Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adjuvants, Immunologic / biosynthesis
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Adjuvants, Immunologic / genetics*
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Adjuvants, Immunologic / physiology
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Adjuvants, Immunologic / radiation effects
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Apoptosis / genetics*
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Apoptosis / physiology
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Apoptosis Regulatory Proteins
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Cell Survival / physiology
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Cells, Cultured
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Enzyme Activation / genetics
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Gene Expression Profiling
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Gene Expression Regulation* / radiation effects
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Gene Targeting / methods*
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Hepatocytes / cytology
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Hepatocytes / enzymology
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Hepatocytes / metabolism*
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Humans
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Immediate-Early Proteins / biosynthesis
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Immediate-Early Proteins / genetics*
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Immediate-Early Proteins / physiology
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Immediate-Early Proteins / radiation effects
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Membrane Proteins
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Multigene Family
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NF-kappa B / metabolism*
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NF-kappa B / physiology
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Neoplasm Proteins / biosynthesis
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Neoplasm Proteins / genetics*
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Neoplasm Proteins / physiology
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Neoplasm Proteins / radiation effects
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Oligonucleotide Array Sequence Analysis
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Phosphatidylinositol 3-Kinases / metabolism
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Protein Serine-Threonine Kinases*
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Proto-Oncogene Proteins / antagonists & inhibitors*
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins / physiology
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Proto-Oncogene Proteins c-akt
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Proto-Oncogene Proteins c-bcl-2 / biosynthesis
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Proto-Oncogene Proteins c-bcl-2 / genetics
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Signal Transduction / genetics
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Transfection
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Tumor Necrosis Factor-alpha / pharmacology*
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X-Rays
Substances
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Adjuvants, Immunologic
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Apoptosis Regulatory Proteins
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IER3 protein, human
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Immediate-Early Proteins
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Membrane Proteins
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NF-kappa B
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Neoplasm Proteins
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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Tumor Necrosis Factor-alpha
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AKT1 protein, human
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-akt