Diagnostic accuracy of intrathecal kappa free light chains compared with OCBs in MS.

OBJECTIVE: To determine what kappa free light chain (KFLC) metric has the highest capacity to separate healthy patients from patients with MS, we evaluated the sensitivity, specificity, and the overall diagnostic accuracy of 4 different KFLC metrics. To assess the usefulness of KFLC in the diagnostics of MS, we compared the different KFLC metrics with oligoclonal bands (OCBs), the current gold standard biochemical method to demonstrate intrathecal antibody production. METHODS: CSF and plasma were collected from patients with confirmed or suspected MS, other neurological diseases, as well as symptomatic and healthy controls between May 2017 and May 2018 (n = 335) at the Department of Neurology, Karolinska University Hospital, as part of routine diagnostic workup. KFLC analysis and isoelectric focusing for the detection of oligoclonal bands (OCB) were determined and correlated with diagnosis. Receiver operating characteristic (ROC) curve analysis was used to determine accuracy. RESULTS: OCBs yielded a sensitivity of 87% and a specificity of 100%. All KFLC metrics showed a high sensitivity (89%-95%) and specificity (95%-100%). Using the optimal cutoff according to the Youden Index resulted for the KFLC intrathecal fraction in a cutoff of -0.41 with a sensitivity of 95% and a specificity of 97% and for CSF KFLC/CSF albumin with a cutoff of 1.93 × 10-3 with a sensitivity of 94% and specificity of 100%. CONCLUSION: All evaluated KFLC metrics have excellent accuracy, and both KFLC intrathecal fraction and CSF KFLC/CSF albumin are at least as good as OCB in separating patients with MS from a control group. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that CSF KFLC accurately distinguishes patients with MS from healthy controls.

Human apolipoprotein CIII levels; evaluation of three assay methods.

Apolipoprotein CIII (apoCIII) is associated with triglyceride (TG)-rich particles like VLDL and exerts an inhibitory effect of lipoprotein lipase. Increased levels are related to cardiovascular diseases and diabetes and therefore apoCIII has been proposed as a useful biomarker. Even if several commercial assays for measuring apoCIII in human plasma/serum are available, data is scarce concerning their reliability and none is used clinically. In the present study a comparative investigation has been done. Two ELISA-based methods (Cusabio Biotech and Assay Pro) and one nephelometric assay (Siemens Healthcare) were investigated. Serum and plasma samples were obtained from healthy volunteers and from samples sent to the Laboratory of Clinical Chemistry, preferably with higher levels of TGs. The Cusabio Biotech assay did not yield any valid results. However, both the methods from Assay Pro and Siemens Healthcare showed good performance with similar dynamic ranges. The latter assay had lower CV and required less work. In healthy individuals, apoCIII levels were not affected by fasting, freezing or thawing, nor did we find any gender differences. Individuals with elevated levels of TG displayed higher apoCIII values. Females with oral intake of contraceptives had higher levels. In conclusion, the nephelometric assay showed the best performance with the lowest CV, was less labor intensive than an assay based on ELISA and could therefore be suitable for clinical use.

The tyrosine kinase receptor ROR1 is constitutively phosphorylated in chronic lymphocytic leukemia (CLL) cells.

Phosphorylation of receptor tyrosine kinases (RTKs) has a key role in cellular functions contributing to the malignant phenotype of tumor cells. We and others have previously demonstrated that RTK ROR1 is overexpressed in chronic lymphocytic leukemia (CLL). Silencing siRNA downregulated ROR1 and induced apoptosis of CLL cells. In the present study we analysed ROR1 isoforms and the phosphorylation pattern in CLL cells (n=38) applying western blot and flow-cytometry using anti-ROR1 antibodies and an anti-phospho-ROR1 antibody against the TK domain. Two major ROR1 bands with the size of 105 and 130 kDa respectively were identified, presumably representing unglycosylated (immature) and glycosylated (mature) ROR1 respectively as well as a 260 kDa band which may represent dimerized ROR1. A ROR1 band of 64 kDa that may correspond to a C-terminal fragment was also noted, present only in the nucleus. The 105 kDa ROR1 isoform was more frequently expressed in non-progressive as compared to progressive CLL patients (p=0.03). The 64, 105, 130 and 260 kDa bands were constitutively phosphorylated both at tyrosine and serine residues. Phosphorylation intensity of the mature (130 kDa) isoform was significantly higher in progressive than in non-progressive disease (p<0.001). Incubation of CLL cells with a mouse anti-ROR1 KNG or an anti-ROR1 CRD mAb respectively induced dephosphorylation of ROR1 before entering apoptosis. In conclusion CLL cells expressed different isoforms of ROR1 which were constitutively phosphorylated. The mature, phosphorylated ROR1 isoform was associated with a progressive disease stage. Targeting ROR1 by mAbs induced specific dephosphorylation and leukemic cell death. ROR1 might be an interesting therapeutic target.

Regulation of protein tyrosine phosphatases by reversible oxidation.

Oxidation of the catalytic cysteine of protein-tyrosine phosphatases (PTP), which leads to their reversible inactivation, has emerged as an important regulatory mechanism linking cellular tyrosine phosphorylation and signalling by reactive-oxygen or -nitrogen species (ROS, RNS). This review focuses on recent findings about the involved pathways, enzymes and biochemical mechanisms. Both the general cellular redox state and extracellular ligand-stimulated ROS production can cause PTP oxidation. Members of the PTP family differ in their intrinsic susceptibility to oxidation, and different types of oxidative modification of the PTP catalytic cysteine can occur. The role of PTP oxidation for physiological signalling processes as well as in different pathologies is described on the basis of well-investigated examples. Criteria to establish the causal involvement of PTP oxidation in a given process are proposed. A better understanding of mechanisms leading to selective PTP oxidation in a cellular context, and finding ways to pharmacologically modulate these pathways are important topics for future research.

Hypoxia followed by re-oxygenation induces oxidation of tyrosine phosphatases.

Hypoxia and hypoxia/reoxygenation (H/R) are components of tissue ischemia and reperfusion implicated in myocardial infarction, organ transplantation, and tumor perfusion. H/R enhances production of reactive oxygen species (ROS). Candidate molecular targets of ROS are the catalytic site cysteine of protein tyrosine phosphatases (PTPs), which are major regulators of tyrosine kinase signaling. This study aimed at analyzing potential effects of H/R on PTP-oxidation in cultured cells and in heart tissue. Exposure of mouse NIH3T3 fibroblasts to H/R increased the oxidation of the PTPs SHP-2- and DEP-1. The catalytic pan-PTP- and SHP-2-activity after H/R were also decreased in rat cardiomyoblasts. In vivo dephosphorylation of the Platelet-derived Growth Factor (PDGF)-receptor in NIH3T3 fibroblasts was delayed following H/R. Erk1/2 displayed an antioxidant-sensitive increase in H/R. Furthermore, increased PDGF-induced cytoskeleton re-arrangements were evident following H/R and could be prevented by antioxidant pretreatment. Finally, decreased pan-PTP- and SHP-2 activity was demonstrated in tissue extracts from an ex vivo Langendorff-model of rat heart ischemia-reperfusion. This study thus demonstrates PTP-oxidation as a previously unrecognized molecular component of the cellular response to H/R in cells and tissues. The study additionally provides the first demonstration of increased PTP-oxidation in tissues under patho-physiological settings.

12/15-lipoxygenase-derived lipid peroxides control receptor tyrosine kinase signaling through oxidation of protein tyrosine phosphatases.

Protein tyrosine phosphatases (PTPs) are regulated through reversible oxidation of the active-site cysteine. Previous studies have implied soluble reactive oxygen species (ROS), like H(2)O(2), as the mediators of PTP oxidation. The potential role(s) of peroxidized lipids in PTP oxidation have not been described. This study demonstrates that increases in cellular lipid peroxides, induced by disruption of glutathione peroxidase 4, induce cellular PTP oxidation and reduce the activity of PDGF receptor targeting PTPs. These effects were accompanied by site-selective increased PDGF beta-receptor phosphorylation, sensitive to 12/15-lipoxygenase (12/15-LOX) inhibitors, and increased PDGF-induced cytoskeletal rearrangements. Importantly, the 12/15-LOX-derived 15-OOH-eicosatetraenoic acid lipid peroxide was much more effective than H(2)O(2) in induction of in vitro PTP oxidation. Our study thus establishes that lipid peroxides are previously unrecognized inducers of oxidation of PTPs. This identifies a pathway for control of receptor tyrosine kinase signaling, which might also be involved in the etiology of diseases associated with increased lipid peroxidation.

Differential up-regulation of MAP kinase phosphatases MKP3/DUSP6 and DUSP5 by Ets2 and c-Jun converge in the control of the growth arrest versus proliferation response of MCF-7 breast cancer cells to phorbol ester.

Different levels of regulation account for the inactivation of MAP kinases by MAPK phosphatases (MKPs), in a cell type- and stimuli-dependent manner. MCF-7 human breast carcinoma cells treated with the phorbol 12-myristate 13-acetate (PMA) suffer growth arrest and show morphological alterations, which depend on the activation of the ERK1/2 MAP kinases. MKP3/DUSP6 and DUSP5 MAP kinase phosphatases, two negative regulators of ERK1/2, were specifically up-regulated in MCF-7 and SKBR3 cells in response to PMA. MKP3 and DUSP5 up-regulation required the prolonged activation of the ERK1/2 pathway, and correlated with the shutdown of this route. MKP3 induction relied on the activation of the Ets2 transcription factor, whereas DUSP5 induction depended on the activation of c-Jun. Diminishing the expression of MKP3 and DUSP5 raised the activation of ERK1/2, and accelerated growth arrest of PMA-treated MCF-7 cells. Conversely, MCF-7 cell lines expressing high levels of MKP3 or DUSP5 did not undergo PMA-triggered growth arrest, displayed a migratory phenotype, and formed colonies in soft agar. We propose that the differential up-regulation of MKP3 by Ets2 and of DUSP5 by c-Jun may converge in similar functional roles for these MAP kinase phosphatases in the growth arrest versus proliferation decisions of breast cancer cells.

Antioxidants relieve phosphatase inhibition and reduce PDGF signaling in cultured VSMCs and in restenosis.

OBJECTIVE: Growth factor- and reactive oxygen species (ROS)-induced activation of VSMCs is involved in vascular disease. This study investigates whether inhibitory oxidation of protein tyrosine phosphatases (PTPs) contributes to signaling in VSMCs in vitro and in vivo, and analyzes whether ROS- and growth factor-dependent vascular smooth muscle cell (VSMC) signaling is blunted by antioxidants that are able to activate oxidized PTPs. METHODS AND RESULTS: Signaling induced by H2O2 and platelet-derived growth factor (PDGF) was analyzed in VSMCs with or without the antioxidants N-acetyl-cysteine (NAC) and tempol. Effects of antioxidants on PDGF-stimulated chemotaxis and proliferation were determined. In vivo effects of antioxidants were analyzed in the rat carotid balloon-injury model, by analyzing neointima formation, cell proliferation, PDGF beta-receptor status, and PTP expression and activity. NAC treatment prevented H2O2-induced PTP inhibition, and reduced H2O2- and ligand-induced PDGF beta-receptor phosphorylation, PDGF-induced proliferation, and chemotaxis of VSMCs. Antioxidants inhibited neointima formation and reduced PDGF receptor phosphorylation in the neointima and also increased PTP activity. CONCLUSIONS: PTP-inhibition was identified as an intrinsic component of H2O2- and PDGF-induced signaling in cultured VSMCs. The reduction in PDGF beta-receptor phosphorylation in vivo, and the increase in PTP activity, by antioxidants indicate activation of oxidized PTPs as a previously unrecognized mechanism for the antirestenotic effects of antioxidants. The findings thus suggest, in general terms, reactivation of oxidized PTPs as a novel antirestenotic strategy.

Loss of T-cell protein tyrosine phosphatase induces recycling of the platelet-derived growth factor (PDGF) beta-receptor but not the PDGF alpha-receptor.

We have previously shown that the T-cell protein tyrosine phosphatase (TC-PTP) dephosphorylates the platelet-derived growth factor (PDGF) beta-receptor. Here, we show that the increased PDGF beta-receptor phosphorylation in TC-PTP knockout (ko) mouse embryonic fibroblasts (MEFs) occurs primarily on the cell surface. The increased phosphorylation is accompanied by a TC-PTP-dependent, monensin-sensitive delay in clearance of cell surface PDGF beta-receptors and delayed receptor degradation, suggesting PDGF beta-receptor recycling. Recycled receptors could also be directly detected on the cell surface of TC-PTP ko MEFs. The effect of TC-PTP depletion was specific for the PDGF beta-receptor, because PDGF alpha-receptor homodimers were cleared from the cell surface at the same rate in TC-PTP ko MEFs as in wild-type MEFs. Interestingly, PDGF alphabeta-receptor heterodimers were recycling. Analysis by confocal microscopy revealed that, in TC-PTP ko MEFs, activated PDGF beta-receptors colocalized with Rab4a, a marker for rapid recycling. In accordance with this, transient expression of a dominant-negative Rab4a construct increased the rate of clearance of cell surface receptors on TC-PTP ko MEFs. Thus, loss of TC-PTP specifically redirects the PDGF beta-receptor toward rapid recycling, which is the first evidence of differential trafficking of PDGF receptor family members.