Fig. 2

Treatment with 10 μM ATRA stimulated the secretion of TGF-β₂ protein in the supernatants of D407 cells. TGF-β₂ protein in the conditioned media was measured by ELISA and normalized to cell counts (1 × 10⁶). The concentration of secreted TGF-β₂ in the control group increased at 8 h and peaked at 24 h, and there was no statistically significant difference between 24 h and 48 h. After treatment with 10 μM ATRA for 2 h, the concentration of secreted TGF-β₂ of the ATRA-treat group increased (p < 0.001) and peaked at 16 h. However, there was no statistically significant difference the concentrations of secreted TGF-β₂ in the 10 μM ATRA-treated group at 16 h, 24 h and 48 h (p > 0.05; n = 3 per treatment). The effects of U73122 on the ATRA-induced secretion of TGF-β2 in D407 Cells . Cells were pretreated with U73122 (5 μM, 10 μM, 20 μM and 40 μM) for 30 min, followed by exposure to ATRA (10 μM) for 24 h. After treatment with 5–40 40 μM U73122 + 10 μM ATRA, the concentrations of secreted TGF-β2 in the supernatants were significantly lower than those of the ATRA-treated group (p < 0.01). The concentration of secreted TGF-β2 decreased with the increase of U73122. When the concentration of U73122 reached 40 μM, the concentration of secreted TGF-β2 was not significantly different from that of the control group (p > 0.05) (Fig. 3). The results indicated that the secretion of TGF-β₂ induced by ATRA is inhibited by U73122 (5–40 μM) in D407 cells. This suppressive effect of U73122 was enhanced with increasing concentrations, and the effect of 10 μM ATRA was completely inhibited by 40 μM U73122