A Novel Protein with Homology to the Junctional Adhesion Molecule

Abstract

We have cloned a novel cDNA belonging to the Ig superfamily that shows 44% similarity to the junctional adhesion molecule (JAM) and maps to chromosome 21q21.2. The open reading frame of JAM2 predicts a 34-kDa type I integral membrane protein that features two Ig-like folds and three N-linked glycosylation sites in the extracellular domain. A single protein kinase C phosphorylation consensus site and a PDZ-binding motif are present in the short intracellular tail. Heterologous expression of JAM2 in Chinese hamster ovary cells defined a 48-kDa protein that localizes predominantly to the intercellular borders. Northern blot analysis showed that JAM2 is preferentially expressed in the heart. JAM2 homotypic interactions were demonstrated by the ability of JAM2-Fc to capture JAM2-expressing Chinese hamster ovary cells. We further showed that JAM2, but not JAM1, is capable of adhering to the HSB and HPB-ALL lymphocyte cell lines. Neutralizing mouse anti-JAM2 polyclonal antibodies provided evidence against homotypic interactions in this assay. Biotinylation of HSB cell membranes revealed a 43-kDa counterreceptor that precipitates specifically with JAM2-Fc. These characteristics of JAM2 led us to hypothesize a role for this novel protein in adhesion events associated with cardiac inflammatory conditions.

Vascular Endothelial-Junctional Adhesion Molecule (VE-JAM)/JAM 2 Interacts with T, NK, and Dendritic Cells Through JAM 3

“…In normal fetal tissue, VE-JAM/JAM 2 is present in the vascular endothelium of small and large vessels, while in normal adult tissue, VE-JAM/JAM 2 is found in the endothelium of tonsillar and lymphatic HEV, as previously reported (1,2). We also identified VE-JAM/JAM 2 mRNA expression the spermatogenic cells of the epithelium in testicular seminiferous tubules, and in the intermediate trophoblasts of placenta for the first time.…”

“…In search of a molecule, we identified an endothelial-specific JAM homolog that proved to be the previously reported vascular endothelia-JAM (VE-JAM) (1) or JAM 2 (2), termed herein as VE-JAM/JAM 2. VE-JAM/JAM 2 is described in this work, as previously reported (1,2). It is expressed in a variety of fetal vascular endothelia, the HEV of the adult tonsil and lymph nodes.…”

“…In the previously published JAM 2 report, T cell lines were demonstrated to interact with JAM 2-transfected CHO cells (2). We 1 and 2) or Ramos (lanes 3 and 4) cells were lysed and immunoprecipitated against an Fc-cross-linked VE-JAM/JAM 2.Fc protein A matrix (lanes 2 and 4) or an Fc-cross-linked human IgG1/protein A matrix (lanes 1 and 3).…”

“…Furthermore, VE-JAM/JAM 2 mRNA was also detected in the spermatogenic cells of the epithelium in testicular seminiferous tubules as well as the intermediate trophoblasts of the placenta. VE-JAM/ JAM 2 was also confirmed as an adhesion molecule for T cell lines (2) and observed to interact with a very specific subpopulation of circulating lymphocytes, namely the CD56 ϩ NK cells, the CD56 ϩ CD3 ϩ NK/T cells, the CD56 ϩ CD8 ϩ CD3 ϩ cytolytic T cells, and peripheral blood, GM-CSF/IL-4-derived dendritic cells (PBDC). Also reported in this work are the cloning and identification of the VE-JAM/JAM 2 counterligand, which was identified as JAM 3 (accession number NP_113658), making VE-JAM/JAM 2 and JAM 3 the first known interacting pair in the A33/JAM family of adhesion molecules.…”

“…T he recent discovery and description of junctional adhesion molecule (JAM) 2 and A33-Ag introduced a new subfamily of Ig-like adhesion molecules to the study of epithelial biology and tight junction regulations. These reports also suggested that molecules similar to JAM and A33-Ag might exist in an endothelial-specific fashion, playing an important role in endothelial biology and lymphocyte trafficking into and out of the specific endothelial environments termed high endothelial venules (HEV).…”