Iron-induced C3 expression is not dependent on TGF-β ligand/receptor-mediated canonical signaling.
A, C3 mRNA levels in ARPE-19 cells are repressed by exogenous TGF-β1 (10 ng/ml; 2 days (d)), and this inhibition is partially relieved by TGF-β receptor inhibitor SB431542 (100 nm; 2 days). In contrast, PAI-1 mRNA levels are significantly increased by TGF-β1, and this increase is partially inhibited by SB431542. B, TGFB1 mRNA levels show an increase with FAC treatment; TGF-β1 protein levels in the conditioned medium of FAC-treated cells show a significant decrease relative to untreated. C, C3 mRNA levels are increased with addition of neutralizing antibody anti-TGF-β1/2/3 (10 μg/ml; 2 days) when compared with control or IgG treatment conditions. PAI-1 mRNA levels are decreased in the same comparison. D, C3 mRNA levels are not significantly changed with co-treatment with anti-TGF-β1/2/3 antibody and FAC when compared with FAC only. PAI-1 mRNA levels are decreased to similar levels with co-treatment with anti-TGF-β1/2/3 antibody and FAC compared with FAC only. Data are expressed as mean ± S.E. (error bars) (n ≥ 3 with the following statistical notations: *, p ≤ 0.05; ***, p ≤ 0.001; ****, p ≤ 0.0001; ns, not significant).