Regulation of class A scavenger receptor-mediated cell adhesion and surface localization by PI3K: identification of a regulatory cytoplasmic motif.
The importance of cytoplasmic motifs in differentially regulating SR-A function was demonstrated by deleting the first 49 cytoplasmic aa (SR-A(Delta1-49)), which abolished SR-A-mediated ligand internalization without reducing cell adhesion. To identify additional cytoplasmic motifs within the first 49 aa that regulate SR-A function, the acidic residues in a conserved motif (EDAD) were changed to their amide derivatives (SR-A(QNAN)). The function and regulation of SR-A(QNAN) were compared with that of SR-A(Delta1-49) and SR-A in transfected HEK-293 cells. Blocking PI3K activation inhibited SR-A, but not SR-A(Delta1-49)- or SR-A(QNAN)-mediated cell adhesion. Although deleting (SR-A(Delta1-49)) or mutating (SR-A(QNAN)) the EDAD motif abolished the PI3K sensitivity of SR-A-mediated cell adhesion, these mutations did not affect ligand internalization or PI3K activation during cell adhesion. To define the mechanism by which PI3K regulates SR-A-mediated cell adhesion, the cellular localization of wild-type and mutant SR-A was examined. PI3K inhibition reduced surface localization of SR-A but not of SR-A(Delta1-49) or SR-A(QNAN). The regulation of SR-A surface localization by PI3K was confirmed in peritoneal macrophages, which endogenously express SR-A. Together, these results suggest a pathway in which SR-A binding to an immobilized ligand activates PI3K to recruit more receptor to the plasma membrane and enhances cell adhesion.
Cholewa
Jill
J
Graduate Center for Nutritional Sciences, The University of Kentucky, Lexington, Kentucky, USA.
Nikolic
Dejan
D
Post
Steven R
SR
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002448:Cell Adhesion; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology*; D003593:Cytoplasm / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D008024:Ligands; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000201:enzymology; D051379:Mice; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051117:Scavenger Receptors, Class A / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014162:Transfection
D008024:Ligands; D051117:Scavenger Receptors, Class A; D019869:Phosphatidylinositol 3-Kinases