Chemokine Receptor CCR6 Expression in Colorectal Liver Metastasis

The mechanisms on evasion of anti-tumor immune responses in gastric cancer

The immune system and the tumor have been at each other's throats for so long that the neoplasm has learned to avoid detection and avoid being attacked, which is called immune evasion. Malignant tumors, such as gastric cancer (GC), share the ability to evade the body's immune system as a defining feature. Immune evasion includes alterations to tumor-associated antigens (TAAs), antigen presentation mechanisms (APMs), and the tumor microenvironment (TME). While TAA and APM are simpler in nature, they both involve mutations or epigenetic regulation of genes. The TME is comprised of numerous cell types, cytokines, chemokines and extracellular matrix, any one of which might be altered to have an effect on the surrounding ecosystem. The NF-kB, MAPK, PI3K/AKT, JAK/STAT, Wnt/β-catenin, Notch, Hippo and TGF-β/Smad signaling pathways are all associated with gastric cancer tumor immune evasion. In this review, we will delineate the functions of these pathways in immune evasion.

TNF-α increases the membrane expression of the chemokine receptor CCR6 in thyroid tumor cells, but not in normal thyrocytes: potential role in the metastatic spread of thyroid cancer

The chemokine receptor CCR6, selectively bound by CCL20, is involved in the metastatic spread of cancer cells. Tumor necrosis factor-α (TNF-α) displays a complex pro-tumorigenic actions, but it is unknown whether this cytokine could modulate the expression of chemokine receptors in thyroid tumors. The membrane expression of CCR6 was assessed by flow cytometry and immunofluorescence, in primary cultures of normal human thyroid (NHT) cells and in thyroid cancer cell lines (TPC-1 and BCPAP), both in basal conditions and after stimulation with TNF-α. In basal conditions, CCR6+ cells were virtually absent in NHT cells (0.4 ± 0.4 %), while they were detected in TPC-1 (23.6 ± 6.6 %) and in BCPAP (12.9 ± 9.4 %) tumor cells (ANOVA F: 10.534; p < 0.005). The incubation with TNF-α significantly increased the percentage of CCR6+ cells in TPC-1 (23.6 ± 6.6 % vs. 33.1 ± 8.7; p < 0.033) and in BCPAP (12.9 ± 9.4 % vs. 18.1 ± 11.5; p < 0.030), but not in NHT (0.4 ± 0.4 % vs. 0.2 ± 0.3; NS) cells. The magnitude of the TNF-α effect was similar for TPC-1 and BCPAP (∼40 % vs. baseline) cells. TPC-1 cells were characterized by a greater amount of CCR6 per cell as compared with BCPAP cells, both in basal conditions (148.3 ± 33.7 fluorescence intensity vs. 102.5 ± 22.1 p < 0.016) and after TNF-α stimulation (147.8 ± 46.3 fluorescence intensity vs. 95.3 ± 18.5; p < 0.025). Cell migration assays showed that TNF-α treatment significantly increased the rate of migrated cells in those cells in which it also increased the membrane expression of CCR6 (TPC-1 and BCPAP) as compared to basal condition (p < 0.05 for both TPC-1 and BCPAP cells). No effect was observed in NHT cells in which TNF-α stimulation had no effect in terms of CCR6 expression. We first report that TNF-α enhances the expression of CCR6 in thyroid tumor cells, thus providing evidence that TNF-α increases the metastatic potential of thyroid tumors.

The role of toll-like receptors in colorectal cancer progression: evidence for epithelial to leucocytic transition

Toll-like receptors (TLRs) are expressed by immune cells, intestinal epithelium, and tumor cells. In the homeostatic setting, they help to regulate control over invading pathogens and maintain the epithelial lining of the large and small intestines. Aberrant expression of certain TLRs by tumor cells can induce growth inhibition while others contribute to tumorigenesis and progression. Activation of these TLRs can induce inflammation, tumor cell proliferation, immune evasion, local invasion, and distant metastasis. These TLR-influenced behaviors have similarities with properties observed in leukocytes, suggesting that tumors may be hijacking immune programs to become more aggressive. The concept of epithelial to leucocytic-transition (ELT) is proposed, akin to epithelial to mesenchymal transition, in which tumors develop the ability to activate leucocytic traits otherwise inaccessible to epithelial cells. Understanding the mechanisms of ELT could lead to novel therapeutic strategies for inhibiting tumor metastasis.

Differential Expression of Chemokine Receptors and their Roles in Cancer Imaging

Chemokine/chemokine receptor interactions play diverse roles in cell migration and homeostasis. Emerging evidence suggests that cancer cells co-opt chemokine networks for survival, proliferation, immune evasion, and metastasis. Most of the chemokine receptors are reported to be involved in tumor progression. Given their extensive implication in cancer progression, several chemokine receptor/ligand axes are considered as potential therapeutic targets. This review provides a survey of chemokine receptor expression in cancer and evaluates the potential of chemokine receptor imaging as a tool for molecular characterization of cancer.

MiR-21 is involved in cervical squamous cell tumorigenesis and regulates CCL20

MicroRNA 21 (miR-21) has been implicated in various aspects of carcinogenesis. However, its function and molecular mechanism in cervical squamous carcinoma have not been studied. Using TaqMan quantitative real-time PCR and Northern blot, we confirmed that miR-21 is significantly overexpressed in human cervical squamous cancer tissues and cell lines. Remarkably, we showed that the level of miR-21 correlates with the tumor differentiation and nodal status by ISH. Furthermore, we demonstrated that miR-21 regulates proliferation, apoptosis, and migration of HPV16-positive cervical squamous cells. In order to identify candidate target genes for miR-21, we used gene expression profiling. By luciferase reporter assays, we confirmed that CCL20 is one of its target genes, which is related to the HPV16 E6 and E7 oncogenes. Our results suggest that miR-21 may be involved in cervical squamous cell tumorigenesis.

Circulating tumour-derived microvesicles in plasma of gastric cancer patients

Cell membrane microfragments called microvesicles (MV) originating from different cells are circulating in the blood of healthy subjects and their elevated numbers are found in different diseases, including cancer. This study was designed to characterise MV present in plasma of gastric cancer patients. Since majority of MV in blood are platelets-derived (PMV), plasma samples deprived of PMV were used. In comparison to control, the number of MV in patients was significantly elevated in all stages, higher in more advanced disease. Patients' MV showed an increased membrane expression of CCR6 and HER-2/neu. The proportion of MV carrying some leucocyte determinants was low and similar in patients and control. Transmission electron microscopy showed their substantial heterogeneity in size and shape. The size determined by dynamic light scattering analysis confirmed this heterogeneity. The MV size distribution in patients was broader within the range of 10-800 nm, while in control MV showed 3-mode distribution within the range of 10-400 nm. Atomic force microscopy confirmed MV size heterogeneity with implication that larger objects represented aggregates of smaller microparticles. Patients' MV exhibited increased absolute values of zeta potential, indicating a higher surface charge. Tumour markers HER-2/neu, MAGE-1, c-MET and EMMPRIN were detected both in control and patients' samples with stronger expression in the latter. Significantly higher expression of MAGE-1 and HER-2/neu mRNA was observed in individual patients. All together, it suggests that at least some MV in plasma of gastric cancer patients are tumour-derived. However, their role in cancer requires further studies.

Increased migration of Langerhans cells in response to HPV16 E6 and E7 oncogene silencing: role of CCL20

Human papillomavirus (HPV) infection, particularly type 16, is causally associated with cancer of the uterine cervix. The persistence or progression of cervical lesions suggests that viral antigens are not adequately presented to the immune system. This hypothesis is reinforced by the observation that most squamous intraepithelial lesions (SILs) show quantitative and functional alterations of Langerhans cells (LC). The infiltration of immature LC in the squamous epithelium is mainly controlled by Macrophage Inflammatory Protein 3alpha/CCL20. After having shown that CCL20 production is altered in HPV-transformed keratinocytes (KC), the possible role of HPV16 E6 and E7 viral oncoproteins in the reduced CCL20 levels observed in SILs was investigated by silencing HPV16 E6 and E7 oncogenes by RNA interference (siRNA). This treatment not only increased CCL20 secretion but also resulted in the modulation of NF-kappaB p50, p52 and p65 precursor localization. Moreover, silencing of E6 and E7 oncogenes in HPV16-transformed KC induced a significantly higher migratory capacity of LC in a Boyden chamber assay and in an in vitro formed (pre)neoplastic epithelium reminiscent of high-grade SILs. Anti-CCL20 neutralizing antibody experiments showed that the increased migration of LC is due to the re-expression of CCL20 in E6 and E7 siRNA transfected KC. These data suggest that HPV16 E6/E7-induced down-regulation of CCL20 observed during the cervical carcinogenesis may contribute to a diminished capacity of the immune system to control HPV infection.

Tumorigenicity of IL-1alpha- and IL-1beta-deficient fibrosarcoma cells

Analyzing the growth of fibrosarcoma lines derived from IL-1alpha-, IL-1beta- , or IL-1alphabeta-knockout (-/-) mice in the immunocompetent host revealed that tumor-derived IL-1alpha and IL-1beta exert strong and opposing effects on immune response induction, which prohibited the evaluation of a potential impact on tumorigenicity. Therefore, in vivo growth of IL-1-deficient tumor lines was evaluated in nu/nu mice and was compared with in vitro growth characteristics. All IL-1-deficient fibrosarcoma lines grow in immunocompromised mice. However, IL-1alpha(-/-)beta-competent (comp) lines grow more aggressively, efficiently induce angiogenesis, and recruit inflammatory cells. Despite stronger tumorigenicity of IL-1beta(comp) lines, IL-1alpha strengthens anchorage-independent growth, but both IL-1alpha and IL-1beta support drug resistance. Corresponding to the aggressive growth, IL-1beta(comp) cells display increased matrix adhesion, motility, and cable formation on matrigel, likely supported by elevated alpha(v)/beta3 and matrix metalloroteinase expression. Recruitment of myeloid cells requires IL-1beta but is regulated by IL-1alpha, because inflammatory chemokine and cytokine expression is stronger in IL-1alpha(-/-)beta(comp) than in IL-1(wt) lines. This regulatory effect of tumor-derived IL-1alpha is restricted to the tumor environment and does not affect systemic inflammatory response induction by tumor-derived IL-1beta. Both sarcoma cell-derived IL-1alpha and IL-1beta promote tumor growth. However, IL-1alpha exerts regulatory activity on the tumor cell-matrix cross-talk, and only IL-1beta initiates systemic inflammation.

Hypoxia transcriptionally induces macrophage-inflammatory protein-3alpha/CCL-20 in primary human mononuclear phagocytes through nuclear factor (NF)-kappaB

Hypoxia, a condition of low oxygen tension, occurring in many pathological processes, modifies the mononuclear phagocyte transcriptional profile. Here, we demonstrate hypoxic up-regulation of the CCL20 chemokine in primary human monocytes (Mn) and macrophages. mRNA induction was paralleled by protein secretion and dependent on gene transcription activation. Functional studies of the CCL20 promoter using a series of 5'-deleted and mutated reporter constructs demonstrated the requirement for the NF-kappaB-binding site located at position -92/-82 for gene transactivation by hypoxia, as 1) transcription was abrogated by a 3-bp mutation of the NF-kappaB motif; 2) three copies of the wild-type NF-kappaB-binding site conferred hypoxia responsiveness to a minimal heterologous promoter; and 3) hypoxia increased specific NF-kappaB binding to this sequence. Furthermore, we provide evidence of the specific role of a single NF-kappaB family member, p50, in mediating CCL20 gene transcription in hypoxic Mn. p50 homodimers were the only detectable NF-kappaB complexes binding the cognate kappaB site on the CCL20 promoter upon hypoxia exposure, and NF-kappaBp50 knockdown by lentiviral-mediated short hairpin RNA interference resulted in complete binding inhibition. NF-kappaBp50 overexpression in transient cotransfection studies promoted CCL20 gene transactivation, which was abrogated by mutation of the -92/-82 kappaB site. Moreover, nuclear expression of the other NF-kappaB family members was inhibited in hypoxic Mn. In conclusion, this study characterizes a previously unrecognized role for hypoxia as a transcriptional inducer of CCL20 in human mononuclear phagocytes and highlights the importance of the NF-kappaB pathway in mediating this response, with potential implications for inflammatory disease and cancer pathogenesis.

A Markov random field model for network-based analysis of genomic data

MOTIVATION

A central problem in genomic research is the identification of genes and pathways involved in diseases and other biological processes. The genes identified or the univariate test statistics are often linked to known biological pathways through gene set enrichment analysis in order to identify the pathways involved. However, most of the procedures for identifying differentially expressed (DE) genes do not utilize the known pathway information in the phase of identifying such genes. In this article, we develop a Markov random field (MRF)-based method for identifying genes and subnetworks that are related to diseases. Such a procedure models the dependency of the DE patterns of genes on the networks using a local discrete MRF model.

RESULTS

Simulation studies indicated that the method is quite effective in identifying genes and subnetworks that are related to disease and has higher sensitivity and lower false discovery rates than the commonly used procedures that do not use the pathway structure information. Applications to two breast cancer microarray gene expression datasets identified several subnetworks on several of the KEGG transcriptional pathways that are related to breast cancer recurrence or survival due to breast cancer.

CONCLUSIONS

The proposed MRF-based model efficiently utilizes the known pathway structures in identifying the DE genes and the subnetworks that might be related to phenotype. As more biological networks are identified and documented in databases, the proposed method should find more applications in identifying the subnetworks that are related to diseases and other biological processes.