Clr-a: A Novel Immune-Related C-Type Lectin-like Molecule Exclusively Expressed by Mouse Gut Epithelium [MUCOSAL IMMUNOLOGY]

Abstract

The mouse gut epithelium represents a constitutively challenged environment keeping intestinal commensal microbiota at bay and defending against invading enteric pathogens. The complex immunoregulatory network of the epithelial barrier surveillance also involves NK gene complex (NKC)–encoded C-type lectin-like molecules such as NKG2D and Nkrp1 receptors. To our knowledge, in this study, we report the first characterization of the orphan C-type lectin-like molecule Clr-a encoded by the Clec2e gene in the mouse NKC. Screening of a panel of mouse tissues revealed that Clec2e transcripts are restricted to the gastrointestinal tract. Using Clr-a–specific mAb, we characterize Clr-a as a disulfide-linked homodimeric cell surface glycoprotein. Of note, a substantial fraction of Clr-a molecules are retained intracellularly, and analyses of Clr-a/Clr-f hybrids attribute intracellular retention to both the stalk region and parts of the cytoplasmic domain. Combining quantitative PCR analyses with immunofluorescence studies revealed exclusive expression of Clr-a by intestinal epithelial cells and crypt cells throughout the gut. Challenge with polyinosinic-polycytidylic acid results in a rapid and strong downregulation of intestinal Clr-a expression in contrast to the upregulation of Clr-f, a close relative of Clr-a, that also is specifically expressed by the intestinal epithelium and acts as a ligand of the inhibitory Nkrp1g receptor. Collectively, we characterize expression of the mouse NKC-encoded glycoprotein Clr-a as strictly associated with mouse intestinal epithelium. Downregulation upon polyinosinic-polycytidylic acid challenge and expression by crypt cells clearly distinguish Clr-a from the likewise intestinal epithelium-restricted Clr-f, pointing to a nonredundant function of these highly related C-type lectin-like molecules in the context of intestinal immunosurveillance.

Footnotes

  • The online version of this article contains supplemental material.

  • Abbreviations used in this article:

    CHO
    Chinese hamster ovary
    CLEC2
    C-type lectin-like 2
    CTLD
    C-type lectin-like domain
    CTLR
    C-type lectin-like receptor
    EndoH
    endoglycosidase H
    EpCAM
    epithelial cell adhesion molecule
    IEC
    intestinal epithelial cell
    IEL
    intestinal intraepithelial lymphocyte
    KACL
    keratinocyte-associated C-type lectin
    LPL
    lamina propria lymphocyte
    NKC
    NK gene complex
    poly(I:C)
    polyinosinic-polycytidylic acid
    qPCR
    quantitative PCR
    sClr-a
    soluble Clr-a.
  • Received April 15, 2016.
  • Accepted November 14, 2016.

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