Cell adhesion molecules acting between C6 glioma and endothelial cells

miR-1246 in tumor extracellular vesicles promotes metastasis via increased tumor cell adhesion and endothelial cell barrier destruction

Background

Tumor blood vessels play a key role in tumor metastasis. We have previously reported that tumor endothelial cells (TECs) exhibit abnormalities compared to normal endothelial cells. However, it is unclear how TECs acquire these abnormalities. Tumor cells secrete extracellular vesicles (EVs) to create a suitable environment for themselves. We have previously identified miR-1246 to be more abundant in high metastatic melanoma EVs than in low metastatic melanoma EVs. In the current study, we focused on miR-1246 as primarily responsible for acquiring abnormalities in TECs and examined whether the alteration of endothelial cell (EC) character by miR-1246 promotes cancer metastasis.

Methods

We analyzed the effect of miR-1246 in metastatic melanoma, A375SM-EVs, in vivo metastasis. The role of tumor EV-miR-1246 in the adhesion between ECs and tumor cells and the EC barrier was addressed. Changes in the expression of adhesion molecule and endothelial permeability were examined.

Results

Intravenous administration of A375SM-EVs induced tumor cell colonization in the lung resulting in lung metastasis. In contrast, miR-1246 knockdown in A375SM decreased lung metastasis in vivo. miR-1246 transfection in ECs increased the expression of adhesion molecule ICAM-1 via activation of STAT3, followed by increased tumor cell adhesion to ECs. Furthermore, the expression of VE-Cadherin was downregulated in miR-1246 overexpressed EC. A375SM-EV treatment enhanced endothelial permeability. VE-Cadherin was validated as the potential target gene of miR-1246 via the target gene prediction database and 3' UTR assay.

Conclusion

miR-1246 in high metastatic tumor EVs promotes lung metastasis by inducing the adhesion of tumor cells to ECs and destroying the EC barrier.

Selection of recombinant phages binding to pathological endothelial and tumor cells of rat glioblastoma by in-vivo display

Pathological endothelial cells are attractive targets to selectively abrogate tumor growth. However, only a few cell surface molecules to address the endothelium of pathological blood vessels are known, but it could be anticipated that many more molecular addresses associated with abnormal endothelial function and proliferation could serve as potential candidates for development of drug delivery agents. To obtain a library of peptides mediating binding of recombinant M13 phages to endothelium of experimental rat brain tumors, in-vivo display of a combinatorial heptapeptide and a splenocyte M13 library was used. Phage clones were selected that bind to rat brain tumor endothelium in-vivo and phage proteins detected in tissues by immunohistochemistry. Some of the recombinant phages diffused or were transported far into the surrounding tumor tissue, where they persisted for several days. Sequence analysis of insertion peptides revealed surprising similarities to angiogenic and anti-angiogenic factors or matrix and guidance molecules that appear to be involved in glioblastoma pathology. In-vivo phage display of recombinant M13 phages is a tool to select peptides targeting pathological endothelium. Insertion peptides, their corresponding cellular proteins and ligands might have a variety of applications in providing molecular tools for targeting tumor vascular beds with diagnostic probes and therapeutic substances and might open new opportunities for treating frequently fatal glial tumors.

Influence of TNFA on the formation of liver metastases in a syngenic mouse model

The level of TNFalpha expression is increased after partial hepatectomy, and experimental evidence exists that TNFalpha plays a key role in liver regeneration. Contradictory results are reported about the influence of TNFalpha on tumor growth: on the one hand, stimulation of tumor growth in various animal models and, on the other hand, intraperitoneally administered TNFalpha leads to reduced metastasis formation. TNFalpha may be one responsible factor for increased metastasis formation after surgical trauma. The objective of our study was to clarify the influence of TNFalpha on the formation of liver metastases in a syngenic mouse model in vivo. We used a novel marker system, EGFP transfected C26 tumor cells for in vivo observation of metastasis formation by intravital microscopy. We analyzed the effect of intraperitoneal TNFalpha-injection on tumor cell adhesion, extravasation and tumor development. The expression of ICAM-1, VCAM-1 and E-Selectin was measured by Western blot and immunohistochemical staining. Tumor load was assessed by determining EGFP in Western blots. GdCl(3) was employed 24 and 48 hr before tumor cell injection to selectively deplete the liver of functioning Kupffer cells. We observed significantly more extravasated tumor cells in the TNFalpha-pre-treated animals at early time points with increased expression of adhesion molecules. Measurement of the EGFP levels showed fewer liver metastases in the TNFalpha-pretreated animals at day 8. After GdCl(3) pretreatment even lower levels of EGFP, i.e., fewer metastases and also lower expression levels of ICAM-1, VCAM-1 and E-Selectin could be observed. TNFalpha, acts in a bidirectional manner: whereas TNFalpha facilitates tumor cell adhesion and extravasation of C26 tumor cells by inducing the expression of adhesion molecules, at later time points, TNFalpha seems to hinder the formation of liver metastases.

Interactions between cancer cells and the endothelium in metastasis

The haematogenous phase of cancer metastasis facilitates the transport of metastatic cells within the blood and incorporates a sequence of interactions between circulating intravascular cancer cells and the endothelium of blood vessels at the sites of tumour cell arrest. Initial interactions involve mechanical contact and transient adhesion, mediated by endothelial selectins and their ligands on the neoplastic cells. This contact initiates a sequence of activation pathways that involves cytokines, growth factors, bioactive lipids, and reactive oxygen species produced by either the cancer cell or the endothelium. These molecules elicit expression of integrin adhesion molecules in cancer cells and the endothelium, matrix metalloproteinases, and chemotactic factors that promote the attachment of tumour cells to the vessel wall and/or transvascular penetration. Induction of endothelial free radicals can be cytotoxic to cancer cells. Collectively, the sum of these interactions constitutes an interdependent relationship, the outcome of which determines the fate of the metastatic process.

Brain tumor development in rats is associated with changes in central nervous system cytokine and neuropeptide systems

Cytokines have roles in tumor biology and induce neurological manifestations. Cytokines produced in response to a brain tumor may generate neurological manifestations via paracrine action. We investigated cytokine modulation in an in vivo brain tumor model with behavioral, morphological, and molecular approaches. Rat C6 glioma cells were implanted into the third cerebral ventricle of Wistar rats, their behavior was monitored, and the development of an intracranial tumor of astrocytic origin was confirmed by histology and positive immunostaining for vimentin, S-100 protein, and glial fibrillary acidic protein. Sensitive and specific RNase protection assays were used to analyze cytokine messenger RNA (mRNA) in brain regions from anorexic brain tumor-bearing animals. Brain tumor formation was associated with significant increased levels of interleukin (IL)-1beta, IL-1 receptor antagonist, IL-1 receptor type I, tumor necrosis factor (TNF)-alpha, and transforming growth factor (TGF)-beta1 mRNAs in the cerebellum, hippocampus, and hypothalamus. IL-1 receptor accessory proteins I and II mRNAs were increased in the cerebellum and hypothalamus. We also examined hypothalamic feeding-associated components: neuropeptide Y and proopiomelanocortin mRNAs were down-regulated, glycoprotein 130 mRNA levels were up-regulated, and leptin receptor (OB-R) mRNA levels were unchanged. These dissimilar profiles of mRNA expression suggest specificity of brain tumor-induced transcriptional changes. The data implicate cytokines as important factors in brain tumor-host interactions in vivo. The data also show that the C6 cell-induced glioma can be used as a behavioral-molecular model to study cytokine and neuropeptide modulation and action during the host biochemical and physiological responses to brain tumor development. Paracrine interactions seem pivotal because cytokine modulation was observed in various brain regions. These results also suggest that cytokine and neuropeptide changes during brain tumor progression are involved in brain tumor-associated neurological and neuropsychiatrical manifestations.

Adhesion of colorectal carcinoma cells to the endothelium is mediated by cytokines from CEA stimulated Kupffer cells

We hypothesize that a major factor regulating hepatic metastasis is the ability of CEA (carcinoembryonic antigen) producing colorectal carcinomas to activate Kupffer cells. CEA and NCA (nonspecific cross-reacting antigen) bind to an 80 kDa Kupffer cell receptor by the peptide sequence PELPK and stimulate cytokine production. Cytokines induce sinusoidal endothelial cells to express intercellular adhesion molecules and increase adhesion of the tumor cells and retention in the liver. In this study human Kupffer cells were activated in vitro with CEA, NCA, and the peptide PELPK. This resulted in release of IL-1beta, TNF-alpha and IL-6. CEA non-producing MIP-101 colon carcinoma cells labeled with 51Cr were incubated on monolayers of ECV-304 human umbilical vein endothelial cells treated with these Kupffer cell derived cytokines or with comparable recombinant human (rH) cytokines. Specific antibodies to the adhesion molecules ICAM-1, VCAM-1, E-selectin and beta2integrin were used to block their functions. A significant enhancement in the adhesion of colorectal carcinoma cells occurred when endothelial cells were stimulated with a very low concentration of Kupffer-cell derived cytokines. Activated endothelium demonstrated significant up-regulation primarily of ICAM-1. The adhesion was blocked by an antibody to ICAM-1. A combination of Kupffer-cell derived cytokines was more effective than IL-1beta or TNF-alpha alone. IL-6 alone did not influence adhesion under our conditions. Our results suggest a mechanism for CEA in the modulation of colorectal carcinoma adhesion to the hepatic endothelium and its enhancement of metastatic potential.

Cell-cell interactions during transendothelial migration of tumor cells

A key event in cancer metastasis is the transendothelial migration of tumor cells. This process involves multiple adhesive interactions between tumor cells and the endothelium. After adhering to the surface of endothelial cells, tumor cells must penetrate the endothelial junction, which contains high concentrations of the cell adhesion molecules VE-cadherin and PECAM-1. Studies using an in vitro model system, consisting of melanoma cells which are seeded onto a monolayer of endothelial cells cultured on Matrigel, have revealed reorganization of the cytoskeleton and dynamic changes in the cell shape of both tumor and endothelial cells. The initial stages of transmigration are characterized by numerous membrane blebs protruding from the basolateral surfaces of the melanoma cells. Contact regions also show an abundance of microfilaments arising from the underlying endothelial cells. These adhesive interactions lead to the redistribution of both VE-cadherin and PECAM-1 and, consequently, a localized dissolution of the endothelial junction. The penetration of the endothelial junction is initiated by melanoma pseudopods. Despite the disappearance of VE-cadherin from the retracting endothelial junction, heterotypic contacts between the tumor cell and its surrounding endothelial cells show a high concentration of pan-cadherin staining, suggesting that transmigration of melanoma cells might yet be facilitated by interactions with another member of the cadherin family. Upon adhesion to the Matrigel, melanoma cells begin to spread and invade the matrix material, while the endothelial cells extend processes over the melanoma cells to reform the monolayer. Interestingly, the leading margins of these endothelial processes contain a high concentration ofN-cadherin. VE-cadherin and PECAM-1 reappear only when the advancing endothelial processes meet to reform the endothelial junction. Together, these observations suggest that endothelial cells actively participate in the transmigration of tumor cells and specific cadherins are involved in different steps of this complex process.