EphB3 protein is a potential ancillary diagnostic biomarker for thyroid cancers

OBJECTIVE

To investigate the expression of ephrin type B receptor 3 (EphB3) in thyroid tumors and its usage as an ancillary diagnostic biomarker for thyroid tumors.

METHODS

Formalin-fixed and paraffin-embedded (FFPE) tissue samples (78 cases) and FNAC samples (57 cases) were assessed with the EphB3 antibody using immunohistochemistry. PTC and other thyroid follicular tumors were compared regarding their EphB3 expression. Sanger sequencing was used to assess for the presence of a BRAF V600E mutation.

RESULTS

EphB3 was positive in 81.8 % (27/33) of papillary thyroid carcinoma (PTC), 83.3 % (5/6) of medullary thyroid carcinoma (MTC), 25 % (1/4) of hyperplastic/adenomatoid nodule (HN), 14.3 % (1/7) of follicular adenoma (FA), and negative in follicular tumors of uncertain malignant potential (FT-UMP) (0/13), noninvasive follicular neoplasm with papillary-like nuclear features (NIFTP) (0/7), thyroid follicular carcinoma (TFC) (0/4), Hashimoto's thyroiditis (0/4), and normal thyroid follicular tissues (0/33). In cellular blocks, EphB3 was positive in 87.1 % (20/23) of PTC, 75 % (3/4) of MTC, 20 % (2/10) of HN, and negative in atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) (0/20) and normal thyroid follicular cells (0/10).

CONCLUSION

EphB3 is expressed in the majority of PTC, but less so in benign follicular nodules. EphB3 expression in fine needle aspiration cytology (FNAC) specimens can be used as a diagnostic tool to differentiate thyroid cancer from other follicular lesions in its differential diagnosis, especially AUS/FLUS and PTC.

Tyrosine-614, the major autophosphorylation site of the receptor tyrosine kinase HEK2, functions as multi-docking site for SH2-domain mediated interactions

HEK2 belongs to the family of EPH-related receptor tyrosine kinases (RTK) which are involved in axonal pathfinding and the formation of the embryonic body plan. The knowledge about intracellular pathways of signal transduction mediated by EPH-related receptors is still limited. Many of the known key players of cellular signalling contain Src homology 2 (SH2) domains, which recognize phosphotyrosine motifs in RTKs. Thus, we examined the interactions of various SH2-containing molecules like PLC-gamma1, rasGAP, p85 subunit of PI3-kinase, Src, Fyn, Crk, Nck, Grb2 and Shc with HEK2 using in vitro binding assays, immunoprecipitations and yeast Two-Hybrid assays. We found that rasGAP, Crk and Fyn bind in a SH2-dependent manner to autophosphorylated HEK2. rasGAP, which contains two SH2- and one SH3-domain, was shown to associate with its N-terminal SH2-domain to HEK2. Furthermore, we demonstrated that a single amino acid substitution (Y614F) clearly reduces the phosphotyrosine content of HEK2 and abrogates its ability to bind rasGAP, Crk and Fyn indicating that this residue functions as major phosphorylation and multi-docking site. The conservation of this predicted binding site among various EPH-related RTKs provides evidence that Fyn, Crk and rasGAP are key players in signal transduction of at least a subset of these receptors.

Overexpression of protein tyrosine kinases in human esophageal cancer

Using a PCR-based cloning technique, we isolated a series of protein tyrosine kinases (PTKs) expressed in a cell line of esophageal squamous cell carcinoma. Sequence analysis revealed 10 different kinds of PTKs of the receptor type [epidermal cell growth factor receptor, insulin-like growth factor I receptor, fibroblast growth factor receptor 4, eck, erk, discoidin domain receptor (DDR)/trkE/cell adhesion kinase (Cak), HEK2, HEK8, axl and sky] and one PTK of the nonreceptor type (tyk2). Subsequently, we examined the expression of the transcripts of these 11 genes in paired samples of normal and carcinomatous esophageal tissues obtained from 12 cases of esophageal cancer. We found that all 11 gene transcripts were expressed in both carcinomatous and normal tissues, and 6 of them were significantly overexpressed in carcinomatous tissues relative to adjacent normal tissues. Among these, the magnitude of mRNA expression of DDR/trkE/Cak PTK was positively correlated with the proliferative activity of carcinoma cells, but not with their degree of differentiation. Immunohistochemically, DDR was expressed in both normal and cancerous esophageal cells. The intensity of the expression was higher in cancer than normal tissue. In addition, we confirmed the expression of two isoforms of DDR/trkE/Cak in normal and cancerous esophagus. Our study suggests that DDR/trkE/Cak plays an important role in the regulation of proliferation of esophageal cancer.

Differentially regulated epithelial expression of an Eph family tyrosine kinase (fHek2) during tracheal surface airway and submucosal gland development

A ferret model was used to evaluate the potential role of an Eph family tyrosine kinase (fHek2) in tracheal development of surface airway epithelium and submucosal glands. A partial 2.6-kb cDNA fragment of fHek2 was isolated from a ferret tracheal/lung cDNA library. Sequence analysis demonstrated that this gene is the ortholog to the previously cloned human Hek2 gene. In situ hybridization analysis of fHek2 mRNA expression on ferret tracheal developmental time points revealed an expression pattern within a subset of surface airway epithelial cells which remained relatively constant throughout tracheal development (from -2 d in utero to adult). In contrast, developing tracheal submucosal glands at 3-day postnatal time points demonstrated little fHek2 mRNA expression. However, expression of fHek2 significantly increased more than 4-fold over the course of gland development to adulthood. These findings, which demonstrate a uniquely regulated pattern of fHek2 mRNA expression between surface airway epithelium and submucosal glands, have implications on regulatory processes which control differentiation and/or maturation of secretory structures in the lung. Such findings may be useful in further delineating the mechanisms which control cellular differentiation in the lung and how these processes are abnormally regulated in hypersecretory diseases such as chronic bronchitis, asthma, and cystic fibrosis.

Cell-cell adhesion mediated by binding of membrane-anchored ligand LERK-2 to the EPH-related receptor human embryonal kinase 2 promotes tyrosine kinase activity

Human embryonal kinase 2 (HEK2) is a protein-tyrosine kinase that is a member of the EPH family of receptors. Transcripts for HEK2 have a wide tissue distribution. Recently, a still growing family of ligands, which we have named LERKs, for ligands of the eph-related kinases, has been isolated. In order to analyze functional effects between the LERKs and the HEK2 receptor, we expressed HEK2 cDNA in an interleukin-3-dependent progenitor cell line 32D that grows as single cells in culture. Within the group of LERKs, LERK-2 and -5 were shown to bind to HEK2. Membrane-bound and soluble forms of LERK-2 were demonstrated to signal through HEK2 as judged by receptor phosphorylation. Coincubation of HEK2 and LERK-2 expressing cells induced cell-cell adhesion and formation of cell aggregates. This interaction could be inhibited by preincubation of HEK2 expressing cells with soluble LERK-2. Coexpression of HEK2 and LERK-2 in 32D cells showed reduced kinase activity and autophosphorylation of HEK2 compared with the juxtacrine stimulation, which seems to be due to a reduced sensitivity of the receptor.

Similarities and differences in the way transmembrane-type ligands interact with the Elk subclass of Eph receptors

The Eph family of receptor tyrosine kinases and their cell surface bound ligands have been implicated in a number of developmental processes, including axon pathfinding and fasciculation, as well as patterning in the central nervous system. To better understand the complex signaling events taking place, we have undertaken a comparative analysis of ligand-receptor interactions between a subset of ligands, those that are tethered to the cell surface via a transmembrane domain, and a subset of Eph receptors, the so-called Elk subclass. Based on binding characteristics, receptor autophosphorylation, and cellular transformation assays, we find that the transmembrane-type ligands Lerk2 and Elf2 have common and specific receptors within the Elk subclass of receptors. The common receptors Cek10 and Elk bind and signal in response to Lerk2 and Elf2, whereas the Myk1 receptor is specific for Elf2. Elf2, however, fails to signal through Cek5 in a cellular transformation assay, suggesting that Lerk2 may be the preferred Cek5 ligand in vivo. A recently identified third transmembrane-type ligand, Elf3, specifically, but weakly, binds Cek10 and only induces focus formation when activated by C-terminal truncation. This suggests that the physiological Elf3 receptor may have yet to be identified. Knowledge regarding functional ligand-receptor interactions as presented in this study will be important for the design and interpretation of in vivo experiments, e.g., loss-of-function studies in transgenic mice.

Novel members of the eph receptor tyrosine kinase subfamily expressed during Xenopus development

Three cDNAs encoding receptor tyrosine kinases (RTKs) of the eph-subfamily have been identified based on their homology to Pagliaccio (Winning and Sargent, 1994, Mech. Dev. 46:219-229). These have been named TCK, Xelk (Xenopus homologue of elk), and PL7a (pag-like clone 7a). Each of these genes is expressed in a distinctive, tissue specific manner during early development. TCK is expressed in pre-somitic mesoderm, caudal somites, midbrain and cement gland. Xelk is expressed in the brain and spinal cord and in the first and fourth visceral arches. PL7a cDNA is expressed throughout the head and in the tip of the tail. All of the genes are represented in maternal mRNA, and are expressed in adult tissues. The Xelk cDNA encodes a protein which is 94% identical to rat elk and therefore is likely to represent the Xenopus homologue of this gene. TCK and PL7a are less related to previously identified eph-subfamily RTKs. The inability to unambiguously assign TCK and PL7a as Xenopus homologues of any previously identified eph RTK leads us to conclude that these cDNAs represent novel members of this family.

Ligands for the receptor tyrosine kinases hek and elk: isolation of cDNAs encoding a family of proteins

Hek is a member of the eph subfamily of receptor tyrosine kinases whose members include elk, hek2, sek, eph and eck among others. Using a soluble form of hek consisting of the extracellular region of the receptor fused to the Fc domain of human IgG1 and an expression cloning strategy, we have isolated two different but related cDNAs from the human T-lymphoma line HSB-2 that encode ligands for hek. The cDNAs encode proteins of 238 and 201 amino acids (44% amino acid identity) that are anchored to the membrane by glycosylphosphatidylinositol (GPI)-linkage. The proteins encoded by these cDNAs are bound by hek with affinity constants of 2 x 10(8) M-1. These proteins also bind the elk tyrosine kinase receptor. These cDNAs are related to other cDNAs that we have recently isolated from a human placental library that encode ligands for both hek and elk and define an emerging family of ligands for eph-related kinases (LERKs).

PCR mediated detection of a new human receptor-tyrosine-kinase, HEK 2

We have previously amplified cDNA subfragments of protein-tyrosine-kinases (PTKs) by using the polymerase chain reaction (PCR) and specific sets of oligonucleotide primers derived from nucleotide sequences of their kinase domain. In this study we have used a more directed approach to identify new members of the EPH/elk-family by PCR of human embryonic cDNA: we utilized oligonucleotide primers specifically designed to a highly conserved N-terminal motif and the kinase region of EPH/elk-PTKs in RNA-PCRs. The 5' and 3' elongation of the primary PCR product was achieved by the RACE (rapid amplification of cDNA ends)-technique. Sequence analysis of 3.8 kb of overlapping PCR products allowed to identify a novel receptor-PTK, HEK 2 (human embryo kinase 2), as an additional member of this family, without the need to screen a cDNA library. This approach should be useful for the rapid isolation of other PTK-genes as well. Analysis of genomic DNA placed HEK 2 on chromosome 3. Northern blot analysis demonstrated the expression of a 4.6 kb HEK 2-mRNA in lung, brain, pancreas, liver, placenta, kidney, skeletal muscle, heart and several human cells. In a protein kinase assay with HEK 2-specific immunoprecipitates from the human epidermoid carcinoma cell line A431, a protein of 130 kDa was found phosphorylated.

Five novel avian Eph-related tyrosine kinases are differentially expressed

We have identified cDNA clones that encode five new avian receptor-like tyrosine kinases of the Eph subclass, by screening two chicken embryonic cDNA libraries with DNA probes. We have designated them Cek6 to Cek10. The identification of these kinases indicates that the Eph subclass comprises at least 10 members and, therefore, represents a very large family of receptor-like tyrosine kinases. Variants of Cek10 and of Cek5 (a previously identified Eph-related kinase) containing amino acid insertion sequences in the juxtamembrane domain were also isolated. The Cek5 variant is expressed in the brain, but not in other tissues of the 10-day chick embryo. Analysis of 10-day chick embryo mRNAs shows the newly identified tyrosine kinases to be all expressed in both the embryonic brain and body tissues. In adult tissues, they display distinct patterns of expression. Cek6, Cek7, Cek8, Cek9 and Cek10 are likely to play significant roles in embryonic signal transduction pathways, including those involved in neural development. Their distinct tissue distributions in the adult suggest that the different members of the Eph family may each serve specific functions.