Improved membrane protein solubilization and clean-up for optimum two-dimensional electrophoresis utilizing GLUT-1 as a classic integral membrane protein

Development of Cell Membrane Electrophoresis to Measure the Diffusivity of a Native Transmembrane Protein

The lateral diffusion of transmembrane proteins in cell membranes is an important process that controls the dynamics and functions of the cell membrane. Several fluorescence-based techniques have been developed to study the diffusivities of transmembrane proteins. However, it is challenging to measure the diffusivity of a transmembrane protein with slow diffusion because of the photobleaching effect caused by long exposure times or multiple exposures to light. In this study, we developed a cell membrane electrophoresis platform to measure diffusivity. We deposited cell membrane vesicles derived from HeLa cells to form supported cell membrane patches. We demonstrated that the electrophoresis platform can be used to drive the movement of not only a lipid probe but also a native transmembrane protein, GLUT1. The movements were halted by the boundaries of the membrane patches and the concentration profiles reached steady states when the diffusion mass flux was balanced with the electrical mass flux. We used the Nernst-Planck equation as the mass balance equation to describe the steady concentration profiles and fitted these equations to our data to obtain the diffusivities. The obtained diffusivities were comparable to those obtained by fluorescence recovery after photobleaching, suggesting the validity of this new method of diffusivity measurement. Only a single snapshot is required for the diffusivity measurement, addressing the problems associated with photobleaching and allowing researchers to measure the diffusivity of transmembrane proteins with slow diffusion.

Development of high-performance two-dimensional gel electrophoresis for human hair shaft proteome

The primary components of human hair shaft—keratin and keratin-associated proteins (KAPs), together with their cross-linked networks—are the underlying reason for its rigid structure. It is therefore requisite to overcome the obstacle of hair insolubility and establish a reliable protocol for the proteome analysis of this accessible specimen. The present study employed an alkaline-based method for the efficient isolation of hair proteins and subsequently examined them using gel-based proteomics. The introduction of two proteomic protocols, namely the conventional and modified protocol, have resulted in the detection of more than 400 protein spots on the two-dimensional gel electrophoresis (2DE). When compared, the modified protocol is deemed to improve overall reproducibility, whilst offering a quick overview of the total protein distribution of hair. The development of this high-performance protocol is hoped to provide a new approach for hair analysis, which could possibly lead to the discovery of biomarkers for hair in health and diseases in the future.

An Improved 2-Dimensional Gel Electrophoresis Method for Resolving Human Erythrocyte Membrane Proteins

The 2-dimensional gel electrophoresis (2-DE) technique is widely used for the analysis of complex protein mixtures extracted from biological samples. It is one of the most commonly used analytical techniques in proteomics to study qualitative and quantitative protein changes between different states of a cell or an organism (eg, healthy and diseased), conditionally expressed proteins, posttranslational modifications, and so on. The 2-DE technique is used for its unparalleled ability to separate thousands of proteins simultaneously. The resolution of the proteins by 2-DE largely depends on the quality of sample prepared during protein extraction which increases results in terms of reproducibility and minimizes protein modifications that may result in artifactual spots on 2-DE gels. The buffer used for the extraction and solubilization of proteins influences the quality and reproducibility of the resolution of proteins on 2-DE gel. The purification by cleanup kit is another powerful process to prevent horizontal streaking which occurs during isoelectric focusing due to the presence of contaminants such as salts, lipids, nucleic acids, and detergents. Erythrocyte membrane proteins serve as prototypes for multifunctional proteins in various erythroid and nonerythroid cells. In this study, we therefore optimized the selected major conditions of 2-DE for resolving various proteins of human erythrocyte membrane. The modification included the optimization of conditions for sample preparation, cleanup of protein sample, isoelectric focusing, equilibration, and storage of immobilized pH gradient strips, which were further carefully examined to achieve optimum conditions for improving the quality of protein spots on 2-DE gels. The present improved 2-DE analysis method enabled better detection of protein spots with higher quality and reproducibility. Therefore, the conditions established in this study may be used for the 2-DE analysis of erythrocyte membrane proteins for different diseases, which may help to identify the proteins that may serve as markers for diagnostics as well as targets for development of new therapeutic potential.

A protein extraction method for low protein concentration solutions compatible with the proteomic analysis of rubber particles

The extraction of high-purity proteins from the washing solution (WS) of rubber particles (also termed latex-producing organelles) from laticifer cells in rubber tree for proteomic analysis is challenging due to the low concentration of proteins in the WS. Recent studies have revealed that proteins in the WS might play crucial roles in natural rubber biosynthesis. To further examine the involvement of these proteins in natural rubber biosynthesis, we designed an efficiency method to extract high-purity WS proteins. We improved our current borax and phenol-based method by adding reextraction steps with phenol (REP) to improve the yield from low protein concentration samples. With this new method, we extracted WS proteins that were suitable for proteomics. Indeed, compared to the original borax and phenol-based method, the REP method improved both the quality and quantity of isolated proteins. By repeatedly extracting from low protein concentration solutions using the same small amount of phenol, the REP method yielded enough protein of sufficiently high-quality from starting samples containing less than 0.02 mg of proteins per milliliter. This method was successfully applied to extract the rubber particle proteins from the WS of natural rubber latex samples. The REP-extracted WS proteins were resolved by 2DE, and 28 proteins were positively identified by MS. This method has the potential to become widely used for the extraction of proteins from low protein concentration solutions for proteomic analysis.

Expression of conventional and novel glucose transporters, GLUT1, -9, -10, and -12, in vascular smooth muscle cells

Intimal hyperplasia is characterized by exaggerated proliferation of vascular smooth muscle cells (VSMCs). Enhanced VSMC growth is dependent on increased glucose uptake and metabolism. Facilitative glucose transporters (GLUTs) are comprised of conventional GLUT isoforms (GLUT1-5) and novel GLUT isoforms (GLUT6-14). Previous studies demonstrate that GLUT1 overexpression or GLUT10 downregulation contribute to phenotypic changes in VSMCs. To date, the expression profile of all 14 GLUT isoforms has not been fully examined in VSMCs. Using the proliferative and differentiated phenotypes of human aortic VSMCs, the present study has determined the relative abundance of GLUT1-14 mRNAs by quantitative real-time PCR analysis. Twelve GLUT mRNAs excluding GLUT7 and GLUT14 were detectable in VSMCs. In the proliferative phenotype, the relative abundance of key GLUT mRNAs was GLUT1 (∼43%)>GLUT10 (∼26%)>GLUT9 (∼13%)>GLUT12 (∼4%), whereas in the differentiated phenotype the relative abundance was GLUT10 (∼28%)>GLUT1 (∼25%)>GLUT12 (∼20%)>GLUT9 (∼14%), together constituting 86-87% of total GLUT transcripts. To confirm the expression of key GLUT proteins, immunoblot and immunocytochemical analyses were performed using GLUT isoform-specific primary antibodies. The protein bands characteristic of GLUT1, -9, -10, and -12 were detected in VSMCs in parallel with respective positive controls. In particular, GLUT1 protein expression showed different molecular forms representative of altered glycosylation. While GLUT1 protein displayed a predominant distribution in the plasma membrane, GLUT9, -10, and -12 proteins were mostly distributed in the intracellular compartments. The present study provides the first direct evidence for GLUT9 and GLUT12 expression in VSMCs in conjunction with the previously identified GLUT1 and GLUT10.

Endothelial Wnt/β-catenin signaling inhibits glioma angiogenesis and normalizes tumor blood vessels by inducing PDGF-B expression

Wnt modulates glioma vascularization by regulating PDGF-B expression.

Endothelial Wnt/β-catenin signaling is necessary for angiogenesis of the central nervous system and blood–brain barrier (BBB) differentiation, but its relevance for glioma vascularization is unknown. In this study, we show that doxycycline-dependent Wnt1 expression in subcutaneous and intracranial mouse glioma models induced endothelial Wnt/β-catenin signaling and led to diminished tumor growth, reduced vascular density, and normalized vessels with increased mural cell attachment. These findings were corroborated in GL261 glioma cells intracranially transplanted in mice expressing dominant-active β-catenin specifically in the endothelium. Enforced endothelial β-catenin signaling restored BBB characteristics, whereas inhibition by Dkk1 (Dickkopf-1) had opposing effects. By overactivating the Wnt pathway, we induced the Wnt/β-catenin–Dll4/Notch signaling cascade in tumor endothelia, blocking an angiogenic and favoring a quiescent vascular phenotype, indicated by induction of stalk cell genes. We show that β-catenin transcriptional activity directly regulated endothelial expression of platelet-derived growth factor B (PDGF-B), leading to mural cell recruitment thereby contributing to vascular quiescence and barrier function. We propose that reinforced Wnt/β-catenin signaling leads to inhibition of angiogenesis with normalized and less permeable vessels, which might prove to be a valuable therapeutic target for antiangiogenic and edema glioma therapy.

Increased cerebral matrix metalloprotease-9 activity is associated with compromised recovery in the diabetic db/db mouse following a stroke

Diabetes is a major risk factor of stroke and is associated with increased frequency of stroke and a poorer prognosis for recovery. In earlier studies we have utilized type 2 diabetic mouse models of stroke and demonstrated that diabetic db/db and ob/ob mice experience larger infarct volumes and impaired recovery associated with greater infiltration of macrophage following hypoxic-ischemic (H/I) insult than their heterozygous non-diabetic db/+ and ob/+ littermates. To obtain a better understanding of the pathogenesis of the impaired recovery, we have investigated the role of matrix metalloproteases and their endogenous inhibitors in the breakdown of the blood-brain barrier (BBB) following H/I. Diabetic db/db mice showed a significant and more rapid increase in matrix metalloprotease (MMP)-9 mRNA, protein and gelatinolytic activity compared with db/+, which resulted in an increased degradation of occludin and collagen IV and subsequently, an increased BBB permeability and greater infiltration of neutrophils into the infarct area. The expression of the MMPs, especially in the db/+ mice, is preceded by an elevated expression of their endogenous tissue inhibitors of metalloproteases (TIMPs) 1, 2, and 3, whereas in the db/db mice, a lower expression of the TIMPs is associated with greater MMP 3 and 9 expression. These results suggest that an imbalance in the MMPs/TIMPs cascade in the diabetic mouse, particularly MMP-9, results in a greater neutrophil invasion, a compromised BBB and consequently a greater insult.

GLUT-1 glucose transporters in the blood-brain barrier: differential phosphorylation

Glucose is the primary metabolic fuel for the mammalian brain, and a continuous supply is required to maintain normal CNS function. The transport of glucose across the blood-brain barrier (BBB) into the brain is mediated by the facilitative glucose transporter GLUT-1. Prior studies (Simpson et al. [2001] J Biol Chem 276:12725-12729) had revealed that the conformations of the GLUT-1 transporter were different in luminal (blood facing) and abluminal (brain facing) membranes of bovine cerebral endothelial cells, based on differential antibody recognition. This study has extended these observations and, by using a combination of 2D-PAGE/Western blotting and immunogold electron microscopy, determined that these different conformations are exhibited in vivo and arise from differential phosphorylation of GLUT-1 and not from alternative splicing or altered O- or N-linked glycosylation.

Assessing variability in gel-based proteomic analysis of Nitrosomonas europaea

Proteomics offers a unique look at the way protein expression changes in response to stimuli, and "gel-based" methods that utilize two-dimensional gel electrophoresis (2-DE) are key technologies in such studies. However, the many steps involved can be technically complex, and the resulting data are subject to variability from both technical and biological sources. Designing 2-DE proteomic studies can be challenging, as a set of standard methods or experimental designs has not been established. This being the case, it is especially important to identify and control sources of variability. Statistically significant results can be obtained if the experimental design includes a sufficient number of replicate 2-DE gels, and if the replicate gels are similar enough to be analyzed in the same experiment. While three or four replicates are often sufficient for compensation of variability, the pilot study illustrated in this chapter showed that statistically significant expression differences could be detected for 90% of the spots matched if six replicate experiments were done.