Connective tissue growth factor gene regulation. Requirements for its induction by transforming growth factor-beta 2...

Area of Science:

• Dermatology
• Molecular Biology
• Cell Biology

Background:

• Connective tissue growth factor (CTGF) is a profibrotic protein.
• CTGF is typically absent in normal skin but induced by transforming growth factor-beta (TGF-beta).
• TGF-beta induces CTGF in fibroblasts, but not epithelial cells, suggesting a cell-specific mechanism.

Purpose of the Study:

• To investigate the molecular requirements for fibroblast-selective CTGF induction by TGF-beta.
• To identify signaling pathways and DNA elements involved in this TGF-beta response.
• To elucidate the role of specific transcription factors and their binding sites.

Main Methods:

• Investigated Smad-dependent signaling pathways.
• Assessed the roles of protein kinase C and Ras/MEK/ERK cascades.
• Analyzed the CTGF promoter's TGF-beta responsiveness using reporter assays.
• Identified and characterized a critical DNA binding element (5'-GAGGAATGG-3') using gel shift analysis.

Main Results:

• TGF-beta induction of the CTGF promoter, but not a generic Smad-responsive promoter, requires protein kinase C and Ras/MEK/ERK.
• The Ras/MEK/ERK and JNK MAPK pathways must be balanced for CTGF induction.
• A tandem repeat of the 5'-GAGGAATGG-3' element is necessary and sufficient for TGF-beta responsiveness in fibroblasts.
• Fibroblast-enriched nuclear factors bind to this specific DNA element.

Conclusions:

• Smads, protein kinase C, Ras/MEK/ERK, and fibroblast-specific factors binding the GAGGAATGG element collaborate to mediate TGF-beta-induced CTGF expression in fibroblasts.
• This identifies a novel mechanism for cell-type-specific gene regulation by TGF-beta in skin.
• Understanding this pathway is critical for targeting fibrotic skin diseases.