Fig. 4: Abrogating IR K1057/1079 phenylalanylation prevents phenylalanine and FARS from inhibiting insulin signaling.
From: Phenylalanine impairs insulin signaling and inhibits glucose uptake through modification of IRβ
a, b K1057/1079 phenylalanylation determines cell responses to insulin stimulation. The phosphorylation levels of components of the insulin signaling pathway were detected in HepG2 cells and HepG2 cells with either IRβ K1057, K1079, or both, and switched to non-phenylalanylation memetic arginine (a) or phenylalanylation memetic phenylalanine (b) with CRISPR-Cas9 in the absence and presence of insulin. c, d K1057/1079 phenylalanylation inactivates IRβ and inhibits glucose uptake. The effects of insulin on the phosphorylation levels of the components of the insulin signaling pathway (c) and 2-DG uptake (n = 5) (d) were detected in IR knockdown 3T3-L1 adipocytes with IRβ, IRβ2K/R, and IRβ2K/F expressed at comparable levels. e, f Absence of K1057/K1079 abrogates Me-Phe to alter insulin signaling and glucose uptake. The responses of insulin signaling (e) and 2-DG uptake (n = 5) (f) to Me-Phe treatment were detected in IR knockdown 3T3-L1 adipocytes treated with IRβ, IRβ2K/R, and IRβ2K/F expressed at comparable levels. g, h FARS overexpression fails to inhibit insulin signaling and glucose uptake when K1057/K1079 is absent in 3T3-L1 cells. The responses of insulin signaling (g) and 2-DG uptake (n = 5) (h) to FARSA/B overexpression were detected in IR knockdown 3T3-L1 adipocytes expressing IRβ, IRβ2K/R, and IRβ2K/F, respectively. One-way ANOVA are applied for all statistical analyses in this figure. Values are expressed as the mean ± SEM. Significance was indicated as *p < 0.05, **p < 0.01, ***p < 0.001.
