PLC-γ1 Signaling Pathway and Villin Activation Are Involved In Actin Cytoskeleton Reorganization Induced by Na+/Pi Cotransport Up-regulation

Abstract

Background: The brief incubation of opossum kidney (OK) cells with low Pi results in Na+/Pi co-transport up-regulation and in substantial, but transient, cytoskeletal reorganization. In this study, we examined signaling events involved in the depolymerization of microfilaments. Results: Confocal laser scanning microscopy, immunoblot and immunoprecipitation experiments revealed villin co-localization with mainly actin short filaments and monomers, indicating that under the conditions used, villin acted as an actin-severing protein. Further analysis revealed that low concentrations of extracellular phosphate resulted in phospholipase Cγ1 (PLC-γ1) translocation to the actin cytoskeleton, without increases in its tyrosine phosphorylation. Additionally, tyrosine phosphorylation of a portion of insoluble villin was increased; whereas, only tyrosine phosphorylated villin associated with PLC-γ1. Although, tyrosine phosphorylation of PLC-γ1 was not observed during Na+/Pi cotransport up-regulation, genistein treatment abolished the enzyme’s translocation to the actin cytoskeleton, as well as its association with villin. In addition, villin was found to associate with the 85-KDa subunit (p85) of phosphatidylinositol (PI)-3 kinase, concomitant with PLC-γ1, in the cytoskeletal fraction of Na+/Pi cotransport up-regulated cells. Conclusions: Our observations suggest a signaling mechanism linking low ambient Pi levels to the acute up-regulation of its cotransport with sodium and the depolymerization of the subcortical actin cytoskeleton.