Interferon induces the interaction of prothymosin-alpha with STAT3 and results in the nuclear translocation of the complex

Prothymosin α promotes colorectal carcinoma chemoresistance through inducing lipid droplet accumulation

Colorectal cancer (CRC) affects millions of people worldwide. Chemoresistance seriously impairs the therapeutic effects. Lipid droplets (LDs) abnormally accumulate in CRC supported chemoresistance. Exploring the mechanism of LD-induced chemoresistance is extremely important for improving prognosis of CRC patients. The expression of PTMA was increased in both CRC tissues and cells, which was positively correlated with LD production. PTMA facilitated chemoresistance to gemcitabine by inducing LD production in CRC cells. PTMA enhanced LD biogenesis and chemoresistance to gemcitabine by promoting SREBP-1-mediated lipogenesis and STAT3 activation in CRC.

Prothymosin α promotes STAT3 acetylation to induce cystogenesis in Pkd1-deficient mice

Polycystic kidney disease (PKD) is characterized by the expansion of fluid-filled cysts in the kidney, which impair the function of kidney and eventually leads to end-stage renal failure. It has been previously demonstrated that transgenic overexpression of prothymosin α (ProT) induces the development of PKD; however, the underlying mechanisms remain unclear. In this study, we used a mouse PKD model that sustains kidney-specific low-expression of Pkd1 to illustrate that aberrant up-regulation of ProT occurs in cyst-lining epithelial cells, and we further developed an in vitro cystogenesis model to demonstrate that the suppression of ProT is sufficient to reduce cyst formation. Next, we found that the expression of ProT was accompanied with prominent augmentation of protein acetylation in PKD, which results in the activation of downstream signal transducer and activator of transcription (STAT) 3. The pathologic role of STAT3 in PKD has been previously reported. We determined that this molecular mechanism of protein acetylation is involved with the interaction between ProT and STAT3; consequently, it causes the deprivation of histone deacetylase 3 from the indicated protein. Conclusively, these results elucidate the significant role of ProT, including protein acetylation and STAT3 activation in PKD, which represent potential for ameliorating the disease progression of PKD.-Chen, Y.-C., Su, Y.-C., Shieh, G.-S., Su, B.-H., Su, W.-C., Huang, P.-H., Jiang, S.-T., Shiau, A.-L., Wu, C.-L. Prothymosin α promotes STAT3 acetylation to induce cystogenesis in Pkd1-deficient mice.

Spatial Cross-Talk between Oxidative Stress and DNA Replication in Human Fibroblasts

MS-based proteomics has been applied to a differential network analysis of the nuclear-cytoplasmic subcellular distribution of proteins between cell-cycle arrest: (a) at the origin activation checkpoint for DNA replication, or (b) in response to oxidative stress. Significant changes were identified for 401 proteins. Cellular response combines changes in trafficking and in total abundance to vary the local compartmental abundances that are the basis of cellular response. Appreciable changes for both perturbations were observed for 245 proteins, but cross-talk between oxidative stress and DNA replication is dominated by 49 proteins that show strong changes for both. Many nuclear processes are influenced by a spatial switch involving the proteins {KPNA2, KPNB1, PCNA, PTMA, SET} and heme/iron proteins HMOX1 and FTH1. Dynamic spatial distribution data are presented for proteins involved in caveolae, extracellular matrix remodelling, TGFβ signaling, IGF pathways, emerin complexes, mitochondrial protein import complexes, spliceosomes, proteasomes, and so on. The data indicate that for spatially heterogeneous cells cross-compartmental communication is integral to their system biology, that coordinated spatial redistribution for crucial protein networks underlies many functional changes, and that information on dynamic spatial redistribution of proteins is essential to obtain comprehensive pictures of cellular function. We describe how spatial data of the type presented here can provide priorities for further investigation of crucial features of high-level spatial coordination across cells. We suggest that the present data are related to increasing indications that much of subcellular protein transport is constitutive and that perturbation of these constitutive transport processes may be related to cancer and other diseases. A quantitative, spatially resolved nucleus-cytoplasm interaction network is provided for further investigations.

The Type I IFN-Induced miRNA, miR-21

The interferon (IFN) family of cytokines not only has antiviral properties at various steps in the viral replication cycle, but also anticancer activity through multiple pathways that include inhibiting cell proliferation, regulating cellular responses to inducers of apoptosis and modulating angiogenesis and the immune system. IFNs are known to induce their biological activity through the induction of protein encoding IFN-stimulated genes. However, recent studies have established that IFNs also induce the expression of microRNAs (miRNAs), which are small endogenous non-coding RNAs that suppress gene expression at the post-transcriptional level. MiRNAs play critical roles in tumorigenesis and have been implicated to act as either oncogenes or tumor suppressors in various human cancers. Therefore, IFN-induced miRNAs play an important role, not only in the host response to innate immune response to cancer, but also in the tumorigenic process itself. Furthermore, IFN-induced miRNAs may participate in and/or orchestrate antiviral defense in certain viral infections. In this review, we describe our recent studies on the induction of miR-21 by type I IFN, the role of the STAT3 and NFκB signaling pathways in IFN-induced miR-21 expression, the role of miR-21 in different cancers and the role of miR-21 in regulating the antiviral response.

Single Cell RNA-Sequencing of Pluripotent States Unlocks Modular Transcriptional Variation

Embryonic stem cell (ESC) culture conditions are important for maintaining long-term self-renewal, and they influence cellular pluripotency state. Here, we report single cell RNA-sequencing of mESCs cultured in three different conditions: serum, 2i, and the alternative ground state a2i. We find that the cellular transcriptomes of cells grown in these conditions are distinct, with 2i being the most similar to blastocyst cells and including a subpopulation resembling the two-cell embryo state. Overall levels of intercellular gene expression heterogeneity are comparable across the three conditions. However, this masks variable expression of pluripotency genes in serum cells and homogeneous expression in 2i and a2i cells. Additionally, genes related to the cell cycle are more variably expressed in the 2i and a2i conditions. Mining of our dataset for correlations in gene expression allowed us to identify additional components of the pluripotency network, including Ptma and Zfp640, illustrating its value as a resource for future discovery.

IFN priming is necessary but not sufficient to turn on a migratory dendritic cell program in lupus monocytes

Blood monocytes from children with systemic lupus erythematosus (SLE) behave similar to dendritic cells (DCs), and SLE serum induces healthy monocytes to differentiate into DCs in a type I IFN-dependent manner. In this study, we found that these monocytes display significant transcriptional changes, including a prominent IFN signature, compared with healthy controls. Few of those changes, however, explain DC function. Exposure to allogeneic T cells in vitro reprograms SLE monocytes to acquire DC phenotype and function, and this correlates with both IFN-inducible (IP10) and proinflammatory cytokine (IL-1β and IL6) expression. Furthermore, we found that both IFN and SLE serum induce the upregulation of CCR7 transcription in these cells. CCR7 protein expression, however, requires a second signal provided by TLR agonists such as LPS. Thus, SLE serum "primes" a subset of monocytes to readily (<24 h) respond to TLR agonists and acquire migratory DC properties. Our findings might explain how microbial infections exacerbate lupus.

Adenovirus-mediated prothymosin α gene transfer inhibits the development of atherosclerosis in ApoE-deficient mice

Prothymosin α (ProT) is involved in regulating expression of the oxidative stress-protective genes and it also exerts immunomodulatory activities. In this study, we investigated the therapeutic effects of ProT gene transfer on atherosclerosis in endothelial cells and in ApoE-deficient mice. Adenoviruses encoding mouse ProT (AdProT) were used for the management of atherosclerosis. In vitro, the effects of ProT on antioxidant gene expressions and the protection effect against oxidant-mediated injury in endothelial cells were examined. In vivo, AdProT were administered intraventricularly into the heart of ApoE(-/-) mice. Histopathological and immunohistochemical assessments of the aortic tissues were performed. Expressions of HO-1 and antioxidant genes in the aortic tissues were also determined. Our results demonstrated that ProT gene transfer increased antioxidant gene expressions, eNOS expression and NO release, as well as reduced the reactive oxygen species production in endothelial cells. Intraventricular administration of AdProT reduced the lesion formation, increased expressions of HO-1 and SOD genes, and reduced infiltrating macrophages in the aorta of ApoE(-/-) mice. This study suggests that ProT gene transfer may have the therapeutic potential for the management of atherosclerosis via inducing antioxidant gene expressions, eNOS expression and NO release, reducing ROS production and macrophage infiltration in endothelium.

Knockdown of prothymosin α leads to apoptosis and developmental defects in zebrafish embryos

Prothymosin alpha (ProTα) is an abundant nuclear protein involved in cellular processes intricately linked to development, such as cell proliferation and apoptosis. Although it is known that ProTα inhibits the formation of apoptosome and blocks caspase-3 activity, its mechanism of function in the apoptotic machinery is still under investigation. We have studied the cellular role of ProTα by knocking down its expression in HeLa cells with small hairpin RNA (shRNA) in the absence of apoptotic stimuli. Flow cytometric analysis showed that the live cell population was significantly decreased with a concomitant increase of the apoptotic populations. To understand the physiological role of ProTα within the context of embryonic development, we knocked down the Ptmab zebrafish ortholog using 2 specific morpholino oligonucleotides. Ptmab morphants exhibited growth retardation, bended trunks, and curly tails. The frequency of occurrence of the phenotypic defects was increased in a morpholino dose-dependent manner. Co-injection of ptmaa mRNA with ptmab morpholino partially rescued the morphological defects. Immunostaining with the anti-phospho-histone H3 (pH3) antibody suggested that the abnormalities of Ptmab morphants could be due to defective cell proliferation that results in growth imbalances. TUNEL fluorescent labelling and Acridine Orange staining of the morphants showed high rates of cell death in the head and tail regions. Concomitantly, the active form of caspase-3 was detected in Ptmab morphants. Our data suggest a conserved anti-apoptotic role of ProTα between zebrafish and humans, and provide the first evidence that ProTα is important for early embryogenesis.

Intracellular and extracellular cytokine-like functions of prothymosin α: implications for the development of immunotherapies

Prothymosin α (ProTα) is a 12.5-kDa, highly acidic protein widely distributed in different cell types expressed intracellularly and extracellularly. ProTα does not contain a secretion-signal sequence and is released by a nonclassical secretory pathway with a cargo protein. New findings on the extracellular function of ProTα have yielded exciting insights into the cytokine-like functions of this host protein that stimulates type I interferon via Toll-like receptor 4. Here, we discuss the intracellular function of ProTα, how new findings of cytokine-like activities of ProTα aid our understanding of mechanisms that direct ProTα functions, and the potential application of these new insights to the development of immunotherapies.

Overexpression of prothymosin alpha predicts poor disease outcome in head and neck cancer

Background

In our recent study, tissue proteomic analysis of oral pre-malignant lesions (OPLs) and normal oral mucosa led to the identification of a panel of biomarkers, including prothymosin alpha (PTMA), to distinguish OPLs from histologically normal oral tissues. This study aimed to determine the clinical significance of PTMA overexpression in oral squamous cell hyperplasia, dysplasia and head and neck squamous cell carcinoma (HNSCC).

Methodology

Immunohistochemistry of PTMA protein was performed in HNSCCs (n = 100), squamous cell hyperplasia (n = 116), dysplasia (n = 50) and histologically normal oral tissues (n = 100). Statistical analysis was carried out to determine the association of PTMA overexpression with clinicopathological parameters and disease prognosis over 7 years for HNSCC patients.

Results

Our immunohistochemical analysis demonstrated significant overexpression of nuclear PTMA in squamous cell hyperplasia (63.8%), dysplasia (50%) and HNSCC (61%) in comparison with oral normal mucosa (p_trend<0.001). Chi-square analysis showed significant association of nuclear PTMA with advanced tumor stages (III+IV). Kaplan Meier survival analysis indicated reduced disease free survival (DFS) in HNSCC patients (p<0.001; median survival 11 months). Notably, Cox-multivariate analysis revealed nuclear PTMA as an independent predictor of poor prognosis of HNSCC patients (p<0.001, Hazard's ratio, HR = 5.2, 95% CI = 2.3–11.8) in comparison with the histological grade, T-stage, nodal status and tumor stage.

Conclusions

Nuclear PTMA may serve as prognostic marker in HNSCC to determine the subset of patients that are likely to show recurrence of the disease.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

Aberrant prothymosin-alpha expression in human bladder cancer

OBJECTIVES

To investigate the prothymosin-alpha (PTMA) expression in human bladder cancer using tissue microarrays.

METHODS

Two tissue microarray slides of 50 bladder tumors and 42 paired normal adjacent tissues were investigated using immunohistochemical staining. The staining distribution was categorized as negative, nuclear, cytoplasmic, and mixed expression. Quantitative immunoreactivity was measured using image analysis, as represented by the integrated optical density for each tissue core.

RESULTS

In 36 of 42 normal adjacent tissues, positive PTMA immunoreactivity could be seen in some nuclei of the normal urothelial cells, but not, or only minimally, in the cytoplasm and underlying submucosal tissues. A statistically significant enhancement of PTMA expression was found in bladder tumors of each grade compared with the normal adjacent tissue (P < .0001 for normal adjacent tissues vs grade 1, 2, or 3 tumors, paired t test). Of 48 transitional cell carcinoma specimens, only 4 (8.3%) were graded as negative and 44 (91.7%) were positive for PTMA expression, including nuclear (n = 8), cytoplasmic (n = 12), and mixed expression (n = 24) patterns. A statistically significant correlation was found between high grade and mixed expression (P = 0.0020, chi(2) test).

CONCLUSIONS

Increased PTMA expression was found in human bladder cancers compared with the paired normal adjacent bladder tissue. The distribution of PTMA expression was changed in high-grade tumors. The clinical significance of such an aberrant PTMA expression in bladder cancer is worthy of additional investigation.

Novel function of prothymosin alpha as a potent inhibitor of human immunodeficiency virus type 1 gene expression in primary macrophages

CD8(+) T lymphocytes control human immunodeficiency virus type 1 (HIV-1) infection by a cytotoxic major histocompatibility complex-restricted pathway as well as by secretion of noncytotoxic soluble inhibitory factors. Several components of CD8(+) cell supernatants have been identified that contribute to the latter activity. In this study we report that prothymosin alpha (ProTalpha), a protein found in the cell culture medium of the herpesvirus saimiri-transformed CD8(+) T-cell line, K#1 50K, has potent HIV-1-inhibitory activity. Depletion of native ProTalpha from an HIV-1-inhibitory fraction of CD8(+) cell supernatants removes the inhibitory activity, supporting its role in inhibition via soluble mediators. ProTalpha is an abundant, acidic peptide that has been reported to be localized in the nucleus and associated with cell proliferation and activation of transcription. In this report we demonstrate that ProTalpha suppresses HIV-1 replication, its activity is target cell specific, and inhibition occurs following viral integration. Native and recombinant ProTalpha protein potently inhibit HIV-1 long terminal repeat (LTR)-driven gene expression in macrophages. Furthermore studies using different promoters in lentiviral vectors (cytomegalovirus and phosphoglycerate kinase) revealed that suppression of viral replication by ProTalpha is not HIV LTR specific.

Overexpression of the oncoprotein prothymosin alpha triggers a p53 response that involves p53 acetylation

Activation of the tumor suppressor protein p53 is a critical cellular response to various stress stimuli and to inappropriate activity of growth-promoting proteins, such as Myc, Ras, E2F, and beta-catenin. Protein stability and transcriptional activity of p53 are modulated by protein-protein interactions and post-translational modifications, including acetylation. Here, we show that inappropriate activity of prothymosin alpha (PTMA), an oncoprotein overexpressed in human cancers, triggers a p53 response. Overexpression of PTMA enhanced p53 transcriptional activity in reporter gene assays for p53 target gene promoters hdm2, p21, and cyclin G. Overexpressed PTMA resulted in increased mRNA and protein levels for endogenous p53 target genes, hdm2 and p21, and in growth suppression. In contrast, reduction of endogenous PTMA through RNA interference decreased p53 transcriptional activity. Histone acetyltransferases (HATs) act as p53 coactivators and acetylate p53. PTMA, known to interact with HATs, led to increased levels of acetylated p53. PTMA did not increase the transcriptional activity of an acetylation-deficient p53 mutant, suggesting that p53 acetylation is an indispensable part of the p53 response to PTMA. Chromatin immunoprecipitation assays showed that excess PTMA associates with the p21 promoter and results in increased levels of acetylated p53 at the p21 promoter. Our findings indicate that overexpressed PTMA elicits a p53 response that involves p53 acetylation.

Profiling of early gene expression induced by erythropoietin receptor structural variants

The development of erythroid progenitor cells is triggered via the expression of the erythropoietin receptor (EPOR) and its activation by erythropoietin. The function of the resulting receptor complex depends critically on the presence of activated JAK2, and the complex contains a large number of signaling molecules recruited to eight phosphorylated tyrosine residues. Studies using mutant receptor forms have demonstrated that truncated receptors lacking all tyrosines are able to support red blood cell development with low efficiency, whereas add-back mutants containing either Tyr343 or Tyr479 reconstitute EPOR signaling and erythropoiesis in vivo. To study the contribution of tyrosines to receptor function, we analyzed the activation of essential signaling pathways and early gene induction promoted by different receptor structural variants using human epidermal growth factor receptor/murine EPOR hybrids. In our experiments, receptors lacking all tyrosine residues or the JAK2-binding site did not induce mitogenic and anti-apoptotic signaling, whereas add-back mutant receptors containing single tyrosine residues (Try343 and Tyr479) supported the activation of these functions efficiently. Profiling of early gene expression using cDNA array hybridization revealed that (i) the high redundancy in the activation of signaling pathways is continued at the level of transcription; (ii) the expression of many genes targeted by the wild-type receptor is not supported by add-back mutants; and (iii) a small set of genes are exclusively induced by add-back receptors. We report the identification of several early genes that have not been implicated in the EPOR-dependent response so far.

Genomic responses in rat cerebral cortex after traumatic brain injury

Background

Traumatic brain injury (TBI) initiates a complex sequence of destructive and neuroprotective cellular responses. The initial mechanical injury is followed by an extended time period of secondary brain damage. Due to the complicated pathological picture a better understanding of the molecular events occurring during this secondary phase of injury is needed. This study was aimed at analysing gene expression patterns following cerebral cortical contusion in rat using high throughput microarray technology with the goal of identifying genes involved in an early and in a more delayed phase of trauma, as genomic responses behind secondary mechanisms likely are time-dependent.

Results

Among the upregulated genes 1 day post injury, were transcription factors and genes involved in metabolism, e.g. STAT-3, C/EBP-δ and cytochrome p450. At 4 days post injury we observed increased gene expression of inflammatory factors, proteases and their inhibitors, like cathepsins, α-2-macroglobulin and C1q. Notably, genes with biological function clustered to immune response were significantly upregulated 4 days after injury, which was not found following 1 day. Osteopontin and one of its receptors, CD-44, were both upregulated showing a local mRNA- and immunoreactivity pattern in and around the injury site. Fewer genes had decreased expression both 1 and 4 days post injury and included genes implicated in transport, metabolism, signalling, and extra cellular matrix formation, e.g. vitronectin, neuroserpin and angiotensinogen.

Conclusion

The different patterns of gene expression, with little overlap in genes, 1 and 4 days post injury showed time dependence in genomic responses to trauma. An early induction of factors involved in transcription could lead to the later inflammatory response with strongly upregulated CD-44 and osteopontin expression. An increased knowledge of genes regulating the pathological mechanisms in trauma will help to find future treatment targets. Since trauma is a risk factor for development of neurodegenerative disease, this knowledge may also reduce late negative effects.

Defective Jak-Stat activation in hepatoma cells is associated with hepatitis C viral IFN-alpha resistance

Interferon-alpha (IFN-alpha) has been widely used to treat viral infections and certain types of cancers. Large numbers of patients with chronic hepatitis C viral (HCV) infection do not respond to IFN and ribavirin combination therapy, and the majority of patients do not respond to IFN monotherapy. The underlying mechanisms of HCV nonresponse to IFN are unknown. In this report, using a HCV subgenomic replicon cell culture system, we show that (1) long-term IFN stimulation can select cells defective for Stat3 activation, and the defect appears to be responsible for HCV IFN resistance in cell culture, (2) HCV subgenomic sequence mutations associated with long-term culture do not appear to be responsible for IFN resistance, (3) expression of the activated Stat3 reverses IFN resistance while a dominant negative form of Stat3 renders an IFN-sensitive cell line resistant to IFN, and (4) the IFN-resistant cell line exhibits enhanced suppressor of cytokine signaling 3 (SOCS3) expression in response to IFN stimulation, and blocking SOCS3 in the IFN-resistant cell line partially restores IFN sensitivity. These findings strongly suggest that the IFN-resistant phenotype in vitro is associated with defective Stat3 activation and an enhanced SOCS3 response but is not associated with viral sequence mutations. Our study implies that long-term IFN stimulation in vitro selects cells that exhibit alterations in the host Jak-Stat signaling pathway, thereby representing a potential mechanism by which HCV resists IFN therapy.

LM. Interferon induces NF-kappa B-inducing kinase/tumor necrosis factor receptor-associated factor-dependent NF-kappa B activation to promote cell survival

Type I interferons (IFNs) play critical roles in the host defense by modulating the expression of various genes via the IFN-dependent activation of signal transducers and activators of transcription and NF-kappaB (nuclear factor kappa B) transcription factors. Previous studies established that IFNalpha/beta activates NF-kappaB to promote cell survival through a phosphatidylinositol 3-kinase (PI3K)/Akt pathway, which involves serine phosphorylation and degradation of IkappaB alpha. We now describe a second pathway by which IFNs activate NF-kappaB that is independent of IkappaB degradation. This pathway involves NF-kappaB-inducing kinase (NIK) and the tumor necrosis factor receptor-associated factor-2 (TRAF2) and results in IFNalpha/beta-induced processing of the p100/NF-kappaB2 precursor into p52. IFNalpha/beta stimulates NF-kappaB DNA binding and NF-kappaB-dependent transcription. Whereas expression of NIK and TRAF2 constructs causes NF-kappaB activation, expression of dominant negative NIK and TRAF2 constructs blocks IFN-promoted NF-kappaB activation and IFN-stimulated kappaB-dependent transcription and IFNalpha/beta-induced processing of the p100/NF-kappaB2 precursor into p52. In contrast, PI3K does not mediate IFNalpha/beta-induced p100 processing, although PI3K is involved in the pathway resulting in IkappaB alpha degradation. Moreover, whereas IFN promotes cell survival in lymphoblastoid cells, expression of dominant negative NIK and TRAF2 constructs enhances IFN-induced apoptosis. Our results for the first time place NIK and TRAF2, previously shown to function in TNF signaling, within the IFN signal transduction pathway. Thus, IFN induces NF-kappaB activation to mediate IFN-dependent cell survival signals through a "canonical" pathway of IkappaB alpha proteolysis mediated by PI3K/Akt and a "noncanonical" pathway of p100 processing mediated by NIK/TRAF.