Phosphorylation of the integrin alpha 4 cytoplasmic domain regulates paxillin binding.
alpha4 integrins are essential for embryogenesis, hematopoiesis, inflammation, and immune response possibly because alpha4 integrins have distinct signaling properties from other integrins. Specifically, the alpha4 cytoplasmic domain binds tightly to paxillin, a signaling adaptor protein, leading to increased cell migration and an altered cytoskeletal organization that results in reduced cell spreading. The alpha4 tail contains potential phosphorylation sites clustered in its core paxillin binding region. We now report that the alpha4 tail is phosphorylated in vitro and in vivo. Furthermore, Ser(988) is a major phosphorylation site. Using antibodies specific for Ser(988)-phosphorylated alpha4, we found the stoichiometry of alpha4 phosphorylation varied in different cells. However, >60% of alpha4 was phosphorylated in Jurkat T cells. Phosphorylation at Ser(988) blocked paxillin binding to the alpha4 tail. A phosphorylation-mimicking mutant of alpha4 (alpha4S988D) blocked paxillin binding and reversed the inhibitory effect of alpha4 on cell spreading. Consequently, alpha4 phosphorylation is a biochemical mechanism to modulate paxillin binding to alpha4 integrins with consequent regulation of alpha4 integrin-dependent cellular functions.
Han
J
J
Department of Vascular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Liu
S
S
Rose
D M
DM
Schlaepfer
D D
DD
McDonald
H
H
Ginsberg
M H
MH
D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D003593:Cytoplasm / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D006801:Humans; D039441:Integrin alpha4; D019169:Jurkat Cells; D008969:Molecular Sequence Data; D051419:Paxillin; D010449:Peptide Mapping; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism
D015703:Antigens, CD; D003598:Cytoskeletal Proteins; C496061:PXN protein, human; D051419:Paxillin; D010750:Phosphoproteins; D011994:Recombinant Proteins; D039441:Integrin alpha4; D012694:Serine