Premium
The Identification of Cytoplasmic Amino Acid Sequences Regulating SR‐A Function
Author(s) -
Cholewa Jill Marie,
Gass Cecelia,
Post Steven
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.lb69-c
Subject(s) - internalization , microbiology and biotechnology , alanine , ligand (biochemistry) , cell adhesion , receptor , phosphorylation , cytoplasm , biology , biochemistry , cell adhesion molecule , amino acid , hek 293 cells , chemistry , cell
Class A scavenger receptors (SR‐A) are macrophage receptors that recognize many polyanionic molecules, including modified forms of lipoproteins and extracellular matrix. In response to ligand binding, SR‐A can mediate ligand internalization (eg. modified lipoprotein) and/or cell adhesion (eg. modified ECM). The functional importance of cytoplasmic sequences in coupling SR‐A to either ligand internalization or cell adhesion is not clear. Sequence analysis of the 55‐amino acid cytoplasmic tail of SR‐A identified three consensus phosphorylation sites, an acidic domain (EDAD), and a nonstructural loop flanked by prolines (P 38 –P 45 ). Site‐directed mutagenesis was used to mutate these sequences and the mutated receptors stably expressed in an inducible human embryonic kidney (HEK 293) cell system. Deletion of the proline‐flanked loop between residues 38 and 45 resulted in the loss of receptor protein expression without altering RNA expression. Replacing the potential phosphorylation site at S 25 with alanine increased SR‐A mediated cell adhesion and surface localization. In contrast, changing the other potential phosphorylation sites at S 46 and S 53 to alanine had no apparent effect on SR‐A function. Mutating the acidic amino acids in the EDAD domain to their amide derivatives (QNAN) increased SR‐A mediated cell adhesion and surface localization, but decreased ligand internalization. Overall, these results identify residues that differentially regulate SR‐A post‐transcriptional processing, surface localization, ligand internalization, and cell adhesion.