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Nuclear-Factor-kappaB (NF-kappaBeta can counteract transforming growth factor-beta1 (TGF-beta1)-induced apoptosis in malignant hepatocytes through up-regulation of its downstream genes, such as X-linked inhibitor of apoptosis protein (XIAP). Reports have demonstrated that TGF-beta1 can induce oxidative stress, and c-Jun N-terminal Kinase1 (JNK1) is indispensable for TGF-beta1-induced apoptosis pathway, but the relationship between radical oxygen species (ROS) and the activation of JNKs is still unclear. In the present study, we found that ROS can induce JNK activation in TGF-beta1 mediated apoptosis in hepatocytes. The inhibitors of hydrogen peroxide and superoxide, which were produced by mitochondria under stress, could inhibit the phosphorylation of c-Jun in XIAP knockdown cells. In conclusion, it is the first time to show that both NF-kappaB and antioxidants can counteract TGF-beta1-induced apoptosis in hepatic cell death through JNK1 pathway.

Background & Aims: We recently identified lysophosphatidic acid (LPA) as a potent antiapoptotic agent for the intestinal epithelium. The objective of the present study was to evaluate the effect of octadecenyl thiophosphate (OTP), a novel rationally designed, metabolically stabilized LPA mimic, on radiation-induced apoptosis of intestinal epithelial cells in vitro and in vivo., Methods: The receptors and signaling pathways activated by OTP were examined in IEC-6 and RH7777 cell lines and wild-type and LPA(1) and LPA(2) knockout mice exposed to different apoptotic stimuli., Results: OTP was more efficacious than LPA in reducing gamma irradiation-, camptothecin-, or tumor necrosis factor alpha/cycloheximide-induced apoptosis and caspase-3-8, and caspase-9 activity in the IEC-6 cell line. In RH7777 cells lacking LPA receptors, OTP selectively protected LPA(2) but not LPA(1) and LPA(3) transfectants. In C57BL/6 and LPA(1) knockout mice exposed to 15 Gy gamma irradiation, orally applied OTP reduced the number of apoptotic bodies and activated caspase-3-positive cells but was ineffective in LPA(2) knockout mice. OTP, with higher efficacy than LPA, enhanced intestinal crypt survival in C57BL/6 mice but was without any effect in LPA(2) knockout mice. Intraperitoneally administered OTP reduced death caused by lethal dose (LD)(100/30) radiation by 50%., Conclusions: Our data indicate that OTP is a highly effective antiapoptotic agent that engages similar prosurvival pathways to LPA through the LPA(2) receptor subtype.

Nuclear factor kappaB (NF-kappaB) is an antiapoptotic factor involved in development, regeneration, and neoplastic progression of the liver. Previously, we have shown that stabilization of inhibitor kappaB (IkappaB)-alpha protein following treatment of hepatocytes with transforming growth factor (TGF)-beta1 promoted NF-kappaB repression, which then permitted induction of AP-1/SMAD-mediated liver cell death. Because basal IkappaB-alpha protein turnover is regulated by protein kinase CK2, here we have elucidated the regulation of CK2 kinase activity and its role in control of NF-kappaB levels following treatment with TGF-beta1. We show that both messenger RNA (mRNA) and protein levels of the CK2alpha catalytic subunit are down-regulated following TGF-beta1 stimulation in murine hepatocyte cells. The ensuing inhibition of CK2 kinase activity promotes stabilization of IkappaB protein, which is followed by the shutoff of constitutive NF-kappaB activity and induction of apoptosis. Ectopic expression of CK2alpha inhibits TGF-beta1-induced apoptosis through sustained activation of NF-kappaB. Conversely, expression of a kinase-dead mutant of CK2alpha potentiates TGF-beta1 cell killing. Importantly, we show that hepatocellular carcinomas (HCCs) derived from TGF-beta1 transgenic mice and human HCC cell lines display enhanced CK2 IkappaB kinase activity that contributes in part to an elevated NF-kappaB activity in vivo. In conclusion, inhibition of CK2 expression levels by TGF-beta1 is crucial for the induction of apoptosis of hepatocytes. Circumvention of this process by up-regulation of CK2 activity in transformed cells may contribute to the promotion of TGF-beta1-induced liver carcinogenesis.

Abstract: Hepatocellular carcinoma (HCC) is the third deadliest and fifth most common human cancer worldwide. Hepatitis C virus (HCV) and hepatitis B virus (HBV) infections along with alcohol and aflatoxin B1 intake are widely recognized etiological agents in HCCs. It is anticipated that HCCs will constitute a major health problem in the next two decades because of the rising incidence of HCV infections in the US. The poor survival rate achieved by current surgical procedures and chemotherapy treatment has prompted the scientific community to gain a better understanding of the molecular events involved in hepatocarcinogenesis in order to define new targets for more effective treatment. Recent findings from several laboratories have implicated constitutive activation of the transcription factor NF-κB as one of the early key events involved in neoplastic progression of the liver. Data is summarized here from recently published studies illustrating a crucial role of NF-κB in bridging the action of growth factors and inflammation to hepatic oncogenesis. Although additional work is needed to fully understand the precise role of NF-κB in the regulation of the various transitions of HCC development, these new findings raise the intriguing possibility that pharmacologic inhibition of NF-κB in the liver could selectively eradicate malignant liver cells without affecting normal liver homeostasis. [Copyright &y& Elsevier]

We have identified a novel pathway of ataxia telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNA-PK) signaling that results in nuclear factor κB (NF-κB) activation and chemoresistance in response to DNA damage. We show that the anthracycline doxorubicin (DOX) and its congener N-benzyladriamycin (AD 288) selectively activate ATM and DNA-PK, respectively. Both ATM and DNA-PK promote sequential activation of the mitogen-activated protein kinase (MAPK)/p90rsk signaling cascade in a p53- independent fashion. In turn, p90rsk interacts with the IκB kinase 2 (IKK-2) catalytic subunit of IKK, thereby inducing NF-κB activity and cell survival. Collectively, our findings suggest that distinct members of the phosphatidylinositol kinase family activate a common prosurvival MAPK/IKK/NF-κB pathway that opposes the apoptotic response following DNA damage. [ABSTRACT FROM AUTHOR]

Upon engagement of the B Cell Receptor (BCR) of WEHI 231 immature B cells, a drop in c-Myc expression is followed by activation of the cyclin-dependent kinase inhibitor (CKI) p27Kip1, which induces growth arrest and apoptosis. Here, we report inverse patterns of p27 and c-Myc protein expression follow BCR engagement. We present evidence demonstrating, for the first time, that the p27Kip1 gene is a target of transcriptional repression by c-Myc. Specifically, the changes in p27 protein levels correlated with changes in p27 mRNA levels, and gene transcription. Induction of p27 promoter activity followed BCR engagement of WEHI 231 cells, and this induction could be repressed upon co-transfection of a c-Myc expression vector. Inhibition of the TATA-less p27 promoter by c-Myc was also observed in Jurkat T cells, vascular smooth muscle, and Hs578T breast cancer cells, extending the observation beyond immune cells. Consistent with a putative Inr element CCAGACC (where +1 is underlined) at the start site of transcription in the p27 promoter, deletion of Myc homology box II reduced the extent of repression. Furthermore, enhanced repression was observed upon transfection of the c-Myc ‘super-repressor’, with mutation of Phe115 to Leu. The sequences mediating transcriptional activity and c-Myc repression were mapped to bp -20 to +20 of the p27 gene. Finally, binding of Max was shown to facilitate c-Myc binding and repression of p27 promoter activity. Overall, these studies identify the p27 CKI gene as a new target whereby c-Myc can control cell proliferation, survival and neoplastic transformation. Oncogene (2001) 20, 1688–1702. [ABSTRACT FROM AUTHOR]

Active NF-κB renders malignant hepatocytes refractory to the growth inhibitory and pro-apoptotic properties of transforming growth factor β1 (TGF-β1). NF-κB counteracts TGF-β1-induced apoptosis through up-regulation of downstream target genes, such as XIAP and Bcl-XL, which in turn inhibit the intrinsic pathway of apoptosis. In addition, induction of NF-κB by TGF-β1 inhibits JNK signaling, thereby attenuating TGF-β1-induced cell death of normal hepatocytes. However, the mechanism involved in the negative cross-talk between the NF-κB and JNK pathways during TGF-β1 signaling has not been determined. In this study, we have identified the XIAP gene as one of the critical mediators of NF-κB-mediated suppression of JNK signaling. We show that NF-κβ plays a role in the up-regulation of XIAP gene expression in response to TGF-β1 treatment and forms a TGF-β1-inducible complex with TAK1. Furthermore, we show that the RING domain of XIAP mediates TAK1 polyubiquitination, which then targets this molecule for proteosomal degradation. Down-regulation of TAK 1 protein expression inhibits TGF-β1 -mediated activation of JNK and apoptosis. Conversely, silencing of XIAP promotes persistent JNK activation and potentiates TGF-β1-induced apoptosis. Collectively, our findings identify a novel mechanism for the regulation of JNK activity by NF-κB during TGF-β1 signaling and raise the possibility that pharmacologic inhibition of the NF-κB/XIAP signaling pathway might selectively abolish the pro-oncogenic activity of TGF-β1 in advanced hepatocellular carcinomas (HCCs) without affecting the proapoptotic effects of TGF-β1 involved in normal liver homeostasis. [ABSTRACT FROM AUTHOR]