RUNX2 is implicated in positive regulation of AKT signaling by stimulating expression of AKT-activating TORC2 complex components MTOR and RICTOR, which may contribute to survival of breast cancer cells (Tandon et al. 2014).

RUNX2 inhibits CDKN1A transcription, thus preventing CDKN1A-induced cell cycle arrest. Phosphorylation of RUNX2 by CDK4 in response to high glucose enhances RUNX2-mediated repression of the CDKN1A gene in endothelial cells (Pierce et al. 2012). In mice, Runx2-mediated repression of Cdkn1a may contribute to the development of acute myeloid leukemia (AML) (Kuo et al. 2009). RUNX2 can stimulate transcription of the LGALS3 gene, encoding Galectin-3 (Vladimirova et al. 2008, Zhang et al. 2009). Galectin 3 is expressed in myeloid progenitors and its levels increase during the maturation process (Le Marer 2000).

For a review of RUNX2 function, please refer to Long 2012 and Ito et al. 2015.