Inhibition of JAK2/STAT5 signaling pathway blocked the promotive effect of Pro-Gly on IGF-1 expression and secretion in the HepG2 cells. (A) Western blot analysis of phospho-JAK2 (p-JAK2), JAK2, phospho-STAT5 (p-STAT5), STAT5 and prepro IGF-1 in HepG2 cells after 6 h or 24 h incubation in the presence of Pro-Gly (0.5 mM) and/or AZD1480 (1 μM), respectively. β-actin was used as loading control. The panels shown are the representative bands of 3 independent experiments with 6 replicates. (B) Mean ± SEM of immunoblotting bands of prepro IGF-1, p-JAK2/JAK2 and p-STAT5/STAT5 ( n = 6). The intensities of the bands were expressed as the arbitrary units. (C) IGF-1 mRNA level in HepG2 cells after 24 h incubation in the presence of Pro-Gly (0.5 mM) and/or AZD1480 (1 μM) ( n = 6). GAPDH was used as housekeeping gene. (D) Effects of Pro-Gly (0.5 mM) and/or AZD1480 (1 μM) on IGF-1 levels in the supernatant of HepG2 cells ( n = 6). Bars that do not share the same letter are significantly different ( P