Biotinylated epidermal growth factor: a useful tool for the histochemical analysis of specific binding sites

Cellular Interactome of Mitochondrial Voltage-Dependent Anion Channels: Oligomerization and Channel (Mis)Regulation

Voltage-dependent anion channels (VDACs) of the outer mitochondrial membrane are known conventionally as metabolite flux proteins. However, research findings in the past decade have revealed the multifaceted regulatory roles of VDACs, from governing cellular physiology and mitochondria-mediated apoptosis to directly regulating debilitating cancers and neurodegenerative diseases. VDACs achieve these diverse functions by establishing isoform-dependent stereospecific interactomes in the cell with the cytosolic constituents and endoplasmic reticulum complexes, and the machinery of the mitochondrial compartments. VDACs are now increasingly recognized as regulatory hubs of the cell. Not surprisingly, even the transient misregulation of VDACs results directly in mitochondrial dysfunction. Additionally, human VDACs are now implicated in interaction with aggregation-prone cytosolic proteins, including Aβ, tau, and α-synuclein, contributing directly to the onset of Alzheimer's and Parkinson's diseases. Deducing the interaction dynamics and mechanisms can lead to VDAC-targeted peptide-based therapeutics that can alleviate neurodegenerative states. This review succinctly presents the latest findings of the VDAC interactome, and the mode(s) of VDAC-dependent regulation of biochemical physiology. We also discuss the relevance of VDACs in pathophysiological states and aggregation-associated diseases and address how VDACs will facilitate the development of next-generation precision medicines.

Introduction to glycopathology: the concept, the tools and the perspectives

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1670639891114983.

Analyzing the flow of biological information is a fundamental challenge for basic sciences. The emerging results will then lend themselves to the development of new approaches for medical applications. Toward this end, the products of protein/lipid glycosylation deserve special attention. The covalent attachment of sugars to these carriers means much more than just a change of the carriers’ physicochemical properties. In principle, the ubiquitous presence of glycoconjugates and the close inspection of the particular structural ‘talents’ of carbohydrates provide suggestive evidence for information coding by sugars. In fact, the theoretical number of ‘words’ (oligomers) formed by ‘letters’ (monosaccharides) is by far higher than by using nucleotides or amino acids. In other words, glycans harbor an unsurpassed coding capacity. The cyto- and histochemical detection of dynamic changes in the profile of cellular glycans (glycome, the equivalent of the proteome) by sugar receptors such as antibodies used as tools underscores the suitability of carbohydrates for such a task. The resulting staining patterns can be likened to a molecular fingerprint. By acting as ligand (counterreceptor) for endogenous receptors (tissue lectins), glycan epitopes become partners in a specific recognition pair, and the sugar-encoded information can then be translated into effects, e.g. in growth regulation. Of note, expression of both sides of such a pair, i.e. lectin and cognate glycan, can physiologically be orchestrated for optimal efficiency. Indeed, examples how to prevent autoimmune diseases by regulatory T cells and restrict carcinoma growth by a tumor suppressor attest occurrence of co-regulation. In consequence, these glycans have potential to establish a new class of functional biomarkers, and mapping presence of their receptors is warranted. In this review, the cyto- and histochemical methods, which contribute to explore information storage and transfer within the sugar code, are described. This introduction to the toolbox is flanked by illustrating the application of each type of tool in histopathology, with focus on adhesion/growth-regulating galectins. Together with an introduction to fundamental principles of the sugar code, the review is designed to guide into this field and to inspire respective research efforts.

Increased serum concentrations of growth factor receptors and Neu in workers previously exposed to asbestos

OBJECTIVES

Epidermal growth factor receptor (EGFR) and oncogene Neu belong to a family of growth factor receptors which may play a part in carcinogenesis. Although increased serum concentrations of Neu and EGFR have been shown in several patients with asbestosis who later developed cancer, serum concentrations have not been studied in workers exposed in the past to asbestos but without asbestos related diseases.

METHODS

Serum concentrations of secreted growth factor receptors were studied in 300 workers exposed in the past to asbestos and the results were compared with those of 70 controls.

RESULTS

In the controls 4.3% (3/70) had EGFR values > 912 units/ml, compared with 39% (117/299) of the exposed group (p < 0.001). The difference in high values was even more pronounced for Neu with 4.3% of controls having Neu values > 2580 fmol/ml compared with 72% (216/299) of the exposed workers (p < 0.001). Pleural plaques predicted lower serum concentrations of EGFR but not lower Neu concentrations, and this finding remained significant after adjustment for age, exposure time, smoking, and time from initial exposure.

CONCLUSIONS

Enhanced secretion of EGFR and Neu was found in a large cohort of retired asbestos workers with a wide range of exposure and latency periods. They did not have asbestosis or cancer and their EGFR values were higher in those without plaques. Further studies are needed to confirm our results, to determine the source of the secreted growth factor receptors, and to study their possible value as risk factors in the development of cancer.

Immunohistochemical localization of the epidermal growth factor-receptor in rhesus-monkey prostate

Epidermal growth-factor receptor (EGF-r), a membrane-bound glycoprotein activated by EGF, is important in maintaining the integrity and function of the prostate. To investigate EGF-r presence in the prostate of the rhesus monkey, monoclonal-antibody immunohistochemical examination was performed. The monkey prostate consisted of the cranial and caudal lobes, and the prostatic epithelial cells were composed of the secretory and basal cells. The distribution patterns of EGF-r in the prostatic epithelial cells were quite different between the cranial and caudal lobes. In the caudal lobe, EGF-r was seen in both secretory and basal cells, whereas, in the cranial lobe, the EGF-r was seen exclusively in the basal cells. The stromal cells of both lobes did not show EGF-r. This study revealed that each prostatic lobe contains specific binding sites for EGF, indicating a biological difference between the two lobes of the prostate of the rhesus monkey.

Autocrine stimulation of a human lung mesothelioma cell line is mediated through the transforming growth factor alpha/epidermal growth factor receptor mitogenic pathway

Malignant cells frequently acquire a certain independency of exogenous growth factors via the coexpression of epidermal growth factor receptor (EGFR) and epidermal growth factor (EGF)-related molecules. In the present study we investigate a possible involvement of EGF-related molecules in the growth of human lung mesothelioma. Four well-characterised cell lines are analysed for their responsiveness to exogenous EGF and transforming growth factor alpha (TGF-alpha) as well as for coexpression of EGFR and EGF/TGF-alpha. Both growth factors are able to stimulate DNA synthesis in three cell lines, although the degree of responsiveness is very variable, but neither EGF nor TGF-alpha has an effect on the cell line ZL34. In contrast, no heterogeneity is observed in the expression of EGFR, which is similarly high in all cell lines. Analysis of cell supernatants reveals that, whereas no EGF is detected, TGF-alpha is released by two cell lines. Furthermore, these two cell lines, ZL5 and ZL34, are shown to express the membrane anchored precursor pro-TGF-alpha. Thus, coexpression of EGFR and TGF-alpha is observed on two mesothelioma cell lines. The potential autocrine mitogenic role of TGF-alpha in these two cell lines was tested using neutralising antibodies against TGF-alpha and EGFR. In ZL5 cells DNA synthesis was not affected by the presence of neutralising antibodies, indicating that an external autocrine mitogenic pathway is not active in these cells. In ZL34 cells, however, the potential autocrine loop could be disrupted, as DNA synthesis was significantly reduced in the presence of neutralising antibodies. This result gives strong evidence for an autocrine role of TGF-alpha in the growth of the mesothelioma cell line ZL34.

Non-radioactive labelling and immunoprecipitation analysis of leukocyte surface proteins using different methods of protein biotinylation

The biotinylation of surface proteins and the detection of immunoprecipitated protein(s) after transfer to nitrocellulose using chemiluminescence methods is a highly sensitive alternative to hazardous radioactive labelling procedures. Ligation of proteins using the common biotin-NHS-ester (N-hydroxysuccinimido-biotin) is often associated with a decrease in immunoreactivity. Here a new non-radioactive method of leukocyte surface glycoprotein labelling using biotin-LC-hydrazide is described. This technique is based on the labelling of glycoproteins after mild oxidation of carbohydrate hydroxyl groups to reactive aldehydes. Flow cytometric and immunoprecipitation analyses of selected leukocyte markers such as CD3, CD26 and CD65 indicated that the alteration in immunoreactivity achieved by NHS-mediated biotin ligation was different from that obtained with hydrazide-mediated biotin ligation. CD3 and CD26 immunoreactivity was diminished using NHS biotinylation but preserved by biotin-LC-hydrazide, whereas CD65 binding to monoclonal antibodies was completely abolished after treatment with biotin-hydrazide. However, the immunoreactivity of CD13 was found to be totally unaffected by both NHS and hydrazide biotinylation. The combination of different biotinylation methods for surface protein labelling offers a viable alternative to radioiodination in the biochemical analysis of membrane proteins.

Binding of a biotinylated neurotrophic ACTH(4-9) analogue, Org 2766, to neurofilament-positive cells in primary or cell line cultures

To study the putative binding sites of the neurotrophic peptide Org 2766, an analogue of ACTH(4-9) [H-Met(O2)-Glu-His-Phe-D-Lys-Phe-OH], biotinylated forms of the peptide were used. After fixation, cultures of rat spinal cord and dorsal root ganglia were incubated with 4-10 microM of biotinyl-Org 2766 (b-Org 2766). Binding of both N- and C-terminally biotinylated Org 2766 was seen to phase-bright, round cells with thin processes, but not to flat, orthogonal-shaped cells with tapering processes. The b-Org 2766 binding was displaceable by an excess of nonbiotinylated Org 2766. Light and electron microscopy showed that the biotinylated peptide binds to a cytoplasmatic component as well as to the cell membrane. Double-labeling experiments with b-Org 2766 and an antibody (RT-97) to a high molecular weight neurofilament protein in dorsal root ganglion cultures showed, using fluorescence and confocal scanning laser microscopy, that all b-Org 2766 binding cells were neurofilament positive. Biotinylated Org 2766 did also bind to the neuronally differentiated cells in cultures of the human neuroblastoma cell line SK-N-SH, but not to those differentiated into epithelial cells. The present data suggest that the neurotrophic peptide Org 2766 binds specifically to cell types with neuronal characteristics.

Expression of epidermal growth factor receptor in human meningiomas and meningeal tissue

The aim of this study was to examine meningeal tissue under normal, reactive, and neoplastic conditions for expression of epidermal growth factor receptor (EGFR) using an improved histochemical method, namely biotinylated epidermal growth factor. EGFR was found in all the examined meningiomas (12 benign and three anaplastic) and in neonatal rat meninges, whereas normal and injured adult human and rat meninges did not exhibit detectable EGFR. These observations indicate that EGFR is involved in the development of meningeal tissue. Further, EGFR is abnormally expressed in meningeal tumours, indicating a role of EGFR in the neoplastic process of these tumours. The regular expression of EGFR in human meningiomas suggests EGFR as a tumour marker for this tumour type.

Analysis of tumour necrosis factor alpha-specific, lactose-specific and mistletoe lectin-specific binding sites in human lung carcinomas by labelled ligands

Receptor sites can be visualized by labelled ligands as an alternative to receptor-specific antibodies, as substantiated for two different receptor classes. Recombinant tumour necrosis factor alpha (TNF) was biotinylated via amino-groups and the resultant probe was applied to formalin-fixed, paraffin-embedded tissue sections of 94 primary bronchial carcinomas and to normal peripheral lung parenchyma. In addition, monoclonal antibodies specific for neuron-specific enolase (NSE) and TNF itself were used. The biotinylated beta-galactoside-specific mistletoe lectin, which exhibits dose-dependent immunomodulatory and toxic potency, and two probes that specifically detect certain types of sugar receptors were employed to illustrate further the feasibility of using ligands for receptor localisation. The tumours comprised 62 small cell lung carcinomas, 10 epidermoid carcinomas, 11 adenocarcinomas and 11 large cell anaplastic carcinomas. Expression of TNF-binding sites was found in 39 of the small cell lung carcinomas and in 13 of the non-small cell lung carcinomas. Binding capacity for the TNF-specific antibody was seen in similar proportions of small cell lung carcinomas and of non-small cell lung carcinomas. None of the normal lung parenchymas revealed significant staining. Binding capacities to mistletoe lectin were seen in all normal lung parenchymas and in nearly all cases of adenocarcinoma (10/11). A correlation between the expression of NSE and the binding capacities to TNF was detected. Endogenous lectins, specific for lactose or beta-GalNAc, were displayed in nearly one half of the small cell lung carcinoma cases (44% or 45% respectively) and in about 25% of the non-small cell lung carcinoma cases.