title: Murine lipid phosphate phosphohydrolase-3 acts as a cell-associated integrin ligand.
abstract: Lipid phosphate phosphohydrolase-3 (LPP3) is a cell surface protein that exhibits ectoenzyme activity. Previously, we identified human LPP3 in a functional assay of angiogenesis and showed that the Arg-Gly-Asp (RGD) motif in the proposed second extracellular domain interacts with a subset of integrins to mediate cell-cell adhesion. In contrast to the RGD domain of human LPP3, murine Lpp3 contains a variant sequence, Arg-Gly-Glu (RGE). Whether the RGE motif of murine Lpp3 mediates cell-cell interaction has not been studied. In this report, we test the hypothesis that the cell adhesion function of the LPP3 protein is conserved across mouse and human. A glutathione S-transferase (GST) fusion protein of the proposed second extracellular loop of the murine Lpp3 sequence (GST-mLpp3-RGE) promoted attachment of cells in a long-term cell adhesion assay. GST-mLpp3-RGE interacted with alpha(5)beta(1) and alpha(v)beta(3) integrins in a solid-phase ELISA, while a mutant control, GST-hLPP3-RAD, did not. Long-term adhesion of endothelial cells to GST-mLpp3-RGE induced phosphorylation of FAK, SHC, and CAS, whereas adhesion to GST-hLPP3-RAD failed to do so. Upon long-term adhesion both the GST-hLPP3-RGD and GST-mLpp3-RGE substrates bound to the alpha(5)beta(1) integrin of FRT-alpha(5)(+) cells, an interaction that was inhibited by an anti-alpha(5) integrin antibody. In addition, a cell aggregation assay showed that the intact mLpp3-RGE protein interacts with alpha(5)beta(1) and alpha(v)beta(3) integrins expressed by adjacent cells, an interaction that can be blocked by GRGDSP peptides and anti-LPP3-RGD antibodies. These data, together with the known importance of integrins in angiogenesis, provide a mechanism for the function of LPP3 in cell-cell interactions in both human and mouse.
authors.affiliation: Center for Extracellular Matrix Biology, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Texas Medical Center, 2121 W. Holcombe Blvd, Houston, TX 77030, USA.
authors.forename: Joseph O
authors.initials: JO
authors.lastname: Humtsoe
authors.forename: Rodney A
authors.initials: RA
authors.lastname: Bowling
authors.forename: Shu
authors.initials: S
authors.lastname: Feng
authors.forename: Kishore K
authors.initials: KK
authors.lastname: Wary
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002448:Cell Adhesion; D002460:Cell Line; D017931:DNA Primers; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D010711:Phosphatidate Phosphatase / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D014443:Tyrosine / Q000378:metabolism
chemical_list: D017931:DNA Primers; D016023:Integrins; D008024:Ligands; D014443:Tyrosine; D010711:Phosphatidate Phosphatase; C479566:Plpp3 protein, mouse