The engagement of the β4 integrin with laminin-332 contributes to the formation of PD-L1 and β4 integrin containing retraction fibers. Related to Fig. 3. (A) The endogenous β4 integrin was tagged with tdTomato using CRISPR/Cas9. The protein expression of β4-tdTomato was validated by immunoblotting. Red arrowhead shows tagged version of the β4 integrin. (B) A representative image of WT MDA-MB-231 cells stained with F-actin (phalloidin, green), integrin β4 (β4, red), and PD-L1 (blue). Arrowhead points to F-actin containing protrusions. Scale bar: 10 μm. (C) Quantification of co-localization of PD-L1 and β4 integrin at the actin containing protrusions using Pearson correlation coefficient R value. Data are shown as means ± SD from three independent experiments, n = 34 cells. (D) Representative images of PD-L1^KO-PD-L1-EGFP MDA-MB-231 cells show merged images (left) of PD-L1 (green), laminin-332 (red), and integrin β4 (blue) distribution. Single channel only images are shown on the right. Scale bar: 10 μm. Source data are available for this figure: SourceData FS2.