Molecular cloning and characterization of a mouse homolog of human TNFSF14, a member of the TNF superfamily

Context-dependent roles for lymphotoxin-β receptor signaling in cancer development

The LTα1β2 and LIGHT TNF superfamily cytokines exert pleiotropic physiological functions through the activation of their cognate lymphotoxin-β receptor (LTβR). Interestingly, since the discovery of these proteins, accumulating evidence has pinpointed a role for LTβR signaling in carcinogenesis. Early studies have shown a potential anti-tumoral role in a subset of solid cancers either by triggering apoptosis in malignant cells or by eliciting an anti-tumor immune response. However, more recent studies provided robust evidence that LTβR signaling is also involved in diverse cell-intrinsic and microenvironment-dependent pro-oncogenic mechanisms, affecting several solid and hematological malignancies. Consequently, the usefulness of LTβR signaling axis blockade has been investigated as a potential therapeutic approach for cancer. Considering the seemingly opposite roles of LTβR signaling in diverse cancer types and their key implications for therapy, we here extensively review the different mechanisms by which LTβR activation affects carcinogenesis, focusing on the diverse contexts and different models assessed.

Lentivirus-mediated LIGHT overexpression inhibits human colorectal carcinoma cell growth in vitro and in vivo

Human LIGHT (lymphotoxin-related inducible ligand that competes for glycoprotein D binding to herpesvirus entry mediator on T cells) is the 14th member of the tumor necrosis factor (TNF) superfamily and is therefore also known as TNFSF14. LIGHT has been proven to be a multifunctional molecule affecting cell proliferation, differentiation and a number of other biological processes, in particular, cell growth inhibition. However, the expression and molecular mechanisms of the LIGHT gene in human colorectal carcinoma cells remain largely unclear. In the present study, the LIGHT gene was overexpressed using a lentiviral expression vector in HCT116 human colorectal carcinoma cells in vitro and in vivo, in order to explore the mechanism by which the LIGHT gene inhibits cell growth and suppresses tumor formation. The results showed that the recombinant lentivirus with LIGHT overexpression inhibited the proliferative capacity of the HCT116 cells and significantly decreased the xenografted tumor volumes in nude mice. Furthermore, LIGHT treatment effectively initiated increased caspase-3 and decreased Bcl-2 activities in the HCT116 cells. This study provides a basis for the improved understanding of the role and molecular mechanisms of the LIGHT gene in human colorectal carcinoma cells and may facilitate further functional studies of LIGHT.

LIGHT is dispensable for CD4+ and CD8+ T cell and antibody responses to influenza A virus in mice

The tumor necrosis factor family ligands, LIGHT (lymphotoxin like, exhibits inducible expression and competes with HSV glycoprotein D for HVEM, a receptor expressed by T lymphocytes), 4-1BBL and CD70, are found in the same gene cluster on mouse chromosome 17. Although the roles of 4-1BB-4-1BBL and CD27-CD70 interactions in anti-viral T cell responses have been well established, the role of LIGHT in T cell activation/expansion in vivo is less clear. Under conditions that were previously employed to demonstrate a role for 4-1BBL in CD8+ T cell memory, wild-type and LIGHT-/- mice were infected with influenza A virus and primary and memory/recall responses were measured at various time points thereafter. Neither primary expansion nor memory/recall CD8+ T cell responses were affected by the absence of LIGHT, as measured up to 2 months post-infection. CD4+ T cell responses were also unaffected by LIGHT deficiency. Furthermore, we found that LIGHT played no role in the induction of influenza-specific IgG1 and IgG2a serum antibodies. Taken together, these data suggest that LIGHT is dispensable for the acquired immune response to influenza virus in mice with no effect on the induction, maintenance or reactivation of CD8+ T cell memory.

Mechanisms regulating expression of the tumor necrosis factor-related light gene. Role of calcium-signaling pathway in the transcriptional control

LIGHT (TNFSF14) is a newly identified tumor necrosis factor superfamily member involved in the regulation of immune responses by control of activation, maturation, and survival of immune effector cells. Despite the immunological relevance of the LIGHT protein, little knowledge is available as to how light gene expression is regulated. In T-lymphocytes, most LIGHT surface expression and transcript accumulation occurs after T cell activation. In this study, we have shown that these events are blocked at the transcriptional level by cyclosporin A, an immuno-suppressive drug. Besides, we identified a role for Ca2+ -signaling pathways and NFAT transcription factors in T cell activation-induced LIGHT expression. To further investigate this process, we have identified, cloned, and characterized a 2.1-kilobase 5'-flanking DNA genomic fragment from the human light gene. We have shown the transcriptional activity of the herein-identified minimal 5' regulatory region of human light gene parallels the endogenous expression of light in T cells. Moreover, we demonstrated that induced LIGHT promoter activity can be equally blocked by cyclosporin A treatment or dominant negative NFAT overexpression and further identified by site-directed mutagenesis and electrophoretic mobility supershift analysis of a NFAT transcription factor binding site within the human light minimal promoter. Finally, Sp1 and Ets1 binding sites were identified and shown to regulate light basal promoter activity. Thus, the present study establishes a molecular basis to further understand the mechanisms governing human light gene expression and, consequently, could potentially lead to novel therapeutic manipulations that control the signaling cascade, resulting in LIGHT production in conditions characterized by immunopathologic activation of T cells.

Targeted disruption of LIGHT causes defects in costimulatory T cell activation and reveals cooperation with lymphotoxin beta in mesenteric lymph node genesis

The recently described tumor necrosis factor (TNF) family member LIGHT (herpes virus entry mediator [HVEM]-L/TNFSF14), a ligand for the lymphotoxin (LT)beta receptor, HVEM, and DcR3, was inactivated in the mouse. In contrast to mice deficient in any other member of the LT core family, LIGHT(-/-) mice develop intact lymphoid organs. Interestingly, a lower percentage of LIGHT(-/-)LTbeta(-/-) animals contain mesenteric lymph nodes as compared with LTbeta(-/-) mice, whereas the splenic microarchitecture of LIGHT(-/-)LTbeta(-/-) and LTbeta(-/-) mice shows a comparable state of disruption. This suggests the existance of an additional undiscovered ligand for the LTbeta receptor (LTbetaR) or a weak LTalpha(3)-LTbetaR interaction in vivo involved in the formation of secondary lymphoid organs. LIGHT acts synergistically with CD28 in skin allograft rejection in vivo. The underlying mechanism was identified in in vitro allogeneic MLR studies, showing a reduced cytotoxic T lymphocyte activity and cytokine production. Detailed analyses revealed that proliferative responses specifically of CD8+ T cells are impaired and interleukin 2 secretion of CD4+ T cells is defective in the absence of LIGHT. Furthermore, a reduced 3[H]-thymidine incorporation after T cell receptor stimulation was observed. This for the first time provides in vivo evidence for a cooperative role for LIGHT and LTbeta in lymphoid organogenesis and indicates important costimulatory functions for LIGHT in T cell activation.

Ionizing radiation sensitizes erythroleukemic cells but not normal erythroblasts to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)--mediated cytotoxicity by selective up-regulation of TRAIL-R1

Cytotoxic activity of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo-2 ligand), used alone or in different combinations with either a low (1.5 Gy) or a high (15 Gy) single dose of ionizing radiation (IR), was investigated on erythroleukemic cells (K562, HEL, Friend, primary leukemic erythroblasts) and on primary CD34(+)-derived normal erythroblasts. Human recombinant TRAIL alone variably affected the survival/growth of erythroleukemic cells; K562 cells were the most sensitive. Moreover, all erythroleukemic cells were radio-resistant, as demonstrated by the fact that cytotoxicity was evident only after treatment with high-dose (15 Gy) IR. Remarkably, when IR and TRAIL were used in combination, an additive effect was noticed in all erythroleukemic cells. Augmentation of TRAIL-induced cell death by IR was observed with both low and high IR doses and required the sequential treatment of IR 3 to 6 hours before the addition of TRAIL. Conversely, both TRAIL and IR showed a moderate cytotoxicity on primary CD34(+)-derived normal erythroblasts when used alone, but their combination did not show any additive effect. Moreover, the cytotoxicity of IR plus TRAIL observed in erythroleukemic cells was accompanied by the selective up-regulation of the surface expression of TRAIL-R1 (DR4), and it was completely blocked by the z-Val-Ala-Asp (OMe)-CH(2) (z-VAD-fmk) caspase inhibitor. On the other hand, the surface expression of TRAIL-R1 in CD34(+)-derived normal erythroblasts was unaffected by IR, which induced the up-regulation of the decoy TRAIL-R3. These data demonstrate that treatment with IR provides an approach to selectively sensitize erythroleukemic cells, but not normal erythroblasts, to TRAIL-induced apoptosis through the functional up-regulation of TRAIL-R1.