Plk1 colocalizes with NPHP1 at the base of the cilium.

<p><b>A</b> Ciliated hTERT-RPE1 (human retinal pigmented epithelial cells and HK2 human kidney cells were stained with antibody to Plk1 (green), acetylated α-tubulin (orange), and γ-tubulin (red), and treated with DAPI to visualize DNA (blue). The scale bar represents 5 µm. <b>B</b> Ciliated hTERT-RPE1 cells and HK2 cells were stained with antibody to acetylated α-tubulin (orange), γ-tubulin (red), to NPHP1 or Plk1 as indicated (green), and with DAPI to visualize DNA (blue). The third row shows merged signals from staining with antibody to Plk1 (orange), NPHP1 (green) acetylated α-tubulin (orange), γ-tubulin (red) and DAPI was used to visualize DNA (blue). The scale bar represents 5 µm.</p

Plk1 directly phosphorylates NPHP1 in vitro.

<p><b>A</b> Alignment of NPHP1 protein sequences from multiple species indicates a conserved candidate Plk1 motif at position T87. <b>B</b> An <i>in vitro</i> kinase assay performed with active Plk1 and recombinant His-fused NPHP1 protein indicates phosphorylation within the NPHP1 N-terminal 205 amino acids. CB, Coomassie Blue.</p

Plk1 associates with NPHP1.

<p><b>A</b> Western blot of immunoprecipitates (IP) or lysates (Lys) from HEK293T cells co-transfected with plasmids expressing V5-tagged NPHP1 and Flag-tagged Plk1 or negative control protein (Eps1–225 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038838#pone.0038838-Habbig1" target="_blank">[13]</a>). β-actin was assessed as a loading control. <b>B</b> Western blot of immunoprecipitates (IP) or cell lysates (Lys) from HEK293T cells co-transfected with plasmids expressing Myc-tagged Plk1 and Flag-tagged NPHP1 or empty Flag vector. <b>C</b> Western blot of immunoprecipitates (IP) or cell lysates (Lys) from HEK293T cells transfected with plasmid expressing Flag-tagged NPHP1 or the negative control protein (Eps1–225 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038838#pone.0038838-Habbig1" target="_blank">[13]</a>). Endogenous Plk1 was detected using a specific antibody against Plk1. <b>D</b> A panel of Flag-tagged NPHP1 derivatives, including truncations, internal deletions and a T87A mutant, was analyzed by co-immunoprecipitation with Myc-tagged Plk1. <b>E</b> Western analysis of immunoprecipitates (IP) or cell lysates (Lys) from HEK293T cells co-transfected with plasmids expressing Myc-tagged Plk1 and Flag-tagged NPHP1 constructs as indicated, or the Flag-tagged control protein (Eps1–225). * indicates immunoglobulin heavy chain.</p

Dysregulated Autophagy Contributes to Podocyte Damage in Fabry’s Disease

<div><p>Fabry’s disease results from an inborn error of glycosphingolipid metabolism that is due to deficiency of the lysosomal hydrolase α-galactosidase A. This X-linked defect results in the accumulation of enzyme substrates with terminally α-glycosidically bound galactose, mainly the neutral glycosphingolipid Globotriaosylceramide (Gb3) in various tissues, including the kidneys. Although end-stage renal disease is one of the most common causes of death in hemizygous males with Fabry’s disease, the pathophysiology leading to proteinuria, hematuria, hypertension, and kidney failure is not well understood. Histological studies suggest that the accumulation of Gb3 in podocytes plays an important role in the pathogenesis of glomerular damage. However, due to the lack of appropriate animal or cellular models, podocyte damage in Fabry’s disease could not be directly studied yet. As murine models are insufficient, a human model is needed. Here, we developed a human podocyte model of Fabry’s disease by combining RNA interference technology with lentiviral transduction of human podocytes. Knockdown of α-galactosidase A expression resulted in diminished enzymatic activity and slowly progressive accumulation of intracellular Gb3. Interestingly, these changes were accompanied by an increase in autophagosomes as indicated by an increased abundance of LC3-II and a loss of mTOR kinase activity, a negative regulator of the autophagic machinery. These data suggest that dysregulated autophagy in α-galactosidase A-deficient podocytes may be the result of deficient mTOR kinase activity. This finding links the lysosomal enzymatic defect in Fabry’s disease to deregulated autophagy pathways and provides a promising new direction for further studies on the pathomechanism of glomerular injury in Fabry patients.</p></div