Screening and detection of apoptosis

Since programmed cell death was first described by the electron microscopic cellular changes demonstrating an organized form of cell death over 30 years ago, it has undergone a great deal of scrutiny as a potential target for several diseases including cancer. The techniques for the study of apoptosis have evolved accordingly. Methodologies for the study of apoptosis were examined by a MEDLINE search of the English-language literature and are summarized in this review. This review discusses the various ways to study apoptosis with specific assays, reagents, and molecules. The particular advantages and disadvantages of each method are reviewed.

Involvement of the TNF-α autocrine–paracrine loop, via NF-κB and YY1, in the regulation of tumor cell resistance to Fas-induced apoptosis

Many tumors are resistant to Fas ligand (FasL)-induced apoptosis. This study examined the role of tumor-derived TNF-alpha, via an autocrine/paracrine loop, in the regulation of tumor-cell resistance to FasL-induced apoptosis. We have reported that Fas expression and sensitivity to FasL is negatively regulated by the transcription repressor factor Yin Yang 1 (YY1). Thus, we hypothesized that tumor-derived TNF-alpha induces the activation of NF-kappaB and the transcription repressor YY1, both of which negatively regulate Fas expression and sensitivity to FasL-induced apoptosis. This hypothesis was tested in PC-3 prostate cancer cells which synthesize and secrete TNF-alpha and express constitutively active NF-kappaB and YY1. Treatment of PC-3 cells with TNF-alpha (10 units) resulted in increased NF-kappaB and YY1 DNA-binding activity, upregulation of YY1 expression, downregulation of surface and total Fas expression and enhanced resistance of PC-3 to apoptosis induced by the FasL agonist antibody CH-11. In contrast, blocking the binding of secreted TNF-alpha on PC-3 cells with soluble recombinant sTNF-RI resulted in significant inhibition of constitutive NF-kappaB and YY1 DNA-binding activity, downregulation of YY1 expression, upregulation of Fas expression and sensitization of tumor cells to CH-11-induced apoptosis. The regulation of YY1 expression and activity by NF-kappaB was demonstrated by the use of the NF-kappaB inhibitor Bay 11-7085 and by the use of a GFP reporter system whereby deletion of the YY1-tandem binding site in the promoter significantly enhanced GFP expression. The direct role of YY1 expression in the regulation of PC-3 resistance to CH-11-induced apoptosis was shown in cells transfected with siRNA YY1 whereby such cells exhibited upregulation of Fas expression and were sensitized to CH-11-induced apoptosis. These findings demonstrate that the TNF-alpha autocrine-paracrine loop is involved in the constitutive activation of the transcription factors NF-kappaB and YY1 in the tumor cells and this loop leads to inhibition of Fas expression and resistance to FasL-induced apoptosis. Further, these findings identify new targets such as TNF-alpha, NF-kappaB and YY1, whose inhibition can reverse tumor cell resistance to FasL-mediated apoptosis.

Inhibition of the transcription factor Yin Yang 1 activity by S-nitrosation

Treatment of several prostate cancer (CaP) cell lines (PC-3, CL-1, and DU-145) with the nitric oxide (NO) donor DETA/NONOate upregulated Fas expression and sensitized the CaP cells to the Fas ligand CH-11 agonist monoclonal antibody-induced apoptosis. Previous findings demonstrated that the transcription repressor Yin Yang 1 (YY1), which is inhibited by NO, negatively regulates Fas transcription [H.J. Garban, B. Bonavida, Nitric oxide inhibits the transcription repressor Yin-Yang 1 binding activity at the silencer region of the Fas promoter: a pivotal role for nitric oxide in the upregulation of Fas gene expression in human tumor cells, J. Immunol. 167 (2001) 75-81]. YY1 is a zinc finger protein and thus, we hypothesized that NO inhibits YY1 activity via S-nitrosation of critical cysteines residues coordinated by Zn2+. Treatment of PC-3 cells with DETA/NONOate inhibited the constitutive DNA-binding activity of YY1 as assessed by EMSA. Further, treatment with DETA/NONOate resulted in S-nitrosation of YY1 as detected by two different methods. The DAN-based method examined NO-treated tumor-derived cell lysates that were immunoprecipitated with an anti-YY1 specific antibody and the NO released was determined quantitatively by fluorometry. The second method consisted of immunoprecipitation of the tumor cell lysates by an anti-SNO cysteine antibody and the immunoprecipitate was immunoblotted with anti-YY1 antibody. Both methods revealed significant S-nitrosation of YY1 by DETA/NONOate treatment over control untreated cells. The S-nitrosation of YY1 was further corroborated by immunohistochemistry using dual color immunofluorescence. The direct role of YY1 in the negative regulation of Fas expression was demonstrated by transfection of cells with siRNA YY1. The transfectants exhibited upregulation of Fas expression in the absence of treatment with DETA/NONOate and were sensitized to CH-11-induced apoptosis. Altogether, these findings reveal that NO inhibits YY1 DNA-binding activity through S-nitrosation and consequently results in upregulation of Fas expression and tumor cell sensitization to Fas-induced apoptosis.

Rituximab (chimeric anti-CD20) sensitizes B-NHL cell lines to Fas-induced apoptosis

Rituximab (chimeric anti-CD20 monoclonal antibodies) is currently being used in the treatment of B non-Hodgkin's lymphoma (NHL). We have recently reported that rituximab triggers and modifies various intracellular signaling pathways in NHL B-cell lines, resulting in reverting the chemoresistant phenotype to a sensitive phenotype. This study investigated whether rituximab also modifies intracellular signaling pathways resulting in the sensitization of NHL cells to Fas-induced apoptosis. Treatment of the Fas-resistant NHL cell lines (2F7, Ramos and Raji) with rituximab sensitized the cells to CH-11 (FasL agonist mAb)-induced apoptosis and synergy was achieved. Fas expression was upregulated by rituximab as early as 6 h post-treatment as determined by flow cytometry, reverse transcriptase-polymerase chain reaction and Western blot. Rituximab inhibited both the expression and activity of the transcription repressor Yin-Yang 1 (YY1) that negatively regulates Fas transcription. Inhibition of YY1 resulted in the upregulation of Fas expression and sensitization of the tumor cells to CH-11-induced apoptosis. The downregulation of YY1 expression was the result of rituximab-induced inhibition of both the p38 mitogen-activated protein kinase (MAPK) signaling pathway and constitutive nuclear factor kappa of B cells (NF-kappaB) activity. The involvement of NF-kappaB and YY1 in the regulation of Fas expression was corroborated by the use of Ramos cells with a dominant-active inhibitor of NF-kappaB (Ramos IkappaB-estrogen receptor (ER) mutant) and by silencing YY1 with YY1 siRNA, respectively. Further, the role of rituximab-mediated inhibition of the p38 MAPK/NF-kappaB/YY1 pathway in the regulation of Fas and sensitization to CH-11-induced apoptosis was validated by the use of specific chemical inhibitors of this pathway and which mimicked rituximab-mediated effects. These findings provide a novel mechanism of rituximab-mediated activity by sensitizing NHL cells to Fas-induced apoptosis.

Rituximab-Induced Inhibition of YY1 and Bcl-xLExpression in Ramos Non-Hodgkin’s Lymphoma Cell Line via Inhibition of NF-κB Activity: Role of YY1 and Bcl-xLin Fas Resistance and Chemoresistance, Respectively

Rituximab treatment of B non-Hodgkin's lymphoma (NHL) cell lines inhibits the constitutive NF-kappaB activity and results in the sensitization of tumor cells to both chemotherapy and Fas-induced apoptosis. Cells expressing dominant active IkappaB or treated with NF-kappaB-specific inhibitors were sensitive to both drugs and Fas agonist mAb (CH-11)-induced apoptosis. Down-regulation of Bcl-xL expression via inhibition of NF-kappaB activity correlated with chemosensitivity. The direct role of Bcl-xL in chemoresistance was demonstrated by the use of Bcl-xL-overexpressing Ramos cells, Ramos hemagglutinin (HA)-Bcl-x, which were not sensitized by rituximab to drug-induced apoptosis. However, inhibition of Bcl-xL in Ramos HA-Bcl-x resulted in sensitization to drug-induced apoptosis. The role of Bcl-xL expression in the regulation of Fas resistance was not apparent; Ramos HA-Bcl-x cells were as sensitive as the wild type to CH-11-induced apoptosis. Several lines of evidence support the direct role of the transcription repressor yin-yang 1 (YY1) in the regulation of resistance to CH-11-induced apoptosis. Inhibition of YY1 activity by either rituximab or the NO donor DETANONOate or after transfection with YY1 small interfering RNA resulted in up-regulation of Fas expression and sensitization to CH-11-induced apoptosis. These findings suggest two mechanisms underlying the chemosensitization and immunosensitization of B-NHL cells by rituximab via inhibition of NF-kappaB. The regulation of chemoresistance by NF-kappaB is mediated via Bcl-xL expression, whereas the regulation of Fas resistance by NF-kappaB is mediated via YY1 expression and activity. The potential clinical significance of these findings is discussed.

Expression of transcription factor Yin Yang 1 in prostate cancer

The transcription repressor Yin Yang 1 (YY1) is expressed in several human cancer cell lines and its expression correlates with resistance to immune-mediated apoptosis. This study used tissue microarrays to investigate the expression and localization of YY1 in 1364 representative tissue samples from 246 hormone naive prostate cancer patients who underwent radical prostatectomy. Staining intensity and frequency measures for both YY1 nuclear and cytoplasmic expression were higher in neoplastic tissues and in PIN samples compared to matched benign cells (p < 0.0001 for all comparisons). Expression of YY1 is predominantly elevated in early malignancy (PIN), as well as in tumors of intermediate to high morphologic grade (Gleason's grade 3-5). Using multivariate Cox proportional hazards analysis, we observed that low nuclear YY1 staining is an independent predictor of a shorter time to recurrence (p = 0.012). Based on these results, we hypothesize that YY1 may play a role in prostate cancer development; however, decreased YY1 may give metastatic cells a survival advantage. These results may also implicate YY1 as a useful diagnostic and prognostic marker.

Rituximab (chimeric anti-CD20 monoclonal antibody) inhibits the constitutive nuclear factor-{kappa}B signaling pathway in non-Hodgkin's lymphoma B-cell lines: role in sensitization to chemotherapeutic drug-induced apoptosis

The chimeric anti-CD20 antibody rituximab (Rituxan, IDEC-C2B8) is widely used in the clinical treatment of patients with non-Hodgkin's lymphoma (NHL). Rituximab sensitizes NHL B-cell lines to drug-induced apoptosis via down-regulation of Bcl-x(L) expression. We hypothesized that the mechanism by which rituximab down-regulates Bcl-x(L) may be, in part, due to inhibition of constitutive nuclear factor-kappaB (NF-kappaB) activity that regulates Bcl-x(L) expression. This hypothesis was tested in CD20(+) drug-resistant Ramos (Bcl-2(-)/Bcl-x(L)(+)) and Daudi (Bcl-2(+)/Bcl-x(L)(+)) cell lines. Rituximab decreased the phosphorylation of NF-kappaB-inducing kinase, IkappaB kinase, and IkappaB-alpha, diminished IKK kinase activity, and decreased NF-kappaB DNA binding activity. These events occurred with similar kinetics and were observed 3 to 6 hours post-rituximab treatment. Rituximab significantly up-regulated Raf-1 kinase inhibitor protein expression, thus interrupting the NF-kappaB signaling pathway concomitant with Bcl-x(L) and Bfl-1/A1 down-regulation. The role of NF-kappaB in the regulation of Bcl-x(L) transcription was shown using promoter reporter assays in which deletion of the two-tandem NF-kappaB binding sites in the upstream promoter region significantly reduced the luciferase activity. This was further corroborated by using IkappaB superrepressor cells and by NF-kappaB-specific inhibitors. The direct role of Bcl-x(L) in drug resistance was assessed by using Bcl-x(L)-overexpressing cells, which exhibited higher drug resistance that was partially reversed by rituximab. Rituximab-mediated inhibition of the NF-kappaB signaling pathway and chemosensitization was corroborated by the use of specific inhibitors. These findings reveal a novel pathway mediated by rituximab through Raf-1 kinase inhibitor protein induction that negatively regulates the constitutive NF-kappaB pathway and chemosensitization of the NHL B-cells.

Rituximab (Chimeric Anti-CD20 Monoclonal Antibody) Inhibits the Constitutive Nuclear Factor-κB Signaling Pathway in Non-Hodgkin's Lymphoma B-Cell Lines: Role in Sensitization to Chemotherapeutic Drug-induced Apoptosis

The chimeric anti-CD20 antibody rituximab (Rituxan, IDEC-C2B8) is widely used in the clinical treatment of patients with non-Hodgkin's lymphoma (NHL). Rituximab sensitizes NHL B-cell lines to drug-induced apoptosis via down-regulation of Bcl-xL expression. We hypothesized that the mechanism by which rituximab down-regulates Bcl-xL may be, in part, due to inhibition of constitutive nuclear factor-κB (NF-κB) activity that regulates Bcl-xL expression. This hypothesis was tested in CD20+ drug-resistant Ramos (Bcl-2−/Bcl-xL+) and Daudi (Bcl-2+/Bcl-xL+) cell lines. Rituximab decreased the phosphorylation of NF-κB-inducing kinase, IκB kinase, and IκB-α, diminished IKK kinase activity, and decreased NF-κB DNA binding activity. These events occurred with similar kinetics and were observed 3 to 6 hours post-rituximab treatment. Rituximab significantly up-regulated Raf-1 kinase inhibitor protein expression, thus interrupting the NF-κB signaling pathway concomitant with Bcl-xL and Bfl-1/A1 down-regulation. The role of NF-κB in the regulation of Bcl-xL transcription was shown using promoter reporter assays in which deletion of the two-tandem NF-κB binding sites in the upstream promoter region significantly reduced the luciferase activity. This was further corroborated by using IκB superrepressor cells and by NF-κB–specific inhibitors. The direct role of Bcl-xL in drug resistance was assessed by using Bcl-xL–overexpressing cells, which exhibited higher drug resistance that was partially reversed by rituximab. Rituximab-mediated inhibition of the NF-κB signaling pathway and chemosensitization was corroborated by the use of specific inhibitors. These findings reveal a novel pathway mediated by rituximab through Raf-1 kinase inhibitor protein induction that negatively regulates the constitutive NF-κB pathway and chemosensitization of the NHL B-cells.

Nitric oxide sensitizes prostate carcinoma cell lines to TRAIL-mediated apoptosis via inactivation of NF-κB and inhibition of Bcl-xL expression

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to be selective in the induction of apoptosis in cancer cells with minimal toxicity to normal tissues and this prompted its potential therapeutic application in cancer. However, not all cancers are sensitive to TRAIL-mediated apoptosis and, therefore, TRAIL-resistant cancer cells must be sensitized first to become sensitive to TRAIL. Treatment of prostate cancer (CaP) cell lines (DU145, PC-3, CL-1, and LNCaP) with nitric oxide donors (e.g. (Z)-1-[2-(2-aminoethyl)-N-(2-ammonio-ethyl)amino]diazen-1-ium-1, 2-diolate (DETANONOate)) sensitized CaP cells to TRAIL-induced apoptosis and synergy was achieved. The mechanism by which DETANONOate mediated the sensitization was examined. DETANONOate inhibited the constitutive NF-kappa B activity as assessed by EMSA. Also, p50 was S-nitrosylated by DETANONOate resulting in inhibition of NF-kappa B. Inhibition of NF-kappa B activity by the chemical inhibitor Bay 11-7085, like DETANONOate, sensitized CaP to TRAIL apoptosis. In addition, DETANONOate downregulated the expression of Bcl-2 related gene (Bcl-(xL)) which is under the transcriptional regulation of NF-kappa B. The regulation of NF-kappa B and Bcl-(xL) by DETANONOate was corroborated by the use of Bcl-(xL) and Bcl-x kappa B reporter systems. DETANONOate inhibited luciferase activity in the wild type and had no effect on the mutant cells. Inhibition of NF-kappa B resulted in downregulation of Bcl-(xL) expression and sensitized CaP to TRAIL-induced apoptosis. The role of Bcl-(xL) in the regulation of TRAIL apoptosis was corroborated by inhibiting Bcl-(xL) function by the chemical inhibitor 2-methoxyantimycin A(3) and this resulted in sensitization of the cells to TRAIL apoptosis. Signaling by DETANONOate and TRAIL for apoptosis was examined. DETANONOate altered the mitochondria by inducing membrane depolarization and releasing modest amounts of cytochrome c and Smac/DIABLO in the absence of downstream activation of caspases 9 and 3. However, the combination of DETANONOate and TRAIL resulted in activation of the mitochondrial pathway and activation of caspases 9 and 3, and induction of apoptosis. These findings demonstrate that DETANONOate-mediated sensitization of CaP to TRAIL-induced apoptosis is via inhibition of constitutive NF-kappa B activity and Bcl-(xL) expression.

A Salmonella typhi OmpC fusion protein expressing the CD154 Trp140-Ser149 amino acid strand binds CD40 and activates a lymphoma B-cell line

CD154 is a type II glycoprotein member of the tumour necrosis factor (TNF) ligand family, which is expressed mainly on the surface of activated T lymphocytes. The interaction with its receptor CD40, plays a central role in the control of several functions of the immune system. Structural models based on the homology of CD154 with TNF and lymphotoxin indicate that binding to CD40 involves three regions surrounding amino acids K143, R203 and Q220, and that strands W140-S149 and S198-A210 are critical for such interactions. Also, it has been reported that two recombinant CD154 fragments, including amino acid residues Y45-L261 or E108-L261 are biologically active, whereas other polypeptides, including S149-L261, are not. Therefore, we decided to construct a fusion protein inserting the W140-S149 amino acid strand (WAEKGYYTMS) in an external loop of the outer membrane protein C (OmpC) from Salmonella enterica serovar Typhi and assess its ability to bind CD40 and activate B cells. The sodium dodecyl sulphate-polyacrylamide gel electrophoresis demonstrated that the chimeric OmpC-gp39 protein conserved its ability to form trimers. Binding to CD40 was established by three variants of enzyme-linked immunosorbent assay, a direct binding assay by coating plates with a recombinant CD40-Fc protein and through two competition assays between OmpC-gp39 and recombinant CD154 or soluble CD40-Fc. Flow cytometry analysis demonstrated that OmpC-gp39 increased the expression levels of major histocompatibility complex II, CD23, and CD80, in Raji human B-cell lymphoma similarly to an antibody against CD40. These results further support that the CD154/CD40 interaction is similar to the TNF/TNF receptor. This is the first report of a bacterial fusion protein containing a small amino acid strand form a ligand that is able to activate its cognate receptor.