Polycystin: new aspects of structure, function, and regulation

A Case Report of the Coexistence of Gastric Cancer With Polycystic Kidney and Liver Disease: Unveiling the Complexity

Polycystic kidney disease (PKD) is a genetic disorder that comprises multiple cystic lesions in the kidneys. The association of PKD with gastric cancer has been studied. We present a rare presentation of stomach cancer with polycystic liver and kidney disease. A male patient in his 40s presented with epigastric pain, nausea, retrosternal burning, and occasional episodes of vomiting. Esophagogastroduodenoscopy revealed ulceroproliferative growth in the prepyloric region. Biopsies revealed moderately differentiated adenocarcinoma which was confirmed by contrast-enhanced computed tomography of the abdomen and pelvis. This showed a chance finding of polycystic kidney and liver disease. After confirmation with a positron emission tomography scan, the patient was diagnosed with gastric carcinoma (cT3N1M0, Stage IIB) with polycystic kidney and liver disease. We provide a case of early-stage stomach cancer in a patient with PKD. More extensive research is needed for a better understanding of this association between polycystic kidney and liver disease and gastric cancer development, to achieve earlier diagnosis.

Crosstalk between the mTOR pathway and primary cilia in human diseases

Autophagy is a fundamental catabolic process whereby excessive or damaged cytoplasmic components are degraded through lysosomes to maintain cellular homeostasis. Studies of mTOR signaling have revealed that mTOR controls biomass generation and metabolism by modulating key cellular processes, including protein synthesis and autophagy. Primary cilia, the assembly of which depends on kinesin molecular motors, serve as sensory organelles and signaling platforms. Given these pathways' central role in maintaining cellular and physiological homeostasis, a connection between mTOR and primary cilia signaling is starting to emerge in a variety of diseases. In this review, we highlight recent advances in our understanding of the complex crosstalk between the mTOR pathway and cilia and discuss its function in the context of related diseases.

Functions of actin-binding proteins in cilia structure remodeling and signaling

Cilia are microtubule-based organelles found on the surfaces of many types of cells, including cardiac fibroblasts, vascular endothelial cells, human retinal pigmented epithelial-1 (RPE-1) cells, and alveolar epithelial cells. These organelles can be classified as immotile cilia, referred to as primary cilia in mammalian cells, and motile cilia. Primary cilia are cellular sensors that detect extracellular signals; this is a critical function associated with ciliopathies, which are characterized by the typical clinical features of developmental disorders. Cilia are extensively studied organelles of the microtubule cytoskeleton. However, the ciliary actin cytoskeleton has rarely been studied. Clear evidence has shown that highly regulated actin cytoskeleton dynamics contribute to normal ciliary function. Actin-binding proteins (ABPs) play vital roles in filamentous actin (F-actin) morphology. Here, we discuss recent progress in understanding the roles of ABPs in ciliary structural remodeling and further downstream ciliary signaling with a focus on the molecular mechanisms underlying actin cytoskeleton-related ciliopathies.

A Multitubular Kidney-on-Chip to Decipher Pathophysiological Mechanisms in Renal Cystic Diseases

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a major renal pathology provoked by the deletion of PKD1 or PKD2 genes leading to local renal tubule dilation followed by the formation of numerous cysts, ending up with renal failure in adulthood. In vivo, renal tubules are tightly packed, so that dilating tubules and expanding cysts may have mechanical influence on adjacent tubules. To decipher the role of this coupling between adjacent tubules, we developed a kidney-on-chip reproducing parallel networks of tightly packed tubes. This original microdevice is composed of cylindrical hollow tubes of physiological dimensions, parallel and closely packed with 100-200 μm spacing, embedded in a collagen I matrix. These multitubular systems were properly colonized by different types of renal cells with long-term survival, up to 2 months. While no significant tube dilation over time was observed with Madin-Darby Canine Kidney (MDCK) cells, wild-type mouse proximal tubule (PCT) cells, or with PCT Pkd1 +/- cells (with only one functional Pkd1 allele), we observed a typical 1.5-fold increase in tube diameter with isogenic PCT Pkd1 -/- cells, an ADPKD cellular model. This tube dilation was associated with an increased cell proliferation, as well as a decrease in F-actin stress fibers density along the tube axis. With this kidney-on-chip model, we also observed that for larger tube spacing, PCT Pkd1 -/- tube deformations were not spatially correlated with adjacent tubes whereas for shorter spacing, tube deformations were increased between adjacent tubes. Our device reveals the interplay between tightly packed renal tubes, constituting a pioneering tool well-adapted to further study kidney pathophysiology.

Aggressive advanced gastric cancer in a patient with autosomal dominant polycystic kidney disease

A 60-year-old man with autosomal dominant polycystic kidney disease presented with malaise, melena, and epigastric discomfort. Esophagogastroduodenoscopy revealed a massive elevated gastric cancer lesion involving the cardia. Histopathological evaluation of a biopsy specimen showed poorly differentiated adenocarcinoma. Fluorodeoxyglucose-positron emission tomography revealed significant fluorodeoxyglucose uptake in the stomach, liver, bones, and bone marrow. He was diagnosed with metastatic gastric cancer resistant to chemotherapy, and he developed bone marrow carcinomatosis and disseminated intravascular coagulation and died 8 weeks after disease onset. A statistically significant association is reported between autosomal dominant polycystic kidney disease and gastric cancer. Moreover, the specific clinical features observed in our patient could be attributed to the molecular disorders like PC-1 and mechanistic target of rapamycin that are known to occur in autosomal dominant polycystic kidney disease.

A cut above (and below): Protein cleavage in the regulation of polycystin trafficking and signaling

The polycystin-1 and 2 proteins, encoded by the genes mutated in Autosomal Dominant Polycystic Kidney Disease, are connected to a large number of biological pathways. While the nature of these connections and their relevance to the primary functions of the polycystin proteins have yet to be fully elucidated, it is clear that many of them are mediated by or depend upon cleavage of the polycystin-1 protein. Cleavage of polycystin-1 at its G protein coupled receptor proteolytic site is an obligate step in the protein's maturation and in aspects of its trafficking. This cleavage may also serve to prime polycystin-1 to play a role as a non-canonical G protein coupled receptor. Cleavage of the cytoplasmic polycystin-1C terminal tail releases fragments that are able to enter the nucleus and the mitochondria and to influence their activities. Understanding the nature of these cleavages, their regulation and their consequences is likely to provide valuable insights into both the physiological functions served by the polycystin proteins and the pathological consequences of their absence.

Reciprocal Regulation between Primary Cilia and mTORC1

In quiescent cells, primary cilia function as a mechanosensor that converts mechanic signals into chemical activities. This unique organelle plays a critical role in restricting mechanistic target of rapamycin complex 1 (mTORC1) signaling, which is essential for quiescent cells to maintain their quiescence. Multiple mechanisms have been identified that mediate the inhibitory effect of primary cilia on mTORC1 signaling. These mechanisms depend on several tumor suppressor proteins localized within the ciliary compartment, including liver kinase B1 (LKB1), AMP-activated protein kinase (AMPK), polycystin-1, and polycystin-2. Conversely, changes in mTORC1 activity are able to affect ciliogenesis and stability indirectly through autophagy. In this review, we summarize recent advances in our understanding of the reciprocal regulation of mTORC1 and primary cilia.

Polycystin-1 affects cancer cell behaviour and interacts with mTOR and Jak signalling pathways in cancer cell lines

Polycystic Kidney Disease (PKD), which is attributable to mutations in the PKD1 and PKD2 genes encoding polycystin‐1 (PC1) and polycystin‐2 (PC2) respectively, shares common cellular defects with cancer, such as uncontrolled cell proliferation, abnormal differentiation and increased apoptosis. Interestingly, PC1 regulates many signalling pathways including Jak/STAT, mTOR, Wnt, AP‐1 and calcineurin‐NFAT which are also used by cancer cells for sending signals that will allow them to acquire and maintain malignant phenotypes. Nevertheless, the molecular relationship between polycystins and cancer is unknown. In this study, we investigated the role of PC1 in cancer biology using glioblastoma (GOS3), prostate (PC3), breast (MCF7), lung (A549) and colorectal (HT29) cancer cell lines. Our in vitro results propose that PC1 promotes cell migration in GOS3 cells and suppresses cell migration in A549 cells. In addition, PC1 enhances cell proliferation in GOS3 cells but inhibits it in MCF7, A549 and HT29 cells. We also found that PC1 up‐regulates mTOR signalling and down‐regulates Jak signalling in GOS3 cells, while it up‐regulates mTOR signalling in PC3 and HT29 cells. Together, our study suggests that PC1 modulates cell proliferation and migration and interacts with mTOR and Jak signalling pathways in different cancer cell lines. Understanding the molecular details of how polycystins are associated with cancer may lead to the identification of new players in this devastating disease.

A novel splicing mutation in the PKD1 gene causes autosomal dominant polycystic kidney disease in a Chinese family: a case report

Background

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenic renal disorder in humans, affecting 1 in 400 to 1000 individuals. Mutations PKD1 (which accounts for 85% of ADPKD and produces polycystin-1) and PKD2 (produces polycystin-2) are responsible for this disease. These two polycystins are critical for maintaining normal renal tubular structures during kidney development.

Case presentation

We performed genetic analysis on a family with ADPKD. DNA samples extracted from ADPKD patient blood were subject to targeted Next generation sequencing for human a panel of renal disease-related genes. A splicing mutation, c.2854-3C > G (also known as IVS11–3C > G), in the PKD1 gene was found in the 3 patients from the family, but was not found in four unaffected relatives and 100 normal control samples. Reverse transcription-PCR (RT-PCR) was performed to analyse the relative mRNA expression in the patient samples. mRNA sequencing showed that 29 bases inserted into the 3′-end of exon 11 in the PKD1 gene lead to a frameshift mutation.

Conclusions

The PKD1 c.2854-3C > G mutation leads to a frameshift mutation during translation of the polycystin-1 protein, which eventually led to ADPKD in the Chinese family.

Transient Receptor Potential (TRP) Channels

Transient Receptor Potential (TRP) channels are evolutionarily conserved integral membrane proteins. The mammalian TRP superfamily of ion channels consists of 28 cation permeable channels that are grouped into six subfamilies based on sequence homology (Fig. 6.1). The canonical TRP (TRPC) subfamily is known for containing the founding member of mammalian TRP channels. The vanilloid TRP (TRPV) subfamily has been extensively studied due to the heat sensitivity of its founding member. The melastatin-related TRP (TRPM) subfamily includes some of the few known bi-functional ion channels, which contain functional enzymatic domains. The ankyrin TRP (TRPA) subfamily consists of a single chemo-nociceptor that has been proposed to be a target for analgesics. The mucolipin TRP (TRPML) subfamily channels are found primarily in intracellular compartments and were discovered based on their critical role in type IV mucolipidosis (ML-IV). The polycystic TRP (TRPP) subfamily is a diverse group of proteins implicated in autosomal dominant polycystic kidney disease (ADPKD). Overall, this superfamily of channels is involved in a vast array of physiological and pathophysiological processes making the study of these channels imperative to our understanding of subcellular biochemistry.

Modeling Renal Disease "On the Fly"

Detoxification is a fundamental function for all living organisms that need to excrete catabolites and toxins to maintain homeostasis. Kidneys are major organs of detoxification that maintain water and electrolyte balance to preserve physiological functions of vertebrates. In insects, the renal function is carried out by Malpighian tubules and nephrocytes. Due to differences in their circulation, the renal systems of mammalians and insects differ in their functional modalities, yet carry out similar biochemical and physiological functions and share extensive genetic and molecular similarities. Evolutionary conservation can be leveraged to model specific aspects of the complex mammalian kidney function in the genetic powerhouse Drosophila melanogaster to study how genes interact in diseased states. Here, we compare the human and Drosophila renal systems and present selected fly disease models.

Insights into cellular and molecular basis for urinary tract infection in autosomal-dominant polycystic kidney disease

Urinary tract infection (UTI) is a broad term referring to an infection of the kidneys, ureters, bladder, and/or urethra. Because of its prevalence, frequent recurrence, and rising resistance to antibiotics, UTI has become a challenge in clinical practice. Autosomal-dominant polycystic kidney disease (ADPKD) is the most common monogenic disorder of the kidney and is characterized by the growth of fluid-filled cysts in both kidneys. Progressive cystic enlargement, inflammation, and interstitial fibrosis result in nephron loss with subsequent decline in kidney function. ADPKD patients frequently develop UTI; however, the cellular and molecular mechanisms responsible for the high UTI incidence in ADPKD patients remain virtually unaddressed. Emerging evidence suggests that α-intercalated cells (α-ICs) of the collecting ducts function in the innate immune defense against UTI. α-ICs inhibit bacterial growth by acidifying urine and secreting neutrophil gelatinase-associated lipocalin (NGAL) that chelates siderophore-containing iron. It is necessary to determine, therefore, if ADPKD patients with recurrent UTI have a reduced number and/or impaired function of α-ICs. Identification of the underlying cellular and molecular mechanisms may lead to the development of novel strategies to reduce UTI in ADPKD.

A potentially crucial role of the PKD1 C-terminal tail in renal prognosis

Background

Autosomal dominant polycystic disease (ADPKD) often results in renal failure. Recently, allelic influences of PKD1 mutation types on renal survival were extensively investigated. Here, we analyzed integrated influences of PKD1 mutation types and positions on renal survival.

Methods

We included 338 (82 pedigrees) and 72 (12 pedigrees) patients with PKD1 and PKD2 mutations, respectively, identified through comprehensive gene analysis of 101 probands with ADPKD. Genetic testing was performed using next-generation sequencing, long-range PCR, and multiplex ligation-dependent probe amplification. Pathogenic mutations were identified by a software package-integrated seven databases and provided access to five cloud-based computing systems.

Results

Mean renal survivals of carriers with PKD1 non-truncating-type mutations at positions upstream of G-protein-coupled receptor proteolytic site (GPS-upstream domain), transmembrane domain, or cytoplasmic C-terminal tail (CTT) domain were 70.2, 67.0, and 50.1 years, respectively (P < 0.0001); renal survival was shorter for mutation positions closer to CTT domain, suggesting its crucial role in renal prognosis. Furthermore, in truncating-type mutations, strong inactivation is anticipated on nucleotides downstream from the mutation site, implying CTT domain inactivation irrespective of mutation site. Shorter mean renal survival was found for PKD1 truncating-type than non-truncating-type mutation carriers (P = 0.0348); mean renal survival was not different between PKD1 3′- and 5′-region truncating-type mutation carriers (P = 0.4375), but was shorter in PKD1 3′-region than in 5′-region non-truncating-type mutation carriers (P = 0.0014). Variable strength of CTT domain inactivation might account for these results.

Conclusions

Aforementioned findings indicate that CTT domain’s crucial role in renal prognosis needs further investigation by larger studies (ClinicalTrials.gov; NCT02322385).

Electronic supplementary material

The online version of this article (doi:10.1007/s10157-017-1477-7) contains supplementary material, which is available to authorized users.

EFA6 regulates lumen formation through alpha-actinin 1

A key step of epithelial morphogenesis is the creation of the lumen. Luminogenesis by hollowing proceeds through the fusion of apical vesicles at cell-cell contact. The small nascent lumens grow through extension, coalescence and enlargement coordinated with cell division to give rise to a single central lumen. Here, using MDCK cells grown in 3D-culture, we show that EFA6A participates in luminogenesis. EFA6A recruits α-actinin 1 (ACTN1) through direct binding. In polarized cells, ACTN1 was found to be enriched at the tight junction where it acts as a primary effector of EFA6A for normal luminogenesis. Both proteins are essential for the lumen extension and enlargement, where they mediate their effect by regulating the cortical acto-myosin contractility. Finally, ACTN1 was also found to act as an effector for the isoform EFA6B in the human mammary tumoral MCF7 cell line. EFA6B restored the glandular morphology of this tumoral cell line in an ACTN1-dependent manner. Thus, we identified new regulators of cyst luminogenesis essential for the proper maturation of a newly-formed lumen into a single central lumen.

Polycystins and intercellular mechanotransduction: A precise dosage of polycystin 2 is necessary for alpha-actinin reinforcement of junctions upon mechanical stimulation

Polycystins 1 and 2, which are mutated in Autosomal Polycystic Kidney Disease, are involved in mechanotransduction through various mechanisms. In renal cells, polycystins not only have an important mechanotransductive role in primary cilia but are also present in intercellular contacts but their role there remains unclear. Here, we address the hypothesis that polycystins are involved in mechanotransduction via intercellular junctions, which would be expected to have consequences on tissue organization. We focused on the role of polycystin 2, which could be involved in mechanical organization at junctions either by its channel activity or by the direct recruitment of cytoskeleton components such as the F-actin cross-linker α-actinin. After mechanical stimulation of intercellular junctions in MDCK renal epithelial cells, α-actinin is rapidly recruited but this is inhibited upon overexpression of PC2 or the D509V mutant that lacks channel activity, and is also decreased upon PC2 silencing. This suggests that a precise dosage of PC2 is necessary for an adequate mechanosensitive α-actinin recruitment at junctions. At the multicellular level, a change in PC2 expression was associated with changes in velocity in confluent epithelia and during wound healing together with a loss of orientation. This study suggests that the mechanosensitive regulation of cytoskeleton by polycystins in intercellular contacts may be important in the context of ADPKD.

Regulation of Polycystin-1 Function by Calmodulin Binding

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a common genetic disease that leads to progressive renal cyst growth and loss of renal function, and is caused by mutations in the genes encoding polycystin-1 (PC1) and polycystin-2 (PC2), respectively. The PC1/PC2 complex localizes to primary cilia and can act as a flow-dependent calcium channel in addition to numerous other signaling functions. The exact functions of the polycystins, their regulation and the purpose of the PC1/PC2 channel are still poorly understood. PC1 is an integral membrane protein with a large extracytoplasmic N-terminal domain and a short, ~200 amino acid C-terminal cytoplasmic tail. Most proteins that interact with PC1 have been found to bind via the cytoplasmic tail. Here we report that the PC1 tail has homology to the regulatory domain of myosin heavy chain including a conserved calmodulin-binding motif. This motif binds to CaM in a calcium-dependent manner. Disruption of the CaM-binding motif in PC1 does not affect PC2 binding, cilia targeting, or signaling via heterotrimeric G-proteins or STAT3. However, disruption of CaM binding inhibits the PC1/PC2 calcium channel activity and the flow-dependent calcium response in kidney epithelial cells. Furthermore, expression of CaM-binding mutant PC1 disrupts cellular energy metabolism. These results suggest that critical functions of PC1 are regulated by its ability to sense cytosolic calcium levels via binding to CaM.

STIM1fl/fl Ksp-Cre Mouse has Impaired Renal Water Balance

BACKGROUND/AIM

STIM1 is as an essential component in store operated Ca2+ entry. However give the paucity of information on the role of STIM1 in kidney, the aim was to study the function of STIM1 in the medulla of the kidney.

METHODS

we crossed a Ksp-cre mouse with another mouse containing two loxP sites flanking Exon 6 of STIM1. The Ksp-cre mouse is based upon the Ksp-cadherin gene promoter which expresses cre recombinase in developing nephrons, collecting ducts (SD) and thick ascending limbs (TAL) of the loop of Henle.

RESULTS

The offspring of these mice are viable without gross morphological changes, however, we noticed that the STIM1 Ksp-cre knockout mice produced more urine compared to control. To examine this more carefully, we fed mice low (LP) and high protein (HP) diets respectively. When mice were fed HP diet STIM1 ko mice had significantly increased urinary volume and lower specific gravity compared to wt mice. In STIM1 ko mice fed HP diet urine creatinine and urea were significantly lower compared to wt mice fed HP diet, however the fractional excretion was the same.

CONCLUSION

These data support the idea that STIM1 ko mice have impaired urinary concentrating ability when challenged with HP diet is most likely caused by impaired Ca2+-dependent signal transduction through the vasopressin receptor cascade.

Polycystin-1 Is a Cardiomyocyte Mechanosensor That Governs L-Type Ca2+ Channel Protein Stability

BACKGROUND

L-type calcium channel activity is critical to afterload-induced hypertrophic growth of the heart. However, the mechanisms governing mechanical stress-induced activation of L-type calcium channel activity are obscure. Polycystin-1 (PC-1) is a G protein-coupled receptor-like protein that functions as a mechanosensor in a variety of cell types and is present in cardiomyocytes.

METHODS AND RESULTS

We subjected neonatal rat ventricular myocytes to mechanical stretch by exposing them to hypo-osmotic medium or cyclic mechanical stretch, triggering cell growth in a manner dependent on L-type calcium channel activity. RNAi-dependent knockdown of PC-1 blocked this hypertrophy. Overexpression of a C-terminal fragment of PC-1 was sufficient to trigger neonatal rat ventricular myocyte hypertrophy. Exposing neonatal rat ventricular myocytes to hypo-osmotic medium resulted in an increase in α1C protein levels, a response that was prevented by PC-1 knockdown. MG132, a proteasomal inhibitor, rescued PC-1 knockdown-dependent declines in α1C protein. To test this in vivo, we engineered mice harboring conditional silencing of PC-1 selectively in cardiomyocytes (PC-1 knockout) and subjected them to mechanical stress in vivo (transverse aortic constriction). At baseline, PC-1 knockout mice manifested decreased cardiac function relative to littermate controls, and α1C L-type calcium channel protein levels were significantly lower in PC-1 knockout hearts. Whereas control mice manifested robust transverse aortic constriction-induced increases in cardiac mass, PC-1 knockout mice showed no significant growth. Likewise, transverse aortic constriction-elicited increases in hypertrophic markers and interstitial fibrosis were blunted in the knockout animals

CONCLUSION

PC-1 is a cardiomyocyte mechanosensor that is required for cardiac hypertrophy through a mechanism that involves stabilization of α1C protein.

Thermotaxis, circadian rhythms, and TRP channels in Drosophila

The fruit fly Drosophila melanogaster is a poikilothermic organism that must detect and respond to both fine and coarse changes in environmental temperature in order maintain optimal body temperature, synchronize behavior to daily temperature fluctuations, and to avoid potentially injurious environmental hazards. Members of the Transient Receptor Potential (TRP) family of cation channels are well known for their activation by changes in temperature and their essential roles in sensory transduction in both invertebrates and vertebrates. The Drosophila genome encodes 13 TRP channels, and several of these have key sensory transduction and modulatory functions in allowing larval and adult flies to make fine temperature discriminations to attain optimal body temperature, detect and avoid large environmental temperature fluctuations, and make rapid escape responses to acutely noxious stimuli. Drosophila use multiple, redundant signaling pathways and neural circuits to execute these behaviors in response to both increases and decreases in temperature of varying magnitudes and time scales. A plethora of powerful molecular and genetic tools and the fly's simple, well-characterized nervous system have given Drosophila neurobiologists a powerful platform to study the cellular and molecular mechanisms of TRP channel function and how these mechanisms are conserved in vertebrates, as well as how these channels function within sensorimotor circuits to generate both simple and complex thermosensory behaviors.

Novel roles of Pkd2 in male reproductive system development

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common inherited genetic diseases, caused by mutations in PKD1 and/ or PKD2. Infertility and reproductive tract abnormalities in male ADPKD patients are very common and have higher incidence than in the general population. In this work, we reveal novel roles of Pkd2 for male reproductive system development. Disruption of Pkd2 caused dilation of mesonephric tubules/efferent ducts, failure of epididymal coiling, and defective testicular development. Deletion of Pkd2 in the epithelia alone was sufficient to cause reproductive tract defects seen in Pkd2(-/-) mice, suggesting that epithelial Pkd2 plays a pivotal role for development and maintenance of the male reproductive tract. In the testis, Pkd2 also plays a role in interstitial tissue and testicular cord development. In-depth analysis of epithelial-specific knockout mice revealed that Pkd2 is critical to maintain cellular phenotype and developmental signaling in the male reproductive system. Taken together, our data for the first time reveal novel roles for Pkd2 in male reproductive system development and provide new insights in male reproductive system abnormality and infertility in ADPKD patients.

Urine microRNA as potential biomarkers of autosomal dominant polycystic kidney disease progression: description of miRNA profiles at baseline

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is clinically heterogenic. Biomarkers are needed to predict prognosis and guide management. We aimed to profile microRNA (miRNA) in ADPKD to gain molecular insight and evaluate biomarker potential.

METHODS

Small-RNA libraries were generated from urine specimens of ADPKD patients (N = 20) and patients with chronic kidney disease of other etiologies (CKD, N = 20). In this report, we describe the miRNA profiles and baseline characteristics. For reference, we also examined the miRNA transcriptome in primary cultures of ADPKD cyst epithelia (N = 10), normal adult tubule (N = 8) and fetal tubule (N = 7) epithelia.

RESULTS

In primary cultures of ADPKD kidney cells, miRNA cistrons mir-143(2) (9.2-fold), let-7i(1) (2.3-fold) and mir-3619(1) (12.1-fold) were significantly elevated compared to normal tubule epithelia, whereas mir-1(4) members (19.7-fold), mir-133b(2) (21.1-fold) and mir-205(1) (3.0-fold) were downregulated (P<0.01). Expression of the dysregulated miRNA in fetal tubule epithelia resembled ADPKD better than normal adult cells, except let-7i, which was lower in fetal cells. In patient biofluid specimens, mir-143(2) members were 2.9-fold higher in urine cells from ADPKD compared to other CKD patients, while expression levels of mir-133b(2) (4.9-fold) and mir-1(4) (4.4-fold) were lower in ADPKD. We also noted increased abundance mir-223(1) (5.6-fold), mir-199a(3) (1.4-fold) and mir-199b(1) (1.8-fold) (P<0.01) in ADPKD urine cells. In ADPKD urine microvesicles, miR-1(2) (7.2-fold) and miR-133a(2) (11.8-fold) were less abundant compared to other CKD patients (P<0.01).

CONCLUSIONS

We found that in ADPKD urine specimens, miRNA previously implicated as kidney tumor suppressors (miR-1 and miR-133), as well as miRNA of presumed inflammatory and fibroblast cell origin (miR-223/miR-199), are dysregulated when compared to other CKD patients. Concordant with findings in the primary tubule epithelial cell model, this suggests roles for dysregulated miRNA in ADPKD pathogenesis and potential use as biomarkers. We intend to assess prognostic potential of miRNA in a followup analysis.

Strategies targeting cAMP signaling in the treatment of polycystic kidney disease

Polycystic kidney disease (PKD) is a leading cause of ESRD worldwide. In PKD, excessive cell proliferation and fluid secretion, pathogenic interactions of mutated epithelial cells with an abnormal extracellular matrix and alternatively activated interstitial macrophages, and the disruption of mechanisms controlling tubular diameter contribute to cyst formation. Studies with animal models suggest that several diverse pathophysiologic mechanisms, including dysregulation of intracellular calcium levels and cAMP signaling, mediate these cystogenic mechanisms. This article reviews the evidence implicating calcium and cAMP as central players in a network of signaling pathways underlying the pathogenesis of PKD and considers the therapeutic relevance of treatment strategies targeting cAMP signaling.

Pkd1 is required for male reproductive tract development

Reproductive tract abnormalities and male infertility have higher incidence in ADPKD patients than in general populations. In this work, we reveal that Pkd1, whose mutations account for 85% of ADPKD cases, is essential for male reproductive tract development. Disruption of Pkd1 caused multiple organ defects in the murine male reproductive tract. The earliest visible defect in the Pkd1(-/-) reproductive tract was cystic dilation of the efferent ducts, which are derivatives of the mesonephric tubules. Epididymis development was delayed or arrested in the Pkd1(-/-) mice. No sign of epithelial coiling was seen in the null mutants. Disruption of Pkd1 in epithelium alone using the Pax2-cre mice was sufficient to cause efferent duct dilation and coiling defect in the epididymis, suggesting that Pkd1 is critical for epithelium development and maintenance in male reproductive tract. In-depth analysis showed that Pkd1 is required to maintain tubulin cytoskeleton and important for Tgf-β/Bmp signal transduction in epithelium of male reproductive tract. Altogether, our results for the first time provide direct evidence for developmental roles of Pkd1 in the male reproductive tract and provide new insights in reproductive tract abnormalities and infertility in ADPKD patients.

A telomerase immortalized human proximal tubule cell line with a truncation mutation (Q4004X) in polycystin-1

Autosomal dominant polycystic kidney disease (ADPKD) is associated with a variety of cellular phenotypes in renal epithelial cells. Cystic epithelia are secretory as opposed to absorptive, have higher proliferation rates in cell culture and have some characteristics of epithelial to mesenchymal transitions [1], [2]. In this communication we describe a telomerase immortalized cell line that expresses proximal tubule markers and is derived from renal cysts of an ADPKD kidney. These cells have a single detectable truncating mutation (Q4004X) in polycystin-1. These cells make normal appearing but shorter cilia and fail to assemble polycystin-1 in the cilia, and less uncleaved polycystin-1 in membrane fractions. This cell line has been maintained in continuous passage for over 35 passages without going into senescence. Nephron segment specific markers suggest a proximal tubule origin for these cells and the cell line will be useful to study mechanistic details of cyst formation in proximal tubule cells.

Genetic diagnosis of autosomal dominant polycystic kidney disease by targeted capture and next-generation sequencing: utility and limitations

Mutation-based molecular diagnostics of autosomal dominant polycystic kidney disease (ADPKD) is complicated by genetic and allelic heterogeneity, large multi-exon genes, and duplication sequences of PKD1. Recently, targeted resequencing by pooling long-range polymerase chain reaction (LR-PCR) amplicons has been used in the identification of mutations in ADPKD. Despite its high sensitivity, specificity and accuracy, LR-PCR is still complicated. We performed whole-exome sequencing on two unrelated typical Chinese ADPKD probands and evaluated the effectiveness of this approach compared with Sanger sequencing. Meanwhile, we performed targeted gene and next-generation sequencing (targeted DNA-HiSeq) on 8 individuals (1 patient from one family, 5 patients and 2 normal individuals from another family). Both whole-exome sequencing and targeted DNA-HiSeq confirmed c.11364delC (p.H3788QfsX37) within the unduplicated region of PKD1 in one proband; in the other family, targeted DNA-HiSeq identified a small insertion, c.401_402insG (p.V134VfsX79), in PKD2. These methods do not overcome the screening complexity of homology. However, the true positives of variants confirmed by targeted gene and next-generation sequencing were 69.4%, 50% and 100% without a false positive in the whole coding region and the duplicated and unduplicated regions, which indicated that the screening accuracy of PKD1 and PKD2 can be largely improved by using a greater sequencing depth and elaborate design of the capture probe.

A novel mutation causing nephronophthisis in the Lewis polycystic kidney rat localises to a conserved RCC1 domain in Nek8

Background

Nephronophthisis (NPHP) as a cause of cystic kidney disease is the most common genetic cause of progressive renal failure in children and young adults. NPHP is characterized by abnormal and/or loss of function of proteins associated with primary cilia. Previously, we characterized an autosomal recessive phenotype of cystic kidney disease in the Lewis Polycystic Kidney (LPK) rat.

Results

In this study, quantitative trait locus analysis was used to define a ~1.6Mbp region on rat chromosome 10q25 harbouring the lpk mutation. Targeted genome capture and next-generation sequencing of this region identified a non-synonymous mutation R650C in the NIMA (never in mitosis gene a)- related kinase 8 ( Nek8) gene. This is a novel Nek8 mutation that occurs within the regulator of chromosome condensation 1 (RCC1)-like region of the protein. Specifically, the R650C substitution is located within a G[QRC]LG repeat motif of the predicted seven bladed beta-propeller structure of the RCC1 domain. The rat Nek8 gene is located in a region syntenic to portions of human chromosome 17 and mouse 11. Scanning electron microscopy confirmed abnormally long cilia on LPK kidney epithelial cells, and fluorescence immunohistochemistry for Nek8 protein revealed altered cilia localisation.

Conclusions

When assessed relative to other Nek8 NPHP mutations, our results indicate the whole propeller structure of the RCC1 domain is important, as the different mutations cause comparable phenotypes. This study establishes the LPK rat as a novel model system for NPHP and further consolidates the link between cystic kidney disease and cilia proteins.

Replication fork stalling and checkpoint activation by a PKD1 locus mirror repeat polypurine-polypyrimidine (Pu-Py) tract

DNA sequences prone to forming noncanonical structures (hairpins, triplexes, G-quadruplexes) cause DNA replication fork stalling, activate DNA damage responses, and represent hotspots of genomic instability associated with human disease. The 88-bp asymmetric polypurine-polypyrimidine (Pu-Py) mirror repeat tract from the human polycystic kidney disease (PKD1) intron 21 forms non-B DNA secondary structures in vitro. We show that the PKD1 mirror repeat also causes orientation-dependent fork stalling during replication in vitro and in vivo. When integrated alongside the c-myc replicator at an ectopic chromosomal site in the HeLa genome, the Pu-Py mirror repeat tract elicits a polar replication fork barrier. Increased replication protein A (RPA), Rad9, and ataxia telangiectasia- and Rad3-related (ATR) checkpoint protein binding near the mirror repeat sequence suggests that the DNA damage response is activated upon replication fork stalling. Moreover, the proximal c-myc origin of replication was not required to cause orientation-dependent checkpoint activation. Cells expressing the replication fork barrier display constitutive Chk1 phosphorylation and continued growth, i.e. checkpoint adaptation. Excision of the Pu-Py mirror repeat tract abrogates the DNA damage response. Adaptation to Chk1 phosphorylation in cells expressing the replication fork barrier may allow the accumulation of mutations that would otherwise be remediated by the DNA damage response.

A non-synonymous mutation in the canine Pkd1 gene is associated with autosomal dominant polycystic kidney disease in Bull Terriers

Polycystic Kidney Disease is an autosomal dominant disease common in some lines of Bull Terriers (BTPKD). The disease is linked to the canine orthologue of human PKD1 gene, Pkd1, located on CFA06, but no disease-associated mutation has been reported. This study sequenced genomic DNA from two Bull Terriers with BTPKD and two without the disease. A non-synonymous G>A transition mutation in exon 29 of Pkd1 was identified. A TaqMan® SNP Genotyping Assay was designed and demonstrated the heterozygous detection of the mutation in 47 Bull Terriers with BTPKD, but not in 102 Bull Terriers over one year of age and without BTPKD. This missense mutation replaces a glutamic acid residue with a lysine residue in the predicted protein, Polycystin 1. This region of Polycystin 1 is highly conserved between species, and is located in the first cytoplasmic loop of the predicted protein structure, close to the PLAT domain and the second transmembrane region. Thus, this change could alter Polycystin 1 binding or localization. Analytic programs PolyPhen 2, Align GVGD and SIFT predict this mutation to be pathogenic. Thus, BTPKD is associated with a missense mutation in Pkd1, and the application of this mutation specific assay could reduce disease transmission by allowing diagnosis of disease in young animals prior to breeding.

A conserved signal and GTPase complex are required for the ciliary transport of polycystin-1

Primary cilia regulate epithelial differentiation and organ function. Failure of mutant polycystins to localize to cilia abolishes flow-stimulated calcium signaling and causes autosomal dominant polycystic kidney disease. We identify a conserved amino acid sequence, KVHPSST, in the C-terminus of polycystin-1 (PC1) that serves as a ciliary-targeting signal. PC1 binds a multimeric protein complex consisting of several GTPases (Arf4, Rab6, Rab11) and the GTPase-activating protein (GAP), ArfGAP with SH3 domain, ankyrin repeat and PH domain 1 (ASAP1) in the Golgi, which facilitates vesicle budding and Golgi exocytosis. A related N-terminal ciliary-targeting sequence in polycystin-2 similarly binds Arf4. Deletion of the extreme C-terminus of PC1 ablates Arf4 and ASAP1 binding and prevents ciliary localization of an integral membrane CD16.7-PC1 chimera. Interactions are confirmed for chimeric and endogenous proteins through quantitated in vitro and cell-based approaches. PC1 also complexes with Rab8; knockdown of trafficking regulators Arf4 or Rab8 functionally blocks CD16.7-PC1 trafficking to cilia. Mutations in rhodopsin disrupt a similar signal and cause retinitis pigmentosa, while Bardet-Biedl syndrome, primary open-angle glaucoma, and tumor cell invasiveness are linked to dysregulation of ASAP1 or Rab8 or its effectors. In this paper, we provide evidence for a conserved GTPase-dependent ciliary-trafficking mechanism that is shared between epithelia and neurons, and is essential in ciliary-trafficking and cell homeostasis.

CaMK-II is a PKD2 target that promotes pronephric kidney development and stabilizes cilia

Intracellular Ca²⁺ signals influence gastrulation, neurogenesis and organogenesis through pathways that are still being defined. One potential Ca²⁺ mediator of many of these morphogenic processes is CaMK-II, a conserved calmodulin-dependent protein kinase. Prolonged Ca²⁺ stimulation converts CaMK-II into an activated state that, in the zebrafish, is detected in the forebrain, ear and kidney. Autosomal dominant polycystic kidney disease has been linked to mutations in the Ca²⁺-conducting TRP family member PKD2, the suppression of which in vertebrate model organisms results in kidney cysts. Both PKD2-deficient and CaMK-II-deficient zebrafish embryos fail to form pronephric ducts properly, and exhibit anterior cysts and destabilized cloacal cilia. PKD2 suppression inactivates CaMK-II in pronephric cells and cilia, whereas constitutively active CaMK-II restores pronephric duct formation in pkd2 morphants. PKD2 and CaMK-II deficiencies are synergistic, supporting their existence in the same genetic pathway. We conclude that CaMK-II is a crucial effector of PKD2 Ca²⁺ that both promotes morphogenesis of the pronephric kidney and stabilizes primary cloacal cilia.

Putative roles of cilia in polycystic kidney disease

The last 10 years has witnessed an explosion in research into roles of cilia in cystic renal disease. Cilia are membrane-enclosed finger-like projections from the cell, usually on the apical surface or facing into a lumen, duct or airway. Ten years ago, the major recognised functions related to classical "9+2" cilia in the respiratory and reproductive tracts, where co-ordinated beating clears secretions and assists fertilisation respectively. Primary cilia, which have a "9+0" arrangement lacking the central microtubules, were anatomical curiosities but several lines of evidence have implicated them in both true polycystic kidney disease and other cystic renal conditions: ranging from the homology between Caenorhabditis elegans proteins expressed on sensory cilia to mammalian polycystic kidney disease (PKD) 1 and 2 proteins, through the discovery that orpk cystic mice have structurally abnormal cilia to numerous recent studies wherein expression of nearly all cyst-associated proteins has been reported in the cilia or its basal body. Functional studies implicate primary cilia in mechanosensation, photoreception and chemosensation but it is the first of these which appears most important in polycystic kidney disease: in the simplest model, fluid flow across the apical surface of renal cells bends the cilia and induces calcium influx, and this is perturbed in polycystic kidney disease. Downstream effects include changes in cell differentiation and polarity. Pathways such as hedgehog and Wnt signalling may also be regulated by cilia. These data support important roles for cilia in the pathogenesis of cystic kidney diseases but one must not forget that the classic polycystic kidney disease proteins are expressed in several other locations where they may have equally important roles, such as in cell-cell and cell-matrix interactions, whilst it is not just aberrant cilia signalling that can lead to de-differentiation, loss of polarity and other characteristic features of polycystic kidney disease. Understanding how cilia fit into the other aspects of polycystic kidney disease biology is the challenge for the next decade. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Phosphorylation, protein kinases and ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disease characterized by renal cyst formation and caused by mutations in the PKD1 and PKD2 genes, which encode polycystin-1(PC-1) and -2 (PC-2) proteins, respectively. PC-1 is a large plasma membrane receptor involved in the regulation of several biological functions and signaling pathways including the Wnt cascade, AP-1, PI3kinase/Akt, GSK3β, STAT6, Calcineurin/NFAT and the ERK and mTOR cascades. PC-2 is a calcium channel of the TRP family. The two proteins form a functional complex and prevent cyst formation, but the precise mechanism(s) involved remains unknown. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Cilium, centrosome and cell cycle regulation in polycystic kidney disease

Polycystic kidney disease is the defining condition of a group of common life-threatening genetic disorders characterized by the bilateral formation and progressive expansion of renal cysts that lead to end stage kidney disease. Although a large body of information has been acquired in the past years about the cellular functions that characterize the cystic cells, the mechanisms triggering the cystogenic conversion are just starting to emerge. Recent findings link defects in ciliary functions, planar cell polarity pathway, and centrosome integrity in early cystic development. Many of the signals dysregulated during cystogenesis may converge on the centrosome for its central function as a structural support for cilia formation and a coordinator of protein trafficking, polarity, and cell division. Here, we will discuss the contribution of proliferation, cilium and planar cell polarity to the cystic signal and will analyze in particular the possible role that the basal bodies/centrosome may play in the cystogenetic mechanisms. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Polycystic liver diseases

Polycystic liver diseases (PCLDs) are genetic disorders with heterogeneous etiologies and a range of phenotypic presentations. PCLD exhibits both autosomal or recessive dominant pattern of inheritance and is characterized by the progressive development of multiple cysts, isolated or associated with polycystic kidney disease, that appear more extensive in women. Cholangiocytes have primary cilia, functionally important organelles (act as mechanosensors) that are involved in both normal developmental and pathological processes. The absence of polycystin-1, 2, and fibrocystin/polyductin, normally localized to primary cilia, represent a potential mechanism leading to cyst formation, associated with increased cell proliferation and apoptosis, enhanced fluid secretion, abnormal cell-matrix interactions, and alterations in cell polarity. Proliferative and secretive activities of cystic epithelium can be regulated by estrogens either directly or by synergizing growth factors including nerve growth factor, IGF1, FSH and VEGF. The abnormalities of primary cilia and the sensitivity to proliferative effects of estrogens and different growth factors in PCLD cystic epithelium provide the morpho-functional basis for future treatment targets, based on the possible modulation of the formation and progression of hepatic cysts.

Down-regulation of Pkd2 by siRNAs suppresses cell-cell adhesion in the mouse melanoma cells

The Pkd2 gene encodes an integral protein (~130 kDa), named polycystin-2 (PC-2). PC-2 is mainly involved in autosomal dominant polycystic kidney disease. Recently, polycystin-1/polycystin-2 complex has been shown to act as an adhesion complex mediating or regulating cell-cell or cell-matrix adhesion, suggesting that PC-2 may play a role in cell-cell/cell-matrix interactions. Here, we knocked down the expression of Pkd2 gene with small interfering RNAs (siRNAs) in the mouse melanoma cells (B16 cells), indicating that the cells transfected with the targeted siRNAs significantly suppressed cell-cell adhesion, but not cell-matrix adhesion, compared to the cells transfected with non-targeted control (NC) siRNA. This study provides the first directly functional evidence that PC-2 mediates cell-cell adhesion. Furthermore, we demonstrated that PC-2 modulated cell-cell adhesion may be, at least partially, associated with E-cadherin. Collectively, these findings for the first time showed that PC-2 may mediate cell-cell adhesion, at least partially, through E-cadherin.

The effect of variation in expression of the candidate dyslexia susceptibility gene homolog Kiaa0319 on neuronal migration and dendritic morphology in the rat

We investigated the postnatal effects of embryonic knockdown and overexpression of the candidate dyslexia gene homolog Kiaa0319. We used in utero electroporation to transfect cells in E15/16 rat neocortical ventricular zone with either 1) small hairpin RNA (shRNA) vectors targeting Kiaa0319, 2) a KIAA0319 expression construct, 3) Kiaa0319 shRNA along with KIAA0319 expression construct ("rescue"), or 4) a scrambled version of Kiaa0319 shRNA. Knockdown, but not overexpression, of Kiaa0319 resulted in periventricular heterotopias that contained large numbers of both transfected and non-transfected neurons. This suggested that Kiaa0319 shRNA disrupts neuronal migration by cell autonomous as well as non-cell autonomous mechanisms. Of the Kiaa0319 shRNA-transfected neurons that migrated into the cortical plate, most migrated to their appropriate lamina. In contrast, neurons transfected with the KIAA0319 expression vector attained laminar positions subjacent to their expected positions. Neurons transfected with Kiaa0319 shRNA exhibited apical, but not basal, dendrite hypertrophy, which was rescued by overexpression of KIAA0319. The results provide additional supportive evidence linking candidate dyslexia susceptibility genes to migrational disturbances during brain development, and extends the role of Kiaa0319 to include growth and differentiation of dendrites.

TRPV4 channels mediate cyclic strain-induced endothelial cell reorientation through integrin-to-integrin signaling

Cyclic mechanical strain produced by pulsatile blood flow regulates the orientation of endothelial cells lining blood vessels and influences critical processes such as angiogenesis. Mechanical stimulation of stretch-activated calcium channels is known to mediate this reorientation response; however, the molecular basis remains unknown. Here, we show that cyclically stretching capillary endothelial cells adherent to flexible extracellular matrix substrates activates mechanosensitive TRPV4 (transient receptor potential vanilloid 4) ion channels that, in turn, stimulate phosphatidylinositol 3-kinase-dependent activation and binding of additional beta1 integrin receptors, which promotes cytoskeletal remodeling and cell reorientation. Inhibition of integrin activation using blocking antibodies and knock down of TRPV4 channels using specific small interfering RNA suppress strain-induced capillary cell reorientation. Thus, mechanical forces that physically deform extracellular matrix may guide capillary cell reorientation through a strain-dependent "integrin-to-integrin" signaling mechanism mediated by force-induced activation of mechanically gated TRPV4 ion channels on the cell surface.

Mechanotransduction in vascular physiology and atherogenesis

Forces that are associated with blood flow are major determinants of vascular morphogenesis and physiology. Blood flow is crucial for blood vessel development during embryogenesis and for regulation of vessel diameter in adult life. It is also a key factor in atherosclerosis, which, despite the systemic nature of major risk factors, occurs mainly in regions of arteries that experience disturbances in fluid flow. Recent data have highlighted the potential endothelial mechanotransducers that might mediate responses to blood flow, the effects of atheroprotective rather than atherogenic flow, the mechanisms that contribute to the progression of the disease and how systemic factors interact with flow patterns to cause atherosclerosis.

Purinergic signaling in the lumen of a normal nephron and in remodeled PKD encapsulated cysts

The nephron is the functional unit of the kidney. Blood and plasma are continually filtered within the glomeruli that begin each nephron. Adenosine 5' triphosphate (ATP) and its metabolites are freely filtered by each glomerulus and enter the lumen of each nephron beginning at the proximal convoluted tubule (PCT). Flow rate, osmolality, and other mechanical or chemical stimuli for ATP secretion are present in each nephron segment. These ATP-release stimuli are also different in each nephron segment due to water or salt permeability or impermeability along different luminal membranes of the cells that line each nephron segment. Each of the above stimuli can trigger additional ATP release into the lumen of a nephron segment. Each nephron-lining epithelial cell is a potential source of secreted ATP. Together with filtered ATP and its metabolites derived from the glomerulus, secreted ATP and adenosine derived from cells along the nephron are likely the principal two of several nucleotide and nucleoside candidates for renal autocrine and paracrine ligands within the tubular fluid of the nephron. This minireview discusses the first principles of purinergic signaling as they relate to the nephron and the urinary bladder. The review discusses how the lumen of a renal tubule presents an ideal purinergic signaling microenvironment. The review also illustrates how remodeled and encapsulated cysts in autosomal dominant polycystic kidney disease (ADPKD) and remodeled pseudocysts in autosomal recessive PKD (ARPKD) of the renal collecting duct likely create an even more ideal microenvironment for purinergic signaling. Once trapped in these closed microenvironments, purinergic signaling becomes chronic and likely plays a significant epigenetic and detrimental role in the secondary progression of PKD, once the remodeling of the renal tissue has begun. In PKD cystic microenvironments, we argue that normal purinergic signaling within the lumen of the nephron provides detrimental acceleration of ADPKD once remodeling is complete.

Co-inheritance of a PKD1 mutation and homozygous PKD2 variant: a potential modifier in autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD), which is caused by mutations in polycystins 1 (PC1) and 2 (PC2), is one of the most commonly inherited renal diseases, affecting ~1 : 1000 Caucasians.

MATERIALS AND METHODS

We screened Greek ADPKD patients with the denaturing gradient gel electrophoresis (DGGE) assay and direct sequencing.

RESULTS

We identified a patient homozygous for a nucleotide change c.1445T > G, resulting in a novel homozygous substitution of the non-polar hydrophobic phenylalanine to the polar hydrophilic cysteine in exon 6 at codon 482 (p.F482C) of the PKD2 gene and a de-novo PKD1 splice-site variant IVS21-2delAG. We did not find this PKD2 variant in a screen of 280 chromosomes of healthy subjects, supporting its pathogenicity. The proband's parents did not have the PKD1 mutation. Real-time PCR of the PKD2 transcript from a skin biopsy revealed 20-fold higher expression in the patient than in a healthy subject and was higher in the patient's peripheral blood mononuclear cells (PBMCs) than in those of her heterozygote daughter and a healthy subject. The greater gene expression was also supported by Western blotting. Inner medullar collecting duct (IMCD) cells transfected with the mutant PKD2 mouse gene presented a perinuclear and diffuse cytoplasmic localization compared with the wild type ER localization. Patch-clamping of PBMCs from the p.F482C homozygous and heterozygous subjects revealed lower polycystin-2 channel function than in controls.

CONCLUSIONS

We report for the first time a patient with ADPKD who is heterozygous for a de novo PKD1 variant and homozygous for a novel PKD2 mutation.

PKD1 inhibits cancer cells migration and invasion via Wnt signaling pathway in vitro

The approximately 14 kb mRNA of the polycystic kidney disease gene PKD1 encodes a large ( approximately 460 kDa) protein, termed polycystin-1 (PC-1), that is responsible for autosomal dominant polycystic kidney disease (ADPKD). The unique organization of its multiple adhesive domains (16 Ig-like domains/PKD domains) suggests that it may play an important role in cell-cell/cell-matrix interactions. Here we demonstrated that PKD1 promoted cell-cell and cell-matrix interactions in cancer cells, indicating that PC-1 is involved in the cell adhesion process. Furthermore in this study, we showed that PKD1 inhibited cancer cells migration and invasion. And we also showed that PC-1 regulated these processes in a process that may be at least partially through the Wnt pathway. Collectively, our data suggest that PKD1 may act as a novel member of the tumor suppressor family of genes.

Loss of apical monocilia on collecting duct principal cells impairs ATP secretion across the apical cell surface and ATP-dependent and flow-induced calcium signals

Renal epithelial cells release ATP constitutively under basal conditions and release higher quantities of purine nucleotide in response to stimuli. ATP filtered at the glomerulus, secreted by epithelial cells along the nephron, and released serosally by macula densa cells for feedback signaling to afferent arterioles within the glomerulus has important physiological signaling roles within kidneys. In autosomal recessive polycystic kidney disease (ARPKD) mice and humans, collecting duct epithelial cells lack an apical central cilium or express dysfunctional proteins within that monocilium. Collecting duct principal cells derived from an Oak Ridge polycystic kidney (orpk ( Tg737 ) ) mouse model of ARPKD lack a well-formed apical central cilium, thought to be a sensory organelle. We compared these cells grown as polarized cell monolayers on permeable supports to the same cells where the apical monocilium was genetically rescued with the wild-type Tg737 gene that encodes Polaris, a protein essential to cilia formation. Constitutive ATP release under basal conditions was low and not different in mutant versus rescued monolayers. However, genetically rescued principal cell monolayers released ATP three- to fivefold more robustly in response to ionomycin. Principal cell monolayers with fully formed apical monocilia responded three- to fivefold greater to hypotonicity than mutant monolayers lacking monocilia. In support of the idea that monocilia are sensory organelles, intentionally harsh pipetting of medium directly onto the center of the monolayer induced ATP release in genetically rescued monolayers that possessed apical monocilia. Mechanical stimulation was much less effective, however, on mutant orpk collecting duct principal cell monolayers that lacked apical central monocilia. Our data also show that an increase in cytosolic free Ca(2+) primes the ATP pool that is released in response to mechanical stimuli. It also appears that hypotonic cell swelling and mechanical pipetting stimuli trigger release of a common ATP pool. Cilium-competent monolayers responded to flow with an increase in cell Ca(2+) derived from both extracellular and intracellular stores. This flow-induced Ca(2+) signal was less robust in cilium-deficient monolayers. Flow-induced Ca(2+) signals in both preparations were attenuated by extracellular gadolinium and by extracellular apyrase, an ATPase/ADPase. Taken together, these data suggest that apical monocilia are sensory organelles and that their presence in the apical membrane facilitates the formation of a mature ATP secretion apparatus responsive to chemical, osmotic, and mechanical stimuli. The cilium and autocrine ATP signaling appear to work in concert to control cell Ca(2+). Loss of a cilium-dedicated autocrine purinergic signaling system may be a critical underlying etiology for ARPKD and may lead to disinhibition and/or upregulation of multiple sodium (Na(+)) absorptive mechanisms and a resultant severe hypertensive phenotype in ARPKD and, possibly, other diseases.

Expression of the Pkd1 gene is momentously regulated by Sp1

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a common human genetic disease that is caused by a mutation of a single gene inherited from either parent. Mutations in the Pkd1 gene result in the formation of multiple fluid-filled cysts in kidneys. In previous studies, the functional regulatory sequences of Pkd1 promoter region were detected by the use of comparative genome analysis.

METHODS

To investigate the transcriptional regulation of the Pkd1 gene, the Pkd1 promoter was isolated. This promoter contains three Sp1-binding sites. Two of the sites which are found in a 300 bp fragment (-127 to +157) were mutated. An electrophoretic mobility shift assay (EMSA) was performed to determine which transcription factors are bound to Pkd1.

RESULTS

Based on studies using a luciferase assay, the Sp1-A site (the nearest Sp1 to the ATG start codon) is more important for activation of Pkd1. The result of EMSA showed that Sp1 transcription factor binds with Pkd1 promoter regions.

CONCLUSIONS

Two of the Sp1 sites were found in a proximal promoter region of Pkd1 (-127 to +157). Sp1 sites affect an important role in the activation of the gene. Especially, the Sp1-A site is more important for expression of Pkd1.

HEF1-dependent Aurora A activation induces disassembly of the primary cilium

The mammalian cilium protrudes from the apical/lumenal surface of polarized cells and acts as a sensor of environmental cues. Numerous developmental disorders and pathological conditions have been shown to arise from defects in cilia-associated signaling proteins. Despite mounting evidence that cilia are essential sites for coordination of cell signaling, little is known about the cellular mechanisms controlling their formation and disassembly. Here, we show that interactions between the prometastatic scaffolding protein HEF1/Cas-L/NEDD9 and the oncogenic Aurora A (AurA) kinase at the basal body of cilia causes phosphorylation and activation of HDAC6, a tubulin deacetylase, promoting ciliary disassembly. We show that this pathway is both necessary and sufficient for ciliary resorption and that it constitutes an unexpected nonmitotic activity of AurA in vertebrates. Moreover, we demonstrate that small molecule inhibitors of AurA and HDAC6 selectively stabilize cilia from regulated resorption cues, suggesting a novel mode of action for these clinical agents.