The transcription factor NF-kappaB: control of oncogenesis and cancer therapy resistance

Inhibitor of apoptosis protein-1 promotes tumor cell survival in mesothelioma

Malignant pleural mesothelioma (MPM) is a highly lethal pleural neoplasm that is often resistant to chemotherapeutic drugs, including cisplatin, and for which little is known regarding carcinogenic pathways. We used differential display to compare gene expression patterns in mesothelioma, normal pleura and normal lung, in order to better understand MPM pathobiology, and to search for genes that may facilitate drug resistance in this cancer. The human inhibitor of apoptosis protein-1 gene (IAP-1/MIHC/cIAP2) was discovered to be highly expressed in MPM. We confirmed overexpression of IAP-1 mRNA and protein in 39 additional human MPM tumor specimens and 3/5 (60%) MPM cell lines by multiple methods, including real time quantitative reverse transcription-PCR and western blot analysis. Using an antisense targeting approach, we found that attenuation of IAP-1 mRNA levels decreases baseline cell viability and increases the sensitivity of MPM cell lines to cisplatin by nearly 20-fold. Reduced IAP-1 gene expression also results in a concordant increase of the pro-apoptotic cleavage product of caspase 9 and a reduction in the number of viable tumor cells. Our observations strongly suggest that IAP-1 is at least partly responsible for promoting carcinogenesis and mediating resistance to cisplatin in many MPM tumors and that further study of this apoptotic pathway is warranted.

Growing old with nuclear factor-kappaB

The transcription factor nuclear factor-kappa B (NF-kappaB) is involved in the regulation of a broad spectrum of genes that play important roles in a myriad of physiological and pathological events ranging from the immune response to carcinogenesis. Interestingly, many processes in which NF-kappa B plays a central role have long been noted for their alteration with age. A number of research groups have reported rather dramatic changes in NF-kappaB activity as humans and animals age, with tissue-specific increases and decreases in NF-kappaB activity being reported. The extent to which changes in NF-kappaB activity drive aging and influence life span in humans and other mammals is not clear. However, given the dramatic impact that NF-kappaB can have on the function of numerous tissues and organs, understanding how NF-kappaB activity changes with age will undoubtedly enhance our understanding of the many diseases associated with growing old.

VCP (p97) regulates NFkappaB signaling pathway, which is important for metastasis of osteosarcoma cell line

In order to identify genes associated with metastasis, suppression subtractive hybridization (SSH) was performed using murine osteosarcoma cell line Dunn and its subline with higher metastatic potential, LM8. SSH revealed expression of the gene encoding valosin-containing protein (VCP; also known as p97) to be constitutively activated in LM8 cells, but it declined in Dunn cells when the cells became confluent. Because VCP is known to be involved in the ubiquitination process of Inhibitor-kappaBalpha (IkappaBalpha), an inhibitor of nuclear factor-kappaB (NFkappaB), whether VCP influences NFkappaB activation or not was examined by using VCP-transfected Dunn cells (Dunn/VCPs). When stimulated with tumor necrosis factor-alpha (TNFalpha), Dunn/VCPs showed constantly activated NFkappaB, although in the original Dunn cells and control vector transfectant (Dunn/Dunn-c) NFkappaB activation ceased when the cells became confluent. Western immunoblot analysis showed an increase of phosphorylated IkappaBalpha (p-IkappaBalpha) in the cytoplasm of confluent Dunn/Dunn-c cells compared to that of Dunn/VCPs. Therefore, decrease of p-IkappaBalpha degrading activity might be responsible for the decrease in NFkappaB activation. In vitro apoptosis assay demonstrated increased apoptosis rates of Dunn/Dunn-c cells after TNFalpha stimulation compared to those of Dunn/VCPs and LM8 cells. In vivo metastasis assay showed increased incidences of metastatic events in Dunn/VCP-1 inoculated male C3H mice compared to those in Dunn/Dunn-c inoculated mice. These findings suggested that VCP expression plays an important role in the metastatic process. Anti-apoptotic potential in these cells owing to constant NFkappaB activation via efficient cytoplasmic p-IkappaBalpha degrading activity may explain the increased metastatic potential of these cells.

NF-kappa B DNA-binding activity in embryos responding to a teratogen, cyclophosphamide

BACKGROUND

The Rel/NF-kappaB transcription factors have been shown to regulate apoptosis in different cell types, acting as inducers or blockers in a stimuli- and cell type-dependent fashion. One of the Rel/NF-kappaB subunits, RelA, has been shown to be crucial for normal embryonic development, in which it functions in the embryonic liver as a protector against TNFalpha-induced physiological apoptosis. This study assesses whether NF-kappaB may be involved in the embryo's response to teratogens. Fot this, we evaluated how NF-KappaB DNA binding activity in embryonic organs demonstrating differential sensitivity to a reference teratogen, cyclophosphamide, correlates with dysmorphic events induced by the teratogen at the cellular level (excessive apoptosis) and at the organ level (structural anomalies).

RESULTS

The embryonic brain and liver were used as target organs. We observed that the Cyclophosphamide-induced excessive apoptosis in the brain, followed by the formation of severe craniofacial structural anomalies, was accompanied by suppression of NF-kappaB DNA-binding activity as well as by a significant and lasting increase in the activity of caspases 3 and 8. However, in the liver, in which cyclophosphamide induced transient apoptosis was not followed by dysmorphogenesis, no suppression of NF-kappaB DNA-binding activity was registered and the level of active caspases 3 and 8 was significantly lower than in the brain. It has also been observed that both the brain and liver became much more sensitive to the CP-induced teratogenic insult if the embryos were exposed to a combined treatment with the teratogen and sodium salicylate that suppressed NF-kappaB DNA-binding activity in these organs.

CONCLUSION

The results of this study demonstrate that suppression of NF-kappaB DNA-binding activity in embryos responding to the teratogenic insult may be associated with their decreased resistance to this insult. They also suggest that teratogens may suppress NF-kappaB DNA-binding activity in the embryonic tissues in an organ type- and dose-dependent fashion.

Activation of NF-kappaB is essential for hepatocyte growth factor-mediated proliferation and tubulogenesis

Hepatocyte growth factor (HGF) and its receptor, Met, regulate a number of biological functions in epithelial and nonepithelial cells, such as survival, motility, proliferation, and tubular morphogenesis. The transcription factor NF-kappaB is activated in response to a wide variety of stimuli, including growth factors, and is involved in biological responses in part overlapping with those triggered by HGF. In this work we used the liver-derived MLP29 cell line to study the possible involvement of NF-kappaB in HGF/Met signaling. HGF stimulates NF-kappaB DNA binding and transcriptional activation via the canonical IkappaB phosphorylation-degradation cycle and via the extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase cascades. Phosphatidylinositol 3-kinase is not involved in Met-mediated NF-kappaB activation. Blockage of NF-kappaB activation in MLP29 cells by forced expression of the NF-kappaB super-repressor IkappaB(alpha)2A does not interfere with HGF-induced scatter but inhibits proliferation and tubulogenesis. Surprisingly, in the same cells NF-kappaB appears to be dispensable for the antiapoptotic function of HGF.

Increased p50/p50 NF-kappaB activation in human papillomavirus type 6- or type 11-induced laryngeal papilloma tissue

We have observed elevated NF-kappaB DNA-binding activity in nuclear extracts from human papillomavirus type 6- and 11-infected laryngeal papilloma tissues. The predominant DNA-binding species is the p50/p50 homodimer. The elevated NF-kappaB activity could be correlated with a reduced level of cytoplasmic IkappaBbeta and could be associated with the overexpression of p21(CIP1/WAF1) in papilloma cells. Increased NF-kappaB activity and cytoplasmic accumulation of p21(CIP1/WAF1) might counteract death-promoting effects elicited by overexpressed PTEN and reduced activation of Akt and STAT3 previously noted in these tissues.

How melanoma cells evade trail-induced apoptosis

At the doses used clinically, chemotherapy is believed to kill melanoma by a final common 'mitochondrial' pathway that leads to apoptosis. Similarly, several natural defence mechanisms kill melanoma by the same pathways. A corollary to the latter is that survival of melanoma in the host is due to the development of anti-apoptotic mechanisms in melanoma cells. What are these mechanisms? And how might we bypass them to improve the treatment of melanoma?

Avicins, a family of triterpenoid saponins from Acacia victoriae (Bentham), inhibit activation of nuclear factor-kappaB by inhibiting both its nuclear localization and ability to bind DNA

Triterpenoid saponins, which are present in leguminous plants and some marine animals, possess a broad range of biological actions. We have earlier reported the extraction of avicins, a family of triterpenoid saponins obtained from the Australian desert tree Acacia victoriae (Leguminosae: Mimosoideae) that inhibit tumor cell growth and induce apoptosis, in part, by perturbing mitochondrial function. These saponins have also been found to prevent chemical-induced carcinogenesis in mice. This study examines the effect of a triterpene mixture (F094) and a single molecular species (avicin G) isolated from the mixture on tumor necrosis factor (TNF)-induced activation of nuclear transcription factor-kappaB (NF-kappaB) in Jurkat cells (human T cell leukemia). Both F094 and avicin G were found to be potent inhibitors of TNF-induced NF-kappaB. Treatment of Jurkat cells with avicin G resulted in a much slower accumulation of the p65 subunit of NF-kappaB into the nucleus whereas the degradation of IkappaBalpha was unaffected. Avicin G also impaired the binding of NF-kappaB to DNA in in vitro binding assays. Treatment of cells with DTT totally reversed the avicin G-induced inhibition of NF-kappaB activity, suggesting that sulfhydryl groups critical for NF-kappaB activation were being affected. Avicin G treatment resulted in decreased expression of NF-kappaB-regulated proteins such as inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX-2). Thus, the avicins may prove important for reducing both oxidative and nitrosative cellular stress and thereby suppressing the development of malignancies and related diseases.

Increased and correlated nuclear factor-kappa B and Ku autoantigen activities are associated with development of multidrug resistance

In this study, we investigated possible engagement of NF-kappaB and Ku autoantigen (Ku) activation in development of multidrug resistance (MDR) and circumvention of MDR by modulation of NF-kappaB and Ku. The NF-kappaB activity and NF-kappaB p65 subunit level were constitutively higher in MDR cells than in drug-sensitive parental cells. Interestingly, a faster running NF-kappaB DNA binding complex was identified as Ku, a DNA damage sensor and a key double strand break repair protein, and was positively correlated with the NF-kappaB activity in MDR cells and Ku- or both subunits of NF-kappaB-transfected cells. Also both NF-kappaB and Ku activities were activated or inhibited by treatment with etoposide (VP-16) or MG-132 (a proteasome inhibitor), respectively. Furthermore, PKA inhibitor suppressed markedly the constitutive and drug-induced activities of NF-kappaB and Ku in MDR cells and subsequently potentiated the cytotoxic activity of anticancer drugs. Our results proposed that the NF-kappaB and Ku activation could be one of multi-factorial MDR mechanism, and PKA inhibitor, likely via inhibition of NF-kappaB and Ku activities, could enhance the effectiveness of anticancer drugs against MDR cells with high activities of NF-kappaB and Ku.

New insights into the role of nuclear factor-kappaB in cell growth regulation

The nuclear factor (NF)-kappaB family of eukaryotic transcription factors plays an important role in the regulation of immune response, embryo and cell lineage development, cell apoptosis, cell-cycle progression, inflammation, and oncogenesis. A wide range of stimuli, including cytokines, mitogens, environmental particles, toxic metals, and viral or bacterial products, activate NF-kappaB, mostly through IkappaB kinase (IKK)-dependent phosphorylation and subsequent degradation of its inhibitor, the IkappaB family of proteins. Activated NF-kappaB translocates into the nucleus where it modulates the expression of a variety of genes, including those encoding cytokines, growth factors, acute phase response proteins, cell adhesion molecules, other transcription factors, and several cell apoptosis regulators. During the past few years, tremendous progress has been achieved in our understanding on how intracellular signaling pathways are transmitted in either a linear or a network manner leading to the activation of NF-kappaB and subsequent cell growth control. However, a detailed molecular mechanism of NF-kappaB regulating cell growth has yet to be determined. Elucidation of the relationships between NF-kappaB activation and cell growth will be important in developing new strategies for the treatment of various human diseases, such as chronic autoimmune disorder and cancer.

NF-kappa B activation results in rapid inactivation of JNK in TNF alpha-treated Ewing sarcoma cells: a mechanism for the anti-apoptotic effect of NF-kappa B

We recently reported that inhibition of NF-kappa B activation as a consequence of the overexpression of a degradation-resistant form of I kappa B alpha [I kappa B alpha(A32/36)] sensitized Ewing sarcoma cells to TNF alpha-induced killing. The c-Jun N-terminal kinases (JNK) have been shown to participate in death signaling triggered by certain stimuli and are activated by TNF alpha. To obtain insight into the mechanism of the anti-apoptotic effect of NF-kappa B, we compared the profiles of JNK activation by TNF alpha in control cells and in cells in which NF-kappa B activation was impaired. We show here that JNK activation was transient in control cells but remained elevated in I kappa B alpha(A32/36)-expressing cells. NF-kappa B repressed specifically the JNK pathway, since the kinetics of activation of the other TNF alpha-activated-MAP kinase p38 were identical in both cells. Prolongation of JNK activation in I kappa B alpha(A32/36)-expressing cells was not inhibited by the broad spectrum caspase inhibitor Z-VAD-FMK and thus was not the consequence of caspase activation. Pretreatment of control cells with the phosphatase inhibitor vanadate greatly prolonged JNK activation by TNF alpha and resulted in induction of apoptosis by this cytokine. Moreover, overexpression of a dominant-negative mutant of JNK1 decreased TNF alpha-induced apoptosis in cells expressing the super repressor of NF-kappa B, indicating that the sustained activation of JNK1 participated in death signaling triggered by TNF alpha. Our results provide evidence that the repression of JNK activation by NF-kappa B participates in the anti-apoptotic effect of this transcription factor in TNF alpha-treated Ewing sarcoma cells.

Two waves of nuclear factor kappaB recruitment to target promoters

Proinflammatory stimuli induce the rapid and transient translocation of nuclear factor (NF)-kappaB to the nucleus, where it activates transcription from several genes, including those encoding inflammatory cytokines and chemokines, adhesion molecules, and cytoprotective proteins. Using chromatin immunoprecipitation, we show that after an acute stimulation two distinct waves of NF-kappaB recruitment to target promoters occur: a fast recruitment to constitutively and immediately accessible (CIA) promoters and a late recruitment to promoters requiring stimulus-dependent modifications in chromatin structure to make NF-kappaB sites accessible (promoters with regulated and late accessibility [RLA]). Our results suggest that a mechanism of specificity in NF-kappaB-dependent transcriptional responses relies on the ability of individual stimuli to make RLA promoters accessible to NF-kappaB before its rapid extrusion from the nucleus.

Inhibition of anchorage-independent growth and lung metastasis of A549 lung carcinoma cells by IkappaBbeta

To evaluate the role of the NF-kappaB signaling pathway in oncogenic transformation, we expressed IkappaBbeta, a specific inhibitor of NF-kappaB, in two human lung adenocarcinoma cell lines, A549 and H441. Expression of IkappaBbeta significantly reduced NF-kappaB activation induced by cotransfection with p65/RelA or TNF-alpha and abrogated the basal NF-kappaB activity in A549 cells. Transfection of IkappaBbeta into A549, H441 and K-ras-transformed NIH3T3 cells suppressed anchorage-independent growth as measured by colony formation in soft agar. Anchorage-independent growth of vector-transfected A549 cells in reduced serum could be enhanced by both EGF and IGF-I. In contrast, only EGF but not IGF-I could induce anchorage-independent growth of IkappaBbeta-expressing A549 cells, suggesting that the IGF-I signaling pathway regulating growth and survival may be blocked by IkappaBbeta. Interestingly, expression of IkappaBbeta suppressed growth of A549 cells in low serum in vitro without affecting in vivo growth subcutaneously in nude mice. However, metastatic growth of IkappaBbeta-expressing A549 cells in the lungs of nude mice was significantly inhibited. These results provide evidence that NFkappaB plays an important role in anchorage-independent growth and metastatic growth of lung carcinoma cells.

Effector genes altered in MCF-7 human breast cancer cells after exposure to fractionated ionizing radiation

Understanding the molecular mechanisms involved in the response of tumors to fractionated exposures to ionizing radiation is important for improving radiotherapy and/or radiochemotherapy. In the present study, we examined the expression of stress-related genes in an MCF-7 cell population (MCF-IR20) that has been derived through treatment with fractionated irradiation (2 Gy per fraction with a total dose of 40 Gy). MCF-IR20 cells showed a 1.6-fold increase in sensitization with dose at 10% isosurvival in a clonogenic assay, and a reduced growth delay ( approximately 15 h compared to approximately 27 h), compared to the parental MCF-7 cells treated with a single dose of 5 Gy. To determine which effector genes were altered in the MCF-IR20 cells, the expression of stress-related effector genes was measured using a filter with 588 genes (Clontech) that included major elements involved in cell cycle control, DNA repair, and apoptosis. Compared to MCF-7 cells that were not exposed to fractionated radiation, 19 genes were up- regulated (2.2-5.1-fold) and 4 were down-regulated (2.7-3.4- fold) in the MCF-IR20 cells. In agreement with the array results, 6 up-regulated genes tested by RT-PCR showed elevated expression. Also, activities of the stress-related transcription factors NFKB, TP53 and AP1 showed a 1.2-4.5-fold increase after a single dose of 5 Gy in MCF-IR20 cells compared with parental MCF-7 cells. However, when the radioresistant MCF-IR20 cell were cultured for more than 12 passages after fractionated irradiation (MCF-RV), radioresistance was lost, with the radiosensitivity being the same as the parental MCF- 7 cells. Interestingly, expression levels of CCNB1, CD9 and CDKN1A in MCF-RV cells returned to levels expressed by the parental cells, whereas the expression levels of three other genes, MSH2, MSH6 and RPA remained elevated. To determine if any of the changes in gene expression could be responsible for the induced radioresistance, CCNB1 and CDKN1A, both of which were up-regulated in MCF-IR20 cells and down-regulated in MCF-RV cells, were studied further by transfection with antisense oligonucleotides. Antisense of CCNB1 significantly reduced the clonogenic survival of MCF- IR20 cells at doses of 5 and 10 Gy, from 42% to 26% and from 5.7% to 1.0%, respectively. Antisense of CDKN1A, however, had no effect on radiation survival of MCF-IR20 cells. In summary, these results suggest that stress-related effector genes are altered in cells after treatment with fractionated irradiation, and that up-regulation of CCNB1 is responsible, at least in part, for radioresistance after fractionated irradiation.

Caretaker or undertaker? The role of the proteasome in aging

Despite intensive studies, the molecular basis of the decline of protein degradation with age still remains unresolved. It is suspected that the proteasome is one of the key factors controlling the age-dependent turnover of intracellular proteins. This hypothesis is based on the observation that the proteasome is a part of the ubiquitin-proteasome pathway, which together with the lysosomal pathway constitute the major mechanisms of protein degradation. While there are alterations in proteasome structure and function with age, the observed changes do not provide a clear mechanism for explaining the decline of protein degradation. In addition, there are no consistent changes in the ubiquitination system to account for this decline. On the other hand, because of the essential role played by the proteasome in the maintenance of cellular homeostasis, the observation of age-related changes in structure and function will ultimately be demonstrated to contribute to the aging process. The fact that food restriction, the only currently available experimental paradigm that can alter the aging process, modulates the age-related changes in proteasome structure and function provides presumptive evidence that the proteasome is involved in the aging process.

Shared pathways of IkappaB kinase-induced SCF(betaTrCP)-mediated ubiquitination and degradation for the NF-kappaB precursor p105 and IkappaBalpha

p105 (NFKB1) acts in a dual way as a cytoplasmic IkappaB molecule and as the source of the NF-kappaB p50 subunit upon processing. p105 can form various heterodimers with other NF-kappaB subunits, including its own processing product, p50, and these complexes are signal responsive. Signaling through the IkappaB kinase (IKK) complex invokes p105 degradation and p50 homodimer formation, involving p105 phosphorylation at a C-terminal destruction box. We show here that IKKbeta phosphorylation of p105 is direct and does not require kinases downstream of IKK. p105 contains an IKK docking site located in a death domain, which is separate from the substrate site. The substrate residues were identified as serines 923 and 927, the latter of which was previously assumed to be a threonine. S927 is part of a conserved DSGPsi motif and is functionally most critical. The region containing both serines is homologous to the N-terminal destruction box of IkappaBalpha, -beta, and -epsilon. Upon phosphorylation by IKK, p105 attracts the SCF E3 ubiquitin ligase substrate recognition molecules betaTrCP1 and betaTrCP2, resulting in polyubiquitination and complete degradation by the proteasome. However, processing of p105 is independent of IKK signaling. In line with this and as a physiologically relevant model, lipopolysaccharide (LPS) induced degradation of endogenous p105 and p50 homodimer formation, but not processing in pre-B cells. In mutant pre-B cells lacking IKKgamma, processing was unaffected, but LPS-induced p105 degradation was abolished. Thus, a functional endogenous IKK complex is required for signal-induced p105 degradation but not for processing.