Endostatin causes G1 arrest of endothelial cells through inhibition of cyclin D1

Area of Science:

• Molecular Biology
• Cell Biology
• Oncology

Background:

• Endostatin, a fragment of type XVIII collagen, is a known antiangiogenic agent.
• It inhibits endothelial cell migration, induces apoptosis, and causes cell cycle arrest.
• The precise molecular mechanisms underlying endostatin's antiangiogenic effects require further elucidation.

Purpose of the Study:

• To investigate the mechanism by which endostatin induces G(1) arrest in endothelial cells.
• To identify the specific molecular targets and pathways involved in endostatin's action.

Main Methods:

• Endothelial cells were treated with endostatin to assess effects on cell cycle regulators.
• Western blotting and quantitative PCR were used to analyze protein and mRNA levels of cyclin D1.
• Reporter assays with cyclin D1 promoter constructs (wild-type, deletion, and mutant) were performed.
• Experiments involved cells overexpressing cyclin D1, beta-catenin, or a LEF1-dependent transcriptional activator.

Main Results:

• Endostatin decreased hyperphosphorylated retinoblastoma protein and downregulated cyclin D1 mRNA and protein.
• Endostatin failed to arrest endothelial cells overexpressing cyclin D1, highlighting cyclin D1 as a critical target.
• Endostatin inhibited cyclin D1 promoter activity, with the LEF1 site identified as essential for this effect.
• Endostatin repressed cyclin D1 promoter activity in beta-catenin overexpressing cells but not in cells with a LEF1-insensitive activator.

Conclusions:

• Cyclin D1, particularly transcription through the LEF1 site, is critical for endostatin's antiangiogenic action in vitro.
• Beta-catenin is suggested to be a molecular target of endostatin, mediating its effects on cyclin D1 transcription.
• These findings provide mechanistic insights into endostatin's antiangiogenic properties and potential therapeutic applications.