Inhibition of the NF-KB Signaling Pathway and Its Effects on Apoptosis and Cancer

The Rel/NF-kB family of inducible transcription factors are evolutionarily conserved structurally and functionally, from insects to humans. They are ubiquitously expressed in a number of mature cell types, playing a pivotal role regulating cell growth, differentiation and apoptosis. Under normal circumstances, the proliferation of new cells is tightly regulated, as is the programmed lifespan of most cells, occasionally however cells loose their responsiveness to growth control mechanisms, resulting in a tumor or neoplasm. Sustained or chronic inflammation has been linked to a number of pathological conditions that destroy tissue and facilitate neoplastic growth. NF-kB in part mediates the opposing signals of cell survival and cell death, associated with this response. We hypothesized that inhibition of NF-kB would inhibit tumor cell growth. A number of anti-neoplastic drugs like some pro-inflammatory cytokines can activate both the cellular apoptotic and pro-survival (via NF-kB) pathways. We demonstrate, in vitro, that the use of Nitric Oxide mitigates NF-kB activation and induces program cell death, when administered as an adjuvant with this subset of pro-inflammatory cytokines. Secondly, several front-line anti-cancer drugs activate NF-kB as a result of their mode of action, resulting in the survival of a resistant population of tumor cells. In order to abrogate this beneficial activity for the tumor cell we explore, both in vitro and in vivo, the use of Nitric Oxide to inhibit NF-kB, augmenting the efficacy of the anti-neoplastic drugs. Thirdly, we identify that the intracellular signaling kinase, Inositol Hexkisphosphate Kinase2 (IHPK2) , binds to a key component in the NF-kB signaling pathway, inhibiting NF-kB activity promoting apoptosis in tumor cells. Lastly, an in depth study investigating the major initiator of pro-inflammatory signaling during bacterial infection of cells by Salmonela sp. was in fact due to recognition of the bacterial protein flagellin by the cell surface receptor Toll-like recepto

Flagellin acting via TLR5 is the major activator of key signaling pathways leading to NF-κB and proinflammatory gene program activation in intestinal epithelial cells

BACKGROUND: Infection of intestinal epithelial cells by pathogenic Salmonella leads to activation of signaling cascades that ultimately initiate the proinflammatory gene program. The transcription factor NF-κB is a key regulator/activator of this gene program and is potently activated. We explored the mechanism by which Salmonella activates NF-κB during infection of cultured intestinal epithelial cells and found that flagellin produced by the bacteria and contained on them leads to NF-κB activation in all the cells; invasion of cells by the bacteria is not required to activate NF-κB. RESULTS: Purified flagellin activated the mitogen activated protein kinase (MAPK), stress-activated protein kinase (SAPK) and Ikappa B kinase (IKK) signaling pathways that lead to expression of the proinflammatory gene program in a temporal fashion nearly identical to that of infection of intestinal epithelial cells by Salmonella. Flagellin expression was required for Salmonella invasion of host cells and it activated NF-κB via toll-like receptor 5 (TLR5). Surprisingly, a number of cell lines found to be unresponsive to flagellin express TLR5 and expression of exogenous TLR5 in these cells induces NF-κB activity in response to flagellin challenge although not robustly. Conversely, overexpression of dominant-negative TLR5 alleles only partially blocks NF-κB activation by flagellin. These observations are consistent with the possibility of either a very stable TLR5 signaling complex, the existence of a low abundance flagellin co-receptor or required adapter, or both. CONCLUSION: These collective results provide the evidence that flagellin acts as the main determinant of Salmonella mediated NF-κB and proinflammatory signaling and gene activation by this flagellated pathogen. In addition, expression of the fli C gene appears to play an important role in the proper functioning of the TTSS since mutants that fail to express fli C are defective in expressing a subset of Sip proteins and fail to invade host cells. Flagellin added in trans cannot restore the ability of the fli C mutant bacteria to invade intestinal epithelial cells. Lastly, TLR5 expression in weak and non-responding cells indicates that additional factors may be required for efficient signal propagation in response to flagellin recognition

Flagellin Acting Via TLR5 is the Major Activator of Key Signaling Pathways Leading to NF-kappa B and Proinflammatory Gene Program activation in intestinal epithelial cells

BACKGROUND: Infection of intestinal epithelial cells by pathogenic Salmonella leads to activation of signaling cascades that ultimately initiate the proinflammatory gene program. The transcription factor NF-kappa B is a key regulator/activator of this gene program and is potently activated. We explored the mechanism by which Salmonella activates NF-kappa B during infection of cultured intestinal epithelial cells and found that flagellin produced by the bacteria and contained on them leads to NF-kappa B activation in all the cells; invasion of cells by the bacteria is not required to activate NF-kappa B. RESULTS: Purified flagellin activated the mitogen activated protein kinase (MAPK), stress-activated protein kinase (SAPK) and I kappa B kinase (IKK) signaling pathways that lead to expression of the proinflammatory gene program in a temporal fashion nearly identical to that of infection of intestinal epithelial cells by Salmonella. Flagellin expression was required for Salmonella invasion of host cells and it activated NF-kappa B via toll-like receptor 5 (TLR5). Surprisingly, a number of cell lines found to be unresponsive to flagellin express TLR5 and expression of exogenous TLR5 in these cells induces NF-kappa B activity in response to flagellin challenge although not robustly. Conversely, overexpression of dominant-negative TLR5 alleles only partially blocks NF-kappa B activation by flagellin. These observations are consistent with the possibility of either a very stable TLR5 signaling complex, the existence of a low abundance flagellin co-receptor or required adapter, or both. CONCLUSION: These collective results provide the evidence that flagellin acts as the main determinant of Salmonella mediated NF-kappa B and proinflammatory signaling and gene activation by this flagellated pathogen. In addition, expression of the fli C gene appears to play an important role in the proper functioning of the TTSS since mutants that fail to express fli C are defective in expressing a subset of Sip proteins and fail to invade host cells. Flagellin added in trans cannot restore the ability of the fli C mutant bacteria to invade intestinal epithelial cells. Lastly, TLR5 expression in weak and non-responding cells indicates that additional factors may be required for efficient signal propagation in response to flagellin recognition

Nitrosylcobalamin Potentiates the Anti-Neoplastic Effects of Chemotherapeutic Agents via Suppression of Survival Signaling

Nitrosylcobalamin (NO-Cbl) is a chemotherapeutic pro-drug derived from vitamin B12 that preferentially delivers nitric oxide (NO) to tumor cells, based upon increased receptor expression. NO-Cbl induces Apo2L/TRAIL-mediated apoptosis and inhibits survival signaling in a variety of malignant cell lines. Chemotherapeutic agents often simultaneously induce an apoptotic signal and activation of NF-kappaB, which has the undesired effect of promoting cell survival. The specific aims of this study were to 1) measure the anti-tumor effects of NO-Cbl alone and in combination with conventional chemotherapeutic agents, and to 2) examine the mechanism of action of NO-Cbl as a single agent and in combination therapy.Using anti-proliferative assays, electrophoretic mobility shift assay (EMSA), immunoblot analysis and kinase assays, we demonstrate an increase in the effectiveness of chemotherapeutic agents in combination with NO-Cbl as a result of suppressed NF-kappaB activation.Eighteen chemotherapeutic agents were tested in combination with NO-Cbl, in thirteen malignant cell lines, resulting in a synergistic anti-proliferative effect in 78% of the combinations tested. NO-Cbl pre-treatment resulted in decreased NF-kappaB DNA binding activity, inhibition of IkappaB kinase (IKK) enzymatic activity, decreased AKT activation, increased caspase-8 and PARP cleavage, and decreased cellular XIAP protein levels.The use of NO-Cbl to inhibit survival signaling may enhance drug efficacy by preventing concomitant activation of NF-kappaB or AKT

Gene Expression Profile of Neuronal Progenitor Cells Derived from hESCs: Activation of Chromosome 11p15.5 and Comparison to Human Dopaminergic Neurons

BACKGROUND: We initiated differentiation of human embryonic stem cells (hESCs) into dopamine neurons, obtained a purified population of neuronal precursor cells by cell sorting, and determined patterns of gene transcription. METHODOLOGY: Dopaminergic differentiation of hESCs was initiated by culturing hESCs with a feeder layer of PA6 cells. Differentiating cells were then sorted to obtain a pure population of PSA-NCAM-expressing neuronal precursors, which were then analyzed for gene expression using Massive Parallel Signature Sequencing (MPSS). Individual genes as well as regions of the genome which were activated were determined. PRINCIPAL FINDINGS: A number of genes known to be involved in the specification of dopaminergic neurons, including MSX1, CDKN1C, Pitx1 and Pitx2, as well as several novel genes not previously associated with dopaminergic differentiation, were expressed. Notably, we found that a specific region of the genome located on chromosome 11p15.5 was highly activated. This region contains several genes which have previously been associated with the function of dopaminergic neurons, including the gene for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, IGF2, and CDKN1C, which cooperates with Nurr1 in directing the differentiation of dopaminergic neurons. Other genes in this region not previously recognized as being involved in the functions of dopaminergic neurons were also activated, including H19, TSSC4, and HBG2. IGF2 and CDKN1C were also found to be highly expressed in mature human TH-positive dopamine neurons isolated from human brain samples by laser capture. CONCLUSIONS: The present data suggest that the H19-IGF2 imprinting region on chromosome 11p15.5 is involved in the process through which undifferentiated cells are specified to become neuronal precursors and/or dopaminergic neurons

Inhibition of the NF-KB Signaling Pathway and Its Effects on Apoptosis and Cancer

The Rel/NF-kB family of inducible transcription factors are evolutionarily conserved structurally and functionally, from insects to humans. They are ubiquitously expressed in a number of mature cell types, playing a pivotal role regulating cell growth, differentiation and apoptosis. Under normal circumstances, the proliferation of new cells is tightly regulated, as is the programmed lifespan of most cells, occasionally however cells loose their responsiveness to growth control mechanisms, resulting in a tumor or neoplasm. Sustained or chronic inflammation has been linked to a number of pathological conditions that destroy tissue and facilitate neoplastic growth. NF-kB in part mediates the opposing signals of cell survival and cell death, associated with this response. We hypothesized that inhibition of NF-kB would inhibit tumor cell growth. A number of anti-neoplastic drugs like some pro-inflammatory cytokines can activate both the cellular apoptotic and pro-survival (via NF-kB) pathways. We demonstrate, in vitro, that the use of Nitric Oxide mitigates NF-kB activation and induces program cell death, when administered as an adjuvant with this subset of pro-inflammatory cytokines. Secondly, several front-line anti-cancer drugs activate NF-kB as a result of their mode of action, resulting in the survival of a resistant population of tumor cells. In order to abrogate this beneficial activity for the tumor cell we explore, both in vitro and in vivo, the use of Nitric Oxide to inhibit NF-kB, augmenting the efficacy of the anti-neoplastic drugs. Thirdly, we identify that the intracellular signaling kinase, Inositol Hexkisphosphate Kinase2 (IHPK2) , binds to a key component in the NF-kB signaling pathway, inhibiting NF-kB activity promoting apoptosis in tumor cells. Lastly, an in depth study investigating the major initiator of pro-inflammatory signaling during bacterial infection of cells by Salmonela sp. was in fact due to recognition of the bacterial protein flagellin by the cell surface receptor Toll-like recepto

Western blot analysis of phospho-AKT.

<p>Cells were pre-treated with NO-Cbl (300 µM, 16 h) followed by doxorubicin (20 µM, 4 h) or cisplatin (20 µM, 1 h) or 5 flurouracil (5-FU, 100 µM, 5 h) or etoposide (20 µM, 4 h) or paclitaxel (20 µΜ, 5 h). Whole cell lysates were probed with anti-phospho-AKT and then re-probed with anti-AKT (unphosphorylated) which served as a loading control.</p

IκB kinase (IKK) activity. IKK activity was assessed using recombinant GST-IκBα(1-54) and γ³²P-ATP as substrates.

<p>The phosphorylated GST fusion protein was detected by autoradiography. IKK activity was determined in cells that were pre-treated with NO-Cbl (300 µM, 16 h) followed by doxorubicin (20 µM, 4 h) or cisplatin (20 µM, 1 h) or 5 flurouracil (5-FU, 100 µM, 5 h) or etoposide (20 µM, 4 h) or paclitaxel (20 µΜ, 5 h). Anti-β-actin antibody was used as an irrelevant antibody control for immunoprecipitation and yielded no signal. After exposure to film, the gel was stained with Coomassie blue to visualize total protein and demonstrated equal loading of the GST-IκBα(1-54) substrate. The same cell extracts were probed for total IKK by immunoblot analysis and demonstrated equal loading of IKK.</p