Polycystin-1 regulates ARHGAP35-dependent centrosomal RhoA activation and ROCK signaling

Abstract

Mutations in PKD1 (encoding for polycystin-1 [PC1]) are found in 80%–85% of patients with autosomal dominant polycystic kidney disease (ADPKD). We tested the hypothesis that changes in actin dynamics result from PKD1 mutations through dysregulation of compartmentalized centrosomal RhoA signaling mediated by specific RhoGAP (ARHGAP) proteins resulting in the complex cellular cystic phenotype. Initial studies revealed that the actin cytoskeleton was highly disorganized in cystic cells derived from patients with PKD1 and was associated with an increase in total and centrosomal active RhoA and ROCK signaling. Using cilia length as a phenotypic readout for centrosomal RhoA activity, we identified ARHGAP5, -29, and -35 as essential regulators of ciliation in normal human renal tubular cells. Importantly, a specific decrease in centrosomal ARHGAP35 was observed in PKD1 -null cells using a centrosome-targeted proximity ligation assay and by dual immunofluorescence labeling. Finally, the ROCK inhibitor hydroxyfasudil reduced cyst expansion in both human PKD1 3D cyst assays and an inducible Pkd1 mouse model. In summary, we report a potentially novel interaction between PC1 and ARHGAP35 in the regulation of centrosomal RhoA activation and ROCK signaling. Targeting the RhoA/ROCK pathway inhibited cyst formation in vitro and in vivo, indicating its relevance to ADPKD pathogenesis and for developing new therapies to inhibit cyst initiation.

MRTF: Basic Biology and Role in Kidney Disease

“…This is accompanied by higher RhoA activity, actin reorganization and shorter cilia. The ROK inhibitor hydroxyfasudyl reversed cyst expansion [ 244 ]. While these studies clearly suggest that Rho activation can contribute to the dysregulation of cell proliferation and thus cyst formation, we propose that it may also underlie the other major feature of the disease i.e., fibrogenesis, by promoting PEP.…”

A cell-based GEF assay reveals new substrates for DENN domains and a role for DENND2B in primary ciliogenesis

“…S19). Activation of RhoA has been linked to cilia length, specifically, cells with higher levels of active RhoA have shorter cilia, possibly through the formation of stress fibers ( 50 , 51 ), whereas reduced RhoA activity leads to longer cilia ( 52 ). We thus considered that DENND2B could control cilia length by acting as a GEF for RhoA.…”

Intraflagellar Transport Proteins as Regulators of Primary Cilia Length

“…In the absence of fluid flow, cultured Pkd1 MEF and renal epithelia also displayed reduced cilia disassembly via disruption of a centrosomal integrity pathway mediated by p53 ( Gerakopoulos et al, 2020 ). In contrast, Streets et al reported shortened primary cilia in Pkd1 -mutant renal epithelial cells via increased actin polymerization mediated by RhoA ( Streets et al, 2020 ). These varied results may reflect that the altered cilia lengths are captured at a particular time point during dynamic modulation of cilia length by these individual pathways.…”