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Deregulation of the receptor tyrosine kinase Axl has been implicated in the progression of several human cancers. However, the role of Axl in prostate cancer remains poorly understood, and the therapeutic efficacy of Axl targeting remains untested. In this report we identified Axl as a new therapeutic target for prostate cancer. Axl is consistently overexpressed in prostate cancer cell lines and human prostate tumors. Interestingly, the blockage of Axl gene expression strongly inhibits proliferation, migration, invasion and tumor growth. Furthermore, inhibition of Axl expression by small interfering RNA regulates a transcriptional program of genes involved in cell survival, strikingly all connected to the nuclear factor-κB pathway. Additionally, blockage of Axl expression leads to inhibition of Akt, IKKα and IκBα phosphorylation, increasing IκBα expression and stability. Furthermore, induction of Akt phosphorylation by insulin-like growth factor 1 in Axl knockdown cells restores Akt activity and proliferation. Taken together, our results establish an unambiguous role for Axl in prostate cancer tumorigenesis with implications for prostate cancer treatment. [ABSTRACT FROM AUTHOR]

Elevated levels of reactive oxygen species (ROS) are found in most oncogenically transformed cells and are proposed to promote cellular transformation through mechanisms such as inhibition of phosphatases. BCR-ABL, the oncoprotein associated with the majority of chronic myeloid leukemias (CMLs), induces accumulation of intracellular ROS, causing enhanced signaling downstream of PI3K. Previously we have shown that the transcription factor nuclear factor-kappa B (NF-κB) is activated by BCR-ABL expression and is required for BCR-ABL-mediated cellular transformation. Inhibition of IκB kinase (IKKβ) and NF-κB leads to cell death through an unknown mechanism. Here, we analyze the potential involvement of NF-κB in moderating BCR-ABL-induced ROS levels to protect from death. The data confirm that BCR-ABL promotes ROS and demonstrate that NF-κB prevents excessive levels. Inhibition of NF-κB leads to an increase in ROS levels and to cell death, which is at least partially controlled through ROS-induced c-Jun N-terminal kinase activity. The data demonstrate that one function for NF-κB in oncogenesis is the suppression of oncoprotein-induced ROS levels and that inhibition of NF-κB in some cancers, including CML, will increase ROS levels and promote cell death. [ABSTRACT FROM AUTHOR]

Nucleus accumbens-1 (Nac1 or NAC-1) belongs to the BTB/POZ (Pox virus and Zinc finger/Bric-a-brac Tramtrack Broad complex) transcription factor family and is a novel protein that potentially participates in self-renewal and pluripotency in embryonic stem cells. In human cancer, NAC-1 is upregulated in several types of neoplasms, but particularly in recurrent chemoresistant ovarian carcinomas, suggesting a biological role for NAC-1 in the development of drug resistance in ovarian cancer. We have assessed this possibility and shown a correlation between NAC-1 expression and ex vivo paclitaxel resistance in ovarian serous carcinoma tissues and cell lines. We found that expression of Gadd45-γ-interacting protein 1 (Gadd45gip1), a downstream target negatively regulated by NAC-1, was reduced in paclitaxel-resistant cells. Ectopic expression of NAC-1 or knockdown of Gadd45gip1 conferred paclitaxel resistance, whereas NAC-1 knockdown or ectopic expression of Gadd45gip1 increased paclitaxel sensitivity. Furthermore, silencing NAC-1 expression or disrupting NAC-1 homodimerization by a dominant negative NAC-1 protein that contained only the BTB/POZ domain induced the expression of Gadd45γ, which interacted with Gadd45gip1. Reducing Gadd45γ expression by small hairpin RNAs partially enhanced paclitaxel resistance. Thus, this study provides new evidence that NAC-1 upregulation and homodimerization contribute to tumor recurrence by equipping ovarian cancer cells with the paclitaxel-resistant phenotype through negative regulation of the Gadd45 pathway.Oncogene (2009) 28, 1941–1948; doi:10.1038/onc.2009.37; published online 23 March 2009 [ABSTRACT FROM AUTHOR]

When administrated by isolated limb perfusion, tumor necrosis factor α (TNFα) is an efficient antitumor agent that improves drug penetration and destroys angiogenic vessels. Moreover, the pronounced potentiation of TNFα-induced apoptosis by NF-κB inhibitors suggest that these compounds could enhance TNFα antitumor efficacy through direct induction of tumor cell apoptosis. Therefore, attempts at amplifying signaling pathways that mediate TNFα antitumor effects could help to design combination therapies improving its efficiency. We report that nanomolar concentrations of all-trans retinoic acid (ATRA) amplify TNFα-induced apoptosis in APL cells expressing a specific repressor of NF-κB activation. This effect is abolished by the pan-caspase inhibitor, Z-VAD-fmk and by caspase-8 and -9 inhibitors. Cell death is accompanied by a drop of mitochondrial potential and by poly (ADP-ribose) polymerase (PARP) activation. Using specific PARP-1 inhibitors and siRNAs, we show that PARP-1 is essential for the synergistic apoptotic effect and c-Jun N-terminal kinase 1 (JNK1) activation triggered by the ATRA/TNFα combination. JNK1 siRNAs reduce ATRA/TNFα-induced apoptosis, mitochondrial release of cytochrome c and caspase-9 activation. Altogether, these results identify a novel mechanism of PARP-1-induced apoptosis, in which JNK1 provides a link between PARP-1 activation and mitochondrial pathway of caspase-9 activation. This study also suggests that inclusion of nanomolar doses of ATRA could be clinically beneficial in amplifying TNFα-induced antitumor signals.Oncogene (2008) 27, 3361–3370; doi:10.1038/sj.onc.1210997; published online 17 December 2007 [ABSTRACT FROM AUTHOR]

Tumors that acquire resistance against death stimuli constitute a severe problem in the context of cancer therapy. To determine genetic alterations that favor the development of stress-resistant tumors in vivo, we took advantage of polyclonal tumors generated after retroviral infection of newborn Eλ-MYC mice, in which the retroviral integration acts as a mutagen to enhance tumor progression. Tumor cells were cultivated ex vivo and exposed to γ-irradiation prior to their transplantation into syngenic recipients, thereby providing a strong selective pressure for pro-survival mutations. Secondary tumors developing from stress-resistant tumor stem cells were analysed for retroviral integration sites to reveal candidate genes whose dysregulation confer survival. In addition to the gene encoding the antiapoptotic Bcl-xL protein, we identified the gadd45b locus to be a novel common integration site in these tumors, leading to enhanced expression. In accord with a thus far undocumented role of Gadd45β in tumorigenesis, we showed that NIH3T3 cells overexpressing Gadd45β form tumors in NOD/SCID mice. Interestingly and differently to other known ‘classical’ antiapoptotic factors, high Gadd45β levels did not protect against MYC-, UV- or γ-irradiation-induced apoptosis, but conferred a strong and specific survival advantage to serum withdrawal.Oncogene (2008) 27, 1429–1438; doi:10.1038/sj.onc.1210772; published online 24 September 2007 [ABSTRACT FROM AUTHOR]

The GADD45γ protein is a potential tumor suppressor whose expression is reduced in several tumors. However, very little is known about the regulation of its expression. We have determined that the most relevant region of its promoter lies between nucleotides −112 and −54, relative to the transcription start site. Putative Oct and NF-Y elements were found in this region and factors belonging to these families interacted with these elements in vitro and with the promoter in vivo. Mutation of these elements reduced the basal activity of the promoter, suggesting that both sites are essential for basal expression. These factors interact with chromatin modifying proteins and we found that histone deacetylase 1 or silencing mediator for retinoid and thyroid hormone receptor overexpression reduced the basal activity of the promoter. In contrast, forced expression of the histone acetylase protein PCAF or cell treatment with the HDAC inhibitor trichostatin A increased GADD45γ mRNA levels and induced GADD45γ promoter activity through its Oct and NF-Y elements. Moreover, ectopic expression of a dominant-negative version of NF-YA strongly inhibited trichostatin A-induced activation of the promoter. Our data strongly suggest that inhibition of deacetylase activity could potentially be used for treatment of tumors where GADD45γ expression is reduced.Oncogene (2008) 27, 1263–1272; doi:10.1038/sj.onc.1210735; published online 27 August 2007 [ABSTRACT FROM AUTHOR]

Integration of the cell signaling circuitry determines the ultimate response of a cell to extracellular stimuli. The transcription factor nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase JNK1 are major players in the cell signaling circuitry, regulating numerous cellular events and being implicated in the process of many human diseases and certain types of cancer. The interplay between NF-κB and JNK1 provides a paradigm that shows how the crosstalk between different signaling pathways decides the function of the cell signaling circuitry. Understanding the wiring of the cell signaling circuitry may hold the key for cell signaling-based therapy of human diseases.Oncogene (2007) 26, 3267–3278. doi:10.1038/sj.onc.1210417 [ABSTRACT FROM AUTHOR]

The nuclear factor-kappaB (NF-κB) transcription factors have emerged as major regulators of programmed cell death (PCD) whether via apoptosis or necrosis. In this context, NF-κB's activity has important ramifications for normal tissue development, homoeostasis and the physiological functions of various cell systems including the immune, hepatic, epidermal and nervous systems. However, improper regulation of PCD by NF-κB can have severe pathologic consequences, ranging from neurodegeneration to cancer, where its activity often precludes effective therapy. Although NF-κB generally protects cells by inducing the expression genes encoding antiapoptotic and antioxidizing proteins, its role in apoptosis and necrosis can vary markedly in different cell contexts, and NF-κB can sensitize cells to death-inducing stimuli in some instances. This article describes our current knowledge of the role of NF-κB in apoptosis and necrosis, and focuses on the many advances since we last reviewed this rapidly evolving topic in Oncogene 3 years ago. There has been substantial progress in understanding NF-κB's mode of action in apoptosis and necrosis and the mechanisms that regulate its anti- vs proapoptotic activities. These recent developments shed new light on the role of NF-κB in many disease conditions including tumor development, tumor progression and anticancer treatment.Oncogene (2006) 25, 6800–6816. doi:10.1038/sj.onc.1209938 [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) are emerging as key effectors in signal transduction. This role of ROS is especially evident in the pathways leading to programmed cell death (PCD) elicited in response to certain stress stimuli and cytokines. In these pathways, cytotoxic ROS signaling appears to be mediated in part by activation of the c-Jun-N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) cascade. Another pathway that is under ROS-mediated control in some systems is that leading to activation of transcription factor nuclear factor-kappa B (NF-κB), which is a central regulator of immunity, inflammation and cell survival. Remarkably, new evidence has unveiled the existence of a reciprocal, negative control that NF-κB exerts on ROS and JNK activities. This NF-κB-imposed restraint on ROS and JNK signaling is crucial for antagonism of PCD elicited by the proinflammatory cytokine tumor necrosis factor (TNF)α and likely other triggers. Effectors of this antagonistic cross-talk between NF-κB and ROS/JNK pathways have recently been identified. Because of the key roles that the prosurvival function of NF-κB plays in organismal physiology and disease, gaining a further mechanistic understanding of this cross-talk and NF-κB-dependent survival may be key to developing new therapies for the treatment of widespread human illnesses, such as cancer and chronic inflammatory conditions.Oncogene (2006) 25, 6731–6748. doi:10.1038/sj.onc.1209936 [ABSTRACT FROM AUTHOR]

The gadd45 family of gene(s) is rapidly induced by genotoxic stress or by differentiation-inducing cytokines. Using bone marrow (BM) from gadd45a−/−, gadd45b−/− and wild-type (wt) mice, we investigated their role in stress responses of myeloid cells to acute stimulation with differentiating cytokines, myelotoxic agents and inflammatory substances. Bone marrow cells from gadd45a−/− and gadd45b−/− mice displayed compromised myeloid differentiation and higher apoptosis in vitro, following acute stimulation with a variety of differentiating cytokines. Intriguingly, gadd45a−/− and gadd45b−/− colony forming units granulocyte/macrophage progenitors displayed prolonged proliferation capacity compared to wt controls upon re-plating in methylcellulose supplemented with interleukin-3. The recovery of the BM myeloid compartment following 5-Fluorouracil-induced myelo-ablation was much slower in gadd45a−/− and gadd45b−/− mice compared to wt controls. Furthermore, the response of myeloid cells to inflammatory stress, inflicted via intraperitoneal administration of sodium caseinate was impaired in gadd45a−/− and gadd45b−/− mice compared to age-matched wt mice, as indicated by lower percentage of Gr-1-positive cells in the BM and lower number of myeloid cells in peritoneal exudates. Overall, these data indicate that both gadd45a and gadd45b play a role in modulating physiological stress responses of myeloid cells to acute stimulation with differentiating cytokines, myelo-ablation and inflammation. These findings should aid in understanding the response of normal and malignant hematopoietic cells to physiological and chemical stressors including anticancer agents.Oncogene (2006) 25, 5537–5546. doi:10.1038/sj.onc.1209555; published online 29 May 2006 [ABSTRACT FROM AUTHOR]

All-trans retinoic acid (ATRA) significantly improves the survival of patients with acute promyelocytic leukemia (APL) by inducing granulocytic differentiation of leukemia cells. Since an activation of the transcription factor NF-κB occurs during ATRA-induced maturation of APL cells, a mechanistic link between these two processes was investigated. Using an in vitro model for APL, we report that ectopic overexpression of a repressor of NF-κB activation did not affect granulocytic differentiation. Importantly, NF-κB inhibition markedly resulted in a decreased viability of the differentiated cells, which correlated with increased apoptosis. Apoptosis was accompanied by a sustained activation of the c-Jun N-terminal kinase (JNK). Inhibition of JNK by the specific inhibitor SP600125 or by transfection of a dominant-negative mutant of JNK1 reduced the percentage of apoptotic cells, thus showing that JNK activation constitutes a death signal. Furthermore, impairment of NF-κB activation resulted in increased levels of reactive oxygen species (ROS) upon ATRA treatment. ROS accumulation was suppressed by the antioxidant butylated hydroxyanisol, which also abolished ATRA-induced JNK activation and apoptosis. Altogether, our results demonstrate an antiapoptotic effect of NF-κB activation during ATRA-induced differentiation of NB4 cells and identify repression of ROS-mediated JNK activation as a mechanism for this effect. Our observations also suggest that NF-κB signalling may contribute to an accumulation of mature APL cells and participate in the development of ATRA syndrome.Oncogene (2005) 24, 7145–7155. doi:10.1038/sj.onc.1208889; published online 25 July 2005 [ABSTRACT FROM AUTHOR]

Two cell lines that exemplify erythropoietin (EPO) receptor-positive tumors, human renal carcinoma cell lines RCC and the myelomonocytic leukemia cell line U937, were investigated for the apoptosis-modulatory potential of EPO. Cells cultured in the presence of EPO exhibited an elevated apoptotic response to cancer chemotherapeutic agents such as daunorubicin (Dauno) and vinblastine (VBL). Chemosensitization by EPO did not involve an increase in p53 activation, yet correlated with enhanced Bax/Bak-dependent mitochondrial membrane perturbation and caspase maturation. In vitro monotherapy with Dauno or VBL induced the degradation of I?Ba, provoked the translocation of NF-?B p65/50 to the nucleus and stimulated the expression of an NF-?B-activatable reporter gene. All these signs of NF-?B activation were perturbed in the presence of EPO. Inhibition of JAK2, one of the receptor-proximal elements of EPO-mediated signal transduction, greatly diminished the EPO-mediated chemosensitization and NF-?B inhibition. EPO lost its death-facilitating effects in the presence of an NF-?B inhibitor, underscoring the cause-effect relationship between EPO-mediated chemosensitization and NF-?B inhibition. Altogether, these results suggest that, at least in a specific subset of tumors, EPO receptor agonists can prevent activation of the NF-?B pathway, thereby enhancing the propensity of EPO receptor-positive tumor cells to undergo apoptosis.Oncogene (2005) 24, 737-745. doi:10.1038/sj.onc.1208205 Published online 6 December 2004 [ABSTRACT FROM AUTHOR]

Tumor necrosis factor-a(TNFa) activates both cell death and cell survival pathways, which render most cancer cells resistant to its cytotoxicity. In this study, we found that pretreatment with luteolin, a plant flavonoid, greatly sensitized TNFa-induced apoptotic cell death in a number of human cancer cell lines; including colorectal cancer COLO205, HCT116 cells and cervical cancer HeLa cells. In the search of the molecular mechanisms responsible for the sensitization effect of luteolin, we discovered that luteolin inhibited TNFa-induced activation of nuclear transcription factor-kappa B (NF-?B), the main survival factor in TNFasignaling. As a result, luteolin suppressed the expression of NF-?B-targeted antiapoptotic genes, including A20 and cellular inhibitor of apoptosis protein-1 (c-IAP1). The role of A20 and c-IAP1 was further confirmed by ectopic expression of these two genes, which significantly protected cell death induced by luteolin followed by TNFa. In addition, inhibition of NF-?B by luteolin led to augmentation and prolongation of c-Jun N-terminal kinase (JNK) activation induced by TNFa. Suppression of JNK activation, either by a synthetic JNK inhibitor (SP600125) or by overexpression of the dominant negative forms of JNK kinase 1 (JNKK1) and JNK kinase 2 (JNKK2), conferred significant protection against apoptotic cell death induced by luteolin and TNFa, suggesting that NF-?B and JNK are closely associated with the sensitization effect of luteolin. Data from this study reveal a novel function of luteolin and enhance the value of luteolin as an anticancer agent.Oncogene (2004) 23, 7712-7721. doi:10.1038/sj.onc.1208046 Published online 30 August 2004 [ABSTRACT FROM AUTHOR]

The antitumor activity of the sesquiterpene lactone parthenolide, an active ingredient of medicinal plants, is believed to be due to the inhibition of DNA binding of transcription factors NF-?B and STAT-3, reduction in MAP kinase activity and the generation of reactive oxygen. In this report, we show that parthenolide activates c-Jun N-terminal kinase (JNK), which is independent of inhibition of NF-?B DNA binding and generation of reactive oxygen species. Parthenolide reversed resistance of breast cancer cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Cancer cells treated with a combination of TRAIL and parthenolide underwent massive typical apoptosis and atypical apoptosis involving the loss of plasma membrane integrity. JNK activity is necessary for the parthenolide-induced sensitization to TRAIL because a dominant-negative JNK or the JNK inhibitor SP600125 reduced TRAIL plus parthenolide-induced apoptosis. Parthenolide induced phosphorylation of Bid and increased TRAIL-dependent cleavage of Bid without affecting caspase 8 activities. Cytochrome c but not Smac/DIABLO was released from the mitochondria in cells treated with parthenolide alone. Parthenolide through JNK increased the TRAIL-mediated degradation of the antiapoptotic protein X-linked inhibitor of apoptosis (XIAP). Enhanced XIAP cleavage correlated with increased and prolonged caspase 3 activity and PARP cleavage, suggesting that the sensitization to TRAIL involves‘feed forward’activation of caspase 3. These results identify a new antitumor activity of parthenolide, which can be exploited to reverse resistance of cancer cells to TRAIL, particularly those with elevated XIAP levels.Oncogene (2004) 23, 7330-7344. doi:10.1038/sj.onc.1207995 Published online 2 August 2004 [ABSTRACT FROM AUTHOR]

During their lifetime, cells encounter many life or death situations that challenge their very own existence. Their survival depends on the interplay within a complex yet precisely orchestrated network of proteins. The Rel/NF-?B signaling pathway and the transcription factors that it activates have emerged as critical regulators of the apoptotic response. These proteins are best known for the key roles that they play in normal immune and inflammatory responses, but they are also implicated in the control of cell proliferation, differentiation, apoptosis and oncogenesis. In recent years, there has been remarkable progress in understanding the pathways that activate the Rel/NF-?B factors and their role in the cell's decision to either fight or surrender to apoptotic challenge. Whereas NF-?B is most commonly involved in suppressing apoptosis by transactivating the expression of antiapoptotic genes, it can promote programmed cell death in response to certain death-inducing signals and in certain cell types. This review surveys our current understanding of the role of NF-?B in the apoptotic response and focuses on many developments since this topic was last reviewed in Oncogene 4 years ago. These recent findings shed new light on the activity of NF-?B as a critical regulator of apoptosis in the immune, hepatic, epidermal and nervous systems, on the mechanisms through which it operates and on its role in tissue development, homoeostasis and cancer.Oncogene (2003) 22, 8961-8982. doi:10.1038/sj.onc.1207230 [ABSTRACT FROM AUTHOR]

Interactions between proteasome and cyclin-dependent kinase inhibitors have been examined in human leukemia cells in relation to induction of apoptosis. Simultaneous exposure (24?h) of U937 myelomonocytic leukemia cells to 100?nM flavopiridol and 300?nM MG-132 resulted in a marked increase in mitochondrial injury (cytochrome c, Smac/DIABLO release, loss of ??m), caspase activation, and synergistic induction of cell death, accompanied by a marked decrease in clonogenic potential. Similar effects were observed with other proteasome inhibitors (e.g., Bortezomib (VELCADE™ bortezomib or injection), lactacystin, LLnL) and cyclin-dependent kinase inhibitors (e.g., roscovitine), as well as other leukemia cell types (e.g., HL-60, Jurkat, Raji). In U937 cells, synergistic interactions between MG-132 and flavopiridol were associated with multiple perturbations in expression/activation of signaling- and survival-related proteins, including downregulation of XIAP and Mcl-1, activation of JNK and p34cdc2, and diminished expression of p21CIP1. The lethal effects of MG-132/flavopiridol were not reduced in leukemic cells ectopically expressing Bcl-2, but were partially attenuated in cells ectopically expressing dominant-negative caspase-8 or CrmA. Flavopiridol/proteasome inhibitor-mediated lethality was also significantly diminished by agents and siRNA blocking JNK activation. Lastly, coadministration of MG-132 with flavopiridol resulted in diminished DNA binding of NF-?B. Notably, pharmacologic interruption of the NF-?B pathway (e.g., by BAY 11-7082, PDTC, or SN-50) or molecular dysregulation of NF-?B (i.e., in cells ectopically expressing an I?Ba super-repressor) mimicked the actions of proteasome inhibitors in promoting flavopiridol-induced mitochondrial injury, JNK activation, and apoptosis. Together, these findings indicate that proteasome inhibitors strikingly lower the apoptotic threshold of leukemic cells exposed to pharmacologic CDK inhibitors, and suggest that interruption of the NF-?B cytoprotective pathway and JNK activation both play key roles in this phenomenon. They also raise the possibility that combining proteasome and CDK inhibitors could represent a novel antileukemic strategy.Oncogene (2003) 22, 7108-7122. doi:10.1038/sj.onc.1206863 [ABSTRACT FROM AUTHOR]

In the last few years, the ubiquitin(Ub)/proteasome system has become increasingly recognized as a controller of numerous physiological processes, including signal transduction, DNA repair, chromosome maintenance, transcriptional activation, cell cycle progression, cell survival, and certain immune cell functions. This is in addition to its more established roles in the removal of misfolded, damaged, and effete proteins. This review examines the role of the Ub/proteasome system in processes underlying the classical effects of irradiation on cells, such as radiation-induced gene expression, DNA repair and chromosome instability, oxidative damage, cell cycle arrest, and cell death. Furthermore, recent evidence suggests that the proteasome is a redox-sensitive target for ionizing radiation and other oxidative stress signals. In other words, the Ub/proteasome system may not simply be a passive player in radiation-induced responses, but may modulate them. The extent of the modulation will be influenced by the functional and structural diversity that is expressed by the system. Cell types vary in the Ub/proteasome structures they possess and the level at which they function, and this changes as they go from the normal to the cancerous condition. Cancer-related functional changes within the Ub/proteasome system may therefore present unique targets for cancer therapy, especially when targeting agents are used in combination with radio- or chemotherapy. The peptide boronic acid compound PS-341, which was designed to inhibit proteasome chymotryptic activity, is in clinical trials for the treatment of solid and hematogenous tumors. It has shown some efficacy on its own and in combination with chemotherapy. Preclinical studies have shown that PS-341 will also potentiate the cytotoxic effects of radiation therapy. In addition, other drugs in common clinical use have been shown to affect proteasome function, and their activities may be valuably reconsidered from this perspective.Oncogene (2003) 22, 5755-5773. doi:10.1038/sj.onc.1206676 [ABSTRACT FROM AUTHOR]

Ras signaling involves the activation of several downstream pathways that exhibit isoform specificity. In this study, the basal and tumor necrosis factor α (TNFα)-induced activation of NF-κB has been examined in cells overexpressing H-Ras, K-Ras or N-Ras. Cells expressing H-Ras exhibited a basal κB activity that correlated with sustained IκB kinase activation and lower steady-state levels of IκBα in the cytosol. Upon activation with TNFα, the cells expressing the distinct Ras isoforms behaved similarly in terms of binding of nuclear proteins to a κB sequence and induction of a κB-dependent reporter gene. The basal activation of NF-κB in cells expressing H-Ras impaired staurosporine-induced apoptosis in these cells, through a mechanism that was NF-κB-dependent and inhibitable in the presence of z-VAD. Moreover, titration of caspase activation in response to staurosporine showed a significant resistance in cells expressing H-Ras when compared with the void vector or the N-Ras counterparts. These results indicate that the distinct Ras proteins have specific effects on the NF-κB pathway and that this action contributes to protect cells against apoptosis.Oncogene (2003) 22, 477–483. doi:10.1038/sj.onc.1206179 [ABSTRACT FROM AUTHOR]

NF-κB has been implicated in the regulation of apoptosis, a key mechanism of normal and malignant growth control. Previously, we demonstrated that inhibition of NF-κB activity by TGF-β1 leads directly to induction of apoptosis of murine B-cell lymphomas and hepatocytes. Thus, we were surprised to determine that NF-κB is transiently activated in response to TGF-β1 treatment. Here we elucidate the mechanism of TGF-β1-mediated regulation of NF-κB and induction of apoptosis in epithelial cells. We report that TGF-β1 activates IKK kinase, which mediates IκB-α phosphorylation. In turn, the activation of IKK following TGF-β1 treatment is mediated by the TAK1 kinase. As a result of NF-κB activation, IκB-α mRNA and protein levels are increased leading to postrepression of NF-κB and induction of cell death. Inhibition of NF-κB following TGF-β1 treatment increased AP-1 complex transcriptional activity through sustained c-Jun phosphorylation, thereby potentiating AP-1/SMADs-mediated cell killing. Furthermore, TGF-β1-mediated upregulation of Smad7 appeared independent of NF-κB. In hepatocellular carcinomas of TGF-β1 or TGF-α/c-myc transgenic mice, we observed constitutive activation of NF-κB that led to inhibition of JNK signaling. Overall, our data illustrate an autocrine mechanism based on the ability of IKK/NF-κB/IκB-α signaling to negatively regulate NF-κB levels thereby permitting TGF-β1-induced apoptosis through AP-1 activity.Oncogene (2003) 22, 412–425. doi:10.1038/sj.onc.1206132 [ABSTRACT FROM AUTHOR]