Differential gene expression of Eph receptors and ephrins in benign human tissues and cancers

The role of ephrins and Eph receptors in cancer

Eph receptors are the largest receptor tyrosine kinase family of transmembrane proteins with an extracellular domain capable of recognizing signals from the cells' environment and influencing cell-cell interaction and cell migration. Ephrins are the ligands to Eph receptors and stimulate bi-directional signaling of the Eph/ephrin axis. Eph receptor and ephrin overexpression can result in tumorigenesis as related to tumor growth and survival and is associated with angiogenesis and metastasis in many types of human cancer. Recent data suggest that Eph/ephrin signaling could play an important role in the development of novel inhibition strategies and cancer treatments to potentially target this receptor tyrosine kinase and/or its ligand. A deeper understanding of the molecular basis for normal versus defective cell-cell interaction through the Eph/ephrin axis will enable the potential development of novel cancer treatments. This review emphasizes the biology of Eph/ephrin as well as the potential for novel targeted therapy through this pathway.

Characterization of a novel Eph receptor tyrosine kinase, EphA10, expressed in testis

In mammals, 14 members of the Eph receptor tyrosine kinase family have been described so far. Here we present a not yet described member of this family denoted EphA10. We report the identification of three putative EphA10 isoforms: one soluble and two transmembrane isoforms. One of the latter isoforms lacked the sterile alpha motif commonly found in Eph receptors. The gene encoding EphA10 is located on chromosome 1p34 and expression studies show that EphA10 mRNA is mainly expressed in testis. Binding studies to ephrin ligands suggests that this receptor belongs to the EphA subclass of Eph receptors binding mainly to ephrin-A ligands.

Gene Expression Profile Changes between Melanoma Metastases and their Daughter Cell Lines: Implication for Vaccination Protocols

Vaccination protocols based on autologous tumor material often require in vitro culturing of tumor cells to obtain enough cellular material for the production of the vaccine. Cancer cells and particularily melanoma cells are known for their genomic instability. Therefore, it can be assumed that melanoma cells acquire genomic changes and thereby changes in the transcriptome during in vitro culturing. This may lead to a shift of epitopes expressed on the tumor cells. We analyzed the transcriptome of in vitro cultured melanoma cells prepared from melanoma metastases. Comparing the gene expression changes between the tumors and their offspring cell lines, we demonstrate that with increasing passage numbers, gene expression changes increase drastically.

Cloning and characterization of the human FCRL2 gene

We report cloning and characterization of FCRL2, a novel human gene that belongs to the FcR family. The gene is closely linked and structurally similar to the recently identified FCRL/FREB/FcRX gene. The encoded protein is composed of three Ig-like domains and a C-terminal mucin-like domain containing a conserved alpha-helical motif with dileucine signals. Intraexonic splicing may generate two alternative transcripts, coding for isoforms with the third and fourth domains replaced by entirely different amino acid sequences. Like FCRL, the full-length isoform of FCRL2 is expressed intracellularly in transfected 293T cells. Expression analysis revealed FCRL2 mRNA only in placenta. The gene transcripts were not detected in lymphoid tissues or in the main leukocyte subsets isolated from peripheral blood. However, we found that FCRL2 is differentially expressed by transformed B cell lines. Of interest is also the finding that the gene expression may be up-regulated in the progression of melanocytic tumors.

Expression of stathmin, a developmentally controlled cytoskeleton-regulating molecule, in demyelinating disorders

Understanding the biological relevance of reexpression of developmental molecules in pathological conditions is crucial for the development of new therapies. In this study, we report the increased expression of stathmin, a developmentally regulated tubulin-binding protein, in the brains of patients with multiple sclerosis (MS). In physiological conditions, stathmin immunoreactivity was observed in polysialic acid-neural cell adhesion molecule-positive migratory progenitors in the subventricular zone, and its expression progressively decreased as the cells matured into oligodendrocytes (OLs). In MS patients, however, stathmin levels were elevated in 2',3'-cyclic nucleotide 3'-phosphodiesterase-positive OLs, in 10 of 10 bioptic samples analyzed. Increased levels of stathmin were confirmed by Western blot analysis of normal-appearing white matter samples from MS brains. In addition, using mass spectrometry, stathmin was identified as the main component of a specific myelin protein fraction consistently increased in MS preparations compared with controls. To test the biological relevance of increased stathmin levels, primary OL progenitors were transfected using a myc-tagged stathmin cDNA and were allowed to differentiate. Consistent with a distinct role played by this molecule in cells of the OL lineage at different developmental stages, transient transfection in progenitors favored the bipolar migratory phenotype but did not affect survival. However, sustained stathmin levels in differentiating OLs, because of overexpression, resulted in enhanced apoptotic susceptibility. We conclude that stathmin expression in demyelinating disorders could have a dual role. On one hand, by favoring the migratory phenotype of progenitors, it may promote myelin repair. On the other hand, stathmin in mature OLs may indicate cell stress and possibly affect survival.

EPHA2/EFNA1 expression in human gastric cancer

The erythropoietin-producing hepatocellular (EPH)A2 receptor, tyrosine kinase, is overexpressed and phosphorylated in several types of human tumors and has been associated with malignant transformation. A recent report, however, indicated that stimulation of the EPHA2 receptor ligand, ephrinA1 (EFNA1), inhibits the growth of EPHA2-expressing breast cancer. The authors examined the expression of EPHA2 and EFNA1 using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) in four gastric cancer cell lines and 49 primary gastric cancer samples, as well as in normal gastric tissue. EPHA2 was more highly expressed in tumor tissue than in normal tissue in 27 cases (55%). EFNA1 was overexpressed in tumor tissue in 28 cases (57%). No significant correlation was detected between the expression levels and histologic features such as tumor size, age, vessel invasion, or lymph node involvement. However, EPHA2 overexpression was more prominent in macroscopic type 3 and 4 tumors than in type 1 or 2 advanced gastric cancer. The authors observed EPHA2 expression in three of the four gastric cancer cell lines (AGS, KATO3, and MKN74) that were examined. In one cell line, TMK1, EPHA2 expression was barely detectable using northern blotting, RT-PCR, and western blotting. In contrast, EFNA1 was detected in all cell lines. In the gastric cancer cell lines that endogenously expressed EPHA2, stimulation with ephrinA1-Fc led to decreased EPHA2 protein expression and increased EPHA2 phosphorylation. Finally, the growth of EPHA2-expressing cells was inhibited by repetitive stimulation with soluble ephrinA1-Fc. Taken together, these findings suggest that EPHA2 and EFNA1 expression may influence the behavior of human gastric cancer.

Ephrin A receptors and ligands in lesions and normal-appearing white matter in multiple sclerosis

Complexes of the tyrosine kinase ephrin ligands (ephrins) and their receptors (Ephs) provide critical cell recognition signals in CNS development. Complementary ephrin/Eph expression gradients present topographic guidance cues that may either stimulate or repulse axon growth. Some ephrin/Ephs are upregulated in adult CNS injury models. To assess their involvement in multiple sclerosis (MS), ephrin A1-5 and Eph A1-8 expression was analyzed in CNS tissues using immunohistochemistry. Control samples showed distinct expression patterns for each ephrin/Eph on different cell types. Perivascular mononuclear inflammatory cells, reactive astrocytes and macrophages expressed ephrin A1-4, Eph A1, -A3, -A4, -A6 and -A7 in active MS lesions. Axonal ephrin A1 and Eph A3, -A4, and -A7 expression was increased in active lesions and was greater in normal-appearing white matter (NAWM) adjacent to active lesions than within or adjacent to chronic MS lesions, in contralateral NAWM, or in control samples. As in development, therefore, there are temporally dynamic, lesion-associated axonal ephrin/Eph A expression gradients in the CNS of MS patients. These results indicate that ephrin/Eph As are useful cell markers in human CNS tissue samples; they likely are involved in the immunopathogenesis of active lesions and in neurodegeneration in MS NAWM; and they represent potential therapeutic targets in MS.

The Versatile Roles of “Axon Guidance” Cues in Tissue Morphogenesis

The Netrin, Slit, Semaphorin, and Ephrin families of secreted proteins were originally characterized in the nervous system as guidance cues for axons; however, recent studies demonstrate that many members of these families contribute to the development of a variety of organs. Here, the current knowledge of their roles is discussed with a focus on four tissues: lung, mammary, cardiovascular, and kidney. While many studies indicate a role for "axon guidance" cues in regulating cell-cell and cell-extracellular matrix (ECM) interactions during organogenesis, there is accumulating evidence that they also contribute to tissue development by regulating the transcription and translation of genes encoding key morphogenetic factors.

Aberrant expression of the tyrosine kinase receptor EphA4 and the transcription factor twist in Sézary syndrome identified by gene expression analysis

Sézary syndrome (Sz) is a malignancy of CD4+ memory skin-homing T cells and presents with erythroderma, lymphadenopathy, and peripheral blood involvement. To gain more insight into the molecular features of Sz, oligonucleotide array analysis was performed comparing gene expression patterns of CD4+ T cells from peripheral blood of patients with Sz with those of patients with erythroderma secondary to dermatitis and healthy controls. Using unsupervised hierarchical clustering gene, expression patterns of T cells from patients with Sz were classified separately from those of benign T cells. One hundred twenty-three genes were identified as significantly differentially expressed and had an average fold change exceeding 2. T cells from patients with Sz demonstrated decreased expression of the following hematopoietic malignancy-linked tumor suppressor genes: TGF-beta receptor II, Mxi1, Riz1, CREB-binding protein, BCL11a, STAT4, and Forkhead Box O1A. Moreover, the tyrosine kinase receptor EphA4 and the potentially oncogenic transcription factor Twist were highly and selectively expressed in T cells of patients with Sz. High expression of EphA4 and Twist was also observed in lesional skin biopsy specimens of a subset of patients with cutaneous T cell lymphomas related to Sz, whereas their expression was nearly undetectable in benign T cells or in skin lesions of patients with inflammatory dermatoses. Detection of EphA4 and Twist may be used in the molecular diagnosis of Sz and related cutaneous T-cell lymphomas. Furthermore, the membrane-bound EphA4 receptor may serve as a target for directed therapeutic intervention.

Eph receptors in the adult brain

The Eph receptors are a large family of receptor tyrosine kinases with important roles in the establishment of neuronal and vascular networks during embryonic development. The functions of Eph receptors in the adult brain have only recently been investigated, and the results are forcing us to amend the conventional view that these molecules function predominantly in a developmental context. This review summarizes this rapidly expanding new area of research, which has shown that the Eph receptors regulate the structure and physiological function of excitatory synapses through multiple mechanisms, and might thus play a significant role in higher brain functions.