Dlg1 is an inhibitor of Fas cell death signaling. (A) Detection of Fas and Dlg1 by IF in control and Dlg1-knockdown HCT15 cells. (B) Line scan profile (yellow line in A) of fluorescence intensity of Fas, Dlg1, and actin in confluent cells. (C) Quantification of the specific enrichment of Fas at cell–cell junctions in control and Dlg1-knockdown HCT15 cells. Error bars in graphs represent means ± SEM (n = 5). (D) PLA was used to determine the interaction of Fas and Dlg1 in HCT15 cells as in Fig. 2 E. PLA dots/cells in each condition were counted, and the right panel shows the mean of dots/cells ± SEM. One representative experiment is shown (n = 3). (E and F) Cell death induced by FasL (15 ng/ml + M2) in HCT15 and SW480 cells transfected with the indicated siRNAs was analyzed as described above. Relative caspase-8 activation (p41/43) and PARP cleavage were quantified by densitometry (n = 3). (G) Schematic model summarizing the inhibitory function of E-cadherin and Dlg1 on Fas pro–cell death signaling. *, P < 0.05; Student’s t test.