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-α and also depend on NF-κB 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-α-induced apoptosis in Hc cells expressing a mutant form of IκB. This proapoptotic action can be explained by its inhibitory findings on survival signals; inhibition of TNF-α-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-α and accelerated TNF-α-induced apoptosis in IκB-treated Hc cells. Overexpression of the dominant-negative Akt enhanced, but the constitutively active Akt suppressed, TNF-α-induced IEX-1S expression, suggesting that PI3K/Akt negatively regulated IEX-1S expression. These results demonstrate that NF-κB-dependent recruitment of IEX-1S may play a proapoptotic role in TNF-α-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-α-induced hepatocyte apoptosis.