In the enhancer region of the human
type I collagen alpha 2 (
COL1A2) gene, we identified cis-elements for the
transcription factor CUX1. However, the role of CUX1 in
fibrosis remains unclear. Here we investigated the role of CUX1 in the regulation of COL1 expression and delineated the mechanisms underlying the regulation of
COL1A2 expression by CUX1 in
systemic sclerosis (SSc) lung fibroblasts. The binding of CUX1 to the
COL1A2 enhancer region was assessed using electrophoretic mobility shift assays
after treatment with
transforming growth factor (TGF)-β. Subsequently, the
protein expression levels of CUX1
isoforms were determined using Western blotting. Finally, the expression levels of COL1 and
fibrosis-related
cytokines, including CTGF, ET-1, Wnt1 and β-
catenin were determined. The binding of CUX1
isoforms to the
COL1A2 enhancer region increased after TGF-β treatment. TGF-β also increased the
protein levels of the CUX1
isoforms p200, p150, p110, p75, p30 and p28. Moreover, SSc lung fibroblasts showed higher levels of CUX1
isoforms than normal lung fibroblasts, and treatment of SSc lung fibroblasts with a
cathepsin L inhibitor (IW-CHO) decreased COL1
protein expression and reduced cell size, as measured using immunocytochemistry. In SSc and diffuse alveolar damage lung tissue sections, CUX1 localised within α-smooth muscle actin-positive cells. Our results suggested that CUX1
isoforms play vital roles in connective tissue deposition during
wound repair and
fibrosis.