Abstract 202: Depletion of PTP4A3 phosphatase disrupts colorectal cancer cell adhesion and extracellular matrix interactions
Authors: McQueeney Kelley E. , Pekic Paula , Salamoun Joseph M. , Ahn Jennifer , Sharlow Elizabeth R. , Wipf Peter , Lazo John S. 
Published: July 2016

Colorectal cancer (CRC) is the third most commonly diagnosed cancer in the United States and the world and the 5-year survival rate in the United States of ∼60% highlights the need for better treatment options. The central challenge in the design and development of drugs to treat CRC has been the validation of novel drug targets and the generation of new therapies aimed at those targets. The goal of this project is to better understand the role of one such potential CRC molecular target. Protein Tyrosine Phosphatase 4A3 (PTP4A3) is currently among the most consistently up-regulated proteins seen in colorectal tumors but it suffers from an incomplete understanding of its substrate(s) and of its participation in tumor formation and progression. To clarify how PTP4A3 expression impacts cell behavior, we isolated primary colon tumor epithelial cells from Ptp4a3fl/fl mice. PTP4A3 was deleted in vitro by adenoviral infection of Ptp4a3fl/fl cells with Cre recombinase accompanied by a green fluorescent protein (GFP) marker. As a control, the Ptp4a3fl/fl cells were infected with GFP alone. Virally infected cells were selected by fluorescence activated cell sorting. In the sorted cells, the expression of Cre resulted in a complete lack of PTP4A3 protein by western blotting and undetectable Ptp4a3 mRNA as determine by quantitative RT-PCR. Analysis of these genetically similar cells revealed that Ptp4a3−/− tumor cells had significantly reduced colony formation and migration as compared to Ptp4a3fl/fl cells. Notably, the growth rate of Ptp4a3fl/fl and Ptp4a3−/− cells was similar when cultured on plastic in a 2D monolayer. In contrast, Ptp4a3fl/fl spheroids grew significantly faster than the Ptp4a3−/− cells when cultured in Matrigel. Moreover, while the Ptp4a3fl/fl cells were able to form cohesive spheroids when cultured in cell repellent plates, there was a striking inability of the Ptp4a3−/− cells to form these 3D structures. In addition, treatment of the Ptp4a3fl/fl cells with a potent and selective PTP4A3 phosphatase inhibitor, thienopyridone, phenocopied the appearance of the Ptp4a3−/− cells grown in cell repellent plates. These results suggest PTP4A3 expression-dependent changes in tumor cell behavior may be rooted in a disruption in the adhesion and extracellular matrix-signaling axis. This hypothesis was supported by significant changes in the gene expression profile of adhesion and extracellular matrix proteins in the Ptp4a3−/− CRC cells. The isogenic Ptp4a3fl/fl and Ptp4a3−/− CRC cells provide an invaluable tool to elucidate further the function of PTP4A3 and its link to adhesion and the extracellular matrix interactions.

Citation Format: Kelley E. McQueeney, Paula Pekic, Joseph M. Salamoun, Jennifer Ahn, Elizabeth R. Sharlow, Peter Wipf, John S. Lazo. Depletion of PTP4A3 phosphatase disrupts colorectal cancer cell adhesion and extracellular matrix interactions. [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 202.