Transforming growth factor-β1 differentially mediates fibronectin and inflammatory cytokine expression in kidney tubular cells

Transforming growth factor-β1 (TGF-β1) is not only an important fibrogenic but also immunomodulatory cytokine in the human kidney. We have recently demonstrated that TGF-β1 induces interleukin-8 (IL-8), macrophage chemoattractant protein-1 (MCP-1), and fibronectin production in renal proximal tubular (HK-2) cells. However, the unique dependence of IL-8, MCP-1, and fibronectin on TGF-β1 expression is unknown. The TGF-β1 gene was effectively silenced in HK-2 cells using small-interference (si) RNA. Basal secretion of IL-8 and MCP-1 decreased (both P < 0.05) but, paradoxically, fibronectin increased (P < 0.05) in TGF-β1-silenced cells compared with cells transfected with nonspecific siRNA. Significant increases were observed in mRNA for the TGF-β2 (P < 0.05), TGF-β3 (P < 0.05) isoforms and pSmad2 (P < 0.05), which were reflected in protein expression. Concurrent exposure to pan-specific TGF-β antibody reversed the observed increase in fibronectin expression, suggesting that TGF-β2 and TGF-β3 isoforms mediate...