Activating transcription factor 2 targets c-Fos, but not c-Jun, in growth plate chondrocytes

Area of Science:

• Molecular Biology
• Cell Biology
• Gene Regulation

Background:

• Activating transcription factor 2 (ATF-2), c-Fos, and c-Jun are bZIP transcription factors involved in cellular processes.
• These factors regulate the expression of genes, including cyclins, which are crucial for cell cycle progression.
• Understanding their specific roles in chondrocytes is important for cartilage biology.

Purpose of the Study:

• To investigate the role of ATF-2 in regulating the promoters of c-Fos, c-Jun, cyclin D1, and cyclin A in primary mouse chondrocytes.
• To determine the specific binding sites and interactions of ATF-2, c-Fos, and c-Jun on these promoters.

Main Methods:

• Luciferase reporter assays were used to measure promoter activity.
• Chromatin immunoprecipitation (ChIP) assays were performed to assess protein-DNA binding.
• Dominant-negative (dn) constructs of c-Fos and c-Jun were employed to study their functional roles.

Main Results:

• ATF-2 enhanced the promoter activity of c-Fos but not c-Jun.
• ATF-2 directly bound to the cyclic AMP response element (CRE) site of the c-Fos promoter.
• Dominant-negative c-Fos inhibited cyclin D1 promoter activity, indicating its crucial role, whereas dominant-negative c-Jun had minimal effect.
• c-Fos interacted with both CRE and activating protein-1 (AP1) sites of the cyclin D1 promoter.
• c-Jun specifically cooperated with the cyclin D1 CRE site.
• Neither c-Fos nor c-Jun affected cyclin A promoter activity, and c-Fos could not bind its regulatory sites, although c-Jun could interact with cyclin A AP1-2 and CRE sites.

Conclusions:

• ATF-2 plays a significant role in regulating c-Fos and cyclin D1 expression in chondrocytes.
• c-Fos is a key regulator of cyclin D1 promoter activity, interacting with specific DNA elements.
• The distinct roles of c-Fos and c-Jun in regulating cyclin A and D1 promoters highlight their differential functions in chondrocyte gene expression.