GR role in control of apoptosis

GCs are used in treatments of certain types of cancers due to GR ability to induce apoptosis (Schlossmacher et al., 2011). GCs are used to treat blood cancer such as multiple myeloma (MM) and ALL (Kervoelen et al., 2015). GR is capable of inducing apoptosis in a cell specific manner, as not all cells are sensitive to this cytotoxic effect. For example fibroblasts are not affected by DEX while osteocytes are much more sensitive to low concentrations of DEX (Mostafa et al., 2011). Researchers found that DEX can also induce apoptosis in monocytes in a dose dependent manner (Schmidt et al., 1999).

Furthermore, GCs give rise to cell cycle arrest and apoptosis in lymphoid cells (Vayssiere et al., 1997). It is documented that GC stimulate apoptosis in leukemia cells through its steroid receptor. It has also been suggested that both transactivation and trans

repression of genes could lead to apoptosis (Saenz et al., 2015, Jing et al., 2015, Liu et al., 2014, Tao et al., 2013, Liu et al., 2013, Guo et al., 2013, Wasim et al., 2012, Heidari et al., 2012, Heidari et al., 2010, Carlet et al., 2010). DEX induces apoptosis in T-

lymphocytic leukemia via GR activation of Programmed cell death 1 (PD-1) expression (Xing et al., 2015). It can induce apoptosis by caspase dependent pathway and through changing mitochondrial membrane permeability leading to cellular death. In addition, GC dependent apoptosis leads to activation of pro-apoptotic Bcl-2 protein family members. This family of proteins possesses Bcl-2 Homology (BH) domains (BH1, BH2, BH3, and BH4), and its members can have pro or anti-apoptotic effects (Taylor et al.,

80

2008). Bcl-2 family (table 8) is important for GC action and modulates GC resistance in ALL (Ploner et al., 2005, Geley et al., 1996, Tsujimoto, 1998).

In particular, B-cell CLL/lymphoma 2 (BCL2) can inhibit GR- initiated- apoptosis and influence cell survival by either modulation of apoptosis or effects on the cell cycle. Also BCL-xL is anti- apoptotic protein and stimulates proliferation of cells by affecting the G0 (resting phase) of the cell cycle, whereas BCL2-associated X protein (BAX) has pro- apoptotic properties through its effect on S-phase. Moreover, apoptosis and cell cycle are regulated by multi-domain BCL2 family members (MCL-1) the anti-apoptotic

biomarker. BCL2-associated agonist of cell death (BAD) is pro-apoptotic marker which is the BH3-only group of Bcl-2 family. BH3 Interacting Domain Death Agonist (BID) is pro- apoptotic member of this family, which binds other members to mediate the damage of mitochondria and provide link between intrinsic and extrinsic pathway.

One of the main mediators of cell death induced by GR is proapoptotic and Bcl2- interacting mediator of cell death (Bim). Bim enhances programmed cell death by its BH3 domain and has the ability to antagonize the effects of some anti-apoptotic

markers. Alternative splicing produces BIMEL (extra-large), BIML (large) and BIMS (small) isoforms (O'Connor et al., 1998), which consist of 198 aa, 138 aa, and 112 aa

respectively, all have BH3 region in their structure (Genes, 2017a).

It is believed that GR mediated apoptosis is linked with Bim expression. Heidari et al. (2012) have studied the relationship between GC-apoptosis and BIM in leukemia cells and their study revealed that apoptosis induction in leukemia cells is accompanied by up-regulation of BIM, C-JUN and Runx2 in GC sensitive cells whereas this interaction are missing in GC resistant cells. This mechanism can be blocked by inhibition of MAPK, thus investigating Bim (which is regulated transcriptionally) and Bim affected targets is

81

important in order to explain how cell death occurs in different cancers. Another report by Jing et al. (2015) suggested that BIM mediated GC induced apoptosis by specific mechanism involves GR-Bim binding at the internal promoter region of BIM. However other reports indicated that main mode of GR mediated induction of Bim is through indirect mechanisms (Adams and Cory, 2007).

It has been found that Programmed Cell Death 4 (Pcd4) gene was up-regulated upon GC therapy inducing apoptosis. In addition PTMs like phosphorylation which takes place at Ser211 accelerate GR apoptotic efficiency (Lankat-Buttgereit and Goke, 2003).

Table 8 GR effect on BH3-family members

Target protein Type of response Type of apoptotic cells Reference BAX Bim, Bcl-xL Bak upregulation upregulation upregulation upregulation

thymocyte apoptosis. (Prenek et al., 2017)

Bax/Bcl-2 ratio increased germ cell apoptosis (Mukherjee et al., 2015)

Bim upregulation multiple myeloma (Kervoelen et al., 2015) Bim BCL2 upregulation downregulation pediatric acute lymphoblastic leukemia cells (Jing et al., 2015)

BCL2 downregulation spinal cord injury (SCI) (Maldonado Bouchard and Hook, 2014) BCL2 upregulation Small cell lung cancer (Schlossmacher et al.,

2013) Bim

BCL-XL MCL-1

upregulation human plasmacytoid dendritic cells

(Hong et al., 2013)

Bim upregulation ALL cells (Beach et al., 2011)

Bim upregulation WEHI7.2 and S49.A2

murine lymphoma cell,

CEM-C7 cells and in primary murine thymocytes

(Wang et al., 2003)

82

However apoptosis does not always have a favourable effect as the early administration of GCs in pregnancy can affect foetus and cause unwanted permanent central nervous system damage due to early apoptosis of nervous cells (Lanshakov et al., 2016). In addition to the crosstalk between glucocorticoid receptor (GR) and T cell antigen receptor (TCR) have been suggested (Jamieson and Yamamoto, 2000)

GR causes downregulation of transcription proinflammatory genes /mediators via suppression of their transcription factors such as AP-1 and NF- κB (Hermoso and Cidlowski, 2003). NF-κB has also attributed to Warburg effect and alteration of metabolism in tumours (Johnson and Perkins, 2012). The NF-κB also modulates the inflammation and immunity (Hoesel and Schmid, 2013). NF-κB contributed to cancer as it is family member of v-Rel oncogen, and NF-κB affected genes are seen to be

modulated during many cancers. The stimulation of NF-κB signaling pathway is preceded by inflammatory events or by inflammation accompanied by a developing cancer (Karin, 2009)