GRAMD1/ASTER-mediated cholesterol transport promotes Smoothened cholesterylation at the endoplasmic reticulum (2022)
Figure 7

Figure 7. Inhibition of GRAMD proteins hampers the maturation of SMO and Hh signaling.

(A) The cholesterol modification of endogenous SMO was decreased in NIH3T3 cells lacking Gramd1a, 1b, 1c, 2, and 3 (Gramd-5KO). The cells were incubated in a cholesterol depletion medium for 12 h, followed by 2 μg/mL of CP and ShhN for an additional 12h.

(B) The glycosylation of endogenous SMO was decreased in Gramd-5KO NIH3T3 cells. The ShhN conditioned medium was applied for 24 h. Black bracket indicates mature glycosylated form.

(C) The ciliary localization of endogenous SMO in WT or Gramd-5KO NIH3T3 cells. Cells were incubated in serum starvation medium for 24 h to fully induce cilia formation and then incubated with or without ShhN conditioned medium for 2 h. Results shown are representative of three independent experiments. Scale bars: 5μm.

(D) Quantitative assessment of the intensity of ciliary SMO in (C). More than 100 cells were randomly selected and counted for each group. Data are presented as median with interquartile. (****p < 0.0001, two-way ANOVA with Tukey's multiple comparisons test).

(E) Quantification of the percentage of cells with ciliary SMO. Data are presented as mean ± SEM from three biological replicates (****p < 0.0001, two-way ANOVA with Sidak's multiple comparisons test). 86-100 cilia were analyzed in each group in each experiment.

(F) The protein levels of Gli1 was significantly reduced in Gramd-5KO cells. The cells were incubated in a serum starvation medium with or without ShhN for 24 h. Results shown are representative of two independent experiments.

(G) GLI-luciferase reporter assay in WT or Gramd-5KO NIH3T3 cells. Data are presented as mean ± SEM from three technical replicates (****p < 0.0001; ***p < 0.001; *p < 0.05, two-way ANOVA with Sidak's multiple comparison test).

(H) The Gli1 mRNA levels were measured in WT, Gramd-5KO, Gramd-5KO overexpression GRAMD1A, 1B, 1C NIH3T3 cells by qRT-PCR after treatment with or without ShhN conditioned medium for 8 h. Data are expressed as mean ± SEM from three technical replicates (****p < 0.0001, two-way ANOVA with Tukey's multiple comparisons test).

(I) The GRAMD inhibitor AI3d inhibited cholesterol modification of SMO in NIH3T3 cells. The cells were incubated in cholesterol depletion medium for 16 h and then treated with 3 μM AI3d for 6 h. Next, cells were incubated in the same medium containing ShhN and 2 μg/mL of CP for an additional 2 h.

(J) The GRAMD inhibitor AI3d decreased the mRNA levels of Gli1 in NIH3T3 cells. Cells were incubated in serum starvation medium for 16 h, depleted of cholesterol by 1.5% HPCD for 0.5 h, and then treated with serum starvation medium containing 1 μM lovastatin, 10 μM mevalonate and 1 μM AI3d for 6 h. Next, cells were incubated in the same medium containing ShhN and 10 μM MβCD-cholesterol for an additional 16 h. Data are expressed as mean ± SEM from three technical replicates (****p < 0.0001, one-way ANOVA with Sidak's multiple comparisons test).

(K) Model for the regulation of intracellular transport of SMO by Hh signaling.