Mercury alters endogenous phosphorylation profiles of SYK in murine B cells

Abstract

BackgroundEpidemiological evidence and animal models suggest that exposure to low and non-neurotoxic concentrations of mercury may contribute to idiosyncratic autoimmune disease. Since defects in function and signaling in B cells are often associated with autoimmunity, we investigated whether mercury exposure might alter B cell responsiveness to self-antigens by interfering with B cell receptor (BCR) signal transduction. In this study we determined the effects of mercury on the protein tyrosine kinase SYK, a critical protein involved in regulation of the BCR signaling pathway.MethodsPhosphorylation sites of murine SYK were mapped before and after treatment of WEHI cell cultures with mercury, or with anti-IgM antibody (positive control) or pervanadate (a potent phosphatase inhibitor). Phosphopeptides were enriched by either titanium dioxide chromatography or anti-phosphotyrosine immunoaffinity, and analyzed by liquid chromatography-mass spectrometry. Select SYK phosphosite cluster regions were profiled for responsiveness to treatments using multiple reaction monitoring (MRM) methodology.ResultsA total of 23 phosphosites were identified with high probability in endogenous SYK, including 19 tyrosine and 4 serine residues. For 10 of these sites phosphorylation levels were increased following BCR activation. Using MRM to profile changes in phosphorylation status we found that 4 cluster regions, encompassing 8 phosphosites, were activated by mercury and differentially responsive to all 3 treatments. Phosphorylation of tyrosine-342 and -346 residues were most sensitive to mercury exposure. This cluster is known to propagate normal BCR signal transduction by recruiting adaptor proteins such as PLC-γ and Vav-1 to SYK during formation of the BCR signalosome.ConclusionsOur data shows that mercury alters the phosphorylation status of SYK on tyrosine sites known to have a role in promoting BCR signals. Considering the importance of SYK in the BCR signaling pathway, these data suggest that mercury can alter BCR signaling in B cells, which might affect B cell responsiveness to self-antigen and have implications with respect to autoimmunity and autoimmune disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s12865-017-0221-0) contains supplementary material, which is available to authorized users.

Environmental Exposures and Autoimmune Diseases: Contribution of Gut Microbiome

“…The study suggested that cytoskeletal proteins are susceptible to Hg exposure and their phosphorylation may alter B cell function and development (15). Mechanistic evidence was also provided to suggest that Hg can alter phosphorylation status of SYK, which is a critical protein in B cell receptor (BCR) signaling (16). In human T cells, both methyl mercuric chloride and inorganic Hg induce mitochondrial dysfunction and glutathione depletion (17), leading to generation of reactive oxygen species (ROS) and apoptotic caspases (18).…”

Associations Between Metal Levels in Whole Blood and IgE Concentrations in Pregnant Women Based on Data From the Japan Environment and Children’s Study

“…29 When JCP enters the human body as an allergen, IgE-switched B cells may not die because of the abnormal BCR signaling pathway, and this may promote the formation of memory B cells and long-lived plasma cells, which can induce excessive IgE production resulting in an allergic response. 30 McCabe et al 31 reported that low levels of InHg attenuate the BCR signaling pathway, and Caruso et al 32 reported that Hg alters the BCR signaling pathway, especially through inducing changes in Syk activity in experimental studies. In short, abnormalities in the BCR signaling pathway may occur in subjects who have been exposed to Hg, and consequently, IgE-switched B cells do not die and JCP-specific IgE is more likely to be produced throughout the year.…”

“…22 – 24 , 44 , 45 Hg exposures were also reported to alter the phosphorylation status of Syk in the BCR signaling pathway associated with IL-4-independent IgE production in WEHI-231 cells, a murine immature B lymphoma cell line. 31 , 32 Taken together, Hg may interact with some components involved in the pathway of IgE production, and this is followed by an increase of IgE.…”

TULA-Family Regulators of Platelet Activation

“…The correlation of the downregulatory effects of TULA-2 on physiological platelet responses with the TULA-2-dependent dephosphorylation of Syk, together with the specificity of these effects for Syk-dependent platelet responses when ITAM-mediated signaling is affected, while G-protein-mediated signaling is not, strongly suggests that Syk is the main regulatory target of TULA-2 [ 48 , 61 , 62 ]. It has been demonstrated that the level of phosphorylation on Syk Y346, Y317, and Y519/Y520 sites, which are known to be phosphorylated in response to receptor stimulation in various cell types [ 66 , 67 , 68 , 69 , 70 ], is significantly reduced in WT platelets as compared to platelets from TULA-2 KO or TULA-1/TULA-2 dKO mice [ 29 , 48 ] ( Figure 3 ). A decrease in pY519/pY520, a major activation marker of Syk [ 71 , 72 ], is likely a consequence of a decrease in the phosphorylation of Syk regulatory sites directly targeted by TULA-2, since Syk kinase activity is thought to be affected by multiple pY-sites [ 45 , 47 , 68 , 69 , 73 ].…”