Abstract 1675: Activation of phosphatase toward the retinoblastoma protein inhibits invasion in MDA-MB-231 breast cancer cells

Abstract

Abstract Excessive phosphorylation of the Retinoblastoma protein (Rb) is found in most cancer tumor types. Several cyclin dependent kinase (cdk) inhibitors are in development or in clinical trials at the present time. Our previous studies have focused on the regulation of Rb phosphorylation by the phosphatase, PP1. In proliferating cells, PP1 is regulated by a protein called PNUTS (Phosphatase Nuclear Targeting Subunit). PNUTS is a competitive inhibitor of Rb binding to PP1 and siRNA mediated knockdown of PNUTS in several cancer cell types (breast, colon, ovarian) leads to an increase in Rb directed PP1 activity, Rb dephosphorylation on several sites, and a dramatic induction of apoptosis. In this study we have used MDA-MB-231 breast cancer cells grown in Matrigel. By lentiviral-mediated doxycycline inducible expression of PNUTS siRNA, expression of PNUTS protein is blocked and phosphorylation of Rb cells is reduced. Cells become less invasive and expression of mesenchymal markers N-cadherin, Zeb and Slug is lost. A reversion to the epithelial phenotype is suggested by an increase in E-cadherin expression. PNUTS knockdown has no effect on cells that do not contain highly phosphorylated Rb such as non-transformed MCF-10A cells or Rb-negative MDA-MB-468 cells. Further experiments using highly invasive HT-1080 cells show that reduction of Rb phosphorylation appears to reduce invasiveness in this cell model, supporting the idea that Rb phosphorylation plays a critical role in the regulation of invasion. Citation Format: Jacklynn Egger, Maria Lane, Brixhilda Dedi, Nancy A. Krucher. Activation of phosphatase toward the retinoblastoma protein inhibits invasion in MDA-MB-231 breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1675.