Autosomal dominant polycystic kidney disease

A latent capacity of the C. elegans polycystins to disrupt sensory transduction is repressed by the single-pass ciliary membrane protein CWP-5

Autosomal dominant polycystic kidney disease (ADPKD) results from loss-of-function mutations in PKD1 or PKD2. The products of these genes, the polycystins PC-1 and PC-2, form a transmembrane channel that is necessary for flow sensing by renal cilia. In C. elegans, the polycystin orthologs LOV-1 and PKD-2 function in sensory neurons that mediate male mating behavior. Here, we report that the novel single-pass membrane protein CWP-5 is necessary for polycystin signaling during the response step of mating behavior. As with the polycystins, CWP-5 localizes to neuronal cilia; this localization requires LOV-1. The response defect of cwp-5 mutants does not appear to result from disruption of ciliogenesis or polycystin localization. Instead, genetic and behavioral analyses indicate that CWP-5 represses a previously undescribed antagonistic effect of the polycystins on sensory function. Although cwp-5 does not have a primary-sequence ortholog in vertebrates, it has intriguing parallels with the autosomal recessive PKD gene FPC (also known as PKHD1). Together, this study identifies a new component of C. elegans polycystin signaling, demonstrates that the polycystins have a latent capacity to hinder sensory transduction, and suggests that aberrant functions of the polycystins could contribute to the pathogenesis of PKD.

Polycystic kidney disease: inheritance, pathophysiology, prognosis, and treatment

Both autosomal dominant and recessive polycystic kidney disease are conditions with severe associated morbidity and mortality. Recent advances in the understanding of the genetic and molecular pathogenesis of both ADPKD and ARPKD have resulted in new, targeted therapies designed to disrupt cell signaling pathways responsible for the abnormal cell proliferation, dedifferentiation, apoptosis, and fluid secretion characteristic of the disease. Herein we review the current understanding of the pathophysiology of these conditions, as well as the current treatments derived from our understanding of the mechanisms of these diseases.

Early renal abnormalities in autosomal dominant polycystic kidney disease

BACKGROUND AND OBJECTIVES

Potential therapeutic interventions are being developed for autosomal dominant polycystic kidney disease (ADPKD). A pivotal question will be when to initiate such treatment, and monitoring disease progression will thus become more important. Therefore, the prevalence of renal abnormalities in ADPKD at different ages was evaluated.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Included were 103 prevalent ADPKD patients (Ravine criteria). Measured were mean arterial pressure (MAP), total renal volume (TRV), GFR, effective renal plasma flow (ERPF), renal vascular resistance (RVR), and filtration fraction (FF). Twenty-four-hour urine was collected. ADPKD patients were compared with age- and gender-matched healthy controls.

RESULTS

Patients and controls were subdivided into quartiles of age (median ages 28, 37, 42, and 52 years). Patients in the first quartile of age had almost the same GFR when compared with controls, but already a markedly decreased ERPF and an increased FF (GFR 117 +/- 32 versus 129 +/- 17 ml/min, ERPF 374 +/- 119 versus 527 +/- 83 ml/min, FF 32% +/- 4% versus 25% +/- 2%, and RVR 12 (10 to 16) versus 8 (7 to 8) dynes/cm(2), respectively). Young adult ADPKD patients also had higher 24-hour urinary volumes, lower 24-hour urinary osmolarity, and higher urinary albumin excretion (UAE) than healthy controls, although TRV in these young adult patients was modestly enlarged (median 1.0 L).

CONCLUSIONS

Already at young adult age, ADPKD patients have marked renal abnormalities, including a decreased ERPF and increased FF and UAE, despite modestly enlarged TRV and near-normal GFR. ERPF, FF, and UAE may thus be better markers for disease severity than GFR.

Monolobar hepatobiliary fibropolycystic disease

We herein report a case of monolobar hepatobiliary fibropolycystic disease. A 75-year-old woman presented with heartburn. Imaging modalities including US, CT, and MRI revealed marked atrophy and multiple biliary cysts of the hepatic left lobe. The hepatic right lobe was normal. ERCP and bile duct endoscopy revealed anomalous pancreaticobiliary union, choledochal dilation, dilation of left intrahepatic bile ducts, and small choledochal non-invasive adenocarcinoma. Polycystic kidney diseases were absent. The patient underwent pancreatico-duodenectomy and extended hepatic left lobectomy. Grossly, the hepatic left lobe was markedly atrophic, and studded with numerous biliary cysts. The left intrahepatic bile ducts were dilated (Caroli's disease) and the common bile duct showed type I choledochal dilation. The right hepatic lobe was normal. Histologically, the hepatic left lobe was replaced by fibroelastosis. The intrahepatic bile ducts showed ductal plate malformation such as irregular contours, invaginations, and protrusions. The numerous biliary cysts also showed ductal plate malformation. There were numerous persistent ductal plates and microhamartomas. Many hyalinized destructive biliary cysts and ductal plates were recognized. The liver parenchyma was scant and free of hepatocellular malformations. The portal veins showed old obliterative portal thrombosis. The right hepatic lobe was normal. Immunohistochemically, the biliary cells were positive for cytokeratin 7, 8, 18 and 19, and MUC6 and CD10, but negative for MUC2 and MUC5AC. The biliary cysts, persistent ductal plate, and microhamartomas were positive for fetal apomucin antigen MUC1.

Prospects for mTOR inhibitor use in patients with polycystic kidney disease and hamartomatous diseases

Mammalian target of rapamycin (mTOR) is the core component of two complexes, mTORC1 and mTORC2. mTORC1 is inhibited by rapamycin and analogues. mTORC2 is impeded only in some cell types by prolonged exposure to these compounds. mTOR activation is linked to tubular cell proliferation in animal models and human autosomal dominant polycystic kidney disease (ADPKD). mTOR inhibitors impede cell proliferation and cyst growth in polycystic kidney disease (PKD) models. After renal transplantation, two small retrospective studies suggested that mTOR was more effective than calcineurin inhibitor-based immunosuppression in limiting kidney and/or liver enlargement. By inhibiting vascular remodeling, angiogenesis, and fibrogenesis, mTOR inhibitors may attenuate nephroangiosclerosis, cyst growth, and interstitial fibrosis. Thus, they may benefit ADPKD at multiple levels. However, mTOR inhibition is not without risks and side effects, mostly dose-dependent. Under certain conditions, mTOR inhibition interferes with adaptive increases in renal proliferation necessary for recovery from injury. They restrict Akt activation, nitric oxide synthesis, and endothelial cell survival (downstream from mTORC2) and potentially increase the risk for glomerular and peritubular capillary loss, vasospasm, and hypertension. They impair podocyte integrity pathways and may predispose to glomerular injury. Administration of mTOR inhibitors is discontinued because of side effects in up to 40% of transplant recipients. Currently, treatment with mTOR inhibitors should not be recommended to treat ADPKD. Results of ongoing studies must be awaited and patients informed accordingly. If effective, lower dosages than those used to prevent rejection would minimize side effects. Combination therapy with other effective drugs could improve tolerability and results.

Evaluation and management of pain in autosomal dominant polycystic kidney disease

Transient episodes of pain are common in autosomal dominant polycystic kidney disease (ADPKD). A small fraction of patients have disabling chronic pain. In this review, we discuss the etiologies of pain in ADPKD; review how ADPKD patients should be assessed; and discuss medical, surgical, and other management options.

Randomized clinical trial of long-acting somatostatin for autosomal dominant polycystic kidney and liver disease

There are no proven, effective therapies for polycystic kidney disease (PKD) or polycystic liver disease (PLD). We enrolled 42 patients with severe PLD resulting from autosomal dominant PKD (ADPKD) or autosomal dominant PLD (ADPLD) in a randomized, double-blind, placebo-controlled trial of octreotide, a long-acting somatostatin analogue. We randomly assigned 42 patients in a 2:1 ratio to octreotide LAR depot (up to 40 mg every 28+/-5 days) or placebo for 1 year. The primary end point was percent change in liver volume from baseline to 1 year, measured by MRI. Secondary end points were changes in total kidney volume, GFR, quality of life, safety, vital signs, and clinical laboratory tests. Thirty-four patients had ADPKD, and eight had ADPLD. Liver volume decreased by 4.95%+/-6.77% in the octreotide group but remained practically unchanged (+0.92%+/-8.33%) in the placebo group (P=0.048). Among patients with ADPKD, total kidney volume remained practically unchanged (+0.25%+/-7.53%) in the octreotide group but increased by 8.61%+/-10.07% in the placebo group (P=0.045). Changes in GFR were similar in both groups. Octreotide was well tolerated; treated individuals reported an improved perception of bodily pain and physical activity. In summary, octreotide slowed the progressive increase in liver volume and total kidney volume, improved health perception among patients with PLD, and had an acceptable side effect profile.

Therapeutic potential of cystic fibrosis transmembrane conductance regulator (CFTR) inhibitors in polycystic kidney disease

In the common genetic disorder autosomal dominant polycystic kidney disease (ADPKD), kidney function is disrupted by multiple fluid-filled epithelial cysts. Cyst growth in ADPKD involves fluid accumulation within the cyst lumen driven by cystic fibrosis transmembrane conductance regulator (CFTR)-mediated transepithelial Cl- secretion. This suggests that inhibitors of the CFTR Cl- channel might retard cyst growth. This review considers how knowledge of CFTR structure and function and its role in transepithelial salt and water movements provides insight into the mechanism of action of CFTR inhibitors. Some small molecules, termed open-channel blockers, inhibit directly the CFTR Cl- channel by physically obstructing the CFTR pore and preventing Cl- flow. By contrast, other small molecules, termed allosteric inhibitors, bind to CFTR at a site remote from the channel pore and interfere with conformational changes that open the pore. The application of high-throughput screening to CFTR drug discovery has led to the identification of new inhibitors of the CFTR Cl- channel including the thiazolidinone CFTR(inh)-172 and the glycine hydrazide GlyH-101. The demonstration that CFTR inhibitors retard cyst expansion and kidney enlargement in mouse models of ADPKD provides proof of concept for the use of small-molecule CFTR inhibitors in the treatment of ADPKD.

Cystic diseases of the kidney: molecular biology and genetics

CONTEXT

Cystic diseases of the kidney are a very heterogeneous group of renal inherited conditions, with more than 33 genes involved and encompassing X-linked, autosomal dominant, and autosomal recessive inheritance. Although mostly monogenic with mendelian inheritance, there are clearly examples of oligogenic inheritance, such as 3 mutations in 2 genes, while the existence of genetic modifiers is perhaps the norm, based on the extent of variable expressivity and the broad spectrum of symptoms.

OBJECTIVES

To present in the form of a mini review the major known cystic diseases of the kidney for which genes have been mapped or cloned and characterized, with some information on their cellular and molecular biology and genetics, and to pay special attention to commenting on the issues of molecular diagnostics, in view of the genetic and allelic heterogeneity. Data Sources.-We used major reviews that make excellent detailed presentation of the various diseases, as well as original publications.

CONCLUSIONS

There is already extensive genetic heterogeneity in the group of cystic diseases of the kidney; however, there are still many more genes awaiting to be discovered that are implicated or mutated in these diseases. In addition, the synergism and interaction among this repertoire of gene products is largely unknown, while a common unifying aspect is the expression of nearly all of them at the primary cilium or the basal body. A major interplay of functions is anticipated, while mutations in all converge in the unifying phenotype of cyst formation.

Mechanisms of p53-mediated repression of the human polycystic kidney disease-1 promoter

We previously reported that the tumor suppressor protein p53 participates in a negative feedback loop to fine-tune PKD1 gene expression. This physiological pathway is believed to prevent polycystin-1 overexpression and thus renal cysts. The present study examined the mechanisms of p53-mediated repression of PKD1. The 5'-upstream region of the human PKD1 gene is TATA-less, GC-rich, and contains four consensus p53 binding sites at positions -2.7 kb (BS4), -1.2 kb (BS3), -0.8 kb (BS2), and -0.2 kb (BS1), respectively. PKD1BS1-4 are bound to endogenous p53 in vivo and in vitro. Transient transfection assays in inner medullary collecting duct cells revealed that disruption of PKD1BS1 enhances baseline PKD1 promoter activity; in contrast, disruption of PKD1BS4 suppressed PKD1 transcription. PKD1BS1 confers p53-mediated repression when substituted for the p53 enhancer element in the bradykinin B2 receptor gene, indicating that PKD1BS1 is a bona fide p53 repressor element. Moreover, PKD1BS1 requires intact BS2-4 and cellular histone deacetylase activity for full functional activity. Indeed, the PKD1BS1/4 regions are occupied by a complex containing HDAC1/2 and mSin3. These findings suggest a model whereby p53 exerts a biphasic control on PKD1 gene transcription, depending on cellular context and the cognate cis-acting element.

Genetic kidney diseases

Knowledge of the primary cause of a disease is essential for elucidation of its mechanisms, and for adequate classification, prognosis, and treatment. Recently, the causes of many kidney diseases have been shown to be single-gene defects-eg, steroid-resistant nephrotic syndrome, which is caused by podocin mutations in about 25% of children and nearly 15% of adults with the disease. Knowledge of a disease-causing mutation in a single-gene disorder represents one of the most robust diagnostic examples of personalised medicine because the mutation conveys an almost 100% risk of developing the disease by a defined age. Whereas single-gene diseases are rare disorders, polygenic risk alleles arise in common adult-onset diseases. In this Review, I will discuss prominent renal single-gene kidney disorders, and polygenic risk alleles of common disorders. I delineate how emerging techniques of total exome capture and large-scale sequencing will assist molecular genetic diagnosis, prognosis, and specific treatment, and lead to an improved elucidation of disease mechanisms, thus enabling development of new targeted drugs.

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.

Autosomal dominant polycystic kidney disease: risk factor for nonmelanoma skin cancer following kidney transplantation

Nonmelanoma skin cancers (NMSC) are the most common malignant tumors following solid organ transplantation. Risk factors for NMSC mainly include immunosuppression, age, sun exposure and patient phototype. Recent findings have suggested that autosomal dominant polycystic kidney disease (ADPKD) may increase the risk of developing NMSC. We performed a monocenter retrospective study including all kidney recipients between 1985 and 2006 (n = 1019). We studied the incidence of NMSC, solid cancers and post-transplantation lymphoproliferative disease (PTLD), and analyzed the following parameters: age, gender, phototype, time on dialysis, graft rank, immunosuppressive regimen, history of cancer and kidney disease (ADPKD versus others). Median follow-up was 5.5 years (range: 0.02-20.6; 79 838 patient-years). The cumulated incidence of NMSC 10 years after transplantation was 12.7% (9.3% for solid cancers and 3.5% for PTLD). Autosomal dominant polycystic kidney disease and age were risk factors for NMSC (HR 2.63; P < 0.0001 and HR 2.21; P < 0.001, respectively) using univariate analysis. The association between ADPKD and NMSC remained significant after adjustments for age, gender and phototype using multivariate analysis (HR 1.71; P = 0.0145) and for immunosuppressive regimens (P < 0.0001). Autosomal dominant polycystic kidney disease was not a risk factor for the occurrence of solid cancers after transplantation (HR 0.96; P = 0.89). Our findings suggest that ADPKD is an independent risk factor for developing NMSC after kidney transplantation.

Molecular advances in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic disease (ADPKD) is the most common form of inherited kidney disease that results in renal failure. The understanding of the pathogenesis of ADPKD has advanced significantly since the discovery of the 2 causative genes, PKD1 and PKD2. Dominantly inherited gene mutations followed by somatic second-hit mutations inactivating the normal copy of the respective gene result in renal tubular cyst formation that deforms the kidney and eventually impairs its function. The respective gene products, polycystin-1 and polycystin-2, work together in a common cellular pathway. Polycystin-1, a large receptor molecule, forms a receptor-channel complex with polycystin-2, which is a cation channel belonging to the TRP family. Both polycystin proteins have been localized to the primary cilium, a nonmotile microtubule-based structure that extends from the apical membrane of tubular cells into the lumen. Here we discuss recent insights in the pathogenesis of ADPKD including the genetics of ADPKD, the properties of the respective polycystin proteins, the role of cilia, and some cell-signaling pathways that have been implicated in the pathways related to PKD1 and PKD2.

Extrarenal manifestations of autosomal dominant polycystic kidney disease

Although asymptomatic in most patients, extrarenal manifestations of ADPKD may become more clinically relevant with the increasing life expectancy of affected patients. They mainly encompass cysts in other organs than the kidney (liver: 94%, seminal vesicle: 40%, pancreas: 9%, arachnoid membrane: 8%, and spinal meningeal, 2%) and connective tissue abnormalities (mitral valve prolapse: 25%, intracranial aneurysms: 8%, and abdominal hernia: 10%). Their recognition may spare the patient from other, useless investigations (eg, when an arachnoid cyst is incidentally found) or lead to the implementation of prophylactic or therapeutic measures (eg, screening, sometimes followed by the treatment of an asymptomatic intracranial aneurysm in at-risk patients, or, in the presence of a severe polycystic liver disease, avoidance from estrogens and treatment aimed to slow cyst growth).

Carbohydrate antigen 19-9 as a diagnostic marker for hepatic cyst infection in autosomal dominant polycystic kidney disease

The diagnosis of hepatic cyst infection is difficult in patients with autosomal dominant polycystic kidney disease (ADPKD). We hypothesized that carbohydrate antigen 19-9 (CA 19-9), secreted by the biliary epithelium lining the cysts, is overproduced in the case of cyst infection. In this report, we describe 3 patients with ADPKD with hepatic cyst infection, all with functioning kidney transplants, who had markedly increased serum CA 19-9 levels. Furthermore, CA 19-9 level was extremely increased in cystic fluid obtained in 2 of these individuals. Corresponding with clinical improvement, there was a marked decrease in serum CA 19-9 level in all 3 patients. To assess the potential applicability of these findings, serum CA 19-9 was measured in asymptomatic patients with ADPKD with known liver cysts and in controls without ADPKD. Although serum CA 19-9 levels were significantly higher in asymptomatic patients with ADPKD than in controls, they were markedly increased in patients with cyst infection compared with either asymptomatic ADPKD patients or controls. Immunostaining for CA 19-9 showed strong positivity in biliary tree epithelia and cysts of polycystic livers from patients with ADPKD that appeared more intense than in normal livers. Although further study is necessary, these data suggest that serum CA 19-9 level is markedly increased during liver cyst infection in kidney transplant recipients with ADPKD and has potential utility as a diagnostic marker.

Reducing polycystic liver volume in ADPKD: effects of somatostatin analogue octreotide

BACKGROUND AND OBJECTIVES

No medical treatment is available for polycystic liver disease, a frequent manifestation of autosomal-dominant polycystic kidney disease (ADPKD). In a prospective, randomized, double-blind, crossover study, 6 months of octreotide (40 mg every 28 days) therapy limited kidney volume growth more effectively than placebo in 12 patients with ADPKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this secondary, post hoc analysis of the above study, octreotide-induced changes in liver volumes compared with placebo and the relationship between concomitant changes in liver and kidney volumes were evaluated. Those analyzing liver and kidney volumes were blinded to treatment.

RESULTS

Liver volumes significantly decreased from 1595 +/- 478 ml to 1524 +/- 453 ml with octreotide whereas they did not appreciably change with placebo. Changes in liver volumes were significantly different between the two treatment periods (-71 +/- 57 ml versus +14 +/- 85 ml). Octreotide-induced liver volume reduction was fully explained by a reduction in parenchyma volume from 1506 +/- 431 ml to 1432 +/- 403 ml. Changes in liver volumes were significantly correlated with concomitant changes in kidney volumes (r = 0.67) during octreotide but not during placebo treatment. Liver and kidney volume changes significantly differed with both treatments (octreotide: -71 +/- 57 ml versus +71 +/- 107; placebo: +14 +/- 85 ml versus +162 +/- 114), but net reductions in liver (-85 +/- 103 ml) and kidney (-91 +/- 125 ml) volume growth on octreotide versus placebo were similar.

CONCLUSIONS

Octreotide therapy reduces liver volumes in patients with ADPKD and is safe.

Molecular diagnostics for autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common nephropathy caused by mutations in either PKD1 or PKD2. Mutations in PKD1 account for approximately 85% of cases and cause more severe disease than mutations in PKD2. Diagnosis of ADPKD before the onset of symptoms is usually performed using renal imaging by either ultrasonography, CT or MRI. In general, these modalities are reliable for the diagnosis of ADPKD in older individuals. However, molecular testing can be valuable when a definite diagnosis is required in young individuals, in individuals with a negative family history of ADPKD, and to facilitate preimplantation genetic diagnosis. Although linkage-based diagnostic approaches are feasible in large families, direct mutation screening is generally more applicable. As ADPKD displays a high level of allelic heterogeneity, complete screening of both genes is required. Consequently, such screening approaches are expensive. Screening of individuals with ADPKD detects mutations in up to 91% of cases. However, only approximately 65% of patients have definite mutations with approximately 26% having nondefinite changes that require further evaluation. Collation of known variants in the ADPKD mutation database and systematic scoring of nondefinite variants is increasing the diagnostic value of molecular screening. Genic information can be of prognostic value and recent investigation of hypomorphic PKD1 alleles suggests that allelic information may also be valuable in some atypical cases. In the future, when effective therapies are developed for ADPKD, molecular testing may become increasingly widespread. Rapid developments in DNA sequencing may also revolutionize testing.

Rosiglitazone inhibits cell proliferation by inducing G1 cell cycle arrest and apoptosis in ADPKD cyst-lining epithelia cells

Abnormal proliferation is an important pathological feature of autosomal dominant polycystic kidney disease (ADPKD). Many drugs inhibiting cell proliferation have been proved to be effective in slowing the disease progression in ADPKD. Recent evidence has suggested that peroxisome proliferator-activated receptor gamma (PPARgamma) ligands have anti-neoplasm effects through inhibiting cell growth and inducing cell apoptosis in various cancer cells. In the present study, we examined the expression of PPARgamma in human ADPKD kidney tissues and cyst-lining epithelial cell line, and found that the expression of PPARgamma was greater in ADPKD kidney tissues and cyst-lining epithelial cell line than in normal kidney tissues and human kidney cortex (HKC) cell line. Rosiglitazone inhibited significantly proliferation of cyst-lining epithelial cells in a concentration- and time-dependent manner. These effects were diminished by GW9662, a specific PPARgamma antagonist. Cell cycle analysis showed a G0/G1 arrest in human ADPKD cyst-lining epithelial cells with rosiglitazone treatment. Analysis of cell cycle regulatory proteins revealed that rosiglitazone decreased the protein levels of proliferating cell nuclear antigen, pRb, cyclin D1, cyclin D2 and Cdk4 but increased the levels of p21 and p27 in a dose-dependent manner. Rosiglitazone also induced apoptosis in cyst-lining epithelial cells, which was correlated with increased bax expression and decreased bcl-2 expression. These results suggest PPARgamma agonist might serve as a promising drug for the treatment of ADPKD.

Carboxy terminal tail of polycystin-1 regulates localization of TSC2 to repress mTOR

Autosomal dominant polycystic kidney disease (ADPKD) is a commonly inherited renal disorder caused by defects in the PKD1 or PKD2 genes. ADPKD is associated with significant morbidity, and is a major underlying cause of end-stage renal failure (ESRF). Commonly, treatment options are limited to the management of hypertension, cardiovascular risk factors, dialysis, and transplantation when ESRF develops, although several new pharmacotherapies, including rapamycin, have shown early promise in animal and human studies. Evidence implicates polycystin-1 (PC-1), the gene product of the PKD1 gene, in regulation of the mTOR pathway. Here we demonstrate a mechanism by which the intracellular, carboxy-terminal tail of polycystin-1 (CP1) regulates mTOR signaling by altering the subcellular localization of the tuberous sclerosis complex 2 (TSC2) tumor suppressor, a gatekeeper for mTOR activity. Phosphorylation of TSC2 at S939 by AKT causes partitioning of TSC2 away from the membrane, its GAP target Rheb, and its activating partner TSC1 to the cytosol via 14-3-3 protein binding. We found that TSC2 and a C-terminal polycystin-1 peptide (CP1) directly interact and that a membrane-tethered CP1 protects TSC2 from AKT phosphorylation at S939, retaining TSC2 at the membrane to inhibit the mTOR pathway. CP1 decreased binding of 14-3-3 proteins to TSC2 and increased the interaction between TSC2 and its activating partner TSC1. Interestingly, while membrane tethering of CP1 was required to activate TSC2 and repress mTOR, the ability of CP1 to inhibit mTOR signaling did not require primary cilia and was independent of AMPK activation. These data identify a unique mechanism for modulation of TSC2 repression of mTOR signaling via membrane retention of this tumor suppressor, and identify PC-1 as a regulator of this downstream component of the PI3K signaling cascade.

Percutaneous nephrolithotomy for large or multiple upper tract calculi and autosomal dominant polycystic kidney disease

PURPOSE

Percutaneous nephrolithotomy is standard therapy for upper tract calculi larger than 2 cm. However, the role of percutaneous nephrolithotomy in patients with autosomal dominant polycystic kidney disease has not been well evaluated. We report our experience with percutaneous nephrolithotomy in patients with autosomal dominant polycystic kidney disease.

MATERIALS AND METHODS

We retrospectively reviewed the charts of all patients with autosomal dominant polycystic kidney disease and subsequent renal calculi managed by percutaneous nephrolithotomy from October 1981 to the present.

RESULTS

We identified 9 patients. Percutaneous nephrolithotomy was performed in 11 kidneys. Flank pain was the presenting symptom in 6 patients. Average stone burden was 2.5 cm (range 1.6 to 3.6). Two access tracts were necessary in 5 kidneys. No intraoperative complications occurred. In 2 kidneys a second stage endoscopic procedure with ultrasonic lithotripsy was required to achieve stone-free status. Nephrostogram 24 hours after the final procedure showed no residual stone fragments in 9 of 11 kidneys (82%). The remaining 2 patients underwent percutaneous basket extraction to render them stone-free. There were no postoperative complications or recurrent stones. No patient required blood transfusion. Mean followup was 2.7 years (range 0.3 to 4). Mean calculated creatinine clearance was stable at 85.6 (range 45.9 to 126.6) and 89.5 mg/dl per minute (range 39.6 to 126.6) preoperatively and at last followup, respectively (p = 0.783).

CONCLUSIONS

Autosomal dominant polycystic kidney disease increased operative complexity, the need for multiple percutaneous access tracts and the likelihood of repeat endoscopy. Despite the altered anatomy percutaneous nephrolithotomy was a safe, efficacious approach for autosomal dominant polycystic kidney disease. At last followup there was no stone recurrence and renal function was stable.

Cyclic nucleotide signaling in polycystic kidney disease

Increased levels of 3'-5'-cyclic adenosine monophosphate (cAMP) stimulate cell proliferation and fluid secretion in polycystic kidney disease. Levels of this molecule are more sensitive to inhibition of phosphodiesterases (PDEs), whose activity far exceeds the rate of cAMP synthesis by adenylyl cyclase. Several PDEs exist, and here we measured the activity and expression of PDE families, their isoforms, and the expression of downstream effectors of cAMP signaling in the kidneys of rodents with polycystic kidney disease. We found a higher overall PDE activity in kidneys from mice as compared with rats, as well as a higher contribution of PDE1, relative to PDE4 and PDE3, to total PDE activity of kidney lysates and lower PDE1, PDE3, and PDE4 activities in the kidneys of cystic as compared with wild-type mice. There were reduced amounts of several PDE1, PDE3, and PDE4 proteins, possibly due to increased protein degradation despite an upregulation of their mRNA. Increased levels of cGMP were found in the kidneys of cystic animals, suggesting in vivo downregulation of PDE1 activity. We found an additive stimulatory effect of cAMP and cGMP on cystogenesis in vitro. Cyclic AMP-dependent protein kinase subunits Ialpha and IIbeta, PKare, the transcription factor CREB-1 mRNA, and CREM, ATF-1, and ICER proteins were upregulated in the kidneys of cystic as compared with wild-type animals. Our study suggests that alterations in cyclic nucleotide catabolism may render cystic epithelium particularly susceptible to factors acting on Gs-coupled receptors. This may account, in part, for increased cyclic nucleotide signaling in polycystic kidney disease and contribute substantially to disease progression.

A mitotic transcriptional switch in polycystic kidney disease

Hepatocyte nuclear factor-1beta (HNF-1beta) is a transcription factor required for the expression of several renal cystic genes and whose prenatal deletion leads to polycystic kidney disease (PKD). We show here that inactivation of Hnf1b from postnatal day 10 onward does not elicit cystic dilations in tubules after their proliferative morphogenetic elongation is over. Cystogenic resistance is intrinsically linked to the quiescent state of cells. In fact, when Hnf1b deficient quiescent cells are forced to proliferate by an ischemia-reperfusion injury, they give rise to cysts, owing to loss of oriented cell division. Remarkably, in quiescent cells, the transcription of crucial cystogenic target genes is maintained even in the absence of HNF-1beta. However, their expression is lost as soon as cells proliferate and the chromatin of target genes acquires heterochromatin marks. These results unveil a previously undescribed aspect of gene regulation. It is well established that transcription is shut off during the mitotic condensation of chromatin. We propose that transcription factors such as HNF-1beta might be involved in reprogramming gene expression after transcriptional silencing is induced by mitotic chromatin condensation. Notably, HNF-1beta remains associated with the mitotically condensed chromosomal barrels. This association suggests that HNF-1beta is a bookmarking factor that is necessary for reopening the chromatin of target genes after mitotic silencing.

Lanreotide reduces the volume of polycystic liver: a randomized, double-blind, placebo-controlled trial

BACKGROUND & AIMS

Therapy for polycystic liver is invasive, expensive, and has disappointing long-term results. Treatment with somatostatin analogues slowed kidney growth in patients with polycystic kidney disease (PKD) and reduced liver and kidney volume in a PKD rodent model. We evaluated the effects of lanreotide, a somatostatin analogue, in patients with polycystic liver because of autosomal-dominant (AD) PKD or autosomal-dominant polycystic liver disease (PCLD).

METHODS

We performed a randomized, double-blind, placebo-controlled trial in 2 tertiary referral centers. Patients with polycystic liver (n = 54) were randomly assigned to groups given lanreotide (120 mg) or placebo, administered every 28 days for 24 weeks. The primary end point was the difference in total liver volume, measured by computerized tomography at weeks 0 and 24. Analyses were performed on an intention-to-treat basis.

RESULTS

Baseline characteristics were comparable for both groups, except that more patients with ADPKD were assigned to the placebo group (P = .03). The mean liver volume decreased 2.9%, from 4606 mL (95% confidence interval (CI): 547-8665) to 4471 mL (95% CI: 542-8401 mL), in patients given lanreotide. In the placebo group, the mean liver volume increased 1.6%, from 4689 mL (95% CI: 613-8765 mL) to 4895 mL (95% CI: 739-9053 mL) (P < .01). Post hoc stratification for patients with ADPKD or PCLD revealed similar changes in liver volume, with statistically significant differences in patients given lanreotide (P < .01 for both diseases).

CONCLUSIONS

In patients with polycystic liver, 6 months of treatment with lanreotide reduces liver volume.

Emerging evidence of a link between the polycystins and the mTOR pathways

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disease characterized by the formation of renal cysts. This disease can be caused by mutations in two genes, PKD1 and PKD2, which encode polycystin-1 (PC-1) and -2 (PC-2), respectively.

PC-1 is a large plasma membrane receptor involved in the regulation of several biological functions and signaling pathways, and PC-2 is a calcium channel of the TRP family. The two proteins associate in a complex to prevent cyst formation, but the precise mechanism(s) involved remain largely unknown.

This review will focus on recent advances in our understanding of the functions of polycystins and their role in signal transduction.

Increased activity of the mammalian target of rapamycin (mTOR) kinase has been observed in cysts found in ADPKD tissues. Rapamycin has been shown to have beneficial effects in rodent models of polycystic kidney disease, prompting the initiation of pilot clinical trials with human patients. Furthermore, a direct role for PC-1 in the regulation of cell growth (size) via mTOR has recently been demonstrated.

Major advancements in the study of mTOR biology have highlighted that this kinase exists in association with two different complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). The mTORC1 complex regulates cell growth (size), proliferation, translation and autophagy, and mTORC2 regulates the actin cytoskeleton and apoptosis. Interestingly, mTORC2 has been shown to contain the kinase responsible for the phosphorylation of Akt at Serine 473. Previous studies have shown that PC-1 controls the PI 3-kinase/Akt cascade to regulate apoptosis and the actin cytoskeleton, suggesting that this receptor might regulate mTOR at several levels.

This review aims to discuss three different, inter-related themes emerging from the literature: (i) studies performed in our and other laboratories collectively suggest that PC-1 might be able to differentially regulate the two mTOR complexes; (ii) several studies point to genetic and functional cross-talk between the PKD and TSC genes, although the molecular details remain obscure; and (iii) studies performed in mammals and in the unicellular algae Chlamidomonas Reinhardtii might highlight a link between cilia, regulation of cell size and regulation of the cell cycle.

Polycystin-1 interacts with inositol 1,4,5-trisphosphate receptor to modulate intracellular Ca2+ signaling with implications for polycystic kidney disease

The PKD1 or PKD2 genes encode polycystins (PC) 1 and 2, which are associated with polycystic kidney disease. Previously we demonstrated that PC2 interacts with the inositol 1,4,5-trisphosphate receptor (IP(3)R) to modulate Ca(2+) signaling. Here, we investigate whether PC1 also regulates IP(3)R. We generated a fragment encoding the last six transmembrane (TM) domains of PC1 and the C-terminal tail (QIF38), a section with the highest homology to PC2. Using a Xenopus oocyte Ca(2+) imaging system, we observed that expression of QIF38 significantly reduced the initial amplitude of IP(3)-induced Ca(2+) transients, whereas a mutation lacking the C-terminal tail did not. Thus, the C terminus is essential to QIF38 function. Co-immunoprecipitation assays demonstrated that through its C terminus, QIF38 associates with the IP(3)-binding domain of IP(3)R. A shorter PC1 fragment spanning only the last TM and the C-terminal tail also reduced IP(3)-induced Ca(2+) release, whereas another C-terminal fragment lacking any TM domain did not. Thus, only endoplasmic reticulum-localized PC1 can modulate IP(3)R. Finally, we show that in the polarized Madin-Darby canine kidney cells, heterologous expression of full-length PC1 resulted in a smaller IP(3)-induced Ca(2+) response. Overexpression of the IP(3)-binding domain of IP(3)R reversed the inhibitory effect of PC1, suggesting interaction of full-length PC1 (or its cleavage forms) with endogenous IP(3)R in Madin-Darby canine kidney cells. These results indicate that the behavior of full-length PC1 in mammalian cells is congruent with that of PC1 C-terminal fragments in the oocyte system. These data demonstrate that PC1 inhibits Ca(2+) release, perhaps opposing the effect of PC2, which facilitates Ca(2+) release through the IP(3)R.

Pkd1 haploinsufficiency increases renal damage and induces microcyst formation following ischemia/reperfusion

Mutations in PKD1 cause the majority of cases of autosomal dominant polycystic kidney disease (ADPKD). Because polycystin 1 modulates cell proliferation, cell differentiation, and apoptosis, its lower biologic activity observed in ADPKD might influence the degree of injury after renal ischemia/reperfusion. We induced renal ischemia/reperfusion in 10- to 12-wk-old male noncystic Pkd1(+/-) and wild-type mice. Compared with wild-type mice, heterozygous mice had higher fractional excretions of sodium and potassium and higher serum creatinine after 48 h. In addition, in heterozygous mice, also cortical damage, rates of apoptosis, and inflammatory infiltration into the interstitium at time points out to 14 d after injury all increased, as well as cell proliferation at 48 h and 7 d. The mRNA and protein expression of p21 was lower in heterozygous mice than wild-type mice at 48 h. After 6 wk, we observed dilated tubules, microcysts, and increased renal fibrosis in heterozygotes. The early mortality of heterozygotes was significantly higher than that of wild-type mice when we extended the duration of ischemia from 32 to 35 min. In conclusion, ischemia/reperfusion induces a more severe injury in kidneys of Pkd1-haploinsufficient mice, a process that apparently depends on a relative deficiency of p21 activity, tubular dilation, and microcyst formation. These data suggest the possibility that humans with ADPKD from PKD1 mutations may be at greater risk for damage from renal ischemia/reperfusion injury.

The biomarker enriched proteome of autosomal dominant polycystic kidney disease cyst fluid

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is characterized by the development of numerous fluid-filled cysts in the kidneys of patients. We recently published our description of the proteome of renal cyst fluid in ADPKD. As a follow-up experiment, we hypothesized that the protein-bound subfraction consists of molecules of mechanistic or diagnostic interest in ADPKD. Using a manual biomarker enrichment kit, we have identified 44 distinct proteins in human cyst fluid.

Differentiation between infection in kidney and liver cysts in autosomal dominant polycystic kidney disease: use of PET-CT in diagnosis and to guide management

Positron emission tomography-computed tomography (PET-CT) is a useful imaging method for localizing infective lesions. We report a case of autosomal dominant polycystic kidney disease in which PET-CT was used to differentiate between infection in the kidney and liver cysts. Localization of infection to the liver rather than to kidney cysts altered patient management. We briefly review the role of PET-CT in localization of an occult focus of infection.

A novel mouse model reveals that polycystin-1 deficiency in ependyma and choroid plexus results in dysfunctional cilia and hydrocephalus

Polycystin-1 (PC-1), the product of the PKD1 gene, mutated in the majority of cases of Autosomal Dominant Polycystic Kidney Disease (ADPKD), is a very large (∼520 kDa) plasma membrane receptor localized in several subcellular compartments including cell-cell/matrix junctions as well as cilia. While heterologous over-expression systems have allowed identification of several of the potential biological roles of this receptor, its precise function remains largely elusive. Studying PC-1 in vivo has been a challenging task due to its complexity and low expression levels. To overcome these limitations and facilitate the study of endogenous PC-1, we have inserted HA- or Myc-tag sequences into the Pkd1 locus by homologous recombination. Here, we show that our approach was successful in generating a fully functional and easily detectable endogenous PC-1. Characterization of PC-1 distribution in vivo showed that it is expressed ubiquitously and is developmentally-regulated in most tissues. Furthermore, our novel tool allowed us to investigate the role of PC-1 in brain, where the protein is abundantly expressed. Subcellular localization of PC-1 revealed strong and specific staining in ciliated ependymal and choroid plexus cells. Consistent with this distribution, we observed hydrocephalus formation both in the ubiquitous knock-out embryos and in newborn mice with conditional inactivation of the Pkd1 gene in the brain. Both choroid plexus and ependymal cilia were morphologically normal in these mice, suggesting a role for PC-1 in ciliary function or signalling in this compartment, rather than in ciliogenesis. We propose that the role of PC-1 in the brain cilia might be to prevent hydrocephalus, a previously unrecognized role for this receptor and one that might have important implications for other genetic or sporadic diseases.

Colchicine treatment in autosomal dominant polycystic kidney disease: many points in common

Autosomal dominant polycystic kidney disease (ADPKD) is the most common of the inherited renal cystic diseases and constitutes 10% of the end stage kidney disease population. ADPKD is caused by PKD1 and PKD2 gene mutations in 85% and 15% of the cases respectively. Its high prevalence and negative impact on health outcomes fostered efforts to explain pathophysiologic pathways of cyst formation in kidneys. Among these are increased apoptosis, unopposed proliferation of tubule cells, impaired polarization and planar cell polarity, impaired cAMP pathway, cilier dysfunction, activated mTOR pathway, increased tumor necrosis factor-alpha (TNF-alpha) production. Many drugs have been tried in an attempt to halt cystogenesis in some point. Despite success to some extent in experimental studies, none reached clinical armamentarium yet. Colchicine, originally extracted from Colchicum autunale, is an anti-inflammatory drug that has been in continuous use for more than 3000 years. It has been used successfully to prevent attacks of familial mediterranien fever and amyloidosis, to treat gout and pseudogout attacks for a few decades. Colchicine principally is a microtubule inhibitor, thus prevents cell migration, division, and polarization. It also has anti-apoptotic, anti-proliferative and anti-inflammatory effects and down-regulates (TNF-alpha) receptors. As can easily be seen, many of the effects of colchicine have pathophysiologic counterparts in ADPKD. Thus, we hypothesized that colchicine would be beneficial to prevent or at least delay cyst formation in ADPKD patients. Indirect evidence also support our hypothesis, in which taxol and paclitaxel, other two microtubule inhibitors, were shown to delay cyst formation in experimental models of ADPKD. To our opinion, despite its narrow therapeutic index, widespread experience makes colchicine a suitable candidate for prolonged clinical use, should experimental studies show any benefit in ADPKD.

Pkd2 dosage influences cellular repair responses following ischemia-reperfusion injury

Autosomal dominant polycystic kidney disease (ADPKD) results from mutations in either PKD1 or PKD2 and accounts for 10% of all patients on renal replacement therapy. The kidney disease phenotype is primarily characterized by cyst formation, but there are also prominent interstitial changes (inflammation, apoptosis, proliferation, and fibrosis). Using a model of unilateral ischemia-reperfusion injury, we tested the hypothesis that Pkd2 heterozygous kidneys are more sensitive to injury and that this could lead to interstitial inflammation and fibrosis. Baseline tubular proliferation in heterozygous kidneys was twofold higher than in wild-type kidneys. The magnitude and duration of tubular and interstitial proliferative responses was consistently greater in injured heterozygous compared with wild-type kidneys at all time points. Conversely, tubular p21 expression in heterozygotes was lower at baseline and following injury at all time points. Significantly more neutrophils and macrophages were detected in injured Pkd2 heterozygous kidneys at 2 days, correlating with increased expression of the cytokines interleukin (IL)-1beta and keratinocyte-derived chemokine and resulting in interstitial fibrosis at 28 days. We conclude that Pkd2 dosage influences both susceptibility and nature of the repair responses following injury. Polycystin-2 is therefore likely to play multiple roles in regulating tubular cell viability, repair, and remodeling in the mature kidney.

Endoplasmic reticulum stress and renal disease

The accumulation of unfolded proteins in the endoplasmic reticulum (ER), leading to ER stress, is caused by a wide range of physiologic and pathologic conditions. Cells respond to ER stress by activating a series of integrative stress pathways termed the unfolded protein response (UPR). This either may be adaptive and promote cell survival, or if the ER stress is chronic or excessive, may lead to cell death. The role of ER stress in the pathophysiology of both acute and chronic kidney diseases has been gaining increasing interest. This review highlights the current knowledge of ER stress in renal disease, with emphasis on more recent advances. Potential therapeutic options targeting ER stress are discussed.

Autosomal dominant polycystic kidney disease: 2009 update for internists

Because autosomal dominant polycystic kidney disease (ADPKD) is one of the most common genetic abnormalities seen in today's medical practice, many internists will likely treat patients affected by this condition. Genetic abnormalities have been increasingly recognized, and the pathophysiology of the disease is beginning to be unraveled. Because of advances in imaging technology, surrogate markers for disease progression have allowed clinical studies of newer therapeutic agents to proceed. In the near future, therapies for this common genetic disease may be available to either prevent or stabilize the disease course for many affected individuals.

Renal Tubular Cyst Formation in Newborn Rats Treated with p-Cumylphenol

In this study, we investigated the sequential changes in the development of renal tubular cysts in newborn rats treated with p-cumylphenol (PCP). Fifteen animals per sex were treated orally with 300 mg/kg/day of PCP for up to 18 days from postnatal day (PND) 4 and were sacrificed on PNDs 8, 12, 19 and 22 and after a 7 day recovery period. On PNDs 8 and 12, slight dilatation of the collecting ducts was frequently observed in the medulla and slight papillary necrosis was also noted in some cases. These dilated collecting ducts were lined with slightly hyperplastic epithelial cells. On PNDs 19 and 22, multiple large cystic changes arising from the collecting ducts in the outer medulla were seen. These cystically dilated ducts were also lined with hyperplastic epithelial cells. During the dosing period, the labeling index of proliferating cell nuclear antigen in the collecting duct epithelium was higher in the PCP-treated group than in the control group at all time points. After a 7 day recovery period, the cystic change still remained, although the cell density was decreased and the epithelial cells became flattened. On the other hand, basophilic tubules with peritubular lymphoid cell infiltration were multifocally observed in the cortex. In conclusion, PCP induced multiple renal cysts that developed in the collecting ducts of the outer medulla in neonatal rats, and it is suggested that epithelial cell proliferation may play some roles in the induction of cystic lesions.

Cyst ablation using a mixture of N-butyl cyanoacrylate and iodized oil in patients with autosomal dominant polycystic kidney disease: the long-term results

Objective

We wanted to assess the long-term results of cyst ablation with using N-butyl cyanoacrylate (NBCA) and iodized oil in patients with autosomal dominant polycystic kidney disease (ADPKD) and symptomatic cysts.

Materials and Methods

Cyst ablation using a mixture of NBCA and iodized oil was performed in 99 cysts from 21 patients who had such symptoms as abdominal distension and pain. The collapse or reaccumulation of the ablated cysts after the procedure was assessed during the follow-up period of 36 to 90 months. The treatment effects, including symptom relief, and the clinical data such as the blood pressure and serum creatinine levels were also assessed, together with the complications.

Results

The procedure was technically successful in all 99 cysts from the 21 patients. Any procedure-related significant complications were not detected. Seventy-seven of 99 cysts (78%) were successfully collapsed on the follow-up CT. Twenty-two cysts showed reaccumulation during long-term follow-up period. The clinical symptoms were relieved in 17 of the 21 patients (76%). Four of 12 patients (33%) with hypertension and two of six patients (33%) with azotemia were improved. End stage renal disease (ESRD) occurred in six of the 21 patients (28%) during the follow-up period. The mean age of ESRD in our patients was 57 years. The mean time interval for the development of ESRD was 19 months.

Conclusion

Ablation using a mixture of NBCA and iodized oil may be an effective, safe method for obtaining symptom relief in patients with ADPKD.

Wnt9b signaling regulates planar cell polarity and kidney tubule morphogenesis

Although many vertebrate organs, such as kidneys, lungs and liver, are composed of epithelial tubules, little is known of the mechanisms that establish the length or diameter of these tubules. In the kidney, defects in the establishment and/or maintenance of tubule diameter are associated with one of the most common inherited human disorders, polycystic kidney disease. Here, we show that attenuation of Wnt9b signaling during kidney morphogenesis affects the planar cell polarity of the epithelium and leads to tubules with significantly increased diameter. Although previous studies showed that polarized cell divisions maintain the diameter of postnatal kidney tubules, we find cell divisions are randomly oriented during embryonic development. Our data suggest that diameter is established during early morphogenetic stages by convergent extension processes and maintained by polarized cell divisions. Wnt9b, signaling through the non-canonical Rho/Jnk branch of the Wnt pathway, is necessary for both of these processes.

Polycystic kidney disease channel and synaptotagmin homologues play roles in schizosaccharomyces pombe cell wall synthesis/repair and membrane protein trafficking

Eukaryotic cells can sense a wide variety of environmental stresses, including changes in temperature, pH, osmolarity and nutrient availability. They respond to these changes through a variety of signal-transduction mechanisms, including activation of Ca(2+)-dependent signaling pathways. This research has discovered important implications in the function(s) of polycystic kidney disease (PKD) channels and the mechanisms through which they act in the control of cell growth and cell polarity in Schizosaccharomyces pombe by ion channel-mediated Ca(2+) signaling. Pkd2 was expressed maximally during the exponential growth phase. At the cell surface pkd2 was localized at the cell tip during the G(2) phase of the cell cycle, although following cell wall damage, the cell surface-expressed protein relocalized to the whole plasma membrane. Pkd2 depletion affected Golgi trafficking, resulting in a buildup of vesicles at the cell poles, and strongly affected plasma membrane protein delivery. Surface-localized pkd2 was present in the plasma membrane for a very short time and was rapidly internalized. Internalization was dependent on Ca(2+), enhanced by amphipaths and inhibited by gadolinium. The pkd2 protein was in a complex with a yeast synaptotagmin homologue and myosin V. Depletion of pkd2 severely affected the localization of glucan synthase. A role for pkd2 in a cell polarity and cell wall synthesis signaling complex with a synaptotagmin homologue, myosin V and glucan synthase is proposed.