Cloning of a soluble isoform of the SgIGSF adhesion molecule that binds the extracellular domain of the membrane-bound isoform.
SgIGSF (spermatogenic immunoglobulin superfamily) is a recently identified intercellular adhesion molecule of the immunoglobulin superfamily. In a mast-cell cDNA library, we found a clone that resulted from the retention of intron 7 within the mature SgIGSF message. This clone was predicted to encode a soluble isoform of SgIGSF (sSgIGSF) with 336 amino-acid residues because its open reading frame ended just before the transmembrane domain. We constructed a plasmid expressing sSgIGSF fused to the human IgG Fc fragment at its C-terminus (sSgIGSF-Fc), and transfected it into COS-7 cells. The fusion protein was readily detectable in the culture supernatant. Solid-phase binding assay showed that sSgIGSF interacted directly the extracellular domain of membrane-bound SgIGSF (mSgIGSF). We next examined whether this interaction inhibited homophilic binding of mSgIGSF by aggregation assays using L cells that did not express mSgIGSF. A stable L-cell clone that overexpressed mSgIGSF aggregated with each other but not with mock-transfected L cells, indicating that a homophilic interaction of mSgIGSF mediated the aggregation. Addition of sSgIGSF-Fc inhibited the aggregation of L cells overexpressing mSgIGSF in a dose-dependent manner. Moreover, FACScan analyses revealed the specific binding of sSgIGSF-Fc to mSgIGSF expressed in L cells. Binding of sSgIGSF-Fc to mSgIGSF appeared to inhibit homophilic interactions of mSgIGSF.
Koma
Yu-ichiro
Y
Department of Pathology, Medical School/Graduate School of Frontier Bioscience, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
Ito
Akihiko
A
Wakayama
Tomohiko
T
Watabe
Kenji
K
Okada
Morihito
M
Tsubota
Noriaki
N
Iseki
Shoichi
S
Kitamura
Yukihiko
Y
D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D000075982:Cell Adhesion Molecule-1; D015815:Cell Adhesion Molecules; D002449:Cell Aggregation; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D006801:Humans; D007136:Immunoglobulins / Q000235:genetics* / Q000378:metabolism; D007739:L Cells; D008407:Mast Cells; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D011485:Protein Binding; D020033:Protein Isoforms; D014018:Tissue Distribution; D014162:Transfection
C498598:Cadm1 protein, mouse; D000075982:Cell Adhesion Molecule-1; D015815:Cell Adhesion Molecules; D007136:Immunoglobulins; D008565:Membrane Proteins; D020033:Protein Isoforms