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TFE-fusion renal cell carcinomas (TFE-fusion RCCs) are caused by chromosomal translocations that lead to overexpression of the TFEB and TFE3 genes (Kauffman et al., 2014). The mechanisms leading to kidney tumor development remain uncharacterized and effective therapies are yet to be identified. Hence, the need to model these diseases in an experimental animal system (Kauffman et al., 2014). Here, we show that kidney-specific TFEB overexpression in transgenic mice, resulted in renal clear cells, multi-layered basement membranes, severe cystic pathology, and ultimately papillary carcinomas with hepatic metastases. These features closely recapitulate those observed in both TFEB- and TFE3-mediated human kidney tumors. Analysis of kidney samples revealed transcriptional induction and enhanced signaling of the WNT β-catenin pathway. WNT signaling inhibitors normalized the proliferation rate of primary kidney cells and significantly rescued the disease phenotype in vivo. These data shed new light on the mechanisms underlying TFE-fusion RCCs and suggest a possible therapeutic strategy based on the inhibition of the WNT pathway.DOI: http://dx.doi.org/10.7554/eLife.17047.001

are contributed equally to this work.Abbreviations: Abcc6, ATP binding cassette subfamily c member 6; BB-FCF, brilliant blue-FCF; Cx30, connexin30; Cx30.3, connexin30.3; Cx37, connexin37; Entpd2, ectonucleoside triphosphate diphosphohydrolase 2; Entpd3, ectonucleoside triphosphate diphosphohydrolase 3; FBS, fetal bovine serum; FSS, fluid shear stress; Gapdh, glyceraldehyde 3-phosphate dehydrogenase; MO, translation blocking morpholino; Nt5e, ecto-5′-nucleotidase; Panx1, pannexin-1; PC1, polycystin-1; PC2, polycystin-2; PKD, polycystic kidney disease; Pkd1, polycystic kidney disease 1; Pkd2, polycystic kidney disease 2; Ptgs2, prostaglandin-endoperoxide synthase 2. AbstractTubular ATP release is regulated by mechanosensation of fluid shear stress (FSS).Polycystin-1/polycystin-2 (PC1/PC2) functions as a mechanosensory complex in the kidney. Extracellular ATP is implicated in polycystic kidney disease (PKD), where PC1/PC2 is dysfunctional. This study aims to provide new insights into the ATP signaling under physiological conditions and PKD. Microfluidics, pharmacologic inhibition, and loss-of-function approaches were combined to assess the ATP release in mouse distal convoluted tubule 15 (mDCT15) cells. Kidney-specific Pkd1 knockout mice (iKsp-Pkd1 −/− ) and zebrafish pkd2 morphants (pkd2-MO) were as models for PKD. FSS-exposed mDCT15 cells displayed increased ATP release. Pannexin-1 inhibition and knockout decreased FSS-modulated ATP release. In iKsp-Pkd1 −/− mice, elevated renal pannexin-1 mRNA expression and urinary ATP were observed. In Pkd1 −/− mDCT15 cells, elevated ATP release was observed upon the FSS mechanosensation. In these cells, increased pannexin-1 mRNA expression was observed.Importantly, pannexin-1 inhibition in pkd2-MO decreased the renal cyst growth. Our results demonstrate that pannexin-1 channels mediate ATP release into the tubular lumen due to pro-urinary flow. We present pannexin-1 as novel therapeutic target to prevent the renal cyst growth in PKD. K E Y W O R D SATP, fluid shear stress, pannexin-1, polycystin-1, purinergic signaling | 6383 VERSCHUREN Et al.

Renal tubular cells respond to mechanical stimuli generated by urinary flow to regulate the activity and transcript abundance of important genes for ion handling, cellular homeostasis, and proper renal development. The primary cilium, a mechanosensory organelle, is postulated to regulate this mRNA response. The aim of this study is to reveal the transcriptome changes of tubular epithelia in response to fluid flow and determine the role of primary cilia in this process. Inner-medullary collecting duct (CD) cells were subjected to either static or physiologically relevant fluid flow (∼0.6 dyn/cm). RNA-sequencing analysis of ciliated cells subjected to fluid flow showed up-regulation of 1379 genes and down-regulation of 1294 genes compared with static control cells. Strikingly, only 54 of these genes were identified as gene candidates sensitive to primary cilia sensing of fluid flow, of which 16 were linked to ion or water transport pathways in the CD. Validation by quantitative real-time PCR revealed that only the expression of transferrin receptor, which is involved in iron transport; and tribbles pseudokinase 3, which is involved in insulin signaling, were unequivocally regulated by primary cilia sensing of fluid flow. This study shows that the involvement of primary cilia in ion transport in the collecting duct is exceptionally specific.-Mohammed, S. G., Arjona, F. J., Verschuren, E. H. J., Bakey, Z., Alkema, W., van Hijum, S., Schmidts, M., Bindels, R. J. M., Hoenderop, J. G. J. Primary cilia-regulated transcriptome in the renal collecting duct.

The PKD1 gene encodes polycystin-1 (PC1), a mechanosensor triggering intracellular responses upon urinary flow sensing in kidney tubular cells. Mutations in PKD1 lead to autosomal dominant polycystic kidney disease (ADPKD). The involvement of PC1 in renal electrolyte handling remains unknown since renal electrolyte physiology in ADPKD patients has only been characterized in cystic ADPKD. We thus studied the renal electrolyte handling in inducible kidney-specific Pkd1 knockout (iKsp- Pkd1) mice manifesting a precystic phenotype. Serum and urinary electrolyte determinations indicated that iKsp- Pkd1 mice display reduced serum levels of magnesium (Mg), calcium (Ca), sodium (Na), and phosphate (P) compared with control ( Pkd1) mice and renal Mg, Ca, and P wasting. In agreement with these electrolyte disturbances, downregulation of key genes for electrolyte reabsorption in the thick ascending limb of Henle's loop (TA;, Cldn16, Kcnj1, and Slc12a1), distal convoluted tubule (DCT; Trpm6 and Slc12a3) and connecting tubule (CNT; Calb1, Slc8a1, and Atp2b4) was observed in kidneys of iKsp- Pkd1 mice compared with controls. Similarly, decreased renal gene expression of markers for TAL ( Umod) and DCT ( Pvalb) was observed in iKsp- Pkd1 mice. Conversely, mRNA expression levels in kidney of genes encoding solute and water transporters in the proximal tubule ( Abcg2 and Slc34a1) and collecting duct ( Aqp2, Scnn1a, and Scnn1b) remained comparable between control and iKsp- Pkd1 mice, although a water reabsorption defect was observed in iKsp- Pkd1 mice. In conclusion, our data indicate that PC1 is involved in renal Mg, Ca, and water handling and its dysfunction, resulting in a systemic electrolyte imbalance characterized by low serum electrolyte concentrations.