LDL receptor-related protein LRP6 senses nutrient levels and regulates Hippo signaling (2020)
Figure 2

Figure 2. LRP6 regulated the phosphorylation, localization and transcriptional activity of YAP.

A. The levels of LRP6 and phosphorylated YAP showed inverse correlation under serum starvation. HEK293 cells were incubated in serum-free medium for the indicated times. Cells were lysed and the cell lysates were analyzed by immunoblotting.

B. Knockdown of LRP6 induced the phosphorylation of YAP even under nutrient-rich condition. HEK293T cells were transfected with GFP siRNA as a control and LRP6 siRNA under nutrient-rich conditions. The ratio of p-YAP/total-YAP of three independent immunoblot bands was quantified (biological replicates, right panel). Error bars indicate standard deviation of biological triplicate measurements. *P < 0.05. Student's t-test was used for statistical analysis.

C. Overexpression of LRP6 blocked the increase of YAP phosphorylation under serum starvation conditions. HEK293T cells were transfected with empty vector (-) or LRP6-EGFP as indicated in the figure. One day after transfection, cells were incubated in serum-free medium for 4 h. Cells were lysed and the cell lysates were analyzed by immunoblotting (left panel). The ratio of LRP6/β-actin and p-YAP/YAP of three independent immunoblots was quantified (middle and right panel, respectively). Error bars indicate standard deviation of biological triplicate measurements. *P < 0.05 and ***P < 0.001. Student's t-test was used for statistical analysis.

D. Knockdown of LRP6 reduced YAP reporter activity. HEK293T cells were transfected with GFP siRNA as a control, LRP6 siRNA, pRL-TK and 8XGTIIC luciferase reporter constructs. One day after transfection, luciferase activity was measured. Error bars indicate standard deviation of biological triplicate measurements. ***P < 0.005. Student's t-test was used for statistical analysis.

E. Knockdown of LRP6 reduced the expression of YAP target genes. Quantitative real-time PCR assay measuring the expression of CTGF, ANKRD1, INHBA, and LRP6 mRNA in GFP and LRP6 siRNA-transfected HEK293T cells was performed. Quantification of CTGF, ANKRD1, INHBA, and LRP6 mRNA was normalized against the level of β-actin. Error bars indicate standard deviation of technical triplicate measurements. *P < 0.05, **P < 0.01 and ***P < 0.001. Student's t-test was used for statistical analysis.

F. Knockdown of LRP6 reduced the interaction between YAP and TEAD. HEK293T cells were transfected with EGFP-YAP, Myc-TEAD4 and siRNA for LRP6. Cells were lysed and the cell lysates were immunoprecipitated with anti-Myc antibody and analyzed by immunoblotting. WCL, whole-cell lysates.

G. Overexpression of LRP6 rescued the reduced YAP reporter activity under serum starvation conditions. HEK293T cells were transfected with an empty vector (-) or VSVG-LRP6, and with pRL-TK and 8XGTIIC luciferase reporter constructs. One day after transfection, cells were incubated in serum-free medium for 4 h and luciferase activity was measured. Error bars indicate standard deviation of biological triplicate measurements. ***P < 0.001. Student's t-test was used for statistical analysis.

H. Knockdown of LRP6 induced cytoplasmic localization of YAP. HEK293A cells were transfected with siRNA for GFP or LRP6 and immunofluorescence analysis was performed. Figure shows representative image of multiple areas. DAPI was used for nucleus staining. Scale bars: 10 μm. Quantification of nuclear YAP is shown in the right panel. Quantification was performed by counting cells that have nuclear-localized YAP per image (n=8). Error bars indicate standard deviation. ***P < 0.001. Student's t-test was used for statistical analysis.

I. Overexpression of LRP6 induced nuclear localization of YAP under starvation conditions. HEK293A cells were transfected with LRP6-EGFP and 1 d after transfected cells were incubated with or without serum-containing medium for 4 h, and immunofluorescence analysis was performed. Figure shows representative image of multiple areas. DAPI was used for nucleus staining. Scale bars: 10μm. Quantification of nuclear YAP is shown in the right panel. Quantification was performed by counting cells that have nuclear localized YAP per image (n=6). Error bars indicate standard deviation. *P < 0.05. Student's t-test was used for statistical analysis.