Elucidation of plasmacytoid dendritic cell development

Most currently defined hematopoietic progenitor pools are heterogeneous, contributing to uncertainty regarding the development of certain blood cells. The origins of plasmacytoid dendritic cells, for instance, have long been controversial and progenitors exclusively committed to this lineage have never been described. We show here that the fate of hematopoietic progenitors is determined in part by their surface levels of 9-O-acetyl sialic acid. Pro-plasmacytoid dendritic cells were identified as lineage negative 9-O-acetyl sialic acid low progenitors that lack myeloid and lymphoid potential but differentiate into pre-plasmacytoid dendritic cells. The latter cells are also lineage negative, 9-O-acetyl sialic acid low cells but are exclusively committed to the plasmacytoid dendritic cell lineage. Levels of 9-O-acetyl sialic acid provide a distinct way to define progenitors and thus facilitate the study of hematopoietic differentiation

M89V Sialic Acid Acetyl Esterase (SIAE) and All Other Non-Synonymous Common Variants of This Gene Are Catalytically Normal

Catalytically defective rare variants of Sialic acid Acetyl Esterase (SIAE) have previously been linked to autoimmunity. Studies presented here confirm that the M89V SIAE protein and all other products of common variant alleles of SIAE are catalytically normal. Although overexpressing transfected non-lymphoid cells secrete small amounts of SIAE that can associate with the cell surface, normal human lymphocytes do not exhibit cell surface SIAE, supporting genetic evidence in mice that indicates that this protein functions in a lymphocyte intrinsic manner. Analyses of the plasma proteome also indicate that SIAE is not secreted in vivo. A re-analysis exclusively of catalytically defective rare variant alleles of SIAE in subjects in which this gene was completely sequenced confirmed an association of SIAE with autoimmunity. A subset of catalytically defective rare variant SIAE alleles has previously been typed in a large genotyping study comparing a diverse group of disease subjects and controls; our re-analysis of this data shows that catalytically defective alleles are enriched in disease subjects. These data suggest that SIAE may be associated with autoimmunity and that further study of catalytically defective rare variant SIAE alleles in terms of autoimmune disease susceptibility is strongly warranted

Murine M89V Siae is functionally normal.

<p>Murine <i>Siae</i> cDNAs encoding WT, S127A, M89V, C196F and Q335P (murine equivalent of human <i>Q309P SIAE</i>) were introduced transiently into HEK 293T cells. Half of each lysate was immunoprecipitated with anti-Flag antibodies revealed in a Western blot assay (A, Lysate). The culture supernatants were also subjected to immunoprecipitation with anti-Flag antibodies to reveal the extent of secretion of each Siae variant at steady state (A, Supernatant). The other half of the cell lysate was similarly immunoprecipitated and examined for esterase activity, presented following normalization for lysate SIAE protein content (B). Each mutant was separately transfected and analyzed on three occasions. A representative experiment is shown. Error bars reflect esterase assays performed in triplicate in a single experiment.</p

Metabolic labeling and pulse-chase analysis comparing the secretion of wild type SIAE with K71R and A467V SIAE proteins.

<p>HEK 293T cells transfected with cDNAs encoding WT, K71R and A467V SIAE were pulse labeled with ³⁵S-methionine and lysates and supernatants were immunoprecipitated with anti-Flag antibodies after 10 min, 2 hrs and 4 hrs of chase. Proteins were separated by SDS/PAGE and revealed by autofluorography. The position of molecular weight markers is indicated on the left in kilodaltons (kDa). (A) A comparison of wild type and A467V SIAE proteins. (B) A comparison of wild type and K71R SIAE proteins.</p

K71R SIAE and A467V SIAE proteins are functionally normal.

<p>The <i>K71R</i> and <i>A467V SIAE</i> variants were re-created by site-directed mutagenesis. Wild type (<i>WT) SIAE</i>, a known catalytic site mutant (<i>S127A SIAE</i>), and the two <i>SIAE</i> common variants were transfected into HEK 293T cells. Half of each cell lysate was immunoprecipitated with anti-Flag antibodies and revealed in a quantitative Western blot assay (A) and the other half was similarly immunoprecipitated and examined for esterase activity, presented following normalization for lysate SIAE protein content (B). Each mutant was separately transfected and analyzed on three occasions. A representative experiment is shown. Error bars reflect esterase assays performed in triplicate in a single experiment.</p

Wild type SIAE is not expressed on the surface of human peripheral blood mononuclear cell (PBMCs).

<p>(A) Flow cytometric analysis of SIAE was performed on unfixed non-permeabilized human PBMC demonstrating the absence of SIAE on the surface of any cells in the lymphocyte gate. (B) The analysis of extracellular CD8 on unfixed, non-permeabilized PBMCs (left) and on fixed, permeabilized PBMCs (right) was used as a positive control for extracellular and intracellular staining. (C) SIAE is expressed intracellularly in peripheral blood mononuclear cells. In the left panel, cells were first stained extracellularly with anti-SIAE, washed, and then subjected to fixation and permeabilization prior to analysis. In the right panel, flow cytometry of PBMC for intracellular SIAE was performed on cells that were fixed, permeabilized and then stained with anti-SIAE (black), with an isotype control (blue) or with no antibodies (red).</p

Frequency of the subset of catalytically defective <i>SIAE</i> variants genotyped by Hunt et al. [7].

<p>Frequency of the subset of catalytically defective <i>SIAE</i> variants genotyped by Hunt et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053453#pone.0053453-Hunt1" target="_blank">[7]</a>.</p

Detection of endogenous and overexpressed SIAE in the native state using a polyclonal anti-SIAE antibody.

<p>293T cells were transfected with Flag-tagged <i>SIAE</i> or left untransfected as a negative control. The IgG heavy chain (IgG HC) was seen in all immunoprecipitated samples. (A) Cell lysates were immunoprecipitated with anti-Flag antibodies and analyzed by Western blotting using polyclonal anti-SIAE. An SIAE-GST fusion protein was run in the third lane as a positive control. (B) Cell lysates in both panels were immunoprecipitated with anti-SIAE, IgG and anti-Flag. The left panel displays the use of anti-SIAE for Western blotting. The immunoprecipitated samples in this panel reveal both overexpressed and endogenous SIAE. Immunoprecipitated proteins in the right panel were revealed by an anti-Flag Western blot. (C) Endogenous SIAE levels were further characterized in the B cell lines BJAB (left) and Ramos (right) by flow cytometric analysis. The data are all representative of three independent experiments.</p

Rare genetic variants of SIAE.^§§

§§<p>The subjects from Surolia et al. (4) and Hirschfield et al. (5) include controls and autoimmune subjects of European ancestry. EVS (Exome variant server) data comprises unannotated American subjects (disease status is unknown) of European and African ancestry and is current as of June 20th 2012. Rare variants reported in both African-Americans and European-Americans are marked with a single asterisk (*n = 6500). Rare variants seen only in European-Americans or only in African-Americans are marked with double (**n = 4299) and triple asterisks (***n = 2201) respectively.</p>nf<p>These variants were found in dbSNP and/or 1000 genomes project but frequency data is not available. The dbSNP data is not ethnically stratified and was derived from the 1000 genomes project.</p

Frequency of catalytically defective rare variants in autoimmune subjects and controls determined by complete sequencing [4].

<p>Frequency of catalytically defective rare variants in autoimmune subjects and controls determined by complete sequencing <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053453#pone.0053453-Surolia1" target="_blank">[4]</a>.</p