PubMed · 7911625
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R Falabella. 1994. Vitiligo.. https://doi.org/10.2340/0001555574147148
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Protein tyrosine phosphorylation cascades are difficult to analyze and are critical for cell signaling in higher eukaryotes. Methodology for profiling tyrosine phosphorylation, considered herein as the assignment of multiple protein tyrosine phosphorylation sites in single analyses, was reported recently (Salomon, A. R.; Ficarro, S. B.; Brill, L. M.; Brinker, A.; Phung, Q. T.; Ericson, C.; Sauer, K.; Brock, A.; Horn, D. M.; Schultz, P. G.; Peters, E. C. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 443-448). The technology platform included the use of immunoprecipitation, immobilized metal affinity chromatography (IMAC), liquid chromatography, and tandem mass spectrometry. In the present report, we show that when using complex mixtures of peptides from human cells, methylation improved the selectivity of IMAC for phosphopeptides and eliminated the acidic bias that occurred with unmethylated peptides. The IMAC procedure was significantly improved by desalting methylated peptides, followed by gradient elution of the peptides to a larger IMAC column. These improvements resulted in assignment of approximately 3-fold more tyrosine phosphorylation sites, from human cell lysates, than the previous methodology. Nearly 70 tyrosine-phosphorylated peptides from proteins in human T cells were assigned in single analyses. These proteins had unknown functions or were associated with a plethora of fundamental cellular processes. This robust technology platform should be broadly applicable to profiling the dynamics of tyrosine phosphorylation.
Patients infected with human immunodeficiency virus (HIV) frequently have increased production of interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha), and these cytokines may in turn contribute to the disease pathogenesis. It has been hypothesized that secretion of these cytokines by HIV-exposed mononuclear cells or HIV-infected monocyte/macrophages (M/Ms) is the principal source of their overproduction in HIV-infected patients, and the present study was undertaken to explore this issue. We observed that in the absence of endotoxin or cytokines, M/Ms productively infected by HIV do not produce detectable IL-6 or TNF-alpha. However, granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine that enhances HIV replication in M/Ms and is frequently used to propagate monocytotropic strains of HIV, can induce the relatively long-term production of IL-6 (up to 47 U/ml) and TNF-alpha (up to 47 pg/ml) by M/Ms, even in the absence of HIV. Also, HIV induced production of a relatively small (< or = 9 U/ml) quantity of IL-6 in M/Ms stimulated with macrophage-colony stimulating factor (M-CSF). Finally, while highly concentrated HIV induced production of both cytokines by either M/Ms or peripheral blood mononuclear cells (PBMCs), this production was almost completely eliminated when care was taken to avoid contamination of HIV by endotoxin. These data suggest that the excess IL-6 and TNF-alpha in HIV-infected patients does not simply result from their production by HIV-infected M/Ms and that alternative mechanisms are involved in this process.
HEK is a member of the EPH-like receptor tyrosine kinase family, which appear to have roles in development and oncogenesis. Recently, we purified a soluble HEK ligand which is also a ligand (AL1) for the HEK-related receptor EHK1. Promiscuity appears to be a characteristic feature of interactions between the EPH-like receptors and their ligands, termed ligands for EPH-related kinases (LERKs). This prompted us to analyze the interactions between the HEK exodomain and fusion proteins comprising candidate LERKs and the Fc portion of human IgG1 (Fc) or a FLAGTM-peptide tag by surface plasmon resonance, size exclusion high performance liquid chromatography, sedimentation equilibrium, and transphosphorylation. Our results indicate that AL1/LERK7 is the preferred high-affinity ligand for HEK, forming a stable 1:1 complex with a dissociation constant of 12 nM. As expected the apparent affinities of bivalent fusion proteins of LERKs and the Fc portion of human IgG1 had significantly reduced dissociation rates compared with their monovalent, FLAGTM-tagged derivatives. High-avidity binding of monovalent ligands can be achieved by antibody-mediated cross-linking of monovalent ligands and with LERK7 results in specific phosphorylation of the receptor. By extrapolation, our findings indicate that some of the reported LERK-receptor interactions are a consequence of the use of bivalent ligand or receptor constructs and may be functionally irrelevant.