High-level expression of a full-length Eph receptor

Insights on the Functional Role of Beta-Glucans in Fungal Immunity Using Receptor-Deficient Mouse Models

Understanding the host anti-fungal immunity induced by beta-glucan has been one of the most challenging conundrums in the field of biomedical research. During the last couple of decades, insights on the role of beta-glucan in fungal disease progression, susceptibility, and resistance have been greatly augmented through the utility of various beta-glucan cognate receptor-deficient mouse models. Analysis of dectin-1 knockout mice has clarified the downstream signaling pathways and adaptive effector responses triggered by beta-glucan in anti-fungal immunity. On the other hand, assessment of CR3-deficient mice has elucidated the compelling action of beta-glucans in neutrophil-mediated fungal clearance, and the investigation of EphA2-deficient mice has highlighted its novel involvement in host sensing and defense to oral mucosal fungal infection. Based on these accounts, this review focuses on the recent discoveries made by these gene-targeted mice in beta-glucan research with particular emphasis on the multifaceted aspects of fungal immunity.

Expression and purification of the extracellular domain of wild-type humanRET and the dimeric oncogenic mutant C634R

The receptor tyrosine kinase RET is essential in a variety of cellular processes. RET gain-of-function is strongly associated with several cancers, notably multiple endocrine neoplasia type 2A (MEN 2A), while RET loss-of-function causes Hirschsprung's disease and Parkinson's disease. To investigate the activation mechanism of RET as well as to enable drug development, over-expressed recombinant protein is needed for in vitro functional and structural studies. By comparing insect and mammalian cells expression of the RET extracellular domain (RET^ECD), we showed that the expression yields of RET^ECD using both systems were comparable, but mammalian cells produced monomeric functional RET^ECD, whereas RET^ECD expressed in insect cells was non-functional and multimeric. This was most likely due to incorrect disulfide formation. By fusing an Fc tag to the C-terminus of RET^ECD, we were able to produce, in HEK293T cells, dimeric oncogenic RET^ECD (C634R) for the first time. The protein remained dimeric even after cleavage of the tag via the cysteine disulfide, as in full-length RET in the context of MEN 2A and related pathologies. Our work thus provides valuable tools for functional and structural studies of the RET signaling system and its oncogenic activation mechanisms.

Role of EphA2 in host defense against oro-pharyngeal candidiasis

Oral defense should be able to sense the burden of, and distinguish between fungal commensals and pathogens, so that an adequate inflammatory response can be set up. Recently, Ephrin type-A receptor 2 (EphA2) was identified on oral epithelial cells and neutrophils that recognizes Candida albicans and induces adaptive protective host responses against this organism. The studies have increased our knowledge of how epithelial cells and neutrophils contribute to host defense against oral yeast infection.

A Detailed Protocol for Large-scale Recombinant Expression and Validation of Human FGFR2 with Its Transmembrane and Extracellular Domains in Escherichia coli

Receptor tyrosine kinases (RTKs) are an important class of transmembrane receptors that mediate some of the most crucial biochemical pathways essential to the growth, differentiation, and survival of a cell and thus, are highly involved in cancers. Due to the complexity of RTKs having biochemically different domains including a transmembrane domain, an intact crystal structure of any of these proteins remain elusive as it is difficult to produce milligram amounts of intact functional RTKs for crystallography studies. A heavily studied RTK is fibroblast growth factor receptor 2 (FGFR2), which plays a key role in fibroblast growth regulation, differentiation, and oncogenesis. Previous studies have focused on expressing FGFR2's extracellular, transmembrane, and intracellular domains individually. For this protocol, we have focused on the extracellular and transmembrane domains of the FGFR2 protein. The function of the expressed protein is validated by demonstrating its ability to bind heparin and fibroblast growth factor 1 (FGF1). The primary contribution of our protocol is expressing two RTK domains together, including the transmembrane domain, in milligram quantities. Being able to express RTKs to define its crystal structures would enable pharmacologists to design cancer drugs that selectively target active conformations.

Recombinant expression in E. coli of human FGFR2 with its transmembrane and extracellular domains

Fibroblast growth factor receptors (FGFRs) are a family of receptor tyrosine kinases containing three domains: an extracellular receptor domain, a single transmembrane helix, and an intracellular tyrosine kinase domain. FGFRs are activated by fibroblast growth factors (FGFs) as part of complex signal transduction cascades regulating angiogenesis, skeletal formation, cell differentiation, proliferation, cell survival, and cancer. We have developed the first recombinant expression system in E. coli to produce a construct of human FGFR2 containing its transmembrane and extracellular receptor domains. We demonstrate that the expressed construct is functional in binding heparin and dimerizing. Size exclusion chromatography demonstrates that the purified FGFR2 does not form a complex with FGF1 or adopts an inactive dimer conformation. Progress towards the successful recombinant production of intact FGFRs will facilitate further biochemical experiments and structure determination that will provide insight into how extracellular FGF binding activates intracellular kinase activity.

Ephs and Ephrins in malignant gliomas

Eph receptor tyrosine kinases and the corresponding ephrin ligands play a pivotal role in the glioma development and progression. Aberrant protein expression levels of the Eph receptors and ephrins are often associated with higher tumor grade and poor prognosis. Their function in tumorigenesis is complex due to the intricate network of possible co-occurring interactions between neighboring tumor cells and tumor microenvironment. Both Ephs and ephrins localize on the surface of tumor cells, tumor vasculature, glioma stem cells, tumor cells infiltrating brain, and immune cells infiltrating tumors. They can both promote and inhibit tumorigenicity depending on the downstream forward and reverse signalling generated. All the above-mentioned features make the Ephs/ephrins system an intriguing candidate for the development of new therapeutic strategies in glioma treatment. This review will give a general overview on the structure and the function of Ephs and ephrins, with a particular emphasis on the state of the knowledge of their role in malignant gliomas.

Binding and function of phosphotyrosines of the Ephrin A2 (EphA2) receptor using synthetic sterile α motif (SAM) domains

The sterile α motif (SAM) domain of the ephrin receptor tyrosine kinase, EphA2, undergoes tyrosine phosphorylation, but the effect of phosphorylation on the structure and interactions of the receptor is unknown. Studies to address these questions have been hindered by the difficulty of obtaining site-specifically phosphorylated proteins in adequate amounts. Here, we describe the use of chemically synthesized and specifically modified domain-length peptides to study the behavior of phosphorylated EphA2 SAM domains. We show that tyrosine phosphorylation of any of the three tyrosines, Tyr(921), Tyr(930), and Tyr(960), has a surprisingly small effect on the EphA2 SAM structure and stability. However, phosphorylation at Tyr(921) and Tyr(930) enables differential binding to the Src homology 2 domain of the adaptor protein Grb7, which we propose will lead to distinct functional outcomes. Setting up different signaling platforms defined by selective interactions with adaptor proteins thus adds another level of regulation to EphA2 signaling.