title: Class A scavenger receptor-mediated adhesion and internalization require distinct cytoplasmic domains.
abstract: Class A scavenger receptors (SR-A) are transmembrane glycoproteins that mediate both ligand internalization and cell adhesion. Previous studies have identified specific amino acids in the cytoplasmic tail of SR-A that regulate receptor internalization; however, the role of cytoplasmic domains in regulating cell adhesion has not been addressed. To investigate the role of cytoplasmic domains in SR-A-mediated adhesion and to address whether SR-A-mediated adhesion and internalization require distinct cytoplasmic domains, different SR-A constructs were stably expressed in human embryonic kidney (HEK 293) cells. Deleting the entire cytoplasmic tail (SR-A Delta 1-55) greatly reduced receptor protein abundance. Retaining the six amino acids proximal to the membrane (SR-A Delta 1-49) restored receptor protein abundance. Although SR-A Delta 1-49 localized to the cell surface, cells expressing this receptor failed to internalize the ligand acetylated low density lipoprotein. Replacing the cytoplasmic tail of SR-A with that of the transferrin receptor (TfR/SR-A) resulted in retention of the chimeric receptor in the endoplasmic reticulum suggesting a specific role for the membrane-proximal amino acids in trafficking SR-A from the endoplasmic reticulum to the Golgi. Like SR-A expressing cells, cells expressing SR-A Delta 1-49 displayed increased spreading and adhesion, demonstrating that the membrane-proximal amino acids were sufficient for SR-A-mediated cell adhesion. Together, our results indicate a critical role for the membrane-proximal amino acids in SR-A trafficking and demonstrate that SR-A-mediated adhesion and internalization require distinct cytoplasmic domains.
authors.affiliation: Department of Internal Medicine, University of Kentucky, Lexington, Kentucky 40536-0298, USA.
authors.forename: Ninetta
authors.initials: N
authors.lastname: Kosswig
authors.forename: Stuart
authors.initials: S
authors.lastname: Rice
authors.forename: Alan
authors.initials: A
authors.lastname: Daugherty
authors.forename: Steven R
authors.initials: SR
authors.lastname: Post
mesh_terms: D000581:Amidohydrolases / Q000737:chemistry; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D019921:Biotinylation; D015153:Blotting, Western; D020126:Brefeldin A / Q000494:pharmacology; D018955:CD36 Antigens / Q000737:chemistry* / Q000378:metabolism*; D002412:Cations; D002448:Cell Adhesion; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005822:Genetic Vectors; D006023:Glycoproteins / Q000737:chemistry; D006026:Glycoside Hydrolases / Q000737:chemistry; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011990:Receptors, Transferrin / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051117:Scavenger Receptors, Class A; D013752:Tetracycline / Q000494:pharmacology; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D018955:CD36 Antigens; D002412:Cations; D018076:DNA, Complementary; D006023:Glycoproteins; D008077:Lipoproteins, LDL; C495139:MSR1 protein, human; C495140:Msr1 protein, mouse; D011990:Receptors, Transferrin; D051117:Scavenger Receptors, Class A; D014415:Tunicamycin; D020126:Brefeldin A; D006026:Glycoside Hydrolases; D000581:Amidohydrolases; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase; D013752:Tetracycline