Mechanical force effect on the two-state equilibrium of the hyaluronan-binding domain of CD44 in cell rolling.

CD44 is the receptor for hyaluronan (HA) and mediates cell rolling under fluid shear stress. The HA-binding domain (HABD) of CD44 interconverts between a low-affinity, ordered (O) state and a high-affinity, partially disordered (PD) state, by the conformational change of the C-terminal region, which is connected to the plasma membrane. To examine the role of tensile force on CD44-mediated rolling, we used a cell-free rolling system, in which recombinant HABDs were attached to beads through a C-terminal or N-terminal tag. We found that the rolling behavior was stabilized only at high shear stress, when the HABD was attached through the C-terminal tag. In contrast, no difference was observed for the beads coated with HABD mutants that constitutively adopt either the O state or the PD state. Steered molecular dynamics simulations suggested that the force from the C terminus disrupts the interaction between the C-terminal region and the core of the domain, thus providing structural insights into how the mechanical force triggers the allosteric O-to-PD transition. Based on these results, we propose that the force applied from the C terminus enhances the HABD-HA interactions by inducing the conformational change to the high-affinity PD transition more rapidly, thereby enabling CD44 to mediate lymphocyte trafficking and hematopoietic progenitor cell homing under high-shear conditions.

Quantitative profiling of endocannabinoids and related N-acylethanolamines in human CSF using nano LC-MS/MS.

Endocannabinoids, a class of lipid messengers, have emerged as crucial regulators of synaptic communication in the CNS. Dysregulation of these compounds has been implicated in many brain disorders. Although some studies have identified and quantified a limited number of target compounds, a method that provides comprehensive quantitative information on endocannabinoids and related N-acylethanolamines (NAEs) in cerebrospinal fluid (CSF) is currently lacking, as measurements are challenging due to low concentrations under normal physiological conditions. Here we developed and validated a high-throughput nano LC-ESI-MS/MS platform for the simultaneous quantification of endocannabinoids (anandamide and 2-arachidonoylglycerol), ten related NAEs, and eight additional putatively annotated NAEs in human CSF. Requiring only 200 µl of CSF, our method has limits of detection from 0.28 to 61.2 pM with precisions of relative SD <15% for most compounds. We applied our method to CSF from 45 healthy humans and demonstrated potential age and gender effects on concentrations of endocannabinoids and NAEs. Notably, our results show that docosahexaenoylethanolamide concentrations increase with age in males. Our method may offer new opportunities to gain insight into regulatory functions of endocannabinoids in the context of (ab)normal brain function.

Detectability of and interference by major and minor hemoglobin variants using a new-generation ion-exchange HPLC system with two switchable analysis modes.

Objectives: High-performance liquid chromatography (HPLC) is commonly used to measure hemoglobin A1c (HbA1c) levels and detect hemoglobin variants (Hb-Vars). HLC-723GR01 (GR01) is a new-generation automated ion-exchange HPLC system with two switchable analysis modes, namely short (30 s/test) and long modes (50 s/test). We evaluated the general performance of both analysis modes of GR01 for quantifying HbA1c and detecting Hb-Vars. Design and methods: We evaluated the instrument's precision based on CLSI protocol EP-05-A3. A comparison of the two analysis modes of GR01 against the standard mode of HLC-723G11 was performed on 100 whole blood samples. The GR01 long mode was compared with affinity HPLC (AF-HPLC) for detecting common Hb-Vars (HbE, HbD, HbS, and HbC, >20 samples). To examine the detection capability for minor Hb-Vars, we analyzed 26 Hb-Vars using multiple analyzers, including both analysis modes of GR01. Results: Both modes of GR01 had within-laboratory coefficients of variation of ≤1.0 % from four samples with HbA1c concentrations of 32-86 mmol/mol. Good correlation was observed between GR01 and HLC-723G11. The results for HbA1c detection in the presence of the major variants revealed a strong correlation between the long mode of GR01 and AF-HPLC (r = 0.986-0.998), and the difference biases ranged 0.1-1.9 mmol/mol. In the long mode, only one variant had a difference bias exceeding 14 % [10 % (%NGSP)]. Conclusion: The two analysis modes of GR01 were fast and had high accuracy and reproducibility, indicating their utility for routine clinical use in measuring HbA1c samples with Hb-Vars.

Intersubject and Intrasubject Variability of Potential Plasma and Urine Metabolite and Protein Biomarkers in Healthy Human Volunteers.

A limited understanding of intersubject and intrasubject variability hampers effective biomarker translation from in vitro/in vivo studies to clinical trials and clinical decision support. Specifically, variability of biomolecule concentration can play an important role in interpretation, power analysis, and sampling time designation. In the present study, a wide range of 749 plasma metabolites, 62 urine biogenic amines, and 1,263 plasma proteins were analyzed in 10 healthy male volunteers measured repeatedly during 12 hours under tightly controlled conditions. Three variability components in relative concentration data are determined using linear mixed models: between (intersubject), time (intrasubject), and noise (intrasubject). Biomolecules such as 3-carboxy-4-methyl-5-propyl-2-furanpropanoate, platelet-derived growth factor C, and cathepsin D with low noise potentially detect changing conditions within a person. If also the between component is low, biomolecules can easier differentiate conditions between persons, for example cathepsin D, CD27 antigen, and prolylglycine. Variability over time does not necessarily inhibit translatability, but requires choosing sampling times carefully.

Observation of NMR signals from proteins introduced into living mammalian cells by reversible membrane permeabilization using a pore-forming toxin, streptolysin O.

We have developed a new in-cell NMR method that is applicable to any type of cell and does not require target protein modification or specialized equipment. The stable-isotope-labeled target protein, thymosin beta4 (Tbeta4), was delivered to 293F cells, which were permeabilized by a pore-forming toxin, streptolysin O, and resealed by Ca(2+) after Tbeta4 uptake. As a result, we successfully observed (1)H-(15)N HSQC signals originating from the Tbeta4, including those from the N-terminal acetylation, which had occurred inside the cell as a post-translational modification.

Two-state conformations in the hyaluronan-binding domain regulate CD44 adhesiveness under flow condition.

The hyaluronan (HA) receptor CD44 mediates cell adhesion in leukocyte trafficking and tumor metastasis. Our previous nuclear magnetic resonance (NMR) studies revealed that the CD44 hyaluronan-binding domain (HABD) alters its conformation upon HA binding, from the ordered (O) to the partially disordered (PD) conformation. Here, we demonstrate that the HABD undergoes an equilibrium between the O and PD conformations, in either the presence or absence of HA, which explains the seemingly contradictory X-ray and NMR structures of the HA-bound HABD. An HABD mutant that exclusively adopts the PD conformation displayed a higher HA affinity than the wild-type. Rolling of the cells expressing the mutant CD44 was less efficient than those expressing the wild-type, due to the decreased tether frequency and the slow cellular off rate. Considering that the mutant CD44, devoid of the low-affinity state, exhibited impaired rolling, we conclude that the coexistence of the high- and low-affinity states of the HABD is essential for the CD44-mediated rolling.

Chondroitin sulfate E fragments enhance CD44 cleavage and CD44-dependent motility in tumor cells.

During tumor cell invasion, certain extracellular matrix (ECM) components such as hyaluronan (HA) are degraded into small oligosaccharides, which are detected in patients. We previously reported that such HA oligosaccharides induce the proteolytic cleavage of an ECM-binding molecule CD44 from tumor cells and promote tumor cell migration in a CD44-dependent manner. Here, we report that chondroitin sulfate E (CSE), another component of the tumor ECM, strongly enhances CD44 cleavage and tumor cell motility when degraded into oligosaccharides. CSE and its degradation products were detected in pancreatic ductal adenocarcinoma. In CD44-expressing pancreatic tumor cells, degraded forms of CSE but not intact CSE enhanced CD44 cleavage; enzymatic digestion of such low-molecular weight CSE (LMW-CSE) abrogated this enhancement. Among the LMW-CSE preparations examined, 3-kDa CSE most potently induced CD44 cleavage. Nuclear magnetic resonance analysis showed that the 3-kDa-CSE bound to CD44, and that blocking such binding abrogated the CD44 cleavage induction. LMW-CSE also induced prominent filopodia formation and cytoskeletal changes in tumor cells; these effects were also abrogated by blocking the LMW-CSE binding to CD44. Chemically synthesized CSE hexasaccharides also enhanced the CD44 cleavage and tumor cell motility in a CD44-dependent manner. We conclude that the degraded forms of CSE modulate cell adhesion and migration by interacting with tumor-cell CD44, suggesting that the degradation products of tumor-associated ECMs that interact with CD44 play a significant role in CD44-mediated tumor progression.

Ligand-induced structural changes of the CD44 hyaluronan-binding domain revealed by NMR.

CD44, a major cell surface receptor for hyaluronan (HA), contains a functional domain responsible for HA binding at its N terminus (residues 21-178). Accumulating evidence indicates that proteolytic cleavage of CD44 in its extracellular region (residues 21-268) leads to enhanced tumor cell migration and invasion. Hence, understanding the mechanisms underlying the CD44 proteolytic cleavage is important for understanding the mechanism of CD44-mediated tumor progression. Here we present the NMR structure of the HA-binding domain of CD44 in its HA-bound state. The structure is composed of the Link module (residues 32-124) and an extended lobe (residues 21-31 and 125-152). Interestingly, a comparison of its unbound and HA-bound structures revealed that rearrangement of the beta-strands in the extended lobe (residues 143-148) and disorder of the structure in the following C-terminal region (residues 153-169) occurred upon HA binding, which is consistent with the results of trypsin proteolysis studies of the CD44 HA-binding domain. The order-to-disorder transition of the C-terminal region by HA binding may be involved in the CD44-mediated cell migration.