Conserved regions in the cytoplasmic domains of the leukocyte integrin alpha L beta 2 are involved in endoplasmic reticulum retention, dimerization, and cytoskeletal association.
Selected functions of integrins, including regulated cytoskeletal association and transmembrane signaling, depend on a poorly defined bidirectional communication between the extracellular and cytoplasmic domains of the alpha and beta subunits. To investigate this problem in the leukocyte integrin alpha L beta 2 (LFA-1), we generated a series of cytoplasmic truncation or internal substitution mutants of the alpha L and beta 2 cytoplasmic domains, and assessed their biochemical and functional properties upon ectopic expression in constitutively adherent cells. Expression of the alpha L beta 2 heterodimer in stably adherent cells is sufficient to promote its constitutive cytoskeletal association. Structural determinants for such association are located in selected regions of the beta 2 cytoplasmic domain, which display functional interdependence. In addition, a conserved region (Arg733-Lys742) in the beta 2 cytoplasmic domain seems to be critical not only for its cytoskeletal association, but also for endoplasmic reticulum retention, assembly, and transport to the plasma membrane of the mature alpha L beta 2 heterodimer. Analysis of deletion mutants of the alpha L subunit demonstrates a role of the conserved, membrane-proximal GFFKR motif in conferring stability to the alpha beta complex, possibly because of its direct involvement in heterodimer formation. We propose that a previously uncharacterized association of defined subregions of the cytoplasmic domains of integrin alpha and beta subunits affects the dimerization and regulated function of the adhesion receptor.
Pardi
R
R
Scientific Institute San Raffaele-DIBIT, University of Milano School of Medicine, Italy.
Bossi
G
G
Inverardi
L
L
Rovida
E
E
Bender
J R
JR
D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D000818:Animals; D002451:Cell Compartmentation; D002461:Cell Line, Transformed; D002522:Chlorocebus aethiops; D003599:Cytoskeleton / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D011487:Protein Conformation; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion; D013601:T-Lymphocytes / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
D016169:Lymphocyte Function-Associated Antigen-1; D011993:Recombinant Fusion Proteins; D013755:Tetradecanoylphorbol Acetate