title: An alternatively spliced isoform of PECAM-1 is expressed at high levels in human and murine tissues, and suggests a novel role for the C-terminus of PECAM-1 in cytoprotective signaling.
abstract: The Ig-ITIM family member PECAM-1 is expressed in vascular and endothelial cells, and its functions include suppression of mitochondria-dependent apoptosis. Previous studies have identified distinct PECAM-1 cytoplasmic domain splice variants at the mRNA, but not protein, level. Several relatively abundant mRNA isoforms lack exon 15 (Delta15) and would theoretically encode a protein with a truncated cytoplasmic domain and a unique C-terminal sequence. Using a novel rabbit polyclonal antibody that specifically recognizes Delta15 PECAM-1, we found that the Delta15 PECAM-1 isoform was expressed in human tissues, including brain, testes and ovary. This isoform was also expressed on the cell surface of human platelets, human umbilical vein endothelial cells (HUVECs) and the Jurkat T-cell leukemia, human erythroleukemia (HEL) and U937 histiocytic lymphoma cell lines. Furthermore, murine platelets and lung lysates demonstrated abundant amounts of exon-15-deficient PECAM-1. Functional studies revealed that Delta15 PECAM-1 retains both its homophilic binding capacity and its ability to signal by means of its immunoreceptor tyrosine-based inhibitory motif (ITIM) domains. Delta15 PECAM-1 was unable, however, to protect against apoptosis induced by overexpression of Bax or treatment with the chemotherapy agent etoposide. These studies suggest a novel role for the PECAM-1 C-terminus in cytoprotective signaling and highlight a need for further characterization of expression of PECAM-1 isoforms in normal and malignant tissues.
authors.affiliation: Blood Research Institute, BloodCenter of Wisconsin, 8727 Watertown Plank Road, Milwaukee, WI 53201, USA.
authors.forename: Carmen
authors.initials: C
authors.lastname: Bergom
authors.forename: Cathy
authors.initials: C
authors.lastname: Paddock
authors.forename: Cunji
authors.initials: C
authors.lastname: Gao
authors.forename: Trudy
authors.initials: T
authors.lastname: Holyst
authors.forename: Debra K
authors.initials: DK
authors.lastname: Newman
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Newman
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D006801:Humans; D051379:Mice; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000737:chemistry / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction
chemical_list: D017931:DNA Primers; D019408:Platelet Endothelial Cell Adhesion Molecule-1