Expression of the NF-kappa B target gene X-ray-inducible immediate early response factor-1 short enhances TNF-alpha-induced hepatocyte apoptosis by inhibiting Akt activation.
Using a cDNA microarray analysis, we identified x-ray-inducible immediate early response factor-1 (IEX-1) as a proapoptotic gene which was induced by TNF-alpha and also depend on NF-kappaB activation in Hc human hepatocytes. In these cells only the original form of IEX-1, termed IEX-1S, but not its longer transcript IEX-1L, was expressed. Overexpression of IEX-1S resulted in promotion of TNF-alpha-induced apoptosis in Hc cells expressing a mutant form of IkappaB. This proapoptotic action can be explained by its inhibitory findings on survival signals; inhibition of TNF-alpha-induced activation and expression of phosphatidylinositol 3-kinase (PI3K)/Akt, and also blockage of expression of Mcl-1, an antiapoptotic Bcl-2 family member which is located downstream of Akt, was inhibited by IEX-1S. LY 294002, an inhibitor of PI3K, increased IEX-1S expression induced by TNF-alpha and accelerated TNF-alpha-induced apoptosis in IkappaB-treated Hc cells. Overexpression of the dominant-negative Akt enhanced, but the constitutively active Akt suppressed, TNF-alpha-induced IEX-1S expression, suggesting that PI3K/Akt negatively regulated IEX-1S expression. These results demonstrate that NF-kappaB-dependent recruitment of IEX-1S may play a proapoptotic role in TNF-alpha-stimulated hepatocytes through blockage of the PI3K/Akt pathway. Moreover, the reciprocal cross-talk between IEX-1S and PI3K/Akt may closely be involved in the regulation of TNF-alpha-induced hepatocyte apoptosis.
Osawa
Yosuke
Y
First Department of Internal Medicine, Gifu University School of Medicine, Tsukasamachi, Gifu, Japan.
Nagaki
Masahito
M
Banno
Yoshiko
Y
Brenner
David A
DA
Nozawa
Yoshinori
Y
Moriwaki
Hisataka
H
Nakashima
Shigeru
S
D000276:Adjuvants, Immunologic / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology / Q000528:radiation effects; D017209:Apoptosis / Q000235:genetics* / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000235:genetics; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000528:radiation effects; D018390:Gene Targeting / Q000379:methods*; D022781:Hepatocytes / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D017874:Immediate-Early Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology / Q000528:radiation effects; D008565:Membrane Proteins; D005810:Multigene Family; D016328:NF-kappa B / Q000378:metabolism* / Q000502:physiology; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology / Q000528:radiation effects; D020411:Oligonucleotide Array Sequence Analysis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D014965:X-Rays
D000276:Adjuvants, Immunologic; D051017:Apoptosis Regulatory Proteins; D017874:Immediate-Early Proteins; D008565:Membrane Proteins; D016328:NF-kappa B; D009363:Neoplasm Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; C099815:IER3 protein, human; C494918:AKT1 protein, human