| Treatment of cultured human fibroblasts with interleukin-4 (IL-4) leads to the increased synthesis of anabolic extracellular matrix proteins, e.g., type I collagen and fibronectin; and the decreased synthesis of catabolic extracellular matrix proteins, e.g., stromelysin and 72-kD type IV collagenase. This phenomenon may be important during the normal process of wound healing and the pathological fibrosis that occurs during hypertrophic scar formation, liver cirrhosis, pulmonary fibrosis, joint ankylosis associated with osteoarthritis, and sclerosing episodes in patients with scleroderma. Fetal human skin fibroblasts demonstrated 6-8 fold increases in mRNA levels for the model anabolic extracellular matrix protein procollagen-1{dollar}alpha{dollar} type I (COL1A1) within 3 hours of treatment with 100 units of recombinant human IL-4 per milliliter of serum free culture media. This increase required the tyrosine phosphorylation of pre-existing cytoplasmic proteins including the IL-4 receptor, the signal transduction and transcription factor STAT6, and the tyrosine kinase Fes. When the expression of either STAT6 or Fes was specifically repressed using antisense RNA/DNA technologies, upregulation of the COL1A1 mRNA levels was prevented.; Tyrosine phosphorylated STAT6 binds specifically to an IL-4 responsive element located within the first intron of the COL1A1 gene as determined by gel-shift and super-shift analyses. This responsive element is absolutely and exclusively required for the IL-4 mediated increase in COL1A1 expression as determined by transient transfection studies conducted with deletion and site-directed mutations of a COL1A1 minigene. |
