NF- kappa B2/p100 induces Bcl-2 expression

Pharmacological inhibitors of NF-kappaB accelerate apoptosis in chronic lymphocytic leukaemia cells

Nuclear factor-kappaB (NF-kappaB) is a transcription factor that plays a critical role in the inappropriate survival of various types of malignant cells. Chronic lymphocytic leukaemia (CLL) is the most common B-cell malignancy in the Western world. Although overexpression and regulation of NF-kappaB has been described in CLL, its function remains unclear. Exposure of CLL cells to BAY117082 or Kamebakaurin, potent pharmacological inhibitors of the NF-kappaB pathway, accelerated apoptosis in approximately 70% of cases. Sensitivity to NF-kappaB pathway inhibitors was not related to the prognostic markers VH status, CD38 or Zap70 expression, or to the levels of nuclear NF-kappaB. Normal peripheral B cells were resistant to the apoptosis-inducing effects of these compounds. Cell death induced by the inhibitors was associated with activation of caspase-9 and -3, and loss of mitochondrial membrane polarization, but did not involve changes in the expression of Bcl-2 or Mcl-1. Inhibitors caused an increase in c-jun NH2-terminal kinase activity in CLL, but this did not appear to be important for apoptosis. Microarray analysis identified some potential novel NF-kappaB target genes, including interleukin-16- and the Bcl-2- related survival protein Bcl-w. These results demonstrate that a substantial proportion of CLL are dependent on NF-kappaB for enhanced survival and suggest that inhibition of NF-kappaB may have therapeutic potential.

BAFF, APRIL and their receptors: structure, function and signaling

BAFF, APRIL and their receptors play important immunological roles, especially in the B cell arm of the immune system. A number of splice isoforms have been described for both ligands and receptors in this subfamily, some of which are conserved between mouse and human, while others are species-specific. Structural and mutational analyses have revealed key determinants of receptor-ligand specificity. BAFF-R has a strong selectivity for BAFF; BCMA has a higher affinity for APRIL than for BAFF, while TACI binds both ligands equally well. The molecular signaling events downstream of BAFF-R, BCMA and TACI are still incompletely characterized. Survival appears to be mediated by upregulation of Bcl-2 family members through NF-kappaB activation, degradation of the pro-apototic Bim protein, and control of subcellular localization of PCKdelta. Very little is known about other signaling events associated with receptor engagement by BAFF and APRIL that lead for example to B cell activation or to CD40L-independent Ig switch.

Hepatocyte growth factor protects human endothelial cells against advanced glycation end products-induced apoptosis

Advanced glycation end products (AGEs) form by a non-enzymatic reaction between reducing sugars and biological proteins, which play an important role in the pathogenesis of atherosclerosis. In this study, we assessed AGEs effects on human umbilical vein endothelial cells (HUVECs) growth, proliferation and apoptosis. Additionally, we investigated whether hepatocyte growth factor (HGF), an anti-apoptotic factor for endothelial cells, prevents AGEs-induced apoptosis of HUVECs. HUVECs were treated with AGEs in the presence or absence of HGF. Treatment of HUVECs with AGEs changed cell morphology, decreased cell viability, and induced DNA fragmentation, leading to apoptosis. Apoptosis was induced by AGEs in a dose- and time-dependent fashion. AGEs markedly elevated Bax and decreased NF-kappaB, but not Bcl-2 expression. Additionally, AGEs significantly inhibited cell growth through a pro-apoptotic action involving caspase-3 and -9 activations in HUVECs. Most importantly, pretreatment with HGF protected against AGEs-induced cytotoxicity in the endothelial cells. HGF significantly promoted the expression of Bcl-2 and NF-kappaB, while decreasing the activities of caspase-3 and -9 without affecting Bax level. Our data suggest that AGEs induce apoptosis in endothelial cells. HGF effectively attenuate AGEs-induced endothelial cell apoptosis. These findings provide new perspectives in the role of HGF in cardiovascular disease.

Predicting which children are at risk for ependymoma relapse

Ependymomas account for 6-12% of all pediatric intracranial tumors. Despite complete resection and radiation, about 50% of patients relapse and have subsequent dismal prognoses. As no clinical findings reliably forecast tumor recurrence, we sought to determine if gene expression profiling could be used to distinguish patients at high risk for relapse at initial diagnosis, and thereby make them candidates for innovative treatments at an early stage. We extracted RNA from 13 ependymoma specimens: 7 from patients who experienced tumor recurrence, and 6 from patients who have not recurred. RNA was applied to Affymetrix HG-U133 plus 2.0 microarray chips, and microarrays were analyzed with GeneSpring 7.0 and Prediction Analysis of Microarrays (PAM) software. The 3-gene subset of PLEK (pleckstrin), NF-kappaB2 (nuclear factor kappa beta-2), and LOC374491 (TPTE and PTEN homologous inositol phosphatase pseudogene) was identified as the minimal subset capable of accurately distinguishing tumors according to recurrence. In summary, gene expression profiling may be valuable, perhaps in combination with clinical findings identified in some studies, for identifying children at high risk for ependymoma relapse.

Expression of the Bcl-3 proto-oncogene suppresses p53 activation

While Bcl-3 expression in cancer was originally thought to be limited to B-cell lymphomas with a 14;19 chromosomal translocation, more recent evidence indicates that expression of this presumptive oncoprotein is significantly more widespread in cancer. However, an oncogenic role for Bcl-3 has not been clearly identified. Experiments presented here indicate that Bcl-3 is inducible by DNA damage and is required for the induction of Hdm2 gene expression and the suppression of persistent p53 activity. Furthermore, constitutive expression of Bcl-3 suppresses DNA damage-induced p53 activation and inhibits p53-induced apoptosis through a mechanism that is at least partly dependent on the up-regulation of Hdm2. The results provide insight into a mechanism whereby altered expression of Bcl-3 leads to tumorigenic potential. Since Bcl-3 is required for germinal center formation, these results suggest functional similarities with the unrelated Bcl-6 oncoprotein in suppressing potential p53-dependent cell cycle arrest and apoptosis in response to somatic hypermutation and class switch recombination.

Tumor-derived p53 mutants induce NF-kappaB2 gene expression

Overexpression of mutant p53 is a common theme in tumors, suggesting a selective pressure for p53 mutation in cancer development and progression. To determine how mutant p53 expression may lead to survival advantage in human cancer cells, we generated stable cell lines expressing p53 mutants p53-R175H, -R273H, and -D281G by use of p53-null human H1299 (lung carcinoma) cells. Compared to vector-transfected cells, H1299 cells expressing mutant p53 showed a survival advantage when treated with etoposide, a common chemotherapeutic agent; however, cells expressing the transactivation-deficient triple mutant p53-D281G (L22Q/W23S) had significantly lower resistance to etoposide. Gene expression profiling of cells expressing transcriptionally active mutant p53 proteins revealed the striking pattern that all three p53 mutants induced expression of approximately 100 genes involved in cell growth, survival, and adhesion. The gene NF-kappaB2 is a prominent member of this group, whose overexpression in H1299 cells also leads to chemoresistance. Treatment of H1299 cells expressing p53-R175H with small interfering RNA specific for NF-kappaB2 made these cells more sensitive to etoposide. We have also observed activation of the NF-kappaB2 pathway in mutant p53-expressing cells. Thus, one possible pathway through which mutants of p53 may induce loss of drug sensitivity is via the NF-kappaB2 pathway.

The Nuclear Transcription Factor κB/bcl-2 Pathway Correlates with Pathologic Complete Response to Doxorubicin-Based Neoadjuvant Chemotherapy in Human Breast Cancer

PURPOSE

Molecular factors involved in apoptosis may affect breast cancer response to chemotherapy. Herein, we studied the nuclear factor kappaB (NF-kappaB)/bcl-2 pathway to determine whether or not activation of this antiapoptotic pathway was associated with a poor response of human breast cancer to anthracycline-based neoadjuvant chemotherapy.

EXPERIMENTAL DESIGN

We studied 82 human breast cancer samples from patients treated with neoadjuvant doxorubicin-based chemotherapy and studied whether or not nuclear location of the transcription factor NF-kappaB was associated with expression of bcl-2 and bax and whether or not expression of these proteins correlated with chemotherapy response. Protein expression was measured with immunohistochemical staining. A dedicated breast cancer pathologist who was unaware of the clinical outcome data dichotomized the slides as positive or negative based on the presence or absence of cytoplasmic staining for bcl-2 and bax or nuclear staining for NF-kappaB.

RESULTS

Sixty-one percent of the tumors were positive for bcl-2, 85% were positive for bax, and 16% were positive for NF-kappaB. All bcl-2-positive tumors were also bax positive (P < 0.0001) and all NF-kappaB-positive tumors were both bcl-2 positive (P = 0.001) and bax positive (P = 0.113). Eleven of the 82 patients (13%) had a pathologic complete response (pCR) to chemotherapy. Patients with positive staining tumors for any of the markers less commonly achieved a pCR to chemotherapy than those with negative tumor staining. The pCR rates were NF-kappaB positive 0% (0 of 13) versus NF-kappaB negative 13% (11 of 69; P = 0.130); bcl-2 positive 4% (2 of 49) versus bcl-2 negative 27% (9 of 33; P = 0.004); and bax positive 6% (4 of 69) versus bax negative 58% (7 of 12; P < 0.001).

CONCLUSION

We conclude that nuclear localization of NF-kappaB correlates with bcl-2 and bax expression and that the NF-kappaB/bcl-2 pathway may be associated with a poor response to neoadjuvant doxorubicin-based chemotherapy.

Regulation of Bcl-3 through interaction with the Lck tyrosine kinase

bcl-3 is a protooncogene which undergoes chromosomal translocation in a subset of chronic B-cell lymphocytic leukemia cells. Bcl-3 is a unique IkappaB family protein that regulates transcription of a number of NF-kappaB target genes through interactions with NF-kappaB dimers. Based on previous studies, suggesting that Bcl-3 interacts with the Fyn tyrosine kinase in platelets, we investigated possible interactions of Bcl-3 with Lck, a related tyrosine kinase important in lymphoid cells. Protein-protein interactions between Bcl-3 and the Lck tyrosine kinase were identified both in vitro and in vivo. Lck enhanced Bcl-3-mediated activation of a p52/Bcl-3-responsive promoter in reporter gene assays independent of its tyrosine kinase activity, but requiring the Lck SH3 protein interaction domain. These studies suggest that Bcl-3 might participate in oncogenic pathways involving Lck.

Inactivation of nuclear factor kappaB by soy isoflavone genistein contributes to increased apoptosis induced by chemotherapeutic agents in human cancer cells

Cancer chemotherapeutic strategies commonly require multiple agents. However, use of multiple agents contributes to added toxicity resulting in poor treatment outcome. Thus, combination chemotherapy must be optimized to increase tumor response and at the same time lower its toxicity. Chemotherapeutic agents are known to induce nuclear factor kappaB (NF-kappaB) activity in tumor cells, resulting in lower cell killing and drug resistance. In contrast, genistein has been shown to inhibit the activity of NF-kappaB and the growth of various cancer cells without causing systemic toxicity. We therefore investigated whether the inactivation of NF-kappaB by genistein before treatment of various cancer cells with chemotherapeutic agents could lead to better tumor cell killing as tested by in vitro studies using gene transfections and also by animal studies. PC-3 (prostate), MDA-MB-231 (breast), H460 (lung), and BxPC-3 (pancreas) cancer cells were pretreated with 15 to 30 micromol/L genistein for 24 hours and then exposed to low doses of chemotherapeutic agents for an additional 48 to 72 hours. We found that 15 to 30 micromol/L genistein combined with 100 to 500 nmol/L cisplatin, 0.5 to 2 nmol/L docetaxel, or 50 ng/mL doxorubicin resulted in significantly greater inhibition of cell growth and induction of apoptosis compared with either agent alone. Moreover, we found that the NF-kappaB activity was significantly increased within 2 hours of cisplatin and docetaxel treatment and that the NF-kappaB inducing activity of these agents was completely abrogated in cells pretreated with genistein. These results were also supported, for the first time, by animal experiments, p65 cDNA transfection and p65 small interfering RNA studies, which clearly showed that a specific target (NF-kappaB) was affected in vivo. Collectively, our results clearly suggest that genistein pretreatment inactivates NF-kappaB and may contribute to increased growth inhibition and apoptosis induced by cisplatin, docetaxel, and doxorubicin in prostate, breast, lung, and pancreatic cancer cells. Theses results warrant carefully designed clinical studies investigating the combination of soy isoflavones and commonly used chemotherapeutic agents for the treatment of human cancers.

Vav proteins regulate peripheral B-cell survival

Mice lacking all 3 Vav proteins fail to produce significant numbers of recirculating follicular or marginal zone B cells. Those B cells that do mature have shortened lifespans. The constitutive nuclear factor-kappaB (NF-κB) activity of resting naive B cells required Vav function and expression of cellular reticuloendotheliosis (c-Rel). Rel-A was reduced in Vav-deficient B cells. Furthermore, expression of the NF-κB-regulated antiapoptotic genes A1 and Bcl-2 was reduced in mature Vav-deficient B cells. Overexpression of Bcl-2 restored the number of mature follicular B cells in the spleens of Vav-deficient mice. When activated by B-cell receptor (BCR) cross-linking, Vav-deficient B cells failed to activate NF-κB. Vav proteins thus regulate an NF-κB-dependent survival signal in naive B cells and are required for NF-κB function after BCR cross-linking.

Effects of nuclear factor-kappaB inhibitors and its implication on natural killer T-cell lymphoma cells

Natural killer/T-cell lymphoma (NKTL) is a highly aggressive disease. Despite the use of various treatment regimens, the prognosis of NKTL is poor, and new treatment strategies need to be determined. Because of the significant survival potential, nuclear factor (NF)-kappaB has become one of the major targets for drug development. In this study, we explored the effect and action mechanism of NF-kappaB inhibitors, BAY 11-7082 and curcumin, on NKTL cell lines (NKL, NK-92 and HANK1). Electrophoretic mobility shift assay showed that NF-kappaB was constitutively active in HANK1, a chemoresistant cell line. BAY 11-7082 and curcumin suppressed NF-kappaB activation in a time- and dose-dependent manner, which finally resulted in cell death. BAY 11-7082- and curcumin-induced cell death was associated with downregulation of Bcl-xL, cyclin D1, XIAP and c-FLIP, followed by caspase-8, poly(ADP-ribose) polymerase cleavage and activation. Given that the chemoresistant NK-92 cells respond to NF-kappaB inhibitors but not to conventional drugs, BAY 11-7082 and curcumin could be potentially useful for achieving improved outcome in chemotherapy-refractory NKTL.

Histone deacetylase inhibition down-regulates cyclin D1 transcription by inhibiting nuclear factor-kappaB/p65 DNA binding

Histone deacetylase (HDAC) inhibitors are emerging as a promising new class of cancer therapeutic agents. HDAC inhibitors relieve the deacetylation of histone proteins. However, little is known about the nonhistone targets of HDAC inhibitors and their roles in gene regulation. In this study, we addressed the molecular basis of the down-regulation of the nuclear factor-kappaB (NF-kappaB)-responsive gene cyclin D1 by the HDAC inhibitor trichostatin A in mouse JB6 cells. Cyclin D1 plays a critical role in cell proliferation and tumor progression. Trichostatin A inhibits cyclin D1 expression in a NF-kappaB-dependent manner in JB6 cells. Electrophoretic mobility shift assay studies showed that trichostatin A treatment prevents p65 dimer binding to NF-kappaB sites on DNA. Moreover, a chromatin immunoprecipitation assay shows that trichostatin A treatment inhibits endogenous cyclin D1 gene transcription by preventing p65 binding to the cyclin D1 promoter. However, acetylation of p65 is not affected by trichostatin A treatment. Instead, trichostatin A enhances p52 acetylation and increases p52 protein level by enhancing p100 processing. This is the first report that trichostatin A, a HDAC inhibitor, activates p100 processing and relieves the repression of p52 acetylation. The enhanced acetylation of p52 in the nuclei may operate to cause nuclear retention of p65 by increasing the p52/p65 interaction and preventing IkappaBalpha-p65 binding. The enhanced p52 acetylation coincides with decreased p65 DNA binding, suggesting a potential role of p52 acetylation in NF-kappaB regulation. Together, the results provide the first demonstration that HDAC inhibitor trichostatin A inhibits cyclin D1 gene transcription through targeting transcription factor NF-kappaB/p65 DNA binding. NF-kappaB is therefore identified as a transcription factor target of trichostatin A treatment.

Genes, pathways and checkpoints in lymphocyte development and homeostasis

A plethora of genes involved in murine B and T cell development have been identified, and developmental pathways within the primary lymphoid tissues have been well delineated. The generation of a functional, but non-self reacting lymphocyte repertoire results from the completion of several checkpoints during lymphocyte development and competition for survival factors in the periphery. Improved knowledge of these developmental checkpoints and homeostatic mechanisms is critical for understanding human immunodeficiency, leukaemia/lymphoma and autoimmunity, which are conditions where checkpoints and homeostasis are likely to be deregulated.

Sodium phenylbutyrate prolongs survival and regulates expression of anti-apoptotic genes in transgenic amyotrophic lateral sclerosis mice

Multiple molecular defects trigger cell death in amyotrophic lateral sclerosis (ALS). Among these, altered transcriptional activity may perturb many cellular functions, leading to a cascade of secondary pathological effects. We showed that pharmacological treatment, using the histone deacetylase inhibitor sodium phenylbutyrate, significantly extended survival and improved both the clinical and neuropathological phenotypes in G93A transgenic ALS mice. Phenylbutyrate administration ameliorated histone hypoacetylation observed in G93A mice and induced expression of nuclear factor-kappaB (NF-kappaB) p50, the phosphorylated inhibitory subunit of NF-kappaB (pIkappaB) and beta cell lymphoma 2 (bcl-2), but reduced cytochrome c and caspase expression. Curcumin, an NF-kappaB inhibitor, and mutation of the NF-kappaB responsive element in the bcl-2 promoter, blocked butyrate-induced bcl-2 promoter activity. We provide evidence that the pharmacological induction of NF-kappaB-dependent transcription and bcl-2 gene expression is neuroprotective in ALS mice by inhibiting programmed cell death. Phenylbutyrate acts to phosphorylate IkappaB, translocating NF-kappaB p50 to the nucleus, or to directly acetylate NF-kappaB p50. NF-kappaB p50 transactivates bcl-2 gene expression. Up-regulated bcl-2 blocks cytochrome c release and subsequent caspase activation, slowing motor neuron death. These transcriptional and post-translational pathways ultimately promote motor neuron survival and ameliorate disease progression in ALS mice. Phenylbutyrate may therefore provide a novel therapeutic approach for the treatment of patients with ALS.

p21WAF1 modulates NF-kappaB signaling and induces anti-apoptotic protein Bcl-2 in Tax-expressing rat fibroblast

Of the cell cycle-associated genes regulated by human T-cell leukemia virus type-1 (HTLV-1) Tax, cyclin-dependent kinase (CDK) inhibitor p21WAF1 is upregulated in HTLV-1-infected cells. Previously, we reported that p21WAF1 stimulated Tax-dependent NF-kappaB activation which influences a variety of cellular processes, including proliferation, differentiation, and apoptosis. In HTLV-1-infected cells, Tax is primarily involved in the constitutive activation of NF-kappaB signaling. Here, we demonstrate that p21WAF1 affects Tax-dependent NF-kappaB signaling by inducing p100/52, an NF-kappaB-related protein. W4, a Tax-transformed rat fibroblast cell line, exhibits the constitutive activation of NF-kappaB signaling, potentially mediated by overexpression of RelB. Ectopic expression of p21WAF1 in W4 cells, which lack endogenous expression due to methylation of the p21WAF1 promoter, induces the expression of p100/52. Bcl-2 expression was also upregulated by ectopic p21WAF1 in this cell line, suggesting that p21WAF1 plays an important role in the regulation of apoptosis by modulating NF-kappaB signaling in Tax-expressing rat fibroblasts. We also address the expression of NF-kappaB-related proteins in HTLV-1-infected cells.

Down-regulation of Bcl-2 enhances estrogen apoptotic action in long-term estradiol-depleted ER+ breast cancer cells

Postmenopausal women with estrogen receptor positive (ER(+)) breast cancer frequently respond paradoxically to estrogen administration with tumor regression. Using both LTED and E8CASS cells derived from MCF-7 breast cancer cells by long-term estrogen-deprivation, we previously reported that 17beta -estradiol (estradiol) is a powerful, pro-apoptotic hormone which kills the cancer cells through activation of the Fas/FasL death receptor pathway. We postulated that the mitochondrial interactive protein Bcl-2 might play a role in the regulation of estradiol-induced apoptosis in both LTED and E8CASS cells. In this study, we assessed estradiol effects on cell growth, proliferation and apoptosis. Additionally we investigated the effect of estradiol on caspase activation, NF-KB and Bcl-2 expression. The functional role of Bcl-2 in estradiol-induced apoptosis was further studied by knockdown or decrease of Bcl-2 with siRNA. Our results show that estradiol significantly inhibited cell growth primarily through a pro-apoptotic action involving caspase-7 and 9 activations (p < 0.01). Basal Bcl-2 and NF-KB levels were greatly elevated and estradiol decreased NF-KB, but not Bcl-2 expression. Knockdown of Bcl-2 expression with siRNA decreased the levels of this protein by 9 fold (p < 0.01). This reduction markedly sensitized both LTED and E8CASS cells to the pro-apoptotic action of estradiol, leading to a synergistic induction of apoptosis and a concomitant reduction in cell number (p < 0.01). Therefore, down-regulation of Bcl-2 synergistically enhanced estradiol-induced apoptosis in ER(+) postmenopausal breast cancer cells.

NF-kappaB inhibition radiosensitizes Ki-Ras-transformed cells to ionizing radiation

Most cancer cells show resistance to ionizing radiation (IR)-induced cell death. Recently, Ki-Ras was reported to be responsible for the increased radioresistance. We report here that inhibition of IR-induced activaton of nuclear transcription factor kappa B (NF-kappaB) but not of either Akt or MAPK kinase (MEK), increased the radiosensitization of Ki-Ras transformed human prostate epithelial 267B1/K-ras cells. Proteosome inhibitor-1 (Pro1) reduced NF-kappaB activation, and this inhibition was accompanied by increased levels of cytoplasmic IkappaBalpha and p65/RelA. However, translocation of p50/NF-kappaB1 did not occur on exposure to IR, suggesting the cell-specific involvement of p50 in radiation signaling. Clonogenic cell survival and soft agar assays further confirmed the increased radiosensitivity of 267B1/K-ras cells by proteosome inhibition. In addition, proteosome inhibition enhanced the IR-induced degradation of apoptotic protein caspases 8 and 3, with the level of antiapoptotic protein Bcl-2 being unaffected, suggesting the involvement of an apoptotic process in IR-induced cell death of 267B1/K-ras cells. LY294002 and PD98059, specific inhibitors of phosphatidylinositol-3-kinase (PI3K) and MEK, respectively however, did not affect the radiosensitization. All these results suggest an application of blocking NF-kappaB activation pathway to the development of anticancer therapeutics in IR-induced radiotherapy of Ki-Ras-transformed cancer cells.

Variability in the degree of expression of phosphorylated IkappaBalpha in chronic lymphocytic leukemia cases with nodal involvement

PURPOSE

Based on previous preliminary observations, we hypothesize that the molecular and clinical variability of chronic lymphocytic leukemia (CLL) reflects differences in the degree of nuclear factor (NF)-kappaB activation, as determined by the expression of phosphorylated IkappaBalpha (p-IkappaBalpha).

EXPERIMENTAL DESIGN

The expression profile (mRNA and protein expression) was analyzed with the Centro Nacional de Investigaciones Oncologicas Oncochip, a cDNA microarray containing 6386 cancer-related genes, and a tissue microarray (TMA). The results were correlated with the IgV(H) mutational status, ZAP-70 expression, cytogenetic alterations, and clinical outcome.

RESULTS

We found correlations between the presence of p-IkappaBalpha, a surrogate marker of NF-kappaB activation, and changes in the expression profile (mRNA and protein expression) and clinical outcome in a series of CLL cases with lymph node involvement. Activation of NF-kappaB, as determined by the expression of p-IkappaBalpha, was associated with the expression of a set of genes comprising key genes involved in the control of B-cell receptor signaling, signal transduction, and apoptosis, including SYK, LYN, BCL2, CCR7, BTK, PIK3CD, and others. Cases with increased expression of p-IkappaBalpha showed longer overall survival than cases with lower expression. A Cox regression model was derived to estimate some parameters of prognostic interest: IgV(H) mutational status, ZAP-70, and p-IkappaBalpha expression. The multivariate analysis disclosed p-IkappaBalpha and ZAP-70 expression as independent prognostic factors of survival.

CONCLUSIONS

A variable degree of activation of NF-kappaB, as determined by the expression of p-IkappaBalpha, is an identifiable event in CLL, and is correlated with changes in the expression profile and overall survival.

Targeting BCL-2 overexpression in various human malignancies through NF-kappaB inhibition by the proteasome inhibitor bortezomib

BACKGROUND

BCL-2 overexpression occurs in many cancer types and is associated with chemoresistance and radioresistance. The mechanisms responsible for its aberrant expression are thought to be transcriptionally mediated but remain unclear. We examined the cell type-specific mechanism of BCL-2 gene transcription in various solid organ malignancies.

METHODS

Regulation of BCL-2 gene transcription was examined in seven different human cancer cell lines including two pancreatic (MIA-PaCa-2, PANC-1), two prostate (LNCaP, PC-3), two lung (Calu-1, A549) and one breast (MCF-7) cancer cell line. Cells were treated with inhibitors of phosphatidylinositol-3 kinase (PI3K), MEK/ERK, and p38MAPK. The effect of mutation of a NF-kappaB site in the BCL-2 promoter was determined, as was the effect of inhibition of NF-kappaB function using a 26S proteasome inhibitor (bortezomib) on both BCL-2 transcription and induction of apoptosis.

RESULTS

BCL-2 expression varied both between and within tumor types; four of seven cell lines demonstrated high BCL-2 levels (MIA-PaCa-2, PC-3, Calu-1 and MCF-7). No signaling pathway was uniformly responsible for overexpression of BCL-2; however, mutation of the NF-kappaB site decreased BCL-2 promoter activity in all cell lines. Inhibition of NF-kappaB activity decreased BCL-2 protein levels independently of the signaling pathway involved in transcriptional activation of the BCL-2 gene.

CONCLUSIONS

Diverse signaling pathways variably regulate BCL-2 gene expression in a cell type-specific fashion. Therapy to decrease BCL-2 levels in various human cancers would be more broadly applicable if targeted to transcriptional activation rather than signal transduction cascades. Finally, the apoptotic efficacy of proteasome inhibition with bortezomib paralleled the ability to inhibit NF-kappaB activity and decrease BCL-2 levels.

GSK3-mediated BCL-3 phosphorylation modulates its degradation and its oncogenicity

The oncoprotein BCL-3 is a nuclear transcription factor that activates NF-kappaB target genes through formation of heterocomplexes with p50 or p52. BCL-3 is phosphorylated in vivo, but specific BCL-3 kinases have not been identified so far. In this report, we show that BCL-3 is a substrate for the protein kinase GSK3 and that GSK3-mediated BCL-3 phosphorylation, which is inhibited by Akt activation, targets its degradation through the proteasome pathway. This phosphorylation modulates its association with HDAC1, -3, and -6 and attenuates its oncogenicity by selectively controlling the expression of a subset of newly identified target genes such as SLPI and Cxcl1. Our results therefore suggest that constitutive BCL-3 phosphorylation by GSK3 regulates BCL-3 turnover and transcriptional activity.

Functions of NF-kappaB1 and NF-kappaB2 in immune cell biology

Two members of the NF-kappaB (nuclear factor kappaB)/Rel transcription factor family, NF-kappaB1 and NF-kappaB2, are produced as precursor proteins, NF-kappaB1 p105 and NF-kappaB2 p100 respectively. These are proteolytically processed by the proteasome to produce the mature transcription factors NF-kappaB1 p50 and NF-kappaB2 p52. p105 and p100 are known to function additionally as IkappaBs (inhibitors of NF-kappaB), which retain associated NF-kappaB subunits in the cytoplasm of unstimulated cells. The present review focuses on the latest advances in research on the function of NF-kappaB1 and NF-kappaB2 in immune cells. NF-kappaB2 p100 processing has recently been shown to be stimulated by a subset of NF-kappaB inducers, including lymphotoxin-beta, B-cell activating factor and CD40 ligand, via a novel signalling pathway. This promotes the nuclear translocation of p52-containing NF-kappaB dimers, which regulate peripheral lymphoid organogenesis and B-lymphocyte differentiation. Increased p100 processing also contributes to the malignant phenotype of certain T- and B-cell lymphomas. NF-kappaB1 has a distinct function from NF-kappaB2, and is important in controlling lymphocyte and macrophage function in immune and inflammatory responses. In contrast with p100, p105 is constitutively processed to p50. However, after stimulation with agonists, such as tumour necrosis factor-alpha and lipopolysaccharide, p105 is completely degraded by the proteasome. This releases associated p50, which translocates into the nucleus to modulate target gene expression. p105 degradation also liberates the p105-associated MAP kinase (mitogen-activated protein kinase) kinase kinase TPL-2 (tumour progression locus-2), which can then activate the ERK (extracellular-signal-regulated kinase)/MAP kinase cascade. Thus, in addition to its role in NF-kappaB activation, p105 functions as a regulator of MAP kinase signalling.

Control of T cell viability

The factors affecting T cell viability vary depending on the type and status of the T cell involved. Naive T cells die via a Bcl-2/Bim dependent route. Their deaths are prevented in animals by IL-7 and contact with MHC. Activated T cells die in many different ways. Among these is a pathway involving signals that come from outside the T cell and affect it via surface receptors such as Fas. Activated T cells also die through a pathway driven by signals generated within the T cell itself, a cell autonomous route. This pathway involves members of the Bcl-2 family, in particular Bcl-2, Bcl-xl, Bim, and probably Bak. The viability of CD8+ and CD4+ memory T cells is controlled in different ways. CD8+ memory T cells are maintained by IL-15 and IL-7. The control of CD4+ memory T cells is more mysterious, with roles reported for IL-7 and/or contact via the TCR.

Novel molecular diagnostic and therapeutic targets in chronic lymphocytic leukaemia

B-cell lymphocytic leukaemia (B-CLL) is an indolent non-Hodgkin's lymphoma and the most frequent leukaemia. However, after many years, the incurable disease CLL has again become an exciting subject for research. Recently, both serum and molecular markers have been identified which could be used to predict the outcome of patients in early stages. With the advent of microarray analysis, novel diagnostic and therapeutic targets have been discovered. Here we describe the molecular strategies for target identification and validation. An evaluation of some established, and the most promising novel factors, with their diagnostic and prognostic applications is given. Potential therapeutic target molecules and their inhibitors are reviewed.

Epstein-Barr virus-encoded latent infection membrane protein 1 regulates the processing of p100 NF-kappaB2 to p52 via an IKKgamma/NEMO-independent signalling pathway

The oncogenic Epstein-Barr virus (EBV)-encoded latent infection membrane protein 1 (LMP1) constitutively activates the 'canonical' NF-kappaB pathway that involves the phosphorylation and degradation of IkappaBalpha downstream of the IkappaB kinases (IKKs). In this study, we show that LMP1 also promotes the proteasome-mediated proteolysis of p100 NF-kappaB2 resulting in the generation of active p52, which translocates to the nucleus in complex with the p65 and RelB NF-kappaB subunits. LMP1-induced NF-kappaB transactivation is reduced in nf-kb2(-/-) mouse embryo fibroblasts, suggesting that p100 processing contributes to LMP1-mediated NF-kappaB transcriptional effects. This pathway is likely to operate in vivo, as the expression of LMP1 in primary EBV-positive Hodgkin's lymphoma and nasopharyngeal carcinoma biopsies correlates with the nuclear accumulation of p52. Interestingly, while the ability of LMP1 to activate the canonical NF-kappaB pathway is impaired in cells lacking IKKgamma/NEMO, the regulatory subunit of the IKK complex, p100 processing remains unaffected. As a result, nuclear translocation of p52, but not p65, occurs in the absence of IKKgamma. These data point to the existence of a novel signalling pathway that regulates NF-kappaB in LMP1-expressing cells, and may thereby play a role in both oncogenic transformation and the establishment of persistent EBV infection.

Nuclear factor-κB as a predictor of treatment response in breast cancer

PURPOSE OF REVIEW

To examine the links of nuclear factor-kappa B (NF-kappa B) to treatment-induced signaling in breast cancer and to propose further studies to elucidate the role of NF-kappa B in breast cancer response to chemotherapy and radiation.

RECENT FINDINGS

The authors' group and others have investigated the clinical relevance of ubiquitously expressed NF-kappa B in breast cancer. Possibly through its effects on apoptosis, NF-kappa B has been implicated in tumor resistance to chemotherapy and radiation in many types of tumors. Furthermore, both in vitro and in vivo studies have shown that targeted inhibition of NF-kappa B can sensitize tumor cells to chemotherapy and radiation.

SUMMARY

The molecular mechanisms involved in chemotherapy-induced and radiation-induced cell death in breast cancer are not fully known, nor are the mechanisms of treatment resistance. NF-kappa B is a transcription factor for a number of genes involved in tumor progression and resistance to systemic therapies and is a major regulator of the apoptotic pathway. Gaining further insights into molecular factors such as NF-kappa B as biomarkers for treatment response may help clinicians predict treatment outcome and lead to the development of targeted therapeutics.

Oncogenes, tumor suppressors and p52 NF-κB

A role for the p52 NF-kappaB subunit in tumorigenesis has been steadily emerging since its discovery as a gene associated with chromosomal translocations in B- and T-cell lymphomas. Now Eliopoulos and co-workers have extended these studies to examine the effect of the Epstein-Barr virus (EBV)-encoded latent infection membrane protein 1 (LMP1) on p52. They find that LMP1 stimulates the processing of p100 to p52 NF-kappaB. Moreover, nuclear p52 is also associated with LMP1 expression in tumor tissue biopsies. They also demonstrate that the pathway leading to p100/p52 processing is distinct from that engaged by LMP1 to activate other NF-kappaB subunits through IkappaBalpha degradation. A clearer picture is now developing of the important role that p52 NF-kappaB plays during normal cell growth and how subverting its function can contribute to oncogenesis.