Distinct Domains for Anti- and Pro-apoptotic Activities of IEX-1

Abstract

IEX-1 (immediate early response gene X-1) is a stress-inducible gene. Its overexpression can suppress or enhance apoptosis dependent on the nature of stress, yet the polypeptide does not possess any of the functional domains that are homologous to those present in well characterized effectors or inhibitors of apoptosis. This study using sequence-targeting mutagenesis reveals a transmembranelike integrated region of the protein to be critical for both pro-apoptotic and anti-apoptotic functions. Substitution of the key hydrophobic residues with hydrophilic ones within this region impairs the capacity IEX-1 to positively and negatively regulate apoptosis. Mutations at N-linked glycosylation and phosphorylation sites or truncation of the C terminus of IEX-1 also abrogated its potential to promote cell survival. However, distinguished from the transmembrane-like domain, these mutants preserved pro-apoptotic activity of IEX-1 fully. On the contrary, mutation of nuclear localization sequence, despite its importance in apoptosis, did not impede IEX-1-mediated cell survival. Strikingly, all the mutants that lose their anti-apoptotic ability are unable to prevent acute increases in production of intracellular reactive oxygen species (ROS) at the initial onset of apoptosis, whereas those mutants that can sustain antideath function also control acute ROS production as sufficiently as wild-type IEX-1. These findings suggest a critical role of IEX-1 in regulation of intracellular ROS homeostasis, providing new insight into the mechanism underlying IEX-1-mediated cell survival.A coordinated balance between cell survival and apoptosis is essential for embryonic development, tissue homeostasis, and cellular responses to various types of stress (1). Defects in this balance may contribute to a variety of diseases, including cancers, autoimmune disorders, and aberrant embryonic development (2). Programmed cell death occurs in mitochondrion-dependent and independent pathways, and the former accounts for most forms of apoptosis in response to cellular stress, loss of survival factors, and developmental cues (3, 4). The mitochondrial pathway triggers cell death as a consequence of alteration in mitochondrial membrane permeability induced by apoptotic effectors like oxidative stress and signaling-mediated translocation of Bax, Bad, Bid, or Bim, leading to the release of cytochrome c and other proteins contained in the mitochondrial intermembrane space (5, 6). Substantial evidence indicates that prior to an irreparable loss of mitochondrial structural integrity, apoptotic effectors often stimulate an acute increase in the mitochondrial membrane potential ⌬ m that facilitates the formation of reactive oxygen species (ROS), 2 the amplitude of which determines a cell to die by apoptosis or to adapt (4, 7-11). Conceivably, prevention of ROS production in the initial phase of apoptosis is essential to guard the integrity of mitochondrial membrane, protecting cells from undergoing apoptosis.IEX-1 (immediate early response gene X-1), also know...

The apoptosis-inducing effect of gastrin on colorectal cancer cells relates to an increased IEX-1 expression mediating NF-κB inhibition

“…IEX-1 as well as its rodent homologues PRG1 and gly96 represent short-lived proteins consisting of 156, 160 and 153 amino acids, respectively, and, to current knowledge, share no significant sequence similarities with any other known protein. Depending on cell type and stimulus-specific conditions, IEX-1 regulates cell growth and cellular viability (reviewed in Wu, 2003), and a significant apoptosis triggering effect by IEX-1 has been described (Scha¨fer et al, 1999;Arlt et al, 2001;Grobe et al, 2001;Schilling et al, 2001;Osawa et al, 2003;Shen et al, 2006). In the present study, we identified IEX-1 as an important mediator of G17-dependent NFkB inhibition and apoptosis in Colo320 cells expressing the wild-type CCK2 receptor.…”

Potential targets of FOXL2, a transcription factor involved in craniofacial and follicular development, identified by transcriptomics

“…IER3 protects from Fas-or TNF-␣-induced apoptosis, and its overexpression can suppress or enhance apoptosis, depending on the nature of stress (22). This gene is also thought to play a critical role in the regulation of intracellular ROS homeostasis (23). Finally, the gene encoding PPP1R15A (protein phosphatase 1, inhibitory subunit 15A) also appeared in this cluster.…”

Low-Level Laser Therapy Effectively Prevents Secondary Brain Injury Induced by Immediate Early Responsive Gene X-1 Deficiency

“…The immediate early responsive gene X-1 (IEX-1) has a pivotal role in regulation of mitochondrial F 1 F 0 -ATPase activity, in protection against apoptosis, and in resolution of inflammation. [13][14][15] Null mutation of IEX-1 enhanced apoptosis, 16 reduced ATP synthase activity, 17 and prolonged inflammatory responses in a tissue-dependent manner in mice. 15,18 Furthermore, IEX-1 is upregulated by NF-kB and in turn inhibits NF-kB activation as a negative feedback mechanism contributing to inflammation resolution.…”