NF-kappaB involvement in the activation of primary adult T-cell leukemia cells and its clinical implications

Neonatal Vitamin C and Cysteine Deficiencies Program Adult Hepatic Glutathione and Specific Activities of Glucokinase, Phosphofructokinase, and Acetyl-CoA Carboxylase in Guinea Pigs' Livers

Premature neonates are submitted to an early-life oxidative stress from parenteral nutrition, which is vitamin C (VC) deficient and induces low endogenous levels of glutathione. The oxidative stress caused by these deficiencies may permanently affect liver glycolysis and lipogenesis. This study evaluates the short- and long-term effects of neonatal VC and cysteine deficient diets on redox and energy metabolism. Three-day-old Hartley guinea pigs from both sexes were given a regular or a deficient diet (VC, cysteine, or both) until week 1 of life. Half of the animals were sacrificed at this age, while the other half ate a complete diet until 12 weeks. Liver glutathione and the activity and protein levels of glucokinase, phosphofructokinase, and acetyl-CoA-carboxylase were measured. Statistics: factorial ANOVA (5% threshold). At 1 week, all deficient diets decreased glutathione and the protein levels of glucokinase and phosphofructokinase, while cysteine deficiency decreased acetyl-CoA-carboxylase levels. A similar enzyme level was observed in control animals at 12 weeks. At this age, VC deficiency decreased glutathione, while cysteine increased it. Acetyl-CoA-carboxylase protein levels were increased, which decreased its specific activity. Early-life VC and cysteine deficiencies induce neonatal oxidative stress and an adult-like metabolism, while predisposing to increased lipogenic rates during adulthood.

The Toxoplasma gondii ME-49 strain upregulates levels of A20 that inhibit NF-κB activation and promotes apoptosis in human leukaemia T-cell lines

Background

Acute T-lymphocyte leukaemia is a form of haematological malignancy with abnormal activation of NF-κB pathway, which results in high expression of A20 and ABIN1, which constitute a negative feedback mechanism for the regulation of NF-κB activation. Clinical studies have found that acute T-lymphocyte leukaemia patients are susceptible to Toxoplasma gondii infection; however, the effect of T. gondii on the proliferation and apoptosis of human leukaemia T-cells remains unclear. Here, we used the T. gondii ME-49 strain to infect human leukaemia T-cell lines Jurkat and Molt-4, to explore the effect of T. gondii on proliferation and apoptosis, which is mediated by NF-κB in human leukaemia T-cells.

Methods

The Tunel assay was used to detect cell apoptosis. Cell Counting Kit-8 was used to detect cell proliferation viability. The apoptosis level and the expression level of NF-κB related proteins in human leukaemia T-cells were detected by flow cytometry and Western blotting.

Results

Western blotting analyses revealed that the T. gondii ME-49 strain increased the expression of A20 and decreased both ABIN1 expression and NF-κB p65 phosphorylation. By constructing a lentiviral-mediated shRNA to knockdown the A20 gene in Jurkat T-cells and Molt-4 T-cells, the apoptosis levels of the two cell lines decreased after T. gondii ME-49 infection, and levels of NF-κB p65 phosphorylation and ABIN1 were higher than in the non-konckdown group. After knockingdown ABIN1 gene expression by constructing the lentiviral-mediated shRNA and transfecting the recombinant expression plasmid containing the ABIN1 gene into two cell lines, apoptosis levels and cleaved caspase-8 expression increased or decreased in response to T. gondii ME-49 infection, respectively.

Conclusions

Our data suggest that ABIN1 protects human leukaemia T-cells by allowing them to resist the apoptosis induced by T. gondii ME-49 and that the T. gondii ME-49 strain induces the apoptosis of human leukaemia T-cells via A20-mediated downregulation of ABIN1 expression.

Human T-cell leukemia virus type 1 (HTLV-1) tax requires CADM1/TSLC1 for inactivation of the NF-κB inhibitor A20 and constitutive NF-κB signaling

Persistent activation of NF-κB by the Human T-cell leukemia virus type 1 (HTLV-1) oncoprotein, Tax, is vital for the development and pathogenesis of adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). K63-linked polyubiquitinated Tax activates the IKK complex in the plasma membrane-associated lipid raft microdomain. Tax also interacts with TAX1BP1 to inactivate the NF-κB negative regulatory ubiquitin-editing A20 enzyme complex. However, the molecular mechanisms of Tax-mediated IKK activation and A20 protein complex inactivation are poorly understood. Here, we demonstrated that membrane associated CADM1 (Cell adhesion molecule1) recruits Ubc13 to Tax, causing K63-linked polyubiquitination of Tax, and IKK complex activation in the membrane lipid raft. The c-terminal cytoplasmic tail containing PDZ binding motif of CADM1 is critical for Tax to maintain persistent NF-κB activation. Finally, Tax failed to inactivate the NF-κB negative regulator ubiquitin-editing enzyme A20 complex, and activate the IKK complex in the lipid raft in absence of CADM1. Our results thus indicate that CADM1 functions as a critical scaffold molecule for Tax and Ubc13 to form a cellular complex with NEMO, TAX1BP1 and NRP, to activate the IKK complex in the plasma membrane-associated lipid rafts, to inactivate NF-κB negative regulators, and maintain persistent NF-κB activation in HTLV-1 infected cells.

HTLV-1 infection leads to the development of Adult T-cell Leukemia (ATL) or HTLV-1 associated myelopathy/ tropical spastic paraparesis (HAM/TSP). One of the major causes responsible for the development of HTLV-1 associated diseases is chronic inflammation directed by NF-kappaB (NF-κB). NF-κB activation in response to a wide variety of signals is transient and tightly controlled by ubiquitin-editing enzyme A20. One of the mechanisms of persistent NF-κB activation in HTLV-1 infected cells is inactivation of NF-κB negative regulators; however, the precise mechanism is unknown. Here, we focused on host tumor suppressor Cell adhesion molecule 1 (CADM1) that is robustly upregulated in HTLV-1 infected cells. The expression of CADM1 is frequently silenced in several cancers; however, it is critical for HTLV-1 associated ATL tumor cell survival. We characterized the role of CADM1 in persistent NF-κB activation in HTLV-1 infected cells. We found that CADM1 is required for the HTLV-1 oncoprotein, Tax, to form a cellular complex with Ubc13, TAX1BP1, NRP and NEMO in the membrane lipid rafts micorodomain. We further demonstrated that Tax requires CADM1 to inactivate NF-κB negative regulator and maintain persistent NF-κB activation. Our study reveals a novel mechanism of chronic NF-κB activation by CADM1 in HTLV-1 infected cells.

The Link between Autoimmunity and Lymphoma: Does NOTCH Signaling Play a Contributing Role?

An association between certain autoimmune conditions and increased risk of developing lymphoma is well documented. Recent evidence points to NOTCH signaling as a strong driver of autoimmunity. Furthermore, a role for NOTCH in various lymphomas, including classical Hodgkin lymphoma, non-Hodgkin lymphoma, and T cell lymphoma has also been described. In this mini-review, we will outline what is known about involvement of NOTCH signaling in those autoimmune conditions, such as rheumatoid arthritis and primary Sjörgren’s syndrome, which show an increased risk for subsequent diagnosis of lymphoma. Furthermore, we will detail what is known about the lymphomas associated with these autoimmune conditions and how aberrant or sustained NOTCH signaling in the immune cells that mediate these diseases may contribute to lymphoma.

Effects of exogenous interleukin-7 on CD8(+) T-cell survival and function in human T-cell lymphotropic virus type 1 infection

Interleukin-7 (IL-7) mediates T-cell homeostasis through its effects on T-cell development, survival and function. In human T-cell lymphotropic virus type 1 (HTLV-1) infection, which is causally implicated in adult T-cell leukemia (ATL), the efficiency with which CD8(+) cytotoxic T-lymphocytes (CTLs) clear HTLV-1-infected cells mediates viral control and may be related to disease progression. We report here that CD127 expression in CD8(+) T-cells is independently related to disease status, and that exogenous IL-7 enhances CD8(+) T-cell survival and clearance of HTLV-1 infected cells in vitro. We conclude that CD127 down-regulation may be associated with disease status in HTLV-1 infection, and propose that exogenous IL-7 may be useful immunotherapy or cytokine adjuvant for an anti-ATL therapeutic vaccine.

Targeted therapy in T-cell malignancies: dysregulation of the cellular signaling pathways

T-cell malignancies, mainly known as T-cell acute lymphoblastic leukemia (T-ALL) and T-cell non-Hodgkin's lymphoma (T-NHL), are aggressive tumors. Although the clinical outcome of the patients has improved dramatically with combination chemotherapy, significant challenges remain, including understanding of the factors that contribute to the malignant behavior of these tumor cells and developing subsequently optimal targeted therapy. Aberrant cell signal transduction is generally involved in tumor progression and drug resistance. This review describes the pathogenetic role of multiple cellular signaling pathways in T-cell malignancies and the potential therapeutic strategies based on the modulation of these key signaling networks.

Blockage of interleukin-6 signaling with 6-amino-4-quinazoline synergistically induces the inhibitory effect of bortezomib in human U266 cells

The transcription factor nuclear factor-kappa B (NF-kappaB) regulates the transcription of a number of genes involved in a variety of cellular responses, including cell survival, inflammation, and differentiation. NF-kappaB is activated by a variety of stimuli, proinflammatory cytokines, mitogens, growth factors, and stress-inducing agents. Aberrant NF-kappaB expression is considered to be one of the oncogenic factors of cancer and the constitutive activation of NF-kappaB is observed in several hematologic disorders [classic Hodgkin's lymphoma, diffuse large B cell lymphoma, and multiple myeloma (MM)], and the modulation of NF-kappaB activation is emerging as a promising novel anticancer therapeutic strategy.Therefore, we focused on the regulation of NF-kappaB activation in MM. When U266 cells were treated with 6-amino-4-quinazoline, an NF-kappaB activation inhibitor, we determined that it most effectively blocked the interleukin (IL)-6-induced activation of MAPK and JAK/STAT pathways among different signaling inhibitors. The results of the luciferase assay indicated that 6-amino-4-quinazoline inhibited NF-kappaB activation with diminished NF-kappaB protein bound to NF-kappaB DNA binding sites. In addition, 6-amino-4-quinazoline suppressed the production of IL-6, which affected MM cell proliferation. Furthermore, combined treatment with bortezomib and 6-amino-4-quinazoline effectively inhibited the IL-6 and soluble IL-6R-induced activation of STAT3 and extracellular signal-regulated kinase phosphorylation. Our data showed that the inhibition of NF-kappaB activation abrogated MM cell proliferation induced by the IL-6 pathway, and might represent a promising therapeutic strategy for the treatment of MM.

Rearranged NF-kappa B2 gene in an adult T-cell leukemia cell line

Adult T-cell leukemia (ATL) is an aggressive type of leukemia, originating from T-cells infected with human T-cell leukemia virus type 1. Accumulating evidence suggests the aberrant activation of NF-kappaB to be a causative factor mediating the abnormal proliferation of leukemic cells, thus resulting in the development of ATL. A rearranged NF-kappa B2/p100 gene was isolated from an ATL-derived cell line, which was generated by a chromosomal translocation. The isolated NF-kappa B2 mutant is fused with the with no (lysine) deficient protein kinase 1 gene, coding for a 58 kDa protein that retains the DNA binding Rel homology domain, but it lacks the entire ankyrin repeat inhibitory domain, thus suggesting its constitutive activation. This rearranged NF-kappa B2 gene product (p58) was localized in the nucleus, and formed a complex with NF-kappaB p65 or RelB. Moreover, a T-cell line expressing p58 increased the amount of an NF-kappa B2-inducible gene, NF-kappa B2/p100 by itself. These results suggest that such NF-kappa B2 gene rearrangement may therefore be a factor in the constitutive activation of NF-kappaB in ATL, and thereby playing a role in the ATL pathogenesis.

Cyclosporin A inhibits HTLV-I tax expression and shows anti-tumor effects in combination with VP-16

Adult T cell leukemia (ATL) is one of the most refractory malignant hematological diseases. Our previous studies demonstrated HTLV-1Tax protein involvement in clinical manifestation of the aggressive type of ATL and suggested the potential application of agents to inhibit Tax expression for ATL treatment. In the present study, we first examined Tax involvement in the resistance to VP-16-induced apoptosis using four HTLV-1 infected T cell clones and cTax DNA-transfected cells. Next, we examined whether cyclosporin A reduced expression of Tax and its related transfer factors on Western blot and CAT assay. We further investigated whether cyclosporin A in combination with VP-16 can induce apoptosis in HTLV-1 infected T cells. Tax-producing T cells, K3T and F6T, were resistant to VP-16 induced growth inhibition compared with that of the nonproducing cells, S1T and Su9T01. Experiments using S1T and Tax-expressing cDNA-transfected S1T demonstrated Tax-induced resistance to VP-16 induction of apoptosis by DNA ladder formation. Cyclosporin A reduced Tax expression in K3T by Western blot analysis and on CAT assay, showing maximal reduction of 61% and 60% compared to control culture using LTR CAT transfected Jurkat cells and K3T cells, respectively. Cyclosporin A also reduced the nuclear expression of two Tax-related transfer factors, ATF-1 and ATF-2 on Western blot. Cyclosporin A alone did not show any cytotoxicity by itself, but sensitized cells to VP-16 when combined with VP-16. Cyclosporin A may be a useful anti-ATL agent when combined with other anti-cancer agents possibly related to Tax inhibition.

Constitutive association of MyD88 to IRAK in HTLV-I-transformed T cells

OBJECTIVE

Constitutive activation of nuclear factor (NF)-kappaB is a common feature of human T-cell leukemia virus type I (HTLV-I)-transformed T cells. Inhibition of NF-kappaB activity reduces cell growth and induces apoptosis of HTLV-I-transformed T cells, suggesting a central role of NF-kappaB in their proliferation and survival. In this study, we investigated whether MyD88, an adaptor protein of Toll-like receptor (TLR) signaling, contributes to constitutive NF-kappaB activation in HTLV-I-transformed T cells.

MATERIALS AND METHODS

Activation status of MyD88 and interleukin (IL)-1R-associated kinase 1 (IRAK1) in HTLV-I-transformed human T cells, MT2, MT4, and HUT102 was examined by using Western blot and immunoprecipitation. TLR expression was evaluated with reverse transcription polymerase chain reaction. An expression vector encoding a dominant negative MyD88 with a deletion of its death domain (MyD88dn) was transfected into MT2 cells to evaluate roles of MyD88 in spontaneous activation of cytokine gene promoters and transcription factors, proliferation, and apoptosis in HTLV-I-transformed T cells.

RESULTS

Constitutive association of MyD88 with IRAK1 was observed in all three of HTLV-I-transformed T cells, but not in HTLV-I-negative T cells, such as Jurkat, HUT78, and MOLT4. MT2 cells showed expression of TLR-1, -6, and -10 mRNAs. Constitutive activation of NF-kappaB and NF-IL-6 and cytokine gene promoters, such as IL-1alpha, interferon-gamma, and tumor necrosis factor-alpha in MT2 cells was inhibited by MyD88dn expression. MyD88dn reduced proliferation and induced apoptosis of MT2 cells. HTLV-I Tax enhanced TLR expression and synergistically activated NF-kappaB with wild-type MyD88.

CONCLUSION

Our results show a novel pathway in NF-kappaB activation in HTLV-I-transformed T cells and further demonstrate a critical role of MyD88 in their dysregulated gene activation, survival, and proliferation.

IRF-4 and c-Rel expression in antiviral-resistant adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is a generally fatal malignancy. Most ATLL patients fare poorly with conventional chemotherapy; however, antiviral therapy with zidovudine (AZT) and interferon alpha (IFN-alpha) has produced long-term clinical remissions. We studied primary ATLL tumors and identified molecular features linked to sensitivity and resistance to antiviral therapy. Enhanced expression of the proto-oncogene c-Rel was noted in 9 of 27 tumors. Resistant tumors exhibited c-Rel (6 of 10; 60%) more often than did sensitive variants (1 of 9; 11%). This finding was independent of the disease form. Elevated expression of the putative c-Rel target, interferon regulatory factor-4 (IRF-4), was observed in 10 (91%) of 11 nonresponders and in all tested patients with c-Rel+ tumors and occurred in the absence of the HTLV-1 oncoprotein Tax. In contrast, tumors in complete responders did not express c-Rel or IRF-4. Gene rearrangement studies demonstrated the persistence of circulating T-cell clones in long-term survivors maintained on antiviral therapy. The expression of nuclear c-Rel and IRF-4 occurs in the absence of Tax in primary ATLL and is associated with antiviral resistance. These molecular features may help guide treatment. AZT and IFN-alpha is a suppressive rather than a curative regimen, and patients in clinical remission should remain on maintenance therapy indefinitely.

Reduced frequency, diversity, and function of human T cell leukemia virus type 1-specific CD8+ T cell in adult T cell leukemia patients

Human T cell lymphotropic virus type 1 (HTLV-1)-specific CTL are thought to be immune effectors that reduce the risk of adult T cell leukemia (ATL). However, in vivo conditions of anti-HTLV-1 CTL before and after ATL development have yet to be determined. To characterize anti-HTLV-1 CTL in asymptomatic HTLV-1 carriers (AC) and ATL patients, we analyzed the frequency and diversity of HTLV-1-specific CD8+ T cells in PBMC of 35 AC and 32 ATL patients using 16 distinct epitopes of HTLV-1 Tax or Env/HLA tetramers along with intracellular cytolytic effector molecules (IFN-gamma, perforin, and granzyme B). Overall frequency of subjects possessing Tax-specific CD8+ T cells was significantly lower in ATL than AC (53 vs 90%; p = 0.001), whereas the difference in Env-specific CD8+ T cells was not statistically significant. AC possessed Tax11-19/HLA-A*0201-specific tetramer+ cells by 90% and Tax301-309/HLA-A*2402-specific tetramer+ cells by 92%. Some AC recognized more than one epitope. In contrast, ATL recognized only Tax11-19 with HLA-A*0201 and Tax301-309 with HLA-A*2402 at frequencies of 30 and 55%. There were also significant differences in percentage of cells binding Tax11-19/HLA-A*0201 and Tax301-309/HLA-A*2402 tetramers between AC and ATL. Anti-HTLV-1 Tax CD8+ T cells in AC and ATL produced IFN-gamma in response to Tax. In contrast, perforin and granzyme B expression in anti-HTLV-1 CD8+ T cells of ATL was significant lower than that of AC. Frequency of Tax-specific CD8+ T cells in AC was related to proviral load in HLA-A*0201. These results suggest that decreased frequency, diversity, and function of anti-HTLV-1 Tax CD8+ T cell clones may be one of the risks of ATL development.

Down-regulation ofASY/Nogo transcription associated with progression of adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive form of human leukemia/lymphoma. Although this disease is initiated by infection with human T-lymphotropic virus type 1 (HTLV-1), many HTLV-1 carriers survive for a long period without aggressive illness, suggesting that other factors may play roles in the progression of ATLL to an aggressive state. However, the mechanism involved in this progression still remains unclear. Previously, we have reported that ASY/Nogo mRNA was markedly down-regulated in human small-cell lung carcinomas, whereas it was expressed in normal tissues and other lung carcinomas, such as adenocarcinoma and squamous cell carcinoma. To understand whether or not ASY/Nogo gene is involved in the progression of ATLL, we examined the expression of ASY/Nogo mRNA in smoldering, chronic and aggressive ATLL, and found that the expression level of ASY/Nogo mRNA was markedly reduced in clinically aggressive ATLL. HTLV-1 Tax expression was not affected by the down-regulation of ASY/Nogo mRNA. These results indicate that the ASY/Nogo gene may act as a suppressor against ATLL progression, independent of Tax expression.

Activation of NF-kappaB by HTLV-I and implications for cell transformation

T-cell transformation by the human T-cell leukemia virus type I (HTLV-I) involves deregulation of cellular transcription factors, including members of the NF-kappaB family. In normal T cells, NF-kappaB activation occurs transiently in response to immune stimuli, which is required for antigen-stimulated T-cell proliferation and survival. However, HTLV-I induces persistent activation of NF-kappaB, causing deregulated expression of a large array of cellular genes, which in turn contributes to the induction of T-cell transformation. The HTLV-I transforming protein Tax functions as an intracellular stimulator of IkappaB kinase (IKK), a cellular kinase mediating NF-kappaB activation by diverse stimuli. Tax physically interacts with IKK and renders this inducible kinase constitutively active. By assembling different Tax/IKK complexes, Tax targets the persistent activation of both canonical and noncanonical NF-kappaB signaling pathways. Whereas Tax plays a primary role in HTLV-I-mediated NF-kappaB activation, recent studies reveal that the IKK/NF-kappaB signaling pathway is also activated in freshly isolated adult T-cell leukemia (ATL) cells that often lack detectable Tax expression. The mechanism underlying this Tax-independent pathway of NF-kappaB activation remains poorly understood. Clarifying the precise nature and consequences of the constitutive NF-kappaB activation in ATL cells is important for developing rational therapeutic strategies for this T-cell malignancy.

Human leukocyte antigen-class II-negative long-term cultured human T-cell leukemia virus type-I-infected T-cell lines with progressed cytological properties significantly induce superantigen-dependent normal T-cell proliferation

While most human T-cell leukemia virus type-I (HTLV-I)-infected T cells express abundant class II antigens, some aggressive-type adult T-cell leukemia (ATL) cells lose their expression. To investigate the significance of the class II antigen of HTLV-I infected cells, the progressiveness of HTLV-I-infected long-term cultured T-cell lines was evaluated, and then their antigen-presenting capacity was examined using a superantigen, staphylococcus enterotoxin B (SEB). Among the cell lines derived from peripheral blood, HPB-ATL-T (ATL-T), HPB-ATL-2 (ATL-2) and HPB-ATL-O were more progressed than Tax exclusively expressing HPB-CTL-I (CTL-I), because the former deleted p16 gene (polymerase chain reaction (PCR)) and strongly transcribed survivin (reverse transcriptase-PCR). Notably, interferon gamma-independent loss of class II expression of ATL-T and ATL-2 was found. In antigen-presenting experiments, however, both cell lines induced SEB-dependent significant T-cell proliferation estimated by [(3)H] thymidine uptake. No class II-re-expressed ATL-2 cells were observed in the SEB-presenting cultures by indirect immunofluorescence, and only minimum inhibition of SEB-dependent T-cell response by anti-human leukocyte antigen (HLA)-DR monoclonal antibody was observed. These findings suggest that both ATL-T and ATL-2 very effectively present SEB to T cells less dependently on class II molecules. These less immunogenic leukemic cells of aggressive ATL may contribute to disease aggression.

Analysis of interleukin-27 (EBI3/p28) expression in Epstein-Barr virus- and human T-cell leukemia virus type 1-associated lymphomas: heterogeneous expression of EBI3 subunit by tumoral cells

Interleukin (IL)-27 is a novel heterodimeric cytokine of the IL-12 family that is composed of two subunits, Epstein-Barr virus (EBV)-induced gene 3 (EBI3) and p28. EBI3 is expressed at high levels in EBV-transformed B-cell lines and is induced in vitro by the EBV oncogene LMP1 in a nuclear factor (NF)-kappaB-dependent manner. We show here that EBI3 expression is up-regulated in human T-cell leukemia virus type 1 (HTLV-1)-infected cell lines and IL-2-dependent leukemic cells from adult T-cell leukemia/lymphoma (ATL) patients, compared to normal activated T cells. EBI3 expression was decreased in HTLV-1-transformed cells after treatment with the NF-kappaB inhibitor BAY11-7082 and was induced in Jurkat cells by expression of HTLV-1 wild-type Tax oncoprotein, but not by the Tax mutant M22, which is defective for NF-kappaB activation. In situ analysis of EBI3 and p28 expression in Hodgkin's lymphomas (HLs), in various EBV-associated lymphoproliferative disorders (LPDs) (including post-transplant LPDs and nasal-type NK/T-cell lymphomas), and in ATL showed that EBI3 was expressed by neoplastic cells in all cases of HL and of LMP1-positive EBV-associated LPD, at variable levels in ATL cases, but rarely in control T-cell lymphomas. In contrast, in all lymphomas tested, no or few tumoral cells expressed p28. Consistent with these data, no significant p28 or IL-27 expression was detected in HL-derived cell lines, or in EBV- or HTLV-1-transformed cell lines. This selective overexpression of EBI3 by transformed cells suggests that EBI3 may play a role, independently from its association to p28, in regulating anti-viral or anti-tumoral immune responses.

HTLV-I Tax protein inhibits apoptosis induction but not G1 arrest by pyrrolidinedithiocarbamate, an anti-oxidant, in adult T cell leukemia cells

OBJECTIVE

We examined the anti-tumor effect of pyrrolidinedithiocarbamate (PDTC) on HTLV-1-infected T clones and the mechanism of HTLV-1 Tax protein inhibition of PDTC-induced apoptosis.

MATERIALS AND METHODS

Tax-nonproducing clones S1T and Su9T01, Tax-producing clones K3T and F6T, and Tax cDNA stably transfected S1TcTax clones S1TcTax04 and S1TcTax05 were examined for PDTC inhibition of thymidine incorporation and apoptosis induction by ISEL method. In addition, S1TcTax clones were analyzed by DNA histography and DNA fragmentation and also examined for p53, p21, or Bax protein expression by Western blot.

RESULTS

PDTC inhibited thymidine incorporation of all four HTLV-1-infected T cells in a similar dose-dependent manner, but K3T and F6T were more resistant than S1T and Su9T01 in apoptosis induction. S1TcTax clones also showed resistance to PDTC-induced apoptosis as compared to Tax-nonproducing S1T and S1Tneo. DNA histography demonstrated that PDTC induces G1 arrest and apoptosis in S1T and S1Tneo, and that S1TcTax clones are also sensitive to PDTC in G1 arrest but resistant in apoptosis induction. DNA fragmentation also demonstrated ladder formation only in S1Tneo but not in S1TcTax04. Western blots demonstrated higher expression of p53 and p21 proteins in S1Tneo than in S1TcTax04 during whole phase after PDTC stimulation with moderate enhancement in S1Tneo but small in S1TcTax04. Bax protein expression was detected only at early phase in S1Tneo but was not detected in S1TcTax04.

CONCLUSION

These findings suggest that PDTC-induced apoptosis is related with Bax, and that G1 arrest is possibly related with p21. Tax might inhibit apoptosis induction mainly via inhibition of Bax expression preceded at least in part by p53 inhibition.

Differential patterns of human cytomegalovirus gene expression in various T-cell lines carrying human T-cell leukemia-lymphoma virus type I: role of Tax-activated cellular transcription factors

Replication of human cytomegalovirus (HCMV) was investigated in various T-cell lines expressing the tax gene product of human T-cell leukemia-lymphoma virus type I (HTLV-I). Differential patterns of HCMV replication were found in HTLV-I-carrying cell lines. HCMV gene expression was restricted to the immediate-early genes in MT-2 and MT-4 cells, whereas full replication cycle of the virus was observed in C8166-45 cells. Productive HCMV infection induced a cytopathic effect resulting in the lysis of infected cells. The results of electrophoretic mobility shift assay (EMSA) showed high levels of NF-kappaB-, CREB/ATF-1-, and SRF-specific DNA binding activity in all Tax-positive cell lines. In contrast, SP1 activity could be detected only in C8166-45 cells. Using an inducible system (Jurkat cell line JPX-9), a dramatic increase in NF-kappaB, CREB/ATF-1, SRF, and SP1 binding activity, as well as productive HCMV infection, were observed upon Tax expression. Overexpression of SP1 in MT-2 and MT-4 cells converted HCMV infection from an abortive to a productive one. These data suggest that the stimulatory effect of Tax protein on HCMV in T cells is accomplished through at least five host-related transcription factor pathways. The results of this study provide possible mechanisms whereby HCMV infections might imply suppression of adult T-cell leukemia.

Capsaicin inhibits growth of adult T-cell leukemia cells

Human T-cell leukemia virus type 1 (HTLV-1)-associated adult T-cell leukemia (ATL) is resistant to conventional chemotherapy. We examined the in vitro effects of capsaicin, the principal ingredients of red pepper, on three ATL cell lines. Capsaicin treatment inhibited the growth of ATL cells both in dose- and time-dependent manner. The inhibitory effect was mainly due to the induction of cell cycle arrest and apoptosis. Capsaicin treatment also induced the degradation of Tax and up-regulation of I kappa-B alpha, resulting in the decrease of nuclear factor (NF)-kappa B/p65 DNA binding activity. In addition, the Bcl-2 level was found to be decreased. Based on these findings, capsaicin may be considered for chemoprevention of ATL.

Autocrine and/or paracrine growth of adult T-cell leukaemia tumour cells by interleukin 15

We previously demonstrated that interleukin 2 (IL-2) autocrine/paracrine growth in adult T-cell leukaemia (ATL) cells was closely correlated with clinical aggressiveness. In the present study, we compared the significance of IL-15 and IL-2 in growth of ATL cells and clinical aggressiveness. Thirty-seven patients with ATL were examined: 19 acute and 18 chronic. Autonomous growth and IL-2- or IL-15-responsive growth activities of ATL cells were measured by [3H]-thymidine incorporation after 24 h cultures in vitro. All of the autonomous, IL-15- and IL-2-responsive growth activities of acute-type cells were higher than those of chronic type (P = 0.04, P = 0.03 and P = 0.02 respectively). IL-15- and IL-2-responsive growth activities were highly correlated (P = 0.0001, R2 = 0.837). Enzyme-linked immunosorbent assay (ELISA) showed detectable serum levels of IL-15 and IL-2 in 18 out of 19 and 14 out of 17 patients respectively. Reverse transcription polymerase chain reaction (RT-PCR) revealed IL-15 and IL-2 mRNA expression in 8 out of 11 patients' cells. Anti-IL-2 antibody partially inhibited autonomous growth of ATL cells; anti-IL-15 antibody was less effective. In situ immunochemistry detected IL-15 in cells of three patients and was consistent with the results of RT-PCR. These results suggest that ATL cells grow in an IL-15 autocrine/paracrine manner and that this growth is related to disease aggressiveness in a manner similar to IL-2.

Clinical significance of serum neuron-specific enolase in patients with adult T-cell leukemia

The present study examines the clinical significance of serum neuron-specific enolase (NSE) in patients with adult T cell-leukemia (ATL). Serum NSE values were measured using a radioimmunoassay in 35 patients (acute type, n = 15; lymphoma type, n = 10; chronic type, n = 10) and in 7 controls carrying T lymphotropic virus type-1 (HTLV-1). Serum NSE values >10 ng/mL were detected in 9 of 15 patients with acute type (60%), 5 of 10 with lymphoma type (50%), and in one of 10 patients with chronic type (10%) ATL, but in none of the HTLV-1 carriers. Contrary to previous findings demonstrating that 20% of patients with non-Hodgkin's lymphoma (NHL) had positive serum NSE, the frequency of a high NSE value in patients with acute and lymphoma type ATL was much higher (60% and 50%, respectively). The serum NSE value positively correlated with serum thymidine kinase activity (TK) and serum soluble interleukin-2 receptor (sIL-2R) levels (P < 0.04 and P < 0.01, respectively). Serum NSE values at the initial diagnosis were adversely related to overall survival time according to the log-rank test (P < 0.02). Pathological examinations demonstrated that both patients with anaplastic large cell lymphoma type ATL had cytoplasmic NSE and CD30 markers on cell membranes. These findings suggest that serum NSE is partially produced by ATL cells and that ATL tumor cells seem preferentially produce NSE compared with other NHL cells. Serum NSE may be a novel marker of disease aggressiveness as well as a prognostic factor for ATL.

Human T-cell lymphotropic-I-associated leukemia/lymphoma

Human T-cell lymphotropic virus-I (HTLV-I)-related adult T-cell leukemia/lymphoma (ATL) is a model disease for proof of viral oncogenesis. HTLV-I infection is endemic in southern Japan and the Caribbean basin, and occurs sporadically in Africa, Central and South America, the Middle East, and the southeastern United States. ATL occurs in only 2% to 4% of HTLV-I-infected people [1-3]. When it does occur, it is usually aggressive and difficult to treat; most people survive for less than 1 year [1-3]. Combination chemotherapy with cytotoxic agents has yielded complete response rates of 20% to 45%, but responses usually last only a few months [3]. Recently, novel treatments, such as monoclonal antibodies directed at the interleukin-2 receptor and the combination of interferon alfa and zidovudine, have been shown to be active in the treatment of patients with ATL. A small percentage of patients achieve long-lasting remissions [2,3].

A mechanism of apoptosis induced by all-trans retinoic acid on adult T-cell leukemia cells: a possible involvement of the Tax/NF-kappaB signaling pathway

In this study, five single clones were randomly established by limiting dilution method from each of the HTLV-I positive T cell lines - HUT 102 and ATL-2, and examined for the all-trans retinoic acid (ATRA) sensitivity, respectively. For each clone, we found a significant correlation between the reduction in 3[H]-thymidine incorporation and the reduction in CD25 expression (r=0.701, P<0.05) following treatment with 10(-5) M ATRA for 48 h. Agarose gel electrophoresis revealed DNA fragmentation of the cell lines treated with ATRA, indicative of apoptosis. These results suggested that the tax gene in the HTLV-I genome might be a key molecule involved in cell proliferation and CD25 expression. Thereafter, we transfected the tax gene in the expression vector (pCMV-Tax-neo) into the HTLV-I(-) T cell line Jurkat and examined the effects of ATRA on cell growth. The results showed that ATRA sensitivity was acquired by the Jurkat cells transfected with the tax gene expression vector, but not in those transfected with the control vector. We also observed NF-kappaB transcriptional activity on Jurkat cells transfected with the tax gene by CAT assay in the presence or absence of ATRA. NF-kappaB transcriptional activity was decreased significantly on Jurkat cells transfected with the tax gene after ATRA treatment. Taken together, these results indicate that ATRA may affect or block the Tax/NF-kappaB signaling pathway in ATL cells.

HTLV-I Tax related dysfunction of cell cycle regulators and oncogenesis of adult T cell leukemia

HTLV-I is causually related to the oncogenesis of adult T cell leukemia (ATL). However, the precise mechanism of HTLV-I oncogenesis is unclear. HTLV-I Tax protein functions as an activator of various cellular genes, including IL-2, IL-2 receptor-alpha, and c-fos through the activation of nuclear transfer factors such as NF-kappaB and SRF, and also potently activates trascription of viral genes through CREB/ATF sites in the viral LTR. However, Tax activation of HTLV-I infected T cells through the above pathways induces polyclonal proliferation of the cells in vitro; Tax however may function only transiently in the immediate post-infection period following infection in vivo. The long latent period of 60 years from infection to onset of disease suggests other mechanisms for ATL oncogenesis. Recent studies suggest that the malignant transformation of ATL is a multi-hit phenomena, suggesting that discrete genetic events are responsible for ATL oncogenesis. These genetic events could be responsible for the different stages of ATL: smoldering, chronic, lymphoma, and acute type, p16 and p53 genes are important negative regulators of the cell cycle and are often found to be mutated in neoplasms. Recent studies including ours demonstrated a high frequency of alteration of these two genes in primary ATL cells. Furthermore, alteration of the two genes is associated with acute but not chronic type ATL. In addition, p16 gene alteration is linked to the growth rate of ATL cells, suggesting that the alteration of these cell cycle regulatory genes may be related to progression from smoldering or chronic to acute or lymphoma type ATL. Tax may be involved in mutagenesis of these genes through suppression of DNA-beta polymerase gene expression during the process from latent period to acute/lymphoma type. Once transformation occurs, activation of the pathway between Tax and the three nuclear transfer factors, NF-kappaB, SRF, and CREB/ATF, contributes to establish the aggressive manifestations of acute/lymphoma type ATL cells.

Bcl-XL is up-regulated by HTLV-I and HTLV-II in vitro and in ex vivo ATLL samples

Human T lymphotropic virus type I (HTLV-I) is the etiological agent of adult T-cell lymphocytic leukemia (ATLL), whereas HTLV-II has not been associated with hematopoietic malignancies. The control of apoptotic pathways has emerged as a critical step in the development of many cancer types. As a result, the underlying mechanism of long-term survival of HTLV-I and HTLV-II was studied in infected T cells in vitro and in ex vivo ATLL samples. Results indicate that HTLV-I– and HTLV-II–infected T cells in vitro express high levels of the antiapoptotic protein Bcl compared with other human leukemic T cell lines or uninfected peripheral blood mononuclear cells. The levels of proapoptotic proteins Bax, BAD, and Bak were not significantly altered. HTLV-I and HTLV-II viral transactivators, Tax1 and Tax2, are known to increase expression of cellular genes. These proteins were tested for increased transcription from the human Bcl2 and Bcl-XL promoters. Whereas no effect was observed on the Bcl2 promoter, both Tax1 and Tax2 increased transcription of the Bcl-XL promoter in T cells, although Tax1 appeared to be more efficient than Tax2. The biological significance of these observations was validated by the finding of an increased expression of Bcl-XL in ex vivo ATLL cells, especially from patients unresponsive to various chemotherapy regimens. Altogether, these data suggest that overexpression of Bcl-XL in vivomay be in part responsible for the resistance of ATLL cells to chemotherapy. In addition, inefficient activation of the Bcl-XL promoter by Tax2 may result in a shorter survival time of HTLV-II–infected cells in vivo and a diminished risk of leukemia development.

Bcl-XL is up-regulated by HTLV-I and HTLV-II in vitro and in ex vivo ATLL samples

Human T lymphotropic virus type I (HTLV-I) is the etiological agent of adult T-cell lymphocytic leukemia (ATLL), whereas HTLV-II has not been associated with hematopoietic malignancies. The control of apoptotic pathways has emerged as a critical step in the development of many cancer types. As a result, the underlying mechanism of long-term survival of HTLV-I and HTLV-II was studied in infected T cells in vitro and in ex vivo ATLL samples. Results indicate that HTLV-I– and HTLV-II–infected T cells in vitro express high levels of the antiapoptotic protein Bcl compared with other human leukemic T cell lines or uninfected peripheral blood mononuclear cells. The levels of proapoptotic proteins Bax, BAD, and Bak were not significantly altered. HTLV-I and HTLV-II viral transactivators, Tax1 and Tax2, are known to increase expression of cellular genes. These proteins were tested for increased transcription from the human Bcl2 and Bcl-XL promoters. Whereas no effect was observed on the Bcl2 promoter, both Tax1 and Tax2 increased transcription of the Bcl-XL promoter in T cells, although Tax1 appeared to be more efficient than Tax2. The biological significance of these observations was validated by the finding of an increased expression of Bcl-XL in ex vivo ATLL cells, especially from patients unresponsive to various chemotherapy regimens. Altogether, these data suggest that overexpression of Bcl-XL in vivomay be in part responsible for the resistance of ATLL cells to chemotherapy. In addition, inefficient activation of the Bcl-XL promoter by Tax2 may result in a shorter survival time of HTLV-II–infected cells in vivo and a diminished risk of leukemia development.