Figure 1.

Talin binding to the β7 cytoplasmic domain activates integrin α4β7. (A) Expression of talin and β7 in parental or talin KO β7-expressing Jurkat T cells. Top: Total expression by Western blot. Bottom: Surface expression by flow cytometry. The filled histograms represent untransfected Jurkat cells, whereas open histograms represent β7-expressing Jurkat cells or talin KO cells. (B) Binding of soluble MAdCAM-1 to β7 expressing Jurkat T cells or talin KO cells. PMA (100 nM) markedly increased binding to parental but not talin KO cells. Mn²⁺ (0.5 mM) stimulated binding to both cell types. Stimulated cells were compared with resting (None) for each cell line using one-way ANOVA. (C) Adhesion of β7-expressing Jurkat T cells or Jurkat-talin KO cells to MAdCAM-1 substrate in the presence or absence of PMA (100 nM) under a wall shear stress of 2 dyn/cm². Nontransfected Jurkat T cells (Jurkat) provided a negative control. Jurkat-β7-Talin KO or Jurkat were compared with the Jurkat-β7 for each condition using one-way ANOVA. (D) Structural model of the talin F3 domain in complex with integrin β7 tail (Arg⁷²⁸ to Thr⁷⁶⁶). Talin F3 domain is shown by a surface representation and colored by charge. A ribbon diagram of the docked β7 tail is highlighted in red. β7-Leu⁷⁵⁸ and -Tyr⁷⁵⁹ in the NPLY motif are shown as light blue–colored stick figures. (E) Soluble MAdCAM-1 binding to 293T cells transfected with WT or mutant α4β7 with or without THD cotransfection. Mn²⁺ (0.5 mM) was used as a positive control for integrin activation. Nontransfected 293T cells (MOCK) provided a negative control. Mutant integrins were compared with the WT for each condition using one-way ANOVA. (F) Adhesion of 293T cells transfected with WT or mutant α4β7 with or without THD cotransfection on MAdCAM-1 under a wall shear stress of 2 dyn/cm². Nontransfected 293T cells (MOCK) provided a negative control. Mutant integrins were compared with the WT for each condition using one-way ANOVA. (G) Binding of soluble MAdCAM-1 to 293T-α4β7 cells transfected with EGFP vector, EGFP-THD, EGFP-THD(L325R), or EGFP-THD(W359A). THD-stimulated cells were compared with vector control (α4β7 + EGFP vector) for each cell line using two-way ANOVA. MFI, mean fluorescent intensity. (H) Adhesion of 293T-α4β7 cells transfected with EGFP vector, EGFP-THD, EGFP-THD(L325R), or EGFP-THD(W359A) on MAdCAM-1 under a wall shear stress of 2 dyn/cm². 293T cells transfected with THD only and nontransfected 293T cells (MOCK) were used as negative controls. THD-stimulated cells were compared with vector control (α4β7 + EGFP vector) for each cell line using one-way ANOVA. Error bars show means ± SD. n = 5. NS, P > 0.05; *, 0.01 < P < 0.05; **, 0.001 < P < 0.01; ***, P < 0.001.