Circulating forms of intercellular adhesion molecule (ICAM)-1 in mice lacking membranous ICAM-1.
Mice deficient in intercellular adhesion molecule-1 (ICAM-1), lacking membranous ICAM-1, show a normal development but abnormalities of inflammatory and immune functions. Although the membrane-bound form of ICAM-1 is not detectable in the mutant strain, circulating ICAM-1 (cICAM) is present in serum from ICAM-1-deficient mice in similar amounts as in serum from wild-type mice. These findings were confirmed in vitro by flow cytometric analysis of lipopolysaccharide-stimulated spleen cells, and cICAM-enzyme-linked immunosorbent assay analysis of supernatants of cultured spleen cells. To analyze for the source of cICAM-1, spleen cell RNA was isolated and ICAM-1 RNA was amplified by reverse transcriptase-polymerase chain reaction using primers binding in the 5' and 3' untranslated regions. Different fragments were cloned and sequenced. In wild-type RNA the common 5 domain form of ICAM-1 was identified. In RNA from ICAM-1 mutant mice only 3 smaller fragments were found. Sequencing these fragments identified 3 alternatively spliced isoforms of ICAM-1, lacking 2 or 3 extracellular domains. However, in all spliced fragments the transmembrane domain was included. Therefore, we postulate that circulating forms of ICAM-1 are generated by proteolytic cleavage of membranous ICAM-1. The data indicate that the expression of membranous ICAM-1 and the appearance of circulating forms in serum are independently regulated mechanisms. (Blood. 2000;95:1350-1355)
van Den Engel
N K
NK
Clinical Department, Diabetes Research Institute at the Heinrich Heine University, Düsseldorf, Germany.
Heidenthal
E
E
Vinke
A
A
Kolb
H
H
Martin
S
S
D017398:Alternative Splicing; D000818:Animals; D002478:Cells, Cultured; D003001:Cloning, Molecular; D003433:Crosses, Genetic; D005091:Exons; D005434:Flow Cytometry; D018799:Intercellular Adhesion Molecule-1 / Q000097:blood* / Q000235:genetics*; D008070:Lipopolysaccharides / Q000633:toxicity; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000187:drug effects / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020033:Protein Isoforms / Q000097:blood / Q000172:deficiency / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D012016:Reference Values; D012772:Shock, Septic / Q000276:immunology*; D013154:Spleen / Q000276:immunology
D008070:Lipopolysaccharides; D020033:Protein Isoforms; D012333:RNA, Messenger; D018799:Intercellular Adhesion Molecule-1