The non-ankyrin C terminus of Ikappa Balpha physically interacts with p53 in vivo and dissociates in response to apoptotic stress, hypoxia, DNA damage, and transforming growth factor-beta 1-mediated growth suppression

WWOX Controls Cell Survival, Immune Response and Disease Progression by pY33 to pS14 Transition to Alternate Signaling Partners

Tumor suppressor WWOX inhibits cancer growth and retards Alzheimer’s disease (AD) progression. Supporting evidence shows that the more strongly WWOX binds intracellular protein partners, the weaker is cancer cell growth in vivo. Whether this correlates with retardation of AD progression is unknown. Two functional forms of WWOX exhibit opposite functions. pY33-WWOX is proapoptotic and anticancer, and is essential for maintaining normal physiology. In contrast, pS14-WWOX is accumulated in the lesions of cancers and AD brains, and suppression of WWOX phosphorylation at S14 by a short peptide Zfra abolishes cancer growth and retardation of AD progression. In parallel, synthetic Zfra4-10 or WWOX7-21 peptide strengthens the binding of endogenous WWOX with intracellular protein partners leading to cancer suppression. Indeed, Zfra4-10 is potent in restoring memory loss in triple transgenic mice for AD (3xTg) by blocking the aggregation of amyloid beta 42 (Aβ42), enhancing degradation of aggregated proteins, and inhibiting activation of inflammatory NF-κB. In light of the findings, Zfra4-10-mediated suppression of cancer and AD is due, in part, to an enhanced binding of endogenous WWOX and its binding partners. In this perspective review article, we detail the molecular action of WWOX in the HYAL-2/WWOX/SMAD4 signaling for biological effects, and discuss WWOX phosphorylation forms in interacting with binding partners, leading to suppression of cancer growth and retardation of AD progression.

Single loss of a Trp53 allele triggers an increased oxidative, DNA damage and cytokine inflammatory responses through deregulation of IκBα expression

Dose of Trp53, the main keeper of genome stability, influences tumorigenesis; however, the causes underlying and driving tumorigenesis over time by the loss of a single p53 allele are still poorly characterized. Here, we found that single p53 allele loss specifically impacted the oxidative, DNA damage and inflammatory status of hematopoietic lineages. In particular, single Trp53 allele loss in mice triggered oxidative stress in peripheral blood granulocytes and spleenocytes, whereas lack of two Trp53 alleles produced enhanced oxidative stress in thymus cells, resulting in a higher incidence of lymphomas in the Trp53 knockout (KO) mice compared with hemizygous (HEM). In addition, single or complete loss of Trp53 alleles, as well as p53 downregulation, led to a differential increase in basal, LPS- and UVB-induced expression of a plethora of pro-inflammatory cytokine, such as interleukin-12 (Il-12a), TNFα (Tnfa) and interleukin (Il-23a) in bone marrow-derived macrophage cells (BMDMs) compared to WT cells. Interestingly, p53-dependent increased inflammatory gene expression correlated with deregulated expression of the NF-κB pathway inhibitor IκBα. Chromatin immunoprecipitation data revealed decreased p65 binding to Nfkbia in the absence of p53 and p53 binding to Nfkbia promoter, uncovering a novel crosstalk mechanism between p53 and NF-κB transcription factors. Overall, our data suggest that single Trp53 allele loss can drive a sustained inflammatory, DNA damage and oxidative stress response that, over time, facilitate and support carcinogenesis.

P53 vs NF-κB: the role of nuclear factor-kappa B in the regulation of p53 activity and vice versa

The onco-suppressor p53 is a transcription factor that regulates a wide spectrum of genes involved in various cellular functions including apoptosis, cell cycle arrest, senescence, autophagy, DNA repair and angiogenesis. p53 and NF-κB generally have opposing effects in cancer cells. While p53 activity is associated with apoptosis induction, the stimulation of NF-κB has been demonstrated to promote resistance to programmed cell death. Although the transcription factor NF-κB family is considered as the master regulator of cancer development and maintenance, it has been mainly studied in relation to its ability to regulate p53. This has revealed the importance of the crosstalk between NF-κB, p53 and other crucial cell signaling pathways. This review analyzes the various mechanisms by which NF-κB regulates the activity of p53 and the role of p53 on NF-κB activity.

A p53/TIAF1/WWOX triad exerts cancer suppression but may cause brain protein aggregation due to p53/WWOX functional antagonism

Background

Tumor suppressor WWOX physically binds p53 and TIAF1 and together induces apoptosis and tumor suppression. To understand the molecular action, here we investigated the formation of WWOX/TIAF1/p53 triad and its regulation of cancer cell migration, anchorage-independent growth, SMAD promoter activation, apoptosis, and potential role in neurodegeneration.

Methods

Time-lapse microscopy was used to measure the extent of cell migration. Protein/protein interactions were determined by co-immunoprecipitation, FRET microscopy, and yeast two-hybrid analysis. The WWOX/TIAF1/p53 triad-mediated cancer suppression was determined by measuring the extent of cell migration, anchorage-independent growth, SMAD promoter activation, and apoptosis. p53-deficient lung cancer cell growth in nude mice was carried out to assess the tumor suppressor function of ectopic p53 and/or WWOX.

Results

Wwox-deficient MEF cells exhibited constitutive Smad3 and p38 activation and migrated individually and much faster than wild type cells. TGF-β increased the migration of wild type MEF cells, but significantly suppressed Wwox knockout cell migration. While each of the triad proteins is responsive to TGF-β stimulation, ectopically expressed triad proteins suppressed cancer cell migration, anchorage-independent growth, and SMAD promoter activation, as well as caused apoptosis. The effects are due in part to TIAF1 polymerization and its retention of p53 and WWOX in the cytoplasm. p53 and TIAF1 were effective in suppressing anchorage-independent growth, and WWOX ineffective. p53 and TIAF1 blocked WWOX or Smad4-regulated SMAD promoter activation. WWOX suppressed lung cancer NCI-H1299 growth and inhibited splenomegaly by inflammatory immune response, and p53 blocked the event in nude mice. The p53/WWOX-cancer mice exhibited BACE upregulation, APP degradation, tau tangle formation, and amyloid β generation in the brain and lung.

Conclusion

The WWOX/TIAF1/p53 triad is potent in cancer suppression by blocking cancer cell migration, anchorage-independent growth and SMAD promoter activation, and causing apoptosis. Yet, p53 may functionally antagonize with WWOX. p53 blocks WWOX inhibition of inflammatory immune response induced by cancer, and this leads to protein aggregation in the brain as seen in the Alzheimer’s disease and other neurodegeneration.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0382-y) contains supplementary material, which is available to authorized users.

The BCR-ABL/NF-κB signal transduction network: a long lasting relationship in Philadelphia positive Leukemias

The Nuclear Factor-kappa B (NF-κB) family of transcription factors plays a key role in cancer pathogenesis due to the ability to promote cellular proliferation and survival, to induce resistance to chemotherapy and to mediate invasion and metastasis. NF-κB is recruited through different mechanisms involving either canonical (RelA/p50) or non-canonical pathways (RelB/p50 or RelB/p52), which transduce the signals originated from growth-factors, cytokines, oncogenic stress and DNA damage, bacterial and viral products or other stimuli. The pharmacological inhibition of the NF-κB pathway has clearly been associated with significant clinical activity in different cancers. Almost 20 years ago, NF-κB was described as an essential modulator of BCR-ABL signaling in Chronic Myeloid Leukemia and Philadelphia-positive Acute Lymphoblastic Leukemia. This review summarizes the role of NF-κB in BCR-ABL-mediated leukemogenesis and provides new insights on the long lasting BCR-ABL/NF-κB connection.

IκB-α: At the crossroad between oncogenic and tumor-suppressive signals

Nuclear factor κB (NF-κB) is an essential component of tumorigenesis and resistance to cancer treatments. NFKB inhibitor α (IκB-α) acts as a negative regulator of the classical NF-κB pathway through its ability to maintain the presence of NF-κB in the cytoplasm. However, IκB-α is also able to form a complex with tumor protein p53, promoting its inactivation. Recently, we demonstrated that IκB-α is able to mediate p53 nuclear exclusion and inactivation in chronic myeloid leukemia, indicating that IκB-α can modulate either oncogenic or tumor-suppressive functions, with important implications for cancer treatment. The present review describes the role of IκB-α in cancer pathogenesis, with particular attention to hematological cancers, and highlights the involvement of IκB-α in the regulation of p53 tumor-suppressive functions.

Mechanisms of p53 Functional De-Regulation: Role of the IκB-α/p53 Complex

TP53 is one of the most frequently-mutated and deleted tumor suppressors in cancer, with a dramatic correlation with dismal prognoses. In addition to genetic inactivation, the p53 protein can be functionally inactivated in cancer, through post-transductional modifications, changes in cellular compartmentalization, and interactions with other proteins. Here, we review the mechanisms of p53 functional inactivation, with a particular emphasis on the interaction between p53 and IκB-α, the NFKBIA gene product.

Non genomic loss of function of tumor suppressors in CML: BCR-ABL promotes IκBα mediated p53 nuclear exclusion

Tumor suppressor function can be modulated by subtle variation of expression levels, proper cellular compartmentalization and post-translational modifications, such as phosphorylation, acetylation and sumoylation. The non-genomic loss of function of tumor suppressors offers a challenging therapeutic opportunity. The reactivation of a tumor suppressor could indeed promote selective apoptosis of cancer cells without affecting normal cells. The identification of mechanisms that affect tumor suppressor functions is therefore essential. In this work, we show that BCR-ABL promotes the accumulation of the NFKBIA gene product, IκBα, in the cytosol through physical interaction and stabilization of the protein. Furthermore, BCR-ABL/IκBα complex acts as a scaffold protein favoring p53 nuclear exclusion. We therefore identify a novel BCR-ABL/IκBα/p53 network, whereby BCR-ABL functionally inactivates a key tumor suppressor.

Role of WW Domain-containing Oxidoreductase WWOX in Driving T Cell Acute Lymphoblastic Leukemia Maturation

Whether tumor suppressor WWOX (WW domain-containing oxidoreductase) stimulates immune cell maturation is largely unknown. Here, we determined that Tyr-33-phosphorylated WWOX physically binds non-phosphorylated ERK and IκBα in immature acute lymphoblastic leukemia MOLT-4 T cells and in the naïve mouse spleen. The IκBα·ERK·WWOX complex was shown to localize, in part, in the mitochondria. WWOX prevents IκBα from proteasomal degradation. Upon stimulating MOLT-4 with ionophore A23187/phorbol myristate acetate, endogenous IκBα and ERK undergo rapid phosphorylation in <5 min, and subsequently WWOX is Tyr-33 and Tyr-287 de-phosphorylated and Ser-14 phosphorylated. Three hours later, IκBα starts to degrade, and ERK returns to basal or non-phosphorylation, and this lasts for the next 12 h. Finally, expression of CD3 and CD8 occurs in MOLT-4 along with reappearance of the IκBα·ERK·WWOX complex near 24 h. Inhibition of ERK phosphorylation by U0126 or IκBα degradation by MG132 prevents MOLT-4 maturation. By time-lapse FRET microscopy, IκBα·ERK·WWOX complex exhibits an increased binding strength by 1-2-fold after exposure to ionophore A23187/phorbol myristate acetate for 15-24 h. Meanwhile, a portion of ERK and WWOX relocates to the nucleus, suggesting their role in the induction of CD3 and CD8 expression in MOLT-4.

IκBα mediates prostate cancer cell death induced by combinatorial targeting of the androgen receptor

Background

Combining different clinical agents to target multiple pathways in prostate cancer cells, including androgen receptor (AR) signaling, is potentially an effective strategy to improve outcomes for men with metastatic disease. We have previously demonstrated that sub-effective concentrations of an AR antagonist, bicalutamide, and the histone deacetylase inhibitor, vorinostat, act synergistically when combined to cause death of AR-dependent prostate cancer cells.

Methods

In this study, expression profiling of human prostate cancer cells treated with bicalutamide or vorinostat, alone or in combination, was employed to determine the molecular mechanisms underlying this synergistic action. Cell viability assays and quantitative real time PCR were used to validate identified candidate genes.

Results

A substantial proportion of the genes modulated by the combination of bicalutamide and vorinostat were androgen regulated. Independent pathway analysis identified further pathways and genes, most notably NFKBIA (encoding IκBα, an inhibitor of NF-κB and p53 signaling), as targets of this combinatorial treatment. Depletion of IκBα by siRNA knockdown enhanced apoptosis of prostate cancer cells, while ectopic overexpression of IκBα markedly suppressed cell death induced by the combination of bicalutamide and vorinostat.

Conclusion

These findings implicate IκBα as a key mediator of the apoptotic action of this combinatorial AR targeting strategy and a promising new therapeutic target for prostate cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2188-2) contains supplementary material, which is available to authorized users.

Expression of WWOX and p53 in gastric cancer

AIM: To examine the expression of WWOX and p53 proteins in gastric cancer, and to analyze the possible mechanisms behind the malignant growth of gastric cancer.

METHODS: The expression of WWOX and p53 proteins was detected by immunohistochemistry in 70 paraffin-embedded samples of gastric cancer and 20 tumor-adjacent normal tissue samples. Statistical analyses were then performed to analyze the relationship between WWOX and p53 expression and clinicopathologic parameters of gastric cancer.

RESULTS: The positive rate of expression of p53 protein in gastric cancer was significantly higher than that in normal gastric tissue (51.42% vs 0.00%, P < 0.05). Expression of p53 protein in gastric cancer was related with depth of invasion, lymph node metastasis, and tumor clinical stage (all P < 0.05). The positive rate of expression of WWOX protein was significantly lower in gastric cancer than in normal gastric tissue (41.43% vs 90.00%, P < 0.05). Expression of WWOX protein in gastric cancer was related with depth of invasion and clinical stage, but not with lymph node metastasis. There is a negative correlation between WWOX and p53 expression in gastric cancer.

CONCLUSION: Detection of expression of p53 protein and WWOX proteins might be useful for early diagnosis and evaluation of prognosis of gastric cancer.

Structural and functional insights into IκB-α/HIV-1 Tat interaction

Protein-protein interactions play fundamental roles in physiological and pathological biological processes. The characterization of the structural determinants of protein-protein recognition represents an important step for the development of molecular entities able to modulate these interactions. We have recently found that IκB-α (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha) blocks the HIV-1 expression and replication in a NF-κB-independent manner by directly binding to the virus-encoded Tat transactivator. Here, we report the evaluation of the entity of binding of IκB-α to Tat through in vitro Surface Plasmon Resonance assay. Moreover, by designing and characterizing a set of peptides of the C-terminus region of IκB-α, we show that the peptide corresponding to the IκB-α sequence 262-287 was able to bind to Tat with high affinity (300 nM). The characterization of a number of IκB-α-based peptides also provided insights into their intrinsic folding properties. These findings have been corroborated by mutagenesis studies on the full-length IκB-α, which unveil that different IκB-α residues are involved in NF-κB or Tat recognition.

Inhibiting NF-κB activation by small molecules as a therapeutic strategy

Because nuclear factor-κB (NF-κB) is a ubiquitously expressed proinflammatory transcription factor that regulates the expression of over 500 genes involved in cellular transformation, survival, proliferation, invasion, angiogenesis, metastasis, and inflammation, the NF-κB signaling pathway has become a potential target for pharmacological intervention. A wide variety of agents can activate NF-κB through canonical and noncanonical pathways. Canonical pathway involves various steps including the phosphorylation, ubiquitination, and degradation of the inhibitor of NF-κB (IκBα), which leads to the nuclear translocation of the p50-p65 subunits of NF-κB followed by p65 phosphorylation, acetylation and methylation, DNA binding, and gene transcription. Thus, agents that can inhibit protein kinases, protein phosphatases, proteasomes, ubiquitination, acetylation, methylation, and DNA binding steps have been identified as NF-κB inhibitors. Because of the critical role of NF-κB in cancer and various chronic diseases, numerous inhibitors of NF-κB have been identified. In this review, however, we describe only small molecules that suppress NF-κB activation, and the mechanism by which they block this pathway.

Complement C1q activates tumor suppressor WWOX to induce apoptosis in prostate cancer cells

BACKGROUND

Tissue exudates contain low levels of serum complement proteins, and their regulatory effects on prostate cancer progression are largely unknown. We examined specific serum complement components in coordinating the activation of tumor suppressors p53 and WWOX (also named FOR or WOX1) and kinases ERK, JNK1 and STAT3 in human prostate DU145 cells.

METHODOLOGY/PRINCIPAL FINDINGS

DU145 cells were cultured overnight in 1% normal human serum, or in human serum depleted of an indicated complement protein. Under complement C1q- or C6-free conditions, WOX1 and ERK were mainly present in the cytoplasm without phosphorylation, whereas phosphorylated JNK1 was greatly accumulated in the nuclei. Exogenous C1q rapidly restored the WOX1 activation (with Tyr33 phosphorylation) in less than 2 hr. Without serum complement C9, p53 became activated, and hyaluronan (HA) reversed the effect. Under C6-free conditions, HA induced activation of STAT3, an enhancer of metastasis. Notably, exogenous C1q significantly induced apoptosis of WOX1-overexpressing DU145 cells, but not vehicle-expressing cells. A dominant negative and Y33R mutant of WOX1 blocked the apoptotic effect. C1q did not enhance p53-mediated apoptosis. By total internal reflection fluorescence (TIRF) microscopy, it was determined that C1q destabilized adherence of WOX1-expressing DU145 cells by partial detaching and inducing formation of clustered microvilli for focal adhesion particularly in between cells. These cells then underwent shrinkage, membrane blebbing and death. Remarkably, as determined by immunostaining, benign prostatic hyperplasia and prostate cancer were shown to have a significantly reduced expression of tissue C1q, compared to age-matched normal prostate tissues.

CONCLUSIONS/SIGNIFICANCE

We conclude that complement C1q may induce apoptosis of prostate cancer cells by activating WOX1 and destabilizing cell adhesion. Downregulation of C1q enhances prostate hyperplasia and cancerous formation due to failure of WOX1 activation.

Transforming growth factor beta1 signaling via interaction with cell surface Hyal-2 and recruitment of WWOX/WOX1

Transforming growth factor beta (TGF-beta) initiates multiple signal pathways and activates many downstream kinases. Here, we determined that TGF-beta1 bound cell surface hyaluronidase Hyal-2 on microvilli in type II TGF-beta receptor-deficient HCT116 cells, as determined by immunoelectron microscopy. This binding resulted in recruitment of proapoptotic WOX1 (also named WWOX or FOR) and formation of Hyal-2.WOX1 complexes for relocation to the nuclei. TGF-beta1 strengthened the binding of the catalytic domain of Hyal-2 with the N-terminal Tyr-33-phosphorylated WW domain of WOX1, as determined by time lapse fluorescence resonance energy transfer analysis in live cells, co-immunoprecipitation, and yeast two-hybrid domain/domain mapping. In promoter activation assay, ectopic WOX1 or Hyal-2 alone increased the promoter activity driven by Smad. In combination, WOX1 and Hyal-2 dramatically enhanced the promoter activation (8-9-fold increases), which subsequently led to cell death (>95% of promoter-activated cells). TGF-beta1 supports L929 fibroblast growth. In contrast, transiently overexpressed WOX1 and Hyal-2 sensitized L929 to TGF-beta1-induced apoptosis. Together, TGF-beta1 invokes a novel signaling by engaging cell surface Hyal-2 and recruiting WOX1 for regulating the activation of Smad-driven promoter, thereby controlling cell growth and death.

Blockage of NF-kappaB by IKKbeta- or RelA-siRNA rather than the NF-kappaB super-suppressor IkappaBalpha mutant potentiates adriamycin-induced cytotoxicity in lung cancer cells

Ambiguous roles of genotoxic anticancer therapeutic-induced NF-kappaB activation in regulating gene expression (activation or suppression) and apoptosis (anti- or pro-apoptosis) have recently been suggested. In order to clarify this controversy and determine the usefulness of NF-kappaB blockage for sensitizing anticancer therapy, we have systematically investigated the effect of distinct NF-kappaB-blocking approaches on lung cancer cells' responses to Adriamycin-induced cytotoxicity. The results show that Adriamycin-induced NF-kappaB activation functions as a transcriptional activator triggering the expression of anti-apoptotic genes. Blocking NF-kappaB with IKKbeta- or RelA siRNA substantially sensitized Adriamycin-induced cytotoxicity, suggesting that the NF-kappaB pathway could be a target for sensitizing lung cancer cells to Adriamycin's anticancer effect. Surprisingly, although it effectively blocks NF-kappaB activation, the IkappaBalpha super-suppressor (IkappaBalphaAA) antagonized Adriamycin-induced cell death. Additionally, the induction of death receptor 5 (DR5), which contributes to Adriamycin-induced cytotoxicity, was not affected by NF-kappaB blockage. Thus, our results suggest that Adriamycin-induced NF-kappaB is a transcriptional activator that protects lung cancer cells against apoptosis, and IKKbeta- or RelA siRNA rather than IkappaBalphaAA is an appropriate NF-kappaB blocking approach for sensitizing lung cancer cells to Adriamycin-induced cytotoxicity.

The Npro product of classical swine fever virus interacts with IκBα, the NF-κB inhibitor

Classical swine fever virus(CSFV) belongs to the genusPestivirusand is the causative agent of classical swine fever, a haemorrhagic disease of pigs. The virus replicates in host cells without activating interferon (IFN) production and has been reported to be an antagonist of double-stranded RNA-induced apoptosis. The N-terminal protease (Npro) of CSFV is responsible for this evasion of the host innate immune response. In order to identify cellular proteins that interact with the Nproproduct of CSFV, a yeast two-hybrid screen of a human library was carried out, which identified IκBα, the inhibitor of NF-κB, a transcription factor involved in the control of apoptosis, the immune response and IFN production. The Npro–IκBαinteraction was confirmed using yeast two-hybrid analysis and additional co-precipitation assays. It was also shown that Nprolocalizes to both the cytoplasmic and nuclear compartments in stably transfected cells and in CSFV-infected cells. Following stimulation by tumour necrosis factor alpha, PK-15 cell lines expressing Nproexhibited transient nuclear accumulation of pIκBα, but no effect of CSFV infection on IκBαlocalization or NF-κB p65 activation was observed.

Zfra affects TNF-mediated cell death by interacting with death domain protein TRADD and negatively regulates the activation of NF-kappaB, JNK1, p53 and WOX1 during stress response

Background

Zfra is a 31-amino-acid zinc finger-like protein, which is known to regulate cell death by tumor necrosis factor (TNF) and overexpressed TNF receptor- or Fas-associated death domain proteins (TRADD and FADD). In addition, Zfra undergoes self-association and interacts with c-Jun N-terminal kinase 1 (JNK1) in response to stress stimuli. To further delineate the functional properties of Zfra, here we investigated Zfra regulation of the activation of p53, WOX1 (WWOX or FOR), NF-κB, and JNK1 under apoptotic stress.

Results

Transiently overexpressed Zfra caused growth suppression and apoptotic death of many but not all types of cells. Zfra either enhanced or blocked cell death caused by TRADD, FADD, or receptor-interacting protein (RIP) in a dose-related manner. This modulation is related with Zfra binding with TRADD, NF-κB, JNK1 and WOX1, as determined by GST pull-down analysis, co-immunoprecipitation, and mapping by yeast two-hybrid analysis. Functionally, transiently overexpressed Zfra sequestered NF-κB (p65), WOX1, p53 and phospho-ERK (extracellular signal-activated kinase) in the cytoplasm, and TNF or UV light could not effectively induce nuclear translocation of these proteins. Zfra counteracted the apoptotic functions of Tyr33-phosphorylated WOX1 and Ser46-phosphorylated p53. Alteration of Ser8 to Gly abolished the apoptotic function of Zfra and its regulation of WOX1 and p53.

Conclusion

In response to TNF, Zfra is upregulated and modulates TNF-mediated cell death via interacting with TRADD, FADD and RIP (death-inducing signaling complex) at the receptor level, and downstream effectors NF-κB, p53, WOX1, and JNK1.

Differential expression and role of p21cip/waf1 and p27kip1 in TNF-alpha-induced inhibition of proliferation in human glioma cells

Background

The role of TNF-α in affecting the fate of tumors is controversial, while some studies have reported apoptotic or necrotic effects of TNF-α, others provide evidence that endogenous TNF-α promotes growth and development of tumors. Understanding the mechanism(s) of TNF-α mediated growth arrest will be important in unraveling the contribution of tissue associated macrophages in tumor resistance. The aim of this study was to investigate the role of Cyclin Dependent Kinase Inhibitors (CDKI) – p21^cip/waf1 and p27^kip1 in TNF-α mediated responses in context with p53 and activation of NF-κB and Akt pathways. The study was done with human glioma cell lines -LN-18 and LN-229 cells, using monolayer cultures and Multicellular Spheroids (MCS) as in vitro models.

Results

TNF-α induced inhibition of proliferation and enhanced the expression of p21^cip/waf1 and p27^kip1 in LN-18 cells. p21 was induced on exposure to TNF-α, localized exclusively in the nucleus and functioned as an inhibitor of cell cycle but not as an antiapoptotic protein. In contrast, p27 was constitutively expressed, localized predominantly in the cytoplasm and was not involved in arrest of proliferation. Our data using IκBα mutant LN-18 cells and PI3K/Akt inhibitor-LY294002 revealed that the expression of p21 is regulated by NF-κB. Loss of IκBα function in LN-229 cells (p53 positive) did not influence TNF-α induced accumulation of pp53 (Ser-20 p53) suggesting that p53 was not down stream of NF-κB. Spheroidogenesis enhanced p27 expression and p21 induced by TNF-α was significantly increased in the MCS compared to monolayers.

Conclusion

This study demarcates the functional roles for CDKIs-p21^cip/waf1 and p27^kip1 during TNF-α stimulated responses in LN-18 glioma cells. Our findings provide evidence that TNF-α-induced p21 might be regulated by NF-κB or p53 independently. p21 functions as an inhibitor of cell proliferation and does not have a direct role in rendering the cells resistant to TNF-α mediated cytotoxicity.

Stabilization of p73 by nuclear IkappaB kinase-alpha mediates cisplatin-induced apoptosis

In response to DNA damage, p53 and its homolog p73 have a function antagonistic to NF-kappaB in deciding cell fate. Here, we show for the first time that p73, but not p53, is stabilized by physical interaction with nuclear IkappaB kinase (IKK)-alpha to enhance cisplatin (CDDP)-induced apoptosis. CDDP caused a significant increase in the amounts of nuclear IKK-alpha and p73alpha in human osteosarcoma-derived U2OS cells. Ectopic expression of IKK-alpha prolonged the half-life of p73 by inhibiting its ubiquitination and thereby enhancing its transactivation and pro-apoptotic activities. Consistent with these results, small interfering RNA-mediated knockdown of endogenous IKK-alpha inhibited the CDDP-mediated accumulation of p73alpha. The kinase-deficient mutant form of IKK-alpha interacted with p73alpha, but failed to stabilize it. Furthermore, CDDP-mediated accumulation of endogenous p73alpha was not detected in mouse embryonic fibroblasts (MEFs) prepared from IKK-alpha-deficient mice, and CDDP sensitivity was significantly decreased in IKK-alpha-deficient MEFs compared with wild-type MEFs. Thus, our results strongly suggest that the nuclear IKK-alpha-mediated accumulation of p73alpha is one of the novel molecular mechanisms to induce apoptotic cell death in response to CDDP, which may be particularly important in killing tumor cells with p53 mutation.

Integrating cell-signalling pathways with NF-kappaB and IKK function

Nuclear factor (NF)-kappaB and inhibitor of NF-kappaB kinase (IKK) proteins regulate many physiological processes, including the innate- and adaptive-immune responses, cell death and inflammation. Disruption of NF-kappaB or IKK function contributes to many human diseases, including cancer. However, the NF-kappaB and IKK pathways do not exist in isolation and there are many mechanisms that integrate their activity with other cell-signalling networks. This crosstalk constitutes a decision-making process that determines the consequences of NF-kappaB and IKK activation and, ultimately, cell fate.

Global gene expression changes underlying Stachybotrys chartarum toxin-induced apoptosis in murine alveolar macrophages: Evidence of multiple signal transduction pathways

The overall mechanism(s) underlying macrophage apoptosis caused by the toxins of the indoor mold Stachybotrys chartarum (SC) are not yet understood. In this direction, we report a microarray-based global gene expression profiling on the murine alveolar macrophage cell line (MH-S) treated with SC toxins for short (2 h) and long (24 h) periods, coinciding with the pre-apoptotic (<3 h) and progressed apoptotic stages of the treated cells, respectively. Microarray results on differential expression were validated by real-time RT-PCR analysis using representative gene targets. The toxin-regulated genes corresponded to multiple cellular processes, including cell growth, proliferation and death, inflammatory/immune response, genotoxic stress and oxidative stress, and to the underlying multiple signal transduction pathways involving MAPK-, NF-kB-, TNF-, and p53-mediated signaling. Transcription factor NF-kB showed dynamic temporal changes, characterized by an initial activation and a subsequent inhibition. Up-regulation of a battery of DNA damage-responsive and DNA repair genes in the early stage of the treatment suggested a possible role of genotoxic stress in the initiation of apoptosis. Simultaneous expression changes in both pro-survival genes and pro-apoptotic genes indicated the role of a critical balance between the two processes in SC toxin-induced apoptosis. Taken together, the results imply that multiple signaling pathways underlie the SC toxin-induced apoptosis in alveolar macrophages.

Introduction to NF-kappaB: players, pathways, perspectives

This article serves as an introduction to the collection of reviews on nuclear factor-kappaB (NF-kappaB). It provides an overview of the discovery and current status of NF-kappaB as a research topic. Described are the structures, activities and regulation of the proteins in the NF-kappaB family of transcription factors. NF-kappaB signaling is primarily regulated by inhibitor kappaB (IkappaB) proteins and the IkappaB kinase complex through two major pathways: the canonical and non-canonical NF-kappaB pathways. The organization and focus of articles included in the following reviews are described, as well as likely future areas of research interest on NF-kappaB.

Lung Tissue Engineering Technique with Adipose Stromal Cells Improves Surgical Outcome for Pulmonary Emphysema

RATIONALE AND OBJECTIVES

Hepatocyte growth factor (HGF) is a potent regenerative factor generated after a lung injury, and HGF supplementation after surgical reduction has been shown to enhance compensatory growth in remnant lungs and improve pathophysiologic conditions in a rat model of emphysema. Adipose tissue-derived stromal cells (ASCs) produce a large amount of angiogenic factors, including HGF. After lung volume reduction surgery (LVRS), we treated rats by implanting HGF-secreting ASCs with a scaffold onto the remnant lung tissue to determine the usefulness of this technique for treating respiratory dysfunction.

METHODS AND MAIN RESULTS

Cells were isolated from rat inguinal adipose tissue and characterized by flow cytometry. ASCs were cultured on a polyglycolic acid felt sheet as a sealant material, and were shown to secrete significantly greater amounts of HGF than other angiogenic factors. Next, ASCs on polyglycolic acid felt sheets were used to cover the cut edge of the remaining lungs after LVRS for emphysema in rats. One week after implantation of the ASCs, both alveolar and vascular regeneration were significantly accelerated as compared with the rats that underwent LVRS alone. Consequently, gas exchange and exercise tolerance were also significantly restored, with these good results persisting for more than 1 mo.

CONCLUSIONS

The present findings demonstrate the therapeutic potential of cell therapy using ASCs with a scaffold for selective delivery of HGF to remnant lungs, which resulted in enhancement of compensatory growth, after surgical resection. This approach may provide a new strategy for lung tissue engineering to improve LVRS outcome.

Effects of IkappaBalpha and its mutants on NF-kappaB and p53 signaling pathways

AIM

To study the effects of IkappaBalpha and its mutants (IkappaBalphaM, IkappaBalpha243N, IkappaBalphaM244C) on NF-kappaB, p53 and their downstream target genes. The relationship of NF-kappaB, p53, and IkappaBalpha was further discussed.

METHODS

pECFP-IkappaBalpha, pECFP-IkappaBalphaM (amino acides 1-317, Ser32, 36A), pECFP-IkappaBalpha243N (amino acides 1-243), pECFP-IkappaBalpha244C (amino acides 244-317), pEYFP-p65 and pp53-DsRed were constructed and transfected to ASTC-alpha-1 cells. Cells were transfected with pECFP-C1 as a control. 30 h after the transfection, location patterns of NF-kappaB, p53 and IkappaBalpha (IkappaBalphaM, IkappaBalpha243N, IkappaBalpha244C) were observed by a laser scanning microscope (LSM510/ConfoCor2, Zeiss). RNA extraction and reverse transcription were performed in cells transfected or co-transfected with different plasmids. Effects of IkappaBalpha and its mutants on the transprition level of NF-kappaB, NF-kappaB downstream target gene TNF-alpha, p53 and p53 downstream target gene Bax were observed by real time QT-PCR. In all experiments beta-actin was reference. Results are expressed as the target/reference ratio of the sample divided by the target/reference ratio of the control. Different transfected cells were incubated with CCK-8 for 2 h in the incubator. Then the absorbance at 450 nm was measured by using a microplate reader.

RESULTS

Cells that were transfected with p53-DsRed revealed a predominant nuclear localization. YFP-p65 mainly existed in the cytoplasm. Cells were transfected with CFP-IkappaBalpha, CFP-IkappaBalphaM, and CFP-IkappaBalpha243N respectively and revealed a predominant cytosolic localization. However, cells transfected of CFP-IkappaBalpha244C revealed a predominant nuclear localization. The mRNA levels of p65, TNF-alpha, p53 and Bax in CFP-IkappaBalpha transfected cells did not change significantly, while in YFP-p65/CFP-IkappaBalpha co-transfected cells, IkappaBalpha decreased the transcription of p65 downstream gene TNF-alpha (2.24+/-0.503) compared with the YFP-p65/CFP-C1 co-transfected cells (5.08+/-0.891) (P<0.05). Phosphorylation defective IkappaBalpha (IkappaBalphaM) decreased the transcription levels of all the four genes compared with the control (P<0.05). The N terminus of IkappaBalpha (IkappaBalpha243N) increased the transcription of NF-kappaB (1.84+/-0.176) and TNF-alpha (1.51+/-0.203) a little bit. However, the C terminus of IkappaBalpha (IkappaBalpha244C) increased the transcription of NF-kappaB, TNF-alpha, p53 and Bax significantly (8.29+/-1.662, 14.16+/-2.121, 10.2+/-0.621, 3.72+/-0.346) (P<0.05). The CCK-8 experiment also showed that IkappaBalpha244C and p53 synergistically mediate apoptosis.

CONCLUSIONS

IkappaBalpha and its mutants (IkappaBalphaM, IkappaBalpha243N, IkappaBalphaM244C) have different effects on NF-kappaB and p53 signaling pathways, according to their different structures. IkappaBalphaM bounds with NF-kappaB and p53 in cytoplasm steadily, and inhibits both of the two signaling pathways. p53 and IkappaBalpha244C may be co-factor in inducing apoptosis. The C terminal of IkappaBalpha enhanced cell death, which suggests that it may be a pro-apoptotic protein existed in cells.

WOX1 Is Essential for Tumor Necrosis Factor-, UV Light-, Staurosporine-, and p53-mediated Cell Death, and Its Tyrosine 33-phosphorylated Form Binds and Stabilizes Serine 46-phosphorylated p53

WW domain-containing oxidoreductase WOX1, also named WWOX or FOR, undergoes Tyr33 phosphorylation at its first N-terminal WW domain and subsequent nuclear translocation in response to sex steroid hormones and stress stimuli. The activated WOX1 binds tumor suppressor p53, and both proteins may induce apoptosis synergistically. Functional suppression of WOX1 by antisense mRNA or a dominant negative abolishes p53-mediated apoptosis. Here, we determined that UV light, anisomycin, etoposide, and hypoxic stress rapidly induced phosphorylation of p53 at Ser46 and WOX1 at Tyr33 (phospho-WOX1) and their binding interactions in several tested cancer cells. Mapping by yeast two-hybrid analysis and co-immunoprecipitation showed that phospho-WOX1 physically interacted with Ser46-phosphorylated p53. Knockdown of WOX1 protein expression by small interfering RNA resulted in L929 fibroblast resistance to apoptosis by tumor necrosis factor, staurosporine, UV light, and ectopic p53, indicating an essential role of WOX1 in stress stimuli-induced apoptosis. Notably, UV light could not induce p53 protein expression in these WOX1 knockdown cells, although p53 mRNA levels were not reduced. Suppression of WOX1 by dominant negative WOX1 (to block Tyr33 phosphorylation) also abolished UV light-induced p53 protein expression. Time course analysis showed that the stability of ectopic wild type p53, tagged with DsRed, was decreased in WOX1 knockdown cells. Inhibition of MDM2 by nutlin-3 increased the binding of p53 and WOX1 and stability of p53. Together, our data show that WOX1 plays a critical role in conferring cellular sensitivity to apoptotic stress and that Tyr33 phosphorylation in WOX1 is essential for binding and stabilizing Ser46-phosphorylated p53.

Immortalized fibroblasts from NF-kappaB RelA knockout mice show phenotypic heterogeneity and maintain increased sensitivity to tumor necrosis factor alpha after transformation by v-Ras

Activation of the NF-kappaB pathway can either promote or block apoptosis and oncogenesis in different cell types and circumstances. In this report, we show that independently derived immortalized mouse embryonic fibroblast cell lines prepared from RelA knockout mice have different phenotypes, based on their sensitivity to tumor necrosis factor alpha (TNFalpha)-induced apoptosis, morphology, ability to form colonies in soft agar, and the presence of distinct kappaB site-binding complexes. In addition, these RelA-deficient cell lines appear to have distinct alterations in the p53 pathway, which correlate with the normal vs transformed status of individual cell lines. We have also infected mouse embryonic fibroblasts lacking RelA, c-Rel or p50 with a retrovirus for the expression of v-Ha-Ras to determine whether individual NF-kappaB family members are required for Ras-mediated transformation. All three NF-kappaB-deficient cell types could be transformed by v-Ha-Ras. However, v-Ras-infected RelA-deficient cells formed colonies in soft agar at an approximately fourfold reduced efficiency compared to v-Ras-transformed control mouse 3T3 and p50-deficient cells. Ras transformation did not alter the sensitivity of RelA-deficient cells to TNFalpha-induced apoptosis, and Ras transformation did not affect the general resistance of 3T3, c-Rel-deficient, and p50-deficient cells to TNFalpha-induced apoptosis. However, TNFalpha specifically and dose-dependently decreased the ability of v-Ras-transformed RelA-deficient cells to form colonies in soft agar. These results suggest that RelA is a potential protein target for human tumors driven by oncogenic Ras mutations, but caution that inhibition of RelA may promote tumorigenesis in some circumstances.

Epstein-Barr virus latent membrane protein 1 represses p53-mediated DNA repair and transcriptional activity

The latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV), a viral oncogene, is essential for transformation of resting B cells by the virus. We previously demonstrated that LMP1 could repress DNA repair in p53-wild-type and p53-deficient human epithelial cells. In this study, using a host cell reactivation (HCR) assay, we demonstrated that p53-enhanced DNA repair was repressed by LMP1 in p53-deficient cells. Moreover, we found that LMP1 was able to repress p53-dependent transcriptional activity. Regarding the mechanisms of p53 repression by LMP1, we found that LMP1 did not inhibit p53 function through direct interaction, by promoting protein degradation or reducing its DNA-binding ability. Using chimeric proteins in the reporter assay, we demonstrated that LMP1 inhibited p53 transactivation by influencing the N-terminal transactivation domain of p53. Subsequent experiments using various LMP1 deletion mutants indicated that a C-terminus-activating region of LMP1, CTAR1 or CTAR2, is responsible for the repression of p53-mediated DNA repair and p53-dependent transcription, which is correlated with the region responsible for NF-kappaB activation. Furthermore, blockage of NF-kappaB signalling by IkappaB-DeltaN was shown to abolish the repression of p53 by LMP1, suggesting that LMP1 likely repressed p53 function through the NF-kappaB pathway. Based on these results, we propose that inhibition of p53-dependent transcriptional activity and DNA repair by LMP1 results in the loss of p53 activity for maintaining genomic stability, which may contribute to the oncogenesis of LMP1 in human epithelial cells.

Modulation of p53 activity by IkappaBalpha: evidence suggesting a common phylogeny between NF-kappaB and p53 transcription factors

BACKGROUND

In this work we present evidence that the p53 tumor suppressor protein and NF-kappaB transcription factors could be related through common descent from a family of ancestral transcription factors regulating cellular proliferation and apoptosis. P53 is a homotetrameric transcription factor known to interact with the ankyrin protein 53BP2 (a fragment of the ASPP2 protein). NF-kappaB is also regulated by ankyrin proteins, the prototype of which is the IkappaB family. The DNA binding sequences of the two transcription factors are similar, sharing 8 out of 10 nucleotides. Interactions between the two proteins, both direct and indirect, have been noted previously and the two proteins play central roles in the control of proliferation and apoptosis.

RESULTS

Using previously published structure data, we noted a significant degree of structural alignment between p53 and NF-kappaB p65. We also determined that IkappaBalpha and p53 bind in vitro through a specific interaction in part involving the DNA binding region of p53, or a region proximal to it, and the amino terminus of IkappaBalpha independently or cooperatively with the ankyrin 3 domain of IkappaBalpha In cotransfection experiments, kappaBalpha could significantly inhibit the transcriptional activity of p53. Inhibition of p53-mediated transcription was increased by deletion of the ankyrin 2, 4, or 5 domains of IkappaBalpha Co-precipitation experiments using the stably transfected ankyrin 5 deletion mutant of kappaBalpha and endogenous wild-type p53 further support the hypothesis that p53 and IkappaBalpha can physically interact in vivo.

CONCLUSION

The aggregate results obtained using bacterially produced IkappaBalpha and p53 as well as reticulocyte lysate produced proteins suggest a correlation between in vitro co-precipitation in at least one of the systems and in vivo p53 inhibitory activity. These observations argue for a mechanism involving direct binding of IkappaBalpha to p53 in the inhibition of p53 transcriptional activity, analogous to the inhibition of NF-kappaB by kappaBalpha and p53 by 53BP2/ASPP2. These data furthermore suggest a role for ankyrin proteins in the regulation of p53 activity. Taken together, the NFkappaB and p53 proteins share similarities in structure, DNA binding sites and binding and regulation by ankyrin proteins in support of our hypothesis that the two proteins share common descent from an ancestral transcriptional factor.

Induction of compensatory lung growth in pulmonary emphysema improves surgical outcomes in rats

RATIONALE AND OBJECTIVES

Although lung volume reduction surgery (LVRS) has been widely used as a therapeutic strategy for pulmonary emphysema, the procedure carries significant disadvantages, including significant operative mortality and a limited duration of effective response. Pulmonary resection is known to elicit compensatory growth in remnant lung tissues; however, it remains unclear whether and how compensatory growth occurs and contributes to clinical outcomes after LVRS. The goal of the present study was to characterize the role of hepatocyte growth factor (HGF) in compensatory lung growth after LVRS in a rat model of elastase-induced emphysema, since HGF is a potent pulmotrophic factor responsible for the regeneration of lung parenchyma in damaged lungs, including after a pulmonary resection.

METHODS AND MAIN RESULTS

Unexpectedly, LVRS did not cause apparent increases in the endogenous HGF profiles of emphysematous lungs. Further, the lowered HGF production reflected a histologically inferior regenerative capacity in remnant lungs and was linked with impaired pulmonary functional recoveries after LVRS. When HGF was exogenously supplemented by gene transfection into emphysematous lungs simultaneously with LVRS, compensatory lung growth (as evidenced by increased lobe weight and alveolar regeneration and angiogenesis) was significantly enhanced as compared with rats that underwent LVRS alone. Consequently, pulmonary function and gas exchange were also significantly improved.

CONCLUSIONS

We concluded that the induction of compensatory growth by growth factors after LVRS may be a new strategy to further improve clinical outcomes of LVRS in patients with pulmonary emphysema.

NF-kappaB: tumor promoter or suppressor?

A role for the NF-kappaB family of transcription factors as tumor promoters is firmly established. However, other data suggest that NF-kappaB can also inhibit tumor growth. Moreover, NF-kappaB activity is modulated by tumor suppressors, such as p53 and ARF, whereby NF-kappaB subunits repress, rather than activate, the expression of tumor-promoting genes. This suggests a dual function of NF-kappaB during tumor progression - in the early stages, NF-kappaB inhibits tumor growth but, as further mutations lead to a loss of tumor suppressor expression, the oncogenic functions of NF-kappaB become unleashed, allowing it to actively contribute to tumorigenesis. Here, I discuss this hypothesis, its implications for NF-kappaB function, and how this might influence the use of NF-kappaB-based anticancer therapies.

Hypoxia Enhances Metastatic Efficiency by Up-Regulating Mdm2 in KHT Cells and Increasing Resistance to Apoptosis

Tumor hypoxia has been reported to be a negative prognostic factor in a number of tumor sites. Both clinical and experimental studies have suggested a positive correlation between tumor hypoxia and increased metastatic efficiency; however, the mechanisms are not understood. In this study, the mechanisms of hypoxia-enhanced metastasis have been investigated in murine KHT fibrosarcoma and SCC VII cells. We have observed that hypoxia-pretreated KHT-C cells have a higher survival rate than control KHT-C cells after being arrested in mouse lungs. cDNA microarray analysis revealed many hypoxia-regulated genes, most of which have been reported to be involved in cell survival and growth. Among these genes, we have confirmed the up-regulation of Mdm2 by hypoxia and have demonstrated that this up-regulation is p53 independent. The up-regulation of Mdm2 by hypoxia is associated with decreased p53 protein and inhibition of the transactivation of p53 downstream proapoptotic genes. Overexpression of Mdm2 or suppression of p53 by transient transfection increased metastatic efficiency in KHT-C cells. These data suggest that hypoxia can increase tumor cell metastatic efficiency by rendering the tumor cells less sensitive to stress-induced cell death, e.g., through modifying the levels of Mdm2 and p53.

Nuclear factor-(kappa)B modulates the p53 response in neurons exposed to DNA damage

Previous studies have shown that DNA damage-evoked death of primary cortical neurons occurs in a p53 and cyclin-dependent kinase-dependent (CDK) manner. The manner by which these signals modulate death is unclear. Nuclear factor-kappaB (NF-kappaB) is a group of transcription factors that potentially interact with these pathways. Presently, we show that NF-kappaB is activated shortly after induction of DNA damage in a manner independent of the classic IkappaB kinase (IKK) activation pathway, CDKs, ATM, and p53. Acute inhibition of NF-kappaB via expression of a stable IkappaB mutant, downregulation of the p65 NF-kappaB subunit by RNA interference (RNAi), or pharmacological NF-kappaB inhibitors significantly protected against DNA damage-induced neuronal death. NF-kappaB inhibition also reduced p53 transcripts and p53 activity as measured by the p53-inducible messages, Puma and Noxa, implicating the p53 tumor suppressor in the mechanism of NF-kappaB-mediated neuronal death. Importantly, p53 expression still induces death in the presence of NF-kappaB inhibition, indicating that p53 acts downstream of NF-kappaB. Interestingly, neurons cultured from p65 or p50 NF-kappaB-deficient mice were not resistant to death and did not show diminished p53 activity, suggesting compensatory processes attributable to germline deficiencies, which allow p53 activation still to occur. In contrast to acute NF-kappaB inhibition, prolonged NF-kappaB inhibition caused neuronal death in the absence of DNA damage. These results uniquely define a signaling paradigm by which NF-kappaB serves both an acute p53-dependent pro-apoptotic function in the presence of DNA damage and an anti-apoptotic function in untreated normal neurons.

The c-Rel transcription factor and B-cell proliferation: a deal with the devil

Activation of the Rel/NF-kappaB signal transduction pathway has been associated with a variety of animal and human malignancies. However, among the Rel/NF-kappaB family members, only c-Rel has been consistently shown to be able to malignantly transform cells in culture. In addition, c-rel has been activated by a retroviral promoter insertion in an avian B-cell lymphoma, and amplifications of REL (human c-rel) are frequently seen in Hodgkin's lymphomas and diffuse large B-cell lymphomas, and in some follicular and mediastinal B-cell lymphomas. Phenotypic analysis of c-rel knockout mice demonstrates that c-Rel has a normal role in B-cell proliferation and survival; moreover, c-Rel nuclear activity is required for B-cell development. Few mammalian model systems are available to study the role of c-Rel in oncogenesis, and it is still not clear what features of c-Rel endow it with its unique oncogenic activity among the Rel/NF-kappaB family. In any event, REL may provide an appropriate therapeutic target for certain human lymphoid cell malignancies.

TIAF1 and p53 functionally interact in mediating apoptosis and silencing of TIAF1 abolishes nuclear translocation of serine 15-phosphorylated p53

TIAF1 is a TGF-beta 1-induced factor that protects L929 fibroblasts from TNF-mediated apoptosis. In contrast, overexpressed TIAF1 induces growth inhibition and apoptosis of monocytic U937 and various nonfibroblast cells. TIAF1-mediated apoptosis of U937 cells involves upregulation of p53, p21, and Smad2/4, but downregulation of ERK phosphorylation. To determine whether p53 and TIAF1 functionally interact in regulating cell death, ectopic TIAF1 and p53 were shown to induce apoptosis of U937 cells in both synergistic and antagonistic manners. At optimal levels both TIAF1 and p53 mediated apoptosis cooperatively. Also, both proteins suppressed adherence-independent growth of L929 cells. In contrast, initiation of apoptosis by overexpressed TIAF1 was blocked by low doses of p53, and vice versa. Furthermore, ectopic p53 blocked an ongoing apoptosis in U937 cells stably expressing TIAF1. Yeast two-hybrid analyses failed to demonstrate the binding of p53 with TIAF1, suggesting an unidentified protein that links the p53/TIFA1 interaction. Suppression of TIAF1 expression by siRNA could not inhibit Ser15 phosphorylation in p53 in response to UV and etoposide. However, nuclear translocation of these Ser15-phosphorylated p53 was significantly reduced in TIAF1-silenced cells. Taken together, TIAF1 and p53 functionally interact in regulating apoptosis, and TIAF1 is likely to participate in the nuclear translocation of activated p53.

Transcriptional profile of postmortem skeletal muscle

Autopsy specimens are often used in molecular biological studies of disease pathophysiology. However, few analyses have focused specifically on postmortem changes in skeletal muscles, and almost all of those investigate protein or metabolic changes. Although some structural and enzymatic changes have been described, the sequence of transcriptional events associated with these remains unclear. We analyzed a series of new and preexisting human skeletal muscle data sets on ≃12,500 genes and expressed sequence tags (ESTs) generated by the Affymetrix U95Av2 GeneChips from seven autopsy and seven surgical specimens. Remarkably, postmortem specimens (up to 46 h) revealed a significant and prominent upregulation of transcripts involved with protein biosynthesis. Additional upregulated transcripts are associated with cellular responses to oxidative stress, hypoxia, and ischemia; however, only a subset of genes in these pathways was affected. Overexpression was also seen for apoptosis-related, cell cycle regulation/arrest-related, and signal transduction-related genes. No major gene expression differences were seen between autopsy specimens with <20-h and 34- to 46-h postmortem intervals or between pediatric and adult cases. These data demonstrate that, likely in response to hypoxia and oxidative stress, skeletal muscle undergoes a highly active transcriptional, and possibly, translational phase during the initial 46-h postmortem interval. Knowledge of these changes is important for proper interpretation of gene expression studies utilizing autopsy specimens.

Hyperoxia activates the ATR-Chk1 pathway and phosphorylates p53 at multiple sites

Hyperoxia has been shown to cause DNA damage resulting in growth arrest of cells in p53-dependent, as well as p53-independent, pathways. Although H2O2 and other peroxides have been shown to induce ataxia telangiectasia-mutated (ATM)-dependent p53 phosphorylation in response to DNA damage, the signal transduction mechanisms in response to hyperoxia are currently unknown. Here we demonstrate that hyperoxia phosphorylates the Ser15 residue of p53 independently of ATM. Hyperoxia phosphorylated p53 (Ser15) in DNA-dependent protein kinase null (DNA-PK-/-) cells, indicating that it may not depend on DNA-PK for phosphorylation of p53 (Ser15). We show that Ser37 and Ser392 residues of p53 are also phosphorylated in an ATM-independent manner in hyperoxia. In contrast, H2O2 did not phosphorylate Ser37 in either ATM+/+ or ATM-/- cells. Furthermore, H2O2 failed to phosphorylate Ser15 in ATM-/- cells. Additionally, overexpression of kinase-inactive ATM-and-Rad3-related (ATR) in HEK293T cells diminished Ser15, Ser37, and Ser392 phosphorylation compared with vector-only transfected cells. In contrast, wild-type ATR overexpression did not diminish Ser15, Ser37, or Ser392 phosphorylation. We also show that checkpoint kinase 1 (Chk1) is phosphorylated on Ser345 in response to hyperoxia, which could be inhibited by caffeine or wortmannin, potent inhibitors of phosphoinositide 3-kinase-related kinases. Hyperoxia also phosphorylated Chk1 in ATM+/+ as well as in ATM-/- cells, demonstrating an ATM-independent mechanism in Chk1 phosphorylation. Together, our data suggest that hyperoxia activates the ATR-Chk1 pathway and phosphorylates p53 at multiple sites in an ATM-independent manner, which is different from other forms of oxidative stress such as H2O2 or UV light.

Transfection of a dominant-negative mutant NF-kB inhibitor (IkBm) represses p53-dependent apoptosis in acute lymphoblastic leukemia cells: interaction of IkBm and p53

To investigate the possible role of inhibiting NF-kB activation in sensitizing tumor cells to chemotherapy-induced apoptosis, we transfected the dominant-negative mutant inhibitor of NF-kB (IkBm) into the EU-1 cell line, an acute lymphoblastic leukemia (ALL) line with constitutive NF-kB activation. Overexpression of IkBm significantly reduced constitutive NF-kB activity in EU-1 cells, resulting in decreased cell growth. In response to apoptosis induced by chemotherapeutic drugs, IkBm-transfected cells (EU-1/IkBm) exhibited increased sensitivity to vincristine (VCR), whereas sensitivity to doxorubicin (Dox) was not changed as compared to neo-transfected control (EU-1/neo) cells. To further evaluate the link between IkBm and sensitivity to Dox and VCR, we demonstrated that both endogenous IkBalpha and ectopic IkBm bind to p53. In response to Dox, the cytosolic p53.IkBalpha complex rapidly dissociated due to downregulation of IkBalpha. However, the p53.IkBm complex did not dissociate under these conditions. Although treatment of EU-1/IkBm cells with Dox increased the expression of p53, the nondissociating p53.IkBm complex resulted in decreased p53 function, as demonstrated by absence of cell-cycle arrest and induction of p53 target genes. Contrastingly, VCR-induced cell death neither downregulated IkBalpha nor induced p53, as shown by the lack of NF-kB activation and p53-mediated gene expression in VCR-treated cells. Our data suggest that IkBm simultaneously downregulates NF-kB activation and sequesters p53 in the cytoplasm, thus enhancing NF-kB-regulated apoptosis but blocking p53-dependent apoptosis.

Molecular mechanisms underlying WOX1 activation during apoptotic and stress responses

Human WWOX gene encodes a putative tumor suppressor WW domain-containing oxidoreductase WOX1 (also known as WWOX or FOR). A high frequency of loss of heterozygosity (LOH) of this gene has been shown in prostate, lung, breast and other cancers. In addition, numerous aberrant WWOX mRNA transcripts have been found in cancer cells. WOX1 is a proapoptotic protein. In response to stress or apoptotic stimuli, WOX1 became phosphorylated at Tyr33, which enabled its complex formation with activated p53 and JNK1. The p53/WOX1 complex translocated to the mitochondria and further to the nuclei to mediate apoptosis. WOX1 mutants, which were inactivated for nuclear translocation or Tyr33 phosphorylation, failed to induce apoptosis, indicating that activation of WOX1 via Tyr33 phosphorylation, followed by nuclear translocation, is essential for inducing cell death. WOX1 induced apoptosis synergistically with p53. In contrast, transiently activated JNK1 induced anti-apoptotic response, and this protective activity inhibited WOX1-induced apoptosis. Taken together, WOX1 is involved in stress and apoptotic responses, and is likely to regulate the activation of both p53 and JNK1.

Ursodeoxycholic acid modulates E2F-1 and p53 expression through a caspase-independent mechanism in transforming growth factor beta1-induced apoptosis of rat hepatocytes

Transforming growth factor beta1 (TGF-beta1)-induced hepatocyte apoptosis is associated with activation of E2F transcription factors and p53 stabilization through Mdm-2, thus potentially modulating a number of target genes. In previous studies, we have shown that ursodeoxycholic acid (UDCA) prevents TGF-beta1-induced hepatocyte apoptosis by inhibiting the mitochondrial pathway of cell death. In this study we examined the role of p53 in the induction of apoptosis by TGF-beta1, and identified additional antiapoptosis targets for UDCA. Our data show a significant transcriptional activation of E2F-1 in primary rat hepatocytes incubated with TGF-beta1, as well as a 5-fold increase in p53 and a 2-fold decrease in its inhibitor, Mdm-2 (p < 0.05). In addition, bax mRNA expression was significantly induced at 36 h (p < 0.01), resulting in increased levels of Bax protein. In contrast, Bcl-2 transcript and protein levels were decreased at all time points (p < 0.01). Notably, UDCA inhibited E2F-1 transcriptional activation, p53 stabilization and Bcl-2 family expression (p < 0.05), in part, through a caspase-independent mechanism. Moreover, in the absence of TGF-beta1, UDCA prevented induction of p53 and Bax by overexpression of E2F-1 and p53, respectively (p < 0.05). In addition, UDCA inhibited TGF-beta1-induced degradation of nuclear factor kappaB (NF-kappaB) and its inhibitor IkappaB (p < 0.05). In conclusion, these results demonstrate that UDCA inhibits E2F-1 transcriptional activation of hepatocyte apoptosis, thus modulating p53 stabilization, NF-kappaB degradation, and expression of Bcl-2 family members.

p53 represses cyclin D1 transcription through down regulation of Bcl-3 and inducing increased association of the p52 NF-kappaB subunit with histone deacetylase 1

The p53 and NF-kappaB transcription factor families are important, multifunctional regulators of the cellular response to stress. Here we have investigated the regulatory mechanisms controlling p53-dependent cell cycle arrest and cross talk with NF-kappaB. Upon induction of p53 in H1299 or U-2 OS cells, we observed specific repression of cyclin D1 promoter activity, correlating with a decrease in cyclin D1 protein and mRNA levels. This repression was dependent on the proximal NF-kappaB binding site of the cyclin D1 promoter, which has been shown to bind the p52 NF-kappaB subunit. p53 inhibited the expression of Bcl-3 protein, a member of the IkappaB family that functions as a transcriptional coactivator for p52 NF-kappaB and also reduced p52/Bcl-3 complex levels. Concomitant with this, p53 induced a significant increase in the association of p52 and histone deacetylase 1 (HDAC1). Importantly, p53-mediated suppression of the cyclin D1 promoter was reversed by coexpression of Bcl-3 and inhibition of p52 or deacetylase activity. p53 therefore induces a transcriptional switch in which p52/Bcl-3 activator complexes are replaced by p52/HDAC1 repressor complexes, resulting in active repression of cyclin D1 transcription. These results reveal a unique mechanism by which p53 regulates NF-kappaB function and cell cycle progression.

JNK1 physically interacts with WW domain-containing oxidoreductase (WOX1) and inhibits WOX1-mediated apoptosis

Transient activation of c-Jun N-terminal kinase (JNK) promotes cell survival, whereas persistent JNK activation induces apoptosis. Bovine testicular hyaluronidase PH-20 activates JNK1 and protects L929 fibroblasts from staurosporine-mediated cell death. PH-20 also induces the expression of a p53-interacting WW domain-containing oxidoreductase (WOX1, also known as WWOX or FOR) in these cells. WOX1 enhances the cytotoxic function of tumor necrosis factor and mediates apoptosis synergistically with p53. Thus, the activated JNK1 is likely to counteract WOX1 in mediating apoptosis. Here it is demonstrated that ectopic JNK1 inhibited WOX1-mediated apoptosis of L929 fibroblasts, monocytic U937 cells, and other cell types. Also, JNK1 blocked WOX1 prevention of cell cycle progression. By stimulating cells with anisomycin or UV light, JNK1 became activated, and WOX1 was phosphorylated at Tyr(33). The activated JNK1 physically interacted with the phosphorylated WOX1, as determined by co-immunoprecipitation. Alteration of Tyr(33) to Arg(33) in WOX1 abrogated its binding interaction with JNK1 and its activity in mediating cell death, indicating that Tyr(33) phosphorylation is needed to activate WOX1. A dominant negative WOX1 was developed and shown to block p53-mediated apoptosis and anisomycin-mediated WOX1 phosphorylation but could not inhibit JNK1 activation. This mutant protein bound p53 but could not interact with JNK1, as determined in yeast two-hybrid analysis. Taken together, phosphorylation of JNK1 and WOX1 is necessary for their physical interaction and functional antagonism.

Transforming growth factor-beta1 blocks the enhancement of tumor necrosis factor cytotoxicity by hyaluronidase Hyal-2 in L929 fibroblasts

BACKGROUND

Functional antagonism between transforming growth factor beta (TGF-beta) and hyaluronidase has been demonstrated. For example, testicular hyaluronidase PH-20 counteracts TGF-beta1-mediated growth inhibition of epithelial cells. PH-20 sensitizes various cancer cells to tumor necrosis factor (TNF) cytotoxicity by upregulating proapoptotic p53 and WW domain-containing oxidoreductase (WOX1). TGF-beta1 blocks PH-20-increased TNF cytotoxicity. In the present study, the functional antagonism between TGF-beta1 and lysosomal hyaluronidases Hyal-1 and Hyal-2 was examined.

RESULTS

Murine L929 fibroblasts were engineered to stably express green-fluorescent protein (GFP)-tagged hyaluronidase (GFP-Hyal-1 or GFP-Hyal-2) or GFP alone. Compared to control cells, Hyal-2-expressing cells had a significantly increased sensitivity to TNF cytotoxicity (approximately 60-110% increase), while Hyal-1-expressing cells were less sensitive to TNF (approximately 20-90% increase). TNF activated NF-kappaB, along with IkappaBalpha degradation, occurred at 20 to 60 min in Hyal-2 cells post stimulation, but at the 20 min time point in both control and Hyal-1 cells. Hyal-2 cells, but not Hyal-1 and control cells, constitutively expressed WOX1, and transiently expressed Hyal-2 enhanced WOX1-mediated cell death. Unlike PH-20, Hyal-1 and Hyal-2 did not induce p53 expression. Hyal-2 translocated from the lysosome to the mitochondria during staurosporine-mediated apoptosis, suggesting that Hyal-2 may damage mitochondria. Finally, Hyal-1 and Hyal-2 blocked TGF-beta1-enhanced L929 cell growth. In contrast, TGF-beta1 inhibited Hyal-1- and Hyal-2-increased TNF cytotoxicity in L929 cells by 30-50%.

CONCLUSIONS

TGF-beta1 limits the ability of Hyal-2 to induce TNF cytotoxicity in L929 cells. Hyal-2-increased TNF cytotoxicity in L929 cells appears to be correlated with upregulation of WOX1, a prolonged NF-kappaB activation, and Hyal-2 translocation to the mitochondria during apoptosis.