PTEN and the PTEN-like phosphatase CnrN have both distinct and overlapping roles in a Dictyostelium chemorepulsion pathway

Abstract

The directed movement of eukaryotic cells is crucial for processes such as embryogenesis and immune cell trafficking. The enzyme Phosphatase and tensin homolog (PTEN) dephosphorylates phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] to phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. Dictyostelium discoideum cells require both PTEN and the PTEN-like phosphatase CnrN to locally inhibit Ras activation to induce biased movement of cells away from the secreted chemorepellent protein AprA. Both PTEN and CnrN decrease basal levels of PI(3,4,5)P3 and increase basal numbers of macropinosomes, and AprA prevents this increase. AprA requires both PTEN and CnrN to increase PI(4,5)P2 levels, decrease PI(3,4,5)P3 levels, inhibit proliferation, decrease myosin II phosphorylation, and increase filopod sizes. AprA causes PTEN, similar to CnrN, to localize to the side of the cell towards AprA in an AprA gradient. However, PTEN and CnrN also have distinct roles in some signaling pathways. PTEN, but not CnrN, decreases basal levels of PI(4,5)P2, AprA requires PTEN, but not CnrN, to induce cell roundness, and CnrN and PTEN have different effects on the number of filopods and pseudopods, and the sizes of filopods. Together, our results suggest that CnrN and PTEN play unique roles in D. discoideum signaling pathways, and possibly dephosphorylate PI(3,4,5)P3 in different membrane domains, to mediate chemorepulsion away from AprA.