AllergoOncology - the impact of allergy in oncology: EAACI position paper

Th2 immunity and allergic immune surveillance play critical roles in host responses to pathogens, parasites and allergens. Numerous studies have reported significant links between Th2 responses and cancer, including insights into the functions of IgE antibodies and associated effector cells in both antitumour immune surveillance and therapy. The interdisciplinary field of AllergoOncology was given Task Force status by the European Academy of Allergy and Clinical Immunology in 2014. Affiliated expert groups focus on the interface between allergic responses and cancer, applied to immune surveillance, immunomodulation and the functions of IgE-mediated immune responses against cancer, to derive novel insights into more effective treatments. Coincident with rapid expansion in clinical application of cancer immunotherapies, here we review the current state-of-the-art and future translational opportunities, as well as challenges in this relatively new field. Recent developments include improved understanding of Th2 antibodies, intratumoral innate allergy effector cells and mediators, IgE-mediated tumour antigen cross-presentation by dendritic cells, as well as immunotherapeutic strategies such as vaccines and recombinant antibodies, and finally, the management of allergy in daily clinical oncology. Shedding light on the crosstalk between allergic response and cancer is paving the way for new avenues of treatment.

LINE-1 induces hTERT and ensures telomere maintenance in tumour cell lines

A hallmark of cancer cells is an activated telomere maintenance mechanism, which allows prolonged survival of the malignant cells. In more than 80% of tumours, telomeres are elongated by the enzyme telomerase, which adds de novo telomere repeats to the ends of chromosomes. Cancer cells are also characterized by expression of active LINE-1 elements (L1s, long interspersed nuclear elements-1). L1 elements are abundant retrotransposons in the eukaryotic genome that are primarily known for facilitating aberrant recombination. Using L1-knockdown (KD), we show for the first time that L1 is critical for telomere maintenance in telomerase-positive tumour cells. The reduced length of telomeres in the L1-KD-treated cells correlated with an increased rate of telomere dysfunction foci, a reduced expression of shelterin proteins and an increased rate of anaphase bridges. The decreased telomere length was associated with a decreased telomerase activity and decreased telomerase mRNA level; the latter was increased upon L1 overexpression. L1-KD also led to a decrease in mRNA and protein expression of cMyc and KLF-4, two main transcription factors of telomerase and altered mRNA levels of other stem-cell-associated proteins such as CD44 and hMyb, as well as a corresponding reduced growth of spheroids. The KD of KLF-4 or cMyc decreased the level of L1-ORF1 mRNA, suggesting a specific reciprocal regulation with L1. Thus, our findings contribute to the understanding of L1 as a pathogenicity factor in cancer cells. As L1 is only expressed in pathophysiological conditions, L1 now appears to be target in the rational treatment of telomerase-positive cancer.

A novel cluster of lectin-like receptor genes expressed in monocytic, dendritic and endothelial cells maps close to the NK receptor genes in the human NK gene complex

The NK gene complex is a region on human chromosome 12 containing several families of lectin-like genes including the CD94 and NKG2 NK receptor genes. We report here that the region telomeric of CD94 contains in addition to the LOX-1 gene the novel human DECTIN-1 and the CLEC-1 and CLEC-2 genes within about 100 kb. Sequence similarities and chromosomal arrangement suggest that these genes form a separate subfamily of lectin-like genes within the NK gene complex. DECTIN-1 is selectively expressed in dendritic cells and to a lower extent in monocytes and macrophages. mRNA forms with and without a stalk exon are observed. During functional maturation of dendritic cells the level of DECTIN-1 mRNA is down-regulated several-fold. CLEC-1 is found to be not only expressed in dendritic cells, but also in endothelial cells and in the latter aspect resembles the LOX-1 gene. Whereas recombinant full-length DECTIN-1 and LOX-1 are transported to the cell surface, CLEC-1 proteins accumulate in perinuclear compartments. We propose that this family of lectin-like genes encodes receptors with important immune and/or scavenger functions in monocytic, dendritic and endothelial cells.

An inhibitory role of the phosphatidylinositol 3-kinase-signaling pathway in vascular endothelial growth factor-induced tissue factor expression

Vascular endothelial growth factor (VEGF) is not only essential for vasculogenesis and angiogenesis but is also capable of inducing tissue factor, the prime initiator of coagulation, in endothelial cells. In this study we have analyzed the VEGF-elicited pathways involved in the induction of tissue factor in human umbilical cord vein endothelial cells. Using specific low molecular weight inhibitors we could demonstrate a crucial role of the p38 and Erk-1/2 mitogen-activated protein (MAP) kinases. In contrast, treatment with wortmannin or LY294002, inhibitors of phosphatidylinositol 3 (PI3)-kinase, resulted in a strong enhancement of the VEGF-induced tissue factor production, indicating a negative regulatory role of the PI3-kinase on tissue factor-inducing pathways. Accordingly, transduction with constitutively active Akt led to a reduction of VEGF-induced tissue factor production. Western blot analyses using antibodies specific for phosphorylated p38 showed an enhanced activation of this MAP kinase in human umbilical cord vein endothelial cells when stimulated with VEGF in the presence of wortmannin in comparison to either agent alone. Thus, the negative regulation of the PI3-kinase pathway on endothelial tissue factor activity can be explained at least in part by a suppression of this MAP kinase-signaling pathway. This is the first demonstration of a reciprocal relationship between procoagulant activity and the PI3-kinase-Akt signaling pathway, and it reveals a novel mechanism by which tissue factor expression can be controlled in endothelial cells.

Specificity, diversity, and convergence in VEGF and TNF-alpha signaling events leading to tissue factor up-regulation via EGR-1 in endothelial cells

Tissue factor (TF) has been shown to be up-regulated in endothelial cells by the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha) as well as by the main angiogenic factor VEGF. Since both stimuli induce the transcription factor EGR-1, which is critically involved in TF gene regulation, we used EGR-1-dependent TF induction as a model to identify potential cross-talks between the various signal transduction cascades initiated by VEGF and TNF-alpha. The data show that at the MAP kinase level, VEGF mainly activates ERK1/2 and p38 MAP kinases in human endothelial cells. TNF-alpha is able to activate all three MAP kinase cascades as well as the classical inflammatory IkappaB/NFkappaB pathway. Furthermore, the MEK/ERK module of MAP kinases appears to act as the convergence point of VEGF- and TNF-alpha-initiated signaling cascades, which lead to the activation of EGR-1 and subsequent TF expression, whereas the upstream signals are distinct. We found that induction of TF by VEGF via EGR-1 is strongly PKC dependent. The TNF-alpha-initiated MEK/ERK cascade connected to EGR-1 and TF expression is clearly less sensitive to PKC inhibition. TNF-alpha-mediated activation of MEK/ERK and EGR-1 can be blocked by adenoviral expression of a dominant negative mutant of IKK2, whereas the VEGF signaling pathway is unaffected. Thus, our data demonstrate a new link between the classical inflammatory IKK/IkappaB and the MEK/ERK cascades triggered by TNF-alpha. The additional finding that EGF induces ERK and EGR-1 in a PKC-independent manner and that this signal is not sufficient to up-regulate TF emphasizes the importance of a VEGF-specific signaling pattern for the induction of TF.

A transcriptional repressor of the tissue factor gene in endothelial cells

Tissue factor, the high-affinity receptor and cofactor for the plasma serine protease VII/VIIa, is the primary cellular initiator of the blood coagulation cascade. Inside the vasculature, expression of the tissue factor gene must be tightly controlled. Whereas the endothelium normally does not express tissue factor, on stimulation with inflammatory cytokines or endotoxin the gene is transcriptionally upregulated leading to a procoagulant state. We have now detected a repressive cis-acting element in the tissue factor promoter that downmodulates tissue factor transcription in endothelial cells. In reporter gene assays, deletion of this element leads to an increase of tissue factor transcription and insertion of a trimerized site reduces transcription. Specific protein/DNA complexes are formed on the element with nuclear extracts in electrophoretic mobility shift assays and cross-linking of the proteins followed by SDS-PAGE detects the presence of at least 2 subunits of approximately 40 and 60 kDa, respectively. After transfection of different cell types with the reporter genes, the suppressive effect of the element can only be revealed in endothelial cells. These data suggest that this element represents a novel transcription factor target sequence that functions to suppress expression of the tissue factor gene, preferentially in endothelial cells thereby supporting a noncoagulant state.

Vascular endothelial cell growth factor-induced tissue factor expression in endothelial cells is mediated by EGR-1

Vascular endothelial cell growth factor (VEGF) is a major regulator of angiogenesis. We report here that treatment of endothelial cells with VEGF leads to upregulation of tissue factor mRNA and protein expression on the cell surface. Reporter gene studies show that transcriptional activation of the tissue factor gene by VEGF is mediated by a GC-rich promoter element containing overlapping binding sites for Sp1 and EGR-1. As shown by immunofluorescence and electrophoretic mobility shift assays, upon VEGF treatment EGR-1 rapidly accumulates in the nucleus and binds to its respective recognition site in the tissue factor promoter. Sp1 occupies this element in unstimulated cells and seems to be partially displaced by increasing amounts of EGR-1. Transfection of endothelial cells with an EGR-1 expression plasmid mimics the upregulation of tissue factor transcription observed after VEGF treatment. In contrast, NFkappaB, the major transcription factor involved in tissue factor upregulation by inflammatory stimuli, is not activated by VEGF. These data show that VEGF induces a response in endothelial cells largely distinct from inflammatory stimuli, and suggest that EGR-1 is a major mediator of the activation of the tissue factor and possibly other VEGF-responsive genes.