The early response gene IEX-1 attenuates NF-kappaB activation in 293 cells, a possible counter-regulatory process leading to enhanced cell death.
The early response gene IEX-1 is involved in the regulation of cellular growth and survival, and its expression is related to stress-, growth- and death-inducing signals. Addressing the role of IEX-1 in the promotion of apoptosis, we investigated the effect of IEX-1 on nuclear factor-kappaB (NF-kappaB) activation. Stably transfected HEK-293 cells conditionally overexpressing IEX-1 exhibit decreased levels of NF-kappaB activity, either basal or TNFalpha induced, as shown by gel-shift and luciferase reporter gene assay. Furthermore, activated p65 accumulated in the nuclei of 293 cells to a lower degree, if IEX-1 expression was increased. This inhibited NF-kappaB activation was preceded by an altered turnover of IkappaBalpha and phospho-IkappaBalpha. In addition, IEX-1 expression also inhibited the activity of the 26S-proteasome, as shown by a fluorometric proteasome assay. Conversely, disruption of IEX-1 expression in 293 cells by stable transfection with specific anti-IEX-1 hammerhead ribozymes increased NF-kappaB activity, and accelerated the degradation of IkappaBalpha. Along with these opposite effects of IEX-1 expression and IEX-1 disruption on NF-kappaB activation, the sensitivity of 293 cells towards various apoptotic stimuli also changed. In contrast to ribozyme-transduced 293 cells that were significantly less sensitive to apoptosis, this sensitivity was enhanced if IEX-1 expression was increased. Our data suggest that IEX-1 - itself an NF-kappaB target gene - inhibits the activation of this transcription factor, and hereby may counteract the antiapoptotic potential of NF-kappaB.
Arlt
Alexander
A
Laboratory of Molecular Gastroenterology & Hepatology, 1st Department of Medicine, Christian-Albrechts University of Kiel, Schittenhelmstr. 12, D-24105 Kiel, Germany.
Kruse
Marie-Luise
ML
Breitenbroich
Maike
M
Gehrz
Andre
A
Koc
Bülent
B
Minkenberg
Jörg
J
Fölsch
Ulrich R
UR
Schäfer
Heiner
H
D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry; D003546:Cysteine Endopeptidases / Q000378:metabolism; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D017874:Immediate-Early Proteins / Q000235:genetics / Q000502:physiology*; D007700:Kinetics; D008565:Membrane Proteins; D009097:Multienzyme Complexes / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000032:analysis / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex; D016337:RNA, Catalytic / Q000235:genetics / Q000378:metabolism; D051996:Transcription Factor RelA; D014162:Transfection
D051017:Apoptosis Regulatory Proteins; D020672:I-kappa B Proteins; C099815:IER3 protein, human; D017874:Immediate-Early Proteins; D008565:Membrane Proteins; D009097:Multienzyme Complexes; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D009363:Neoplasm Proteins; D016337:RNA, Catalytic; D051996:Transcription Factor RelA; C427204:hammerhead ribozyme; D000072000:NF-KappaB Inhibitor alpha; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex