The role of mutant p53R175H in de novo activation of von Willebrand factor expression in tumor cells

Abstract

Background

The glycoprotein von Willebrand Factor (VWF) is essential for primary hemostasis and is normally expressed strictly in endothelial cells and megakaryocytes. However, VWF is aberrantly expressed in some nonendothelial/megakaryocytic cancer cells. We previously showed de novo VWF expression in osteosarcoma cells linked to increased GATA6 (activator) and reduced NF-IB (repressor) binding to the VWF promoter. NF-IB is a downstream target of transcription factor and tumor suppressor p53, which is frequently mutated in cancer. We have also shown that the cell-cell adhesion protein plakoglobin restores the tumor suppressive function of some p53 mutants, including p53^R175H.

Objectives

We explored the role of p53 in de novo activation of VWF expression in cancer cells of non-endothelial/megakaryocytic origin.

Methods

The analyses of 100 VWF-positive cancer cell lines revealed NF-IB downregulation and/or p53 mutation. Using p53-null and plakoglobin-deficient H1299 lung carcinoma cell line, we examined the effect of exogenously expressed p53 (wild type and mutants) on VWF expression. The findings were validated in ovarian cancer lines with endogenous p53 variants. We assessed the functional consequences and molecular mechanisms of de novo VWF expression.

Results

Specifically, p53^R175H activated de novo expression of VWF by interacting with NF-IB and GATA6, preventing NF-IB’s repressive and promoting GATA6’s activating functions on the VWF promoter. VWF expression mediates cancer cell-platelet heteroaggregate formation. Plakoglobin coexpression or VWF knockdown reversed these effects.

Conclusion

These findings identify a novel mechanism of VWF expression involving p53^R175H in cancer cells and reveal plakoglobin as a potent antagonist of this pathway.