Potential mechanism of resistance to TRAIL-induced apoptosis in Burkitt's lymphoma

RNA helicase DHX15 decreases cell apoptosis by NF-κB signaling pathway in Burkitt lymphoma

Background

DHX15 is one of the RNA helicase family members involving in several biological processes. Studies have reported that overexpression of DHX15 is related to cancer progression. However, the role of DHX15 in Burkitt lymphoma (BL) and latent Epstein-Barr virus (EBV) infection remains to be elucidated.

Methods

Expression of DHX15 was measured in BL patient by immunohistochemical staining. In vitro study, a CCK-8 assay was used to analyze cell proliferation and flow cytometry was performed to assess cell cycle, apoptosis and mitochondria membrane potential. Members of NF-κB signaling pathway and apoptotic-related proteins expression were measured by western-blot. EBV latent infection products and RNA polymerase III transcripts expression were determined by quantitative real-time PCR and western-blot. In vivo study, HE, IHC, TUNEL and ISH assays were used to analyze the effect of DHX15 on subcutaneous tumor nodes formation.

Results

DHX15 was overexpressed in Burkitt lymphoma patients and tends to be associated with poor progression-free survival and poor overall survival. Knockdown of DHX15 significantly inhibited BL tumor growth, reduced cell proliferation, induced cell cycle arrest and increased cell apoptosis. Further analysis showed that canonical NF-κB signaling and its downstream targets, mitochondria and Caspase were involved in the increased cell apoptosis after DHX15 gene knockdown. Furthermore, knockdown of DHX15 reduced EBV latent infection products expression and inhibited RNA polymerase III activity.

Conclusion

DHX15 may be an oncogene in the development of BL and a potential therapeutic target for the treatment of BL and latent EBV infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02426-5.

Smac mimetics and TRAIL cooperate to induce MLKL-dependent necroptosis in Burkitt's lymphoma cell lines

Burkitt's lymphoma (BL) is a highly aggressive form of B-cell non-Hodgkin's lymphoma. The clinical outcome in children with BL has improved over the last years but the prognosis for adults is still poor, highlighting the need for novel treatment strategies. Here, we report that the combinational treatment with the Smac mimetic BV6 and TRAIL triggers necroptosis in BL when caspases are blocked by zVAD.fmk (TBZ treatment). The sensitivity of BL cells to TBZ correlates with MLKL expression. We demonstrate that necroptotic signaling critically depends on MLKL, since siRNA-induced knockdown and CRISPR/Cas9-mediated knockout of MLKL profoundly protect BL cells from TBZ-induced necroptosis. Conversely, MLKL overexpression in cell lines expressing low levels of MLKL leads to necroptosis induction, which can be rescued by pharmacological inhibitors, highlighting the important role of MLKL for necroptosis execution. Importantly, the methylation status analysis of the MLKL promoter reveals a correlation between methylation and MLKL expression. Thus, MLKL is epigenetically regulated in BL and might serve as a prognostic marker for treatment success of necroptosis-based therapies. These findings have crucial implications for the development of new treatment options for BL.

3-Bromopyruvate potentiates TRAIL-induced apoptosis in human colon cancer cells through a reactive oxygen species- and caspase-dependent mitochondrial pathway

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a promising anticancer cytokine with minimal toxicity towards normal cells. Nevertheless, most primary cancers are often intrinsically TRAIL-resistant or can acquire resistance after TRAIL therapy. This study aimed to investigate the inhibitory effect of co-treatment of 3-bromopyruvate (3-BP) as a potent anticancer agent with TRAIL on colon cancer cells (HT-29). The results of present study indicated that combined treatment with 3-BP and TRAIL inhibited the proliferation of HT-29 cells to a greater extent (88.4%) compared with 3-BP (54%) or TRAIL (11%) treatment alone. In contrast, the combination of 3-BP and TRAIL had no significant inhibitory effect on the proliferation of normal cells (HEK-293) (8.4%). At a cellular mechanistic level, the present study showed that 3-BP sensitized human colon cancer cells to TRAIL-induced apoptosis via reactive oxygen species generation, upregulation of Bax, downregulation of Bcl-2 and survivin, release of cytochrome c into the cytosol, and activation of caspase-3. In normal cells, 3-BP, TRAIL, or combination of both had no significant effect on the reactive oxygen species levels, release of cytochrome c, and caspase-3 activity. Therefore, the combination of 3-BP and TRAIL can be a promising therapeutic strategy for treatment of colon cancer.

The RCAN1 inhibits NF-κB and suppresses lymphoma growth in mice

Nuclear factor-κB (NF-κB) has a vital role in cell survival. Inhibition of NF-κB has been proven to be an efficient therapeutic pathway for various cancers. Activation of NF-κB is mainly through serine residues' phosphorylation of inhibitor of κBα (IκBα) by IKK complex. Phosphorylation at tyrosine 42 is an alternative pathway in regulation of IκBα and NF-κB signaling, though little is known about the underlying mechanism. Here we identified regulator of calcineurin 1 (RCAN1) as a novel endogenous inhibitor of NF-κB signaling pathway. RCAN1 can interact with IκBα and affect the phosphorylation of IκBα at tyrosine 42. Overexpression of RCAN1 by adenovirus reduced cell viability in lymphoma Raji cells and restrained the growth of lymphoma transplants in mice. We further found that N terminus 1–103aa of RCAN1 is sufficient to inhibit NF-κB and reduce cell viability of lymphoma cells. Our study implicated a novel therapeutic approach for lymphoma by RCAN1 through inhibition of NF-κB signaling.

The NF-κB pathway is rarely spontaneously activated in mantle cell lymphoma (MCL) cell lines and patient's samples

In this study, we investigated the role of NF-κB (canonical and alternative pathways) in the survival or proliferation of mantle cell lymphoma (MCL) cell lines. P50/p65 complexes were detectable by EMSA assays in 4/5 cell lines. Stable expression of a dominant-negative form of IkBa had no effect on proliferation nor on apoptosis in EBV-negative cell lines. Three out of 4 of the cell lines tested exhibited Phospho-p65 (Ser(536)). The alternative NF-κB pathway was not activated in 4/5 cell lines tested. Patient samples were also studied by Western blot, EMSA and Immunohistochemistry (IHC). No p50/p65 complexes were detected in cells freshly collected from 7 patients, but 1/7 cells exhibited Phospho-p65 (Ser(536)). We investigated immunohistochemically, the expression of NF-κB in 86 patients enrolled in two multicentre prospective trials. Patients with MCL exhibiting negative or positive cytoplasmic expression of NF-κB had a median overall survival of 35.7months compared to 22.4months for patients with nuclear NF-κB expression (p=0.0193). All these data suggest that NF-κB does not play a key role in proliferation and apoptotic processes in MCL cell lines. In patient samples, the presence of p65 in the nucleus reflecting NF-κB activation is rare but associated with a poor outcome.

Sulfated small molecules targeting eBV in Burkitt lymphoma: from in silico screening to the evidence of in vitro effect on viral episomal DNA

Epstein-Barr virus (EBV) infects more than 90% of the world population. Following primary infection, Epstein-Barr virus persists in an asymptomatic latent state. Occasionally, it may switch to lytic infection. Latent EBV infection has been associated with several diseases, such as Burkitt lymphoma (BL). To date, there are no available drugs to target latent EBV, and the existing broad-spectrum antiviral drugs are mainly active against lytic viral infection. Thus, using computational molecular docking, a virtual screen of a library of small molecules, including xanthones and flavonoids (described with potential for antiviral activity against EBV), was carried out targeting EBV proteins. The more interesting molecules were selected for further computational analysis, and subsequently, the compounds were tested in the Raji (BL) cell line, to evaluate their activity against latent EBV. This work identified three novel sulfated small molecules capable of decreasing EBV levels in a BL. Therefore, the in silico screening presents a good approach for the development of new anti-EBV agents.

EBV interferes with the sensitivity of Burkitt lymphoma Akata cells to etoposide

Burkitt lymphoma (BL) commonly exhibits Epstein-Barr virus (EBV) positivity associated with latent chronic infection. Models of acute EBV infection have been associated with cellular resistance to apoptosis. However, the effect of latent long-term EBV infection on apoptosis induced by drugs is not well defined. To determine this, we have studied the response of the Akata EBV+ cell line (type I latency) to etoposide, before and after downregulating EBV gene expression. We observed that downregulating EBV nuclear antigen-1 (EBNA-1) expression with siRNAs reverted cellular sensitivity to etoposide. In accordance with this finding, Akata EBV+ cells showed increased sensitivity to etoposide, when compared to the Akata EBV- cells. We also observed that Akata EBV+ cells presented increased apoptosis levels and decreased Bcl-xL mRNA and protein levels, when compared to the Akata EBV- cells. In addition, Akata EBV+ cells contained less endoplasmic reticulum (ER) than EBV- cells. Finally, downregulation of EBV with EBNA-1 siRNAs caused an increase in the expression of Bcl-xL indicating that EBV is responsible for the differences found between the Akata EBV+ and EBV- cell lines.

Reversion of epigenetically mediated BIM silencing overcomes chemoresistance in Burkitt lymphoma

In Burkitt lymphoma/leukemia (BL), achievement of complete remission with first-line chemotherapy remains a challenging issue, as most patients who respond remain disease-free, whereas those refractory have few options of being rescued with salvage therapies. The mechanisms underlying BL chemoresistance and how it can be circumvented remain undetermined. We previously reported the frequent inactivation of the proapoptotic BIM gene in B-cell lymphomas. Here we show that BIM epigenetic silencing by concurrent promoter hypermethylation and deacetylation occurs frequently in primary BL samples and BL-derived cell lines. Remarkably, patients with BL with hypermethylated BIM presented lower complete remission rate (24% vs 79%; P = .002) and shorter overall survival (P = .007) than those with BIM-expressing lymphomas, indicating that BIM transcriptional repression may mediate tumor chemoresistance. Accordingly, by combining in vitro and in vivo studies of human BL-xenografts grown in immunodeficient RAG2(-/-)γc(-/-) mice and of murine B220(+)IgM(+) B-cell lymphomas generated in Eμ-MYC and Eμ-MYC-BIM(+/-) transgenes, we demonstrate that lymphoma chemoresistance is dictated by BIM gene dosage and is reversible on BIM reactivation by genetic manipulation or after treatment with histone-deacetylase inhibitors. We suggest that the combination of histone-deacetylase inhibitors and high-dose chemotherapy may overcome chemoresistance, achieve durable remission, and improve survival of patients with BL.

The TRAIL to viral pathogenesis: the good, the bad and the ugly

Since the discovery of Tumor Necrosis Factor-Related Apoptosis Inducing Ligand (TRAIL) in 1995, much has been learned about the protein, its receptors and signaling cascade to induce apoptosis and the regulation of its expression. However, the physiologic role or roles that TRAIL may play in vivo are still being explored. The expression of TRAIL on effector T cells and the ability of TRAIL to induce apoptosis in virally infected cells provided early clues that TRAIL may play an active role in the immune defense against viral infections. However, increasing evidence is emerging that TRAIL may have a dual function in the immune system, both as a means to kill virally infected cells and in the regulation of cytokine production. TRAIL has been implicated in the immune response to viral infections (good), and in the pathogenesis of multiple viral infections (bad). Furthermore, several viruses have evolved mechanisms to manipulate TRAIL signaling to increase viral replication (ugly). It is likely that whether TRAIL ultimately has a proviral or antiviral effect will be dependent on the specific virus and the overall cytokine milieu of the host. Knowledge of the factors that determine whether TRAIL is proviral or antiviral is important because the TRAIL system may become a target for development of novel antiviral therapies.

The IKK2/NF-{kappa}B pathway suppresses MYC-induced lymphomagenesis

Deregulated c-MYC is found in a variety of cancers where it promotes proliferation as well as apoptosis. In many hematologic malignancies, enhanced NF-kappaB exerts prosurvival functions. Here we investigated the role of NF-kappaB in mouse and human c-MYC-transformed lymphomas. The NF-kappaB pathway is extinguished in murine lymphoma cells, and extrinsic stimuli typically inducing NF-kappaB activity fail to activate this pathway. Genetic activation of the NF-kappaB pathway induces apoptosis in these cells, whereas inhibition of NF-kappaB by an IkappaBalpha superrepressor provides a selective advantage in vivo. Furthermore, in human Burkitt lymphoma cells we find that NF-kappaB activation induces apoptosis. NF-kappaB up-regulates Fas and predisposes to Fas-induced cell death, which is caspase-8 mediated and can be prevented by CFLAR overexpression. We conclude that c-MYC overexpression sensitizes cells to NF-kappaB-induced apoptosis, and persistent inactivity of NF-kappaB signaling is a prerequisite for MYC-mediated tumorigenesis. We could also show that low immunogenicity and Fas insensitivity of MYC-driven lymphoma cells are reversed by activation of NF-kappaB. Our observations provide a molecular explanation for the described absence of the NF-kappaB signaling in Burkitt lymphoma and question the applicability of NF-kappaB inhibitors as candidates for treatment of this cancer.

Role of IG20 splice variants in TRAIL resistance

Tumor necrosis factor receptor-related apoptosis-inducing ligand (TRAIL) can induce apoptosis primarily in cancer cells with little or no effect on normal cells; therefore, it has the potential for use in cancer therapy. TRAIL binding to death receptors DR4 and DR5 triggers the death-inducing signal complex formation and activation of procaspase-8, which in turn activates caspase-3, leading to cell death. Like FasL, TRAIL can trigger type 1 (caspase-8 --> caspase-3) or type 2 (caspase-8 --> Bid cleavage --> capsase-9 --> caspase-3) apoptotic pathways depending on the cell type. Some cancers are resistant to TRAIL treatment because most molecules in the TRAIL signaling pathway, including FLIPs and IAPs, can contribute to resistance. In addition, we have identified an essential role for splice variants of the IG20 gene in TRAIL resistance.

Biology and treatment of Burkitt's lymphoma

PURPOSE OF REVIEW

Burkitt's lymphoma is a unique hematological malignancy remarkable for its biological characteristics, including aberrant expression of the MYC oncogene, and its requirement for intensive treatment regimens. This review will focus on those features, and discuss recent advances in the molecular biology and advancing treatment options for the disease.

RECENT FINDINGS

Advances in molecular biology have provided many new insights into the biology and treatment options for Burkitt's lymphoma. Microarray technology has recently been used to define a molecular gene expression signature for Burkitt's lymphoma. This signature allows for the differentiation of Burkitt's lymphoma from other forms of non-Hodgkin's lymphoma such as diffuse large B-cell lymphoma. Recent advances in the use of biological agents, such as rituximab, have also allowed for a reduction in treatment toxicities while still offering comparable survival outcomes for patients.

SUMMARY

Burkitt's lymphoma is an interesting mature B-cell non-Hodgkin's lymphoma that has numerous distinct features and clinical variants depending on factors such as geographical location, immunological status and patient's age. Although the role of the MYC oncogene has been well studied, we are only now appreciating the defining molecular characteristics of this disease, and using these advances to improve treatment options for patients.

Following the TRAIL to apoptosis

Apoptosis, programmed cell death, eliminates injured or harmful cells. It can mediate its response through the actions of death ligands including TRAIL. TRAIL, a member of TNF superfamily, induces apoptosis of transformed cells through the action of death domain receptors DR-4 and DR5. It directly induces apoptosis through an extrinsic pathway, which involves the activation of caspases. TRAIL also is able to prevent apoptosis through the actions of its decoy receptors DcR-1 and DcR-2. Various regulators of TRAIL include FADD, IAPs, Bcl-2s, p53, and FLIPs. TRAIL is present in cells involved in asthma including eosinophils, mast cells, fibroblasts, and airway epithelial cells. It is expressed in airway remodeling and may be linked with the pathways of transforming growth factor-beta1, which is thought to cause damage to the epithelium. The repair process of the epithelium is hindered as a result of increased apoptosis induced by TGF-beta1, which overlaps with the pathways of TRAIL. Analogs of TRAIL could have therapeutical applications for asthma. TRAIL is also seen as the basis for a "miracle" drug for cancer because of its ability to selectively kill cancer cells.

EBV can protect latently infected B cell lymphomas from death receptor-induced apoptosis

The relationship between EBV infection and sensitivity to death receptor (DR)-induced apoptosis is poorly understood. Using EBV- and EBV+ BJAB cells, we provide the first evidence that EBV can protect latently infected B cell lymphomas from apoptosis triggered through Fas or TRAIL receptors. Caspase 8 activation was impaired and cellular FLIP recruitment was enriched in death-inducing signaling complexes formed in EBV-infected BJAB cells relative to parent BJAB cells. Furthermore, latent membrane protein 1 expression alone could reduce caspase activation and confer partial resistance to DR apoptosis in BJAB cells. This protective effect was dependent on C-terminal activating region 2-driven NF-kappaB activation, which in turn up-regulated cellular FLIP expression in latent membrane protein 1+ BJAB cells. Thus, the ability of latent EBV to block DR apoptosis may help to ensure the survival of host cells during B cell differentiation, and contribute to the development of B cell lymphomas, especially in immunocompromised individuals.

Human soluble TRAIL/Apo2L induces apoptosis in a subpopulation of chemotherapy refractory nodal diffuse large B-cell lymphomas, determined by a highly sensitive in vitro apoptosis assay

Resistance to chemotherapy in therapy-refractory diffuse large B-cell lymphomas (DLBCL) is related to inhibition of the intrinsic apoptosis pathway. Human soluble tumour necrosis factor (TNF)-related apoptosis-inducing ligand (hsTRAIL/Apo2L) induces apoptosis via the alternative, death-receptor mediated apoptosis pathway and might be an effective alternative form of therapy for these lymphomas. This study investigated whether hsTRAIL/Apo2L could actually induce apoptosis in isolated lymphoma cells of DLBCL biopsies of patients with chemotherapy-refractory DLBCL. Twelve out of a total of 22 DLBCL samples were sensitive to hsTRAIL/Apo2L. These sensitive lymphomas included seven clinically chemotherapy-refractory lymphomas. Furthermore, hsTRAIL/Apo2L induced apoptosis in DLBCL cells and in B-cell lines that showed high expression levels of inhibitors of the intrinsic apoptosis pathway: Bcl-2 and/or X-linked inhibitor of apoptosis (XIAP). hsTRAIL/Apo2L-sensitive lymphoma cells showed expression of the TRAIL receptors R1 and/or R2 and absence of R3 and R4. We conclude that hsTRAIL/Apo2L induced apoptosis in a subpopulation of chemotherapy-refractory nodal DLBCL and that disruption of the intrinsic apoptosis-mediated pathway and expression of Bcl-2 and XIAP did not confer resistance to hsTRAIL/Apo2L-induced apoptosis in DLBCL. Thus, based on our results, further exploration of hsTRAIL/Apo2L as an alternative treatment for patients with chemotherapy-refractory DLBCL should be considered.