Sialic acid acetylesterase (SIAE) is an enzyme that negatively regulates B lymphocyte antigen receptor signalling and is required for the maintenance of immunological tolerance in mice. Heterozygous ...loss-of-function germline rare variants and a homozygous defective polymorphic variant of SIAE were identified in 24/923 subjects of European origin with relatively common autoimmune disorders and in 2/648 controls of European origin. All heterozygous loss-of-function SIAE mutations tested were capable of functioning in a dominant negative manner. A homozygous secretion-defective polymorphic variant of SIAE was catalytically active, lacked the ability to function in a dominant negative manner, and was seen in eight autoimmune subjects but in no control subjects. The odds ratio for inheriting defective SIAE alleles was 8.6 in all autoimmune subjects, 8.3 in subjects with rheumatoid arthritis, and 7.9 in subjects with type I diabetes. Functionally defective SIAE rare and polymorphic variants represent a strong genetic link to susceptibility in relatively common human autoimmune disorders.
We show that the enzymatic acetylation and deacetylation of a cell surface carbohydrate controls B cell development, signaling, and immunological tolerance. Mice with a mutation in sialate:O-acetyl ...esterase, an enzyme that specifically removes acetyl moieties from the 9-OH position of alpha2-6-linked sialic acid, exhibit enhanced B cell receptor (BCR) activation, defects in peripheral B cell development, and spontaneously develop antichromatin autoantibodies and glomerular immune complex deposits. The 9-O-acetylation state of sialic acid regulates the function of CD22, a Siglec that functions in vivo as an inhibitor of BCR signaling. These results describe a novel catalytic regulator of B cell signaling and underscore the crucial role of inhibitory signaling in the maintenance of immunological tolerance in the B lineage.
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.
A novel murine membrane-associated protein kinase, PKK (protein kinase C-associatedkinase), was cloned on the basis of its physical association with protein kinase Cβ (PKCβ). The regulated expression ...of PKK in mouse embryos is consistent with a role for this kinase in early embryogenesis. The human homolog of PKK has over 90% identity to its murine counterpart, has been localized to chromosome 21q22.3, and is identical to the PKCδ-interacting kinase, DIK (Bahr, C., Rohwer, A., Stempka, L., Rincke, G., Marks, F., and Gschwendt, M. (2000) J. Biol. Chem. 275, 36350–36357). PKK comprises an N-terminal kinase domain and a C-terminal region containing 11 ankyrin repeats. PKK exhibits protein kinase activity in vitro and associates with cellular membranes. PKK exists in three discernible forms at steady state: an underphosphorylated form of 100 kDa; a soluble, cytosolic, phosphorylated form of 110 kDa; and a phosphorylated, detergent-insoluble form of 112 kDa. PKK is initially synthesized as an underphosphorylated soluble 100-kDa protein that is quantitatively converted to a detergent-soluble 110-kDa form. This conversion requires an active catalytic domain. Although PKK physically associates with PKCβ, it does not phosphorylate this PKC isoform. However, PKK itself may be phosphorylated by PKCβ. PKK represents a developmentally regulated protein kinase that can associate with membranes. The functional significance of its association with PKCβ remains to be ascertained.
AF302127
Protein kinase C-associated kinase (PKK, also known as RIP4/DIK) activates NFκB when overexpressed in cell lines and is required for keratinocyte differentiation in vivo. However, very little is ...understood about the factors upstream of PKK or how PKK activates NFκB. Here we show that certain catalytically inactive mutants of PKK can activate NFκB, although to a lesser degree than wild type PKK. The deletion of specific domains of wild type PKK diminishes the ability of this enzyme to activate NFκB; the same deletions made on a catalytically inactive PKK background completely ablate NFκB activation. PKK may be phosphorylated by two specific mitogen-activated protein kinase kinase kinases, MEKK2 and MEKK3, and this interaction may in part be mediated through a critical activation loop residue, Thr184. Catalytically inactive PKK mutants that block phorbol ester-induced NFκB activation do not interfere with, but unexpectedly enhance, the activation of NFκB by these two mitogen-activated protein kinase kinase kinases. Taken together, these data indicate that PKK may function in both a kinase-dependent as well as a kinase-independent manner to activate NFκB.
Protein kinase C-associated kinase (PKK)/receptor interacting protein 4 (RIP4) is a protein kinase C (PKC) beta-associated kinase that links PKC to NF-kappaB activation. The kinase domain of PKK is ...similar to that of RIP, RIP2, and RIP3. We show in this study that PKK is expressed early during lymphocyte development and can be detected in common lymphoid progenitor cells. Targeting of a catalytically inactive version of PKK to lymphoid cells resulted in a marked impairment in pro-B cell generation in the bone marrow. Although peripheral B cell numbers were markedly reduced, differentiation into follicular and marginal zone B cells was not defective in these mice. B-1a and B-1b B cells could not be detected in these mice, but this might be a reflection of the overall defect in B cell production observed in these animals. In keeping with a possible link to PKCbeta, peripheral B cells in these mice exhibit a defect in anti-IgM-mediated proliferation. These studies suggest that PKK may be required early in B cell development and for BCR-mediated B cell proliferation.
Protein kinase C-associated kinase (PKK, also known as RIP4/DIK) activates NFkappaB when overexpressed in cell lines and is required for keratinocyte differentiation in vivo. However, very little is ...understood about the factors upstream of PKK or how PKK activates NFkappaB. Here we show that certain catalytically inactive mutants of PKK can activate NFkappaB, although to a lesser degree than wild type PKK. The deletion of specific domains of wild type PKK diminishes the ability of this enzyme to activate NFkappaB; the same deletions made on a catalytically inactive PKK background completely ablate NFkappaB activation. PKK may be phosphorylated by two specific mitogen-activated protein kinase kinase kinases, MEKK2 and MEKK3, and this interaction may in part be mediated through a critical activation loop residue, Thr184. Catalytically inactive PKK mutants that block phorbol ester-induced NFkappaB activation do not interfere with, but unexpectedly enhance, the activation of NFkappaB by these two mitogen-activated protein kinase kinase kinases. Taken together, these data indicate that PKK may function in both a kinase-dependent as well as a kinase-independent manner to activate NFkappaB.
A longitudinal study of diarrhea was carried out from May 1988 to April 1989 by household surveillance of 705 children <5 years old in rural Bangladesh. Stool samples were examined for enteric ...pathogens at the beginning of each diarrheal episode. For persistent episodes, stool examination was repeated on days 15-17 of the illness. For each case of persistent diarrhea, stool samples from age-matched acute diarrheal and healthy controls were examined. Compared with healthy controls, cases of diarrhea were associated with Shigella species (P =.07) and rotavirus (P < .05). Diffusely adherent Escherichia coli (P < .05) and Cryptosporidia (P = .07) were the only enteropathogens associated with persistent diarrhea in comparison with acute diarrhea. No more than 15% of children had the same class of pathogen identified from stool on both days 1-3 and days 15-17, indicating that persistent infection was uncommon. However, a different enteropathogen was frequently found on days 15-17, suggesting that sequential infection may be a cause of persistent diarrhea.
Thirty-four strains of enteroinvasive Escherichia coli (EIEC) were examined for their ability to agglutinate erythrocytes from different animal species. All strains cultured in Casamino acid-yeast ...extract medium in the presence of 1 mM CaCl2 at 37 C for 16-22 hr induced maximal expression of hemagglutination (HA) of broad spectrum erythrocytes. The strongest HA was observed with guinea-pig erythrocytes followed by human (O type), rat, mouse, rabbit and sheep erythrocytes. All the strains failed to agglutinate chicken erythrocytes. HA was resistant to D-mannose, D-glucose, D-galactose, L-fucose, and D-fructose. Also HA was resistant to ethylene diamine tetraacetic acid (EDTA) and Na metaperiodic acid, an oxidizing agent. However, it was heat labile and completely inhibited by proteolytic enzymes such as proteinase K and trypsin, suggesting that the possible hemagglutinin of EIEC associated with the cell surface is a proteinaceous substance.
PDF
