SEQUENCE MOTIFS IN THE INTEGRIN ALPHA(4) CYTOPLASMIC TAIL REQUIRED FOR REGULATION OF IN-VIVO EXPANSION OF MURINE LYMPHOMA-CELLS

The binding of integrins to cognate ligands is tightly controlled by i ntracellular signals. Conversely, integrin occupancy generates biochem ical signals inside the cell. The present study examined whether conce pts of integrin function established by in vitro analysis apply to reg ulation of receptor function in complex biologic settings in vivo usin g a mouse model of tumor metastasis, Integrin alpha(4) subunits were t runcated at amino acid Gln(1014) (A4-1014), preserving the conserved G FFKR motif, and at position Glu(1021) (A4-1021), In vitro adhesion ass ays revealed that cytoplasmic tail truncations did not affect constitu tive ligand binding of (alpha(4) integrins, while agonist-induced adhe sion was abolished by the A4-1014, but not by the A4-1021, mutation, I nducible ligand binding of alpha(4) integrins was dependent on cytoske letal function, whereas constitutive adhesion was not, In vivo metasta sis formation assays demonstrated that expansion of murine T lymphoma cells in spleen is strongly inhibited by the wild-type alpha(4) subuni t and the A4-1021 mutant, In contrast, the in vivo phenotype of alpha( 4) integrin expression in lymphoma cells was completely abrogated by t he A4-1014 mutation. Cross-linking of alpha(4) integrins in vitro inhi bited proliferation and induced apoptosis of LB cells expressing wild- type alpha(4) submits or the A4-1021 mutant, but not of LB-A4-1014 cel ls. In summary, these results demonstrate that sequence motifs regulat ing cytoskeleton-dependent alpha(4) integrin activation in vitro are e ssential for the control of LB lymphoma cell expansion both in vitro a nd in vivo.