Transforming growth factor (TGF)-ss1 plays an important role in the development of pulmonary fibrosis. In this study we examined the relationship between TGF-ss1 stimulation and the expression of heparan sulfate (HS) 6-O-endosulfatase 1 (Sulf1) in cultured normal human lung fibroblasts (NHLFs) and in murine lungs in vivo. By removing 6-O-sulfates from specific HS intra-chain sites on the cell surface, Sulf1 has been shown to modulate the activities of many HS binding growth factors and morphogens including fibroblast growth factor (FGF)-2. Real time RT-PCR analysis revealed that TGF-ss1 increased Sulf1 expression in NHLFs in a dose- and time-dependant manner, which was accompanied by a decrease in 6-O-sulfated disaccharides as revealed by HPLC analysis. Decreased ERK activation following FGF-2 stimulation was observed in TGF-ss1 treated NHLFs compared to control cells, without changes in HS-dependent FGF-2 binding or FGF-2*FR1c complex formation. To study the function of Sulf1, negative control or Sulf1 specific siRNA transfected NHLFs were stimulated with TGF-ss1. Enhanced Smad2/3 phosphorylation and elevated total Smad2 protein level were observed in Sulf1 siRNA transfected cells, and were accompanied by enhanced expression of a-smooth muscle actin and fibronectin. In addition, Sulf1 siRNA transfection enhanced the anti-proliferative effect of TGF-ss1. Finally Sulf1 expression was upregulated in the lungs of mice treated with adenovirus encoding active TGF-ss1. Taken together, our data indicate that Sulf1 is a TGF-ss1 responsive gene both in vitro and in vivo, and may function as a negative regulator of TGF-ss1-induced fibrogenesis.