Glucocorticoid Modulatory Element-binding Protein 1 Binds to Initiator Procaspases and Inhibits Ischemia-induced Apoptosis and Neuronal Injury

Abstract

Caspases are divided into two classes: initiator caspases, which include caspase-8 and -9 and possess long prodomains, and effector caspases, which include caspase-3 and -7 and possess short prodomains. Recently, we demonstrated that glucocorticoid modulatory element-binding protein 1 (GMEB1) interacts with the prodomain of procaspase-2, thereby disrupting its autoactivation and the induction of apoptosis. Here we show that GMEB1 is also capable of binding to procaspase-8 and -9. GMEB1 attenuated the Fas-mediated activation of these caspases and the subsequent apoptosis. The knockdown of endogenous GMEB1 using RNA interference revealed that cells with decreased GMEB1 expression are more sensitive to stress and undergo accelerated apoptosis. Transgenic mice expressing a neurospecific GMEB1 had smaller cerebral infarcts and less brain swelling than wildtype mice in response to transient focal ischemia. These results suggest that GMEB1 is an endogenous regulator that selectively binds to initiator procaspases and inhibits caspase-induced apoptosis.Human caspases are the primary executioners of apoptosis and are divided into two classes, initiators and effectors. The effector caspases, which include caspase-3 and -7, possess short prodomains. The initiator caspases, which include caspase-8 and -9, possess long prodomains that consist of interaction domains essential for their activation. In response to the binding of ligands to death receptors, such as Fas, the adaptor protein FADD 3 and procaspase-8 are recruited to the activated receptor and are incorporated into a death-inducing signaling complex (DISC) (1). The interaction between FADD and procaspase-8 is mediated by the death effector domains (DED) of both proteins (2-4). A second molecule of procaspase-8 then binds to the complex, thus facilitating the autocatalytic activation of caspase-8.Procaspase-9 is activated by a variety of internal and external death stimuli that promote cytochrome c release from mitochondria. In the cytosol, cytochrome c binds the adaptor protein Apaf-1 in a dATPdependent fashion. The binding of cytochrome c and dATP induces a conformational change in Apaf-1 that allows it to associate with procaspase-9 via their respective caspase recruitment domains (CARD) (5, 6). The oligomerization of these procaspases while associated with these specific adapter molecules leads to autoactivation of the caspases (7). The enzymatic activation of initiator caspases leads to proteolytic activation of downstream effector caspases, the subsequent caspase-dependent cleavage of many vital proteins, and ultimately to programmed cell death. Thus, the regulation of initiator caspases is critical in determining whether a cell lives or dies.Caspases are synthesized in the cell as inactive precursors (procaspases), and their activation is strictly controlled by a variety of regulatory proteins, including Bcl-2, heat-shock proteins (HSPs), and the inhibitor of apoptosis (IAP) family of proteins (8 -13). Recently, we showed that glucocorticoid modulatory element...

IL-12 inhibits glucocorticoid-induced T cell apoptosis by inducing GMEB1 and activating PI3K/Akt pathway

“…Nakagawa et al (2008) reported that GMEB1 is capable of binding to caspase-2, caspase-8, and caspase-9, and thus protect against apoptosis of neurons, another cell type susceptible to GC-induced apoptosis. In addition, the knockdown of endogenous GMEB1 using siRNA renders mice more sensitive to stress and leads to accelerated apoptosis in the central nervous system (Tsuruma et al 2006). GMEB1 and GMEB2 are co-modulators of GR and can modify the potency of agonists (EC 50 ) or the partial agonist activity (PAA) of antisteroids without direct changes in the binding affinity of the steroids.…”

“…Glucocorticoid modulatory element-binding protein 1 and 2 (GMEB1 and GMEB2), members of the family of KDWK proteins, form a heterodimer that binds DNA and modulates the transactivation function of GR and thus GC effects (Zeng et al 2000). Furthermore, GMEB1 has been reported to be capable of binding to caspase-2, -8 and -9, and to inhibit caspase-mediated apoptosis (Nakagawa et al 2008;Tsuruma et al 2006Tsuruma et al , 2004.…”

Use of gene profiling to evaluate the effects of a feed additive on immune function in periparturient dairy cattle

“…Changes (p < 0.05) in expression of five genes (GME, HPK, caspase‐13, WTR and FW) are consistent with potential for a decline in apoptosis. For example, Tsuruma et al. (2006) reported that GME binds to initiator pro‐caspases and thereby inhibits apoptosis in neuronal injury.…”

“…Changes (p < 0.05) in expression of five genes (GME, HPK, caspase-13, WTR and FW) are consistent with potential for a decline in apoptosis. For example, Tsuruma et al (2006) reported that GME binds to initiator pro-caspases and thereby inhibits apoptosis in neuronal injury. Haematopoeitic progenitor kinase is a functional component of the endogenous IkappaB kinase complex and is crucial for T-cell receptor-mediated NFkappaB activation (Brenner et al, 2005).…”

Neural Stem Cell Protects Aged Rat Brain from Ischemia–Reperfusion Injury through Neurogenesis and Angiogenesis

“…30 Neural stem cells transplantation into youngadult ischemic rodents greatly reduced TUNEL þ apoptotic cells and inflammatory infiltration, further improved neurobehavioral outcomes. 31 We found that brain ischemia induced more neuronal apoptosis in aged rats compared with the young-adult rats, while NSC transplantation greatly attenuated neuronal apoptosis in both young-adult and aged rats.…”