Podocyte structural and transcriptional phenotypic plasticity characterizes glomerular injury. Activity of the transcription factor Wilm’s Tumor-1 (WT1) is required for normal podocyte structure and is repressed by the podocyte adherens junction protein, WT1 Interacting Protein (WTIP). We show that WTIP translocated into podocyte nuclei in lipopolysaccharide (LPS)-treated mice and cultured podocytes, a model of transient nephrotic syndrome. LPS-stimulated WTIP nuclear translocation required JNK activity, which assembled a multiprotein complex of the scaffolding protein JIP3 and the molecular motor dynein. Intact microtubule (MT) networks and dynein activity were necessary for LPS-stimulated WTIP translocation. Stress signaling pathways initiate WTIP nuclear translocation, suggesting a mechanism that transmits changes in podocyte morphology to the nucleus.
Podocytes respond to environmental cues by remodeling their slit diaphragms and cell-matrix adhesive junctions. WTIP, an Ajuba family Lin11, Isl-1 and Mec-3 (LIM) domain scaffold protein expressed in the podocyte, coordinates cell adhesion changes and transcriptional responses to regulate podocyte phenotypic plasticity. We evaluated effects of Wtip on podocyte cell-cell and cell-matrix contact organization using gain-of- and loss-of-function methods. Endogenous Wtip targeted to focal adhesions in isolated adherent podocytes and then shifted to adherens junctions after cells made stable, homotypic contacts. Podocytes with Wtip knockdown (shWtip) adhered but failed to spread normally. Non-contacted shWtip podocytes did not assemble actin stress fibers and their focal adhesions failed to mature. As shWtip podocytes established cell-cell contacts, stable adherens junctions failed to form and F-actin structures were disordered. In shWtip cells, cadherin and B-catenin clustered in irregularly distributed spots that failed to laterally expand. Since normal actin dynamics are required for organization of adherens junctions and focal adhesions, we determined if Wtip regulates F-actin assembly. Undifferentiated podocytes did not elaborate F-actin stress fibers, but when induced to overexpress WTIP, formed abundant stress fibers, a process blocked by the RhoA inhibitor, C3 toxin, and a RhoA kinase inhibitor. WTIP directly interacted with Rho guanine nucleotide exchange factor (GEF) 12 (Arhgef12), a RhoA-specific GEF enriched in the glomerulus. In conclusion, stable assembly of podocyte adherens junctions and cell-matrix requires Wtip, a process that may be mediated by spatio-temporal regulation of RhoA activity through appropriate targeting of Arhgef12.