Cystic Cholangiocytes Research Articles

Dysregulation of the Scribble/YAP/β-catenin axis sustains the fibroinflammatory response in a PKHD1-/- mouse model of congenital hepatic fibrosis.

Congenital hepatic fibrosis (CHF), a genetic cholangiopathy characterized by fibropolycystic changes in the biliary tree, is caused by mutations in the PKHD1gene, leading to defective fibrocystin (FPC), changes in planar cell polarity (PCP) and increased β-catenin-dependent chemokine secretion. In this study, we aimed at understanding the role of Scribble (a protein involved in PCP), Yes-associated protein (YAP), and β-catenin in the regulation of the fibroinflammatory phenotype of FPC-defective cholangiocytes. Immunohistochemistry showed that compared with wild type (WT) mice, in FPC-defective (Pkhd1del4/del4 ) mice nuclear expression of YAP/TAZ in cystic cholangiocytes, significantly increased and correlated with connective tissue growth factor (CTGF) expression and pericystic fibrosis, while Scribble expression on biliary cyst cells was markedly decreased. Cholangiocytes isolated from WT mice showed intense Scribble immunoreactivity at the membrane, but minimal nuclear expression of YAP, which conversely increased, together with CTGF, after small interfering RNA (siRNA) silencing of Scribble. In FPC-defective cholangiocytes, inhibition of YAP nuclear import reduced β-catenin nuclear expression, and CTGF, integrin β6, CXCL1, and CXCL10mRNA levels, whereas inhibition of β-catenin signaling did not affect nuclear translocation of YAP. Notably, siRNA silencing of Scribble and YAP in WT cholangiocytes mimics the fibroinflammatory changes of FPC-defective cholangiocytes. Conditional deletion of β-catenin in Pkhd1del4/del4 mice reduced cyst growth, inflammation and fibrosis, without affecting YAP nuclear expression. In conclusion, the defective anchor of Scribble to the membrane facilitates the nuclear translocation of YAP and β-catenin with gain of a fibroinflammatory phenotype. The Scribble/YAP/β-catenin axis is a critical factor in the sequence of events linking the genetic defect to fibrocystic trait of cholangiocytes in CHF.

Inhibition of NAE-dependent protein hyper-NEDDylation in cystic cholangiocytes halts cystogenesis in experimental models of polycystic liver disease.

BackgroundPolycystic liver diseases (PLDs) are genetic inherited disorders characterized by the progressive growth of numerous intrahepatic biliary cysts, which are the main cause of morbidity. Previous studies revealed that cystic cholangiocytes are characterized by endoplasmic reticulum stress and aberrant posttranslational modification (PTM) of proteins, in particular hyper‐SUMOylation, that promote PLD pathobiology. Protein NEDDylation is a newly characterized PTM that modulates a plethora of biological processes and its dysregulation is associated with the development and progression of several human diseases. However, the role of NEDDylation in PLD remains elusive.ObjectiveTo explore the role of protein NEDDylation in PLD and its potential therapeutic regulatory value.MethodsLevels and functional effects of NEDDylation, including response to Pevonedistat (first‐in‐class selective inhibitor of the NEDDylation E1 enzyme NAE), were assessed in vitro, in vivo, and/or in patients with PLD. NEDDylated protein levels in normal and cystic human cholangiocytes were assessed by immunoprecipitation, and the proteomic profile was further analyzed by mass spectrometry.Results and ConclusionThe genes involved in the NEDDylation pathway were found overexpressed (mRNA) in polycystic human and rat liver tissue, as well as in cystic cholangiocytes in culture, compared to controls. Elevated levels of NEDDylated proteins were further confirmed in cystic cholangiocytes in vitro, which diminished under Pevonedistat incubation. Pevonedistat promoted apoptotic cell death and reduced proliferation in cystic cholangiocytes in vitro. Comparative proteomic profiling of NEDD8‐immunoprecipitated proteins between normal and cystic cholangiocytes in culture reported candidate proteins involved in cystogenesis, mostly associated with protein biogenesis and quality control. All these data indicate that cystic cholangiocytes display increased protein NEDDylation, contributing to cell survival and proliferation, ultimately supporting hepatic cystogenesis. Targeting of protein hyper‐NEDDylation in cystic cholangiocytes inhibits cystogenesis in experimental models, representing a novel therapeutic opportunity in PLD.

Estrogens in polycystic liver disease: A target for future therapies?

Background and AimsPatients suffering from polycystic liver disease (PLD) can develop large liver volumes, leading to physical and psychological complaints, reducing quality of life. There is an unmet need for new therapies in these patients. Estrogen seems to be a promising target for new therapies. In this review, we summarize the available experimental and epidemiological evidence to unravel the role of estrogens and other female hormones in PLD, to answer clinical questions and identify new targets for therapy.MethodsWe identified all experimental and epidemiologial studies concerning estrogens or other female hormones and PLD, to answer pre‐defined clinial questions.ResultsFemale sex is the most important risk factor for the presence and severity of disease; estrogen supplementation enhances liver growth and after menopause, liver growth decreases. Experimental studies show the presence of the estrogen receptors alfa and beta on cystic cholangiocytes, and increased in vitro growth after administration of estrogen.ConclusionsBased on the available evidence, female PLD patients should be discouraged from taking estrogen‐containing contraceptives or hormone replacement therapy. Since liver growth rates decline after menopause, treatment decisions should be based on measured liver growth in postmenopausal women. Finally, blockage of estrogen receptors or estrogen production is a promising target for new therapies.

Targeting UBC9-mediated protein hyper-SUMOylation in cystic cholangiocytes halts polycystic liver disease in experimental models

Targeting UBC9-mediated protein hyper-SUMOylation in cystic cholangiocytes halts polycystic liver disease in experimental models

Synthetic Conjugates of Ursodeoxycholic Acid Inhibit Cystogenesis in Experimental Models of Polycystic Liver Disease.

Background and AimsPolycystic liver diseases (PLDs) are genetic disorders characterized by progressive development of symptomatic biliary cysts. Current surgical and pharmacological approaches are ineffective, and liver transplantation represents the only curative option. Ursodeoxycholic acid (UDCA) and histone deacetylase 6 inhibitors (HDAC6is) have arisen as promising therapeutic strategies, but with partial benefits.Approach and ResultsHere, we tested an approach based on the design, synthesis, and validation of a family of UDCA synthetic conjugates with selective HDAC6i capacity (UDCA‐HDAC6i). Four UDCA‐HDAC6i conjugates presented selective HDAC6i activity, UDCA‐HDAC6i #1 being the most promising candidate. UDCA orientation within the UDCA‐HDAC6i structure was determinant for HDAC6i activity and selectivity. Treatment of polycystic rats with UDCA‐HDAC6i #1 reduced their hepatomegaly and cystogenesis, increased UDCA concentration, and inhibited HDAC6 activity in liver. In cystic cholangiocytes UDCA‐HDAC6i #1 restored primary cilium length and exhibited potent antiproliferative activity. UDCA‐HDAC6i #1 was actively transported into cells through BA and organic cation transporters.ConclusionsThese UDCA‐HDAC6i conjugates open a therapeutic avenue for PLDs.

Targeting UBC9-mediated protein hyper-SUMOylation in cystic cholangiocytes halts polycystic liver disease in experimental models

Background & Aims:Polycystic liver diseases (PLDs) are genetic disorders characterized by progressive development of multiple fluid-filled biliary cysts. Most PLD-causative genes participate in protein biogenesis and/or transport. Post-translational modifications (PTMs) are implicated in protein stability, localization and activity, contributing to human pathobiology; however, their role in PLD is unknown. Herein, we aimed to unveil the role of protein SUMOylation in PLD and its potential therapeutic targeting.Methods:Levels and functional effects of SUMOylation, along with response to S-adenosylmethionine (SAMe, inhibitor of the SUMOylation enzyme UBC9) and/or short-hairpin RNAs (shRNAs) against UBE2I (UBC9), were evaluated in vitro, in vivo and/or in patients with PLD. SUMOylated proteins were determined by immunoprecipitation and proteomic analyses by mass spectrometry.Results:Most SUMOylation-related genes were found overexpressed (mRNA) in polycystic human and rat liver tissue, as well as in cystic cholangiocytes in culture compared to controls. Increased SUMOylated protein levels were also observed in cystic human cholangiocytes in culture, which decreased after SAMe administration. Chronic treatment of polycystic (PCK: Pkdhl-mut) rats with SAMe halted hepatic cystogenesis and fibrosis, and reduced liver/body weight ratio and liver volume. In vitro, both SAMe and shRNA-mediated UBE2I knockdown increased apoptosis and reduced cell proliferation of cystic cholangiocytes. High-throughput proteomic analysis of SUM01-immunoprecipitated proteins in cystic cholangiocytes identified candidates involved in protein biogenesis, ciliogenesis and proteasome degradation. Accordingly, SAMe hampered proteasome hyperactivity in cystic cholangiocytes, leading to activation of the unfolded protein response and stress-related apoptosis.Conclusions:Cystic cholangiocytes exhibit increased SUMOylation of proteins involved in cell survival and proliferation, thus promoting hepatic cystogenesis. Inhibition of protein SUMOylation with SAMe halts PLD, representing a novel therapeutic strategy.

Targeting UBC9-mediated protein hyper-SUMOylation in cystic cholangiocytes halts polycystic liver disease in experimental models

Targeting UBC9-mediated protein hyper-SUMOylation in cystic cholangiocytes halts polycystic liver disease in experimental models

Proteostasis improvement in cystic cholangiocytes alleviates endoplasmic reticulum stress and halts polycystic liver disease

Proteostasis improvement in cystic cholangiocytes alleviates endoplasmic reticulum stress and halts polycystic liver disease

Proteostasis disturbances and endoplasmic reticulum stress contribute to polycystic liver disease: New therapeutic targets

Polycystic liver diseases (PLDs) are genetic disorders characterized by progressive development of multiple biliary cysts. Recently, novel PLD-causative genes, encoding for endoplasmic reticulum (ER)-resident proteins involved in protein biogenesis and transport, were identified. We hypothesized that aberrant proteostasis contributes to PLD pathogenesis, representing a potential therapeutic target. ER stress was analysed at transcriptional (qPCR), proteomic (mass spectrometry), morphological (transmission electron microscopy, TEM) and functional (proteasome activity) levels in different PLD models. The effect of ER stress inhibitors [4-phenylbutyric acid (4-PBA)] and/or activators [tunicamycin (TM)] was tested in polycystic (PCK) rats and cystic cholangiocytes in vitro. The expression levels of unfolded protein response (UPR) components were upregulated in liver tissue from PLD patients and PCK rats, as well as in primary cultures of human and rat cystic cholangiocytes, compared to normal controls. Cystic cholangiocytes showed altered proteomic profiles, mainly related to proteostasis (ie synthesis, folding, trafficking and degradation of proteins), marked enlargement of the ER lumen (by TEM) and hyperactivation of the proteasome. Notably, chronic treatment of PCK rats with 4-PBA decreased liver weight, as well as both liver and cystic volumes, of animals under baseline conditions or after TM administration compared to controls. In vitro, 4-PBA downregulated the expression (mRNA) of UPR effectors, normalized proteomic profiles related to protein synthesis, folding, trafficking and degradation and reduced the proteasome hyperactivity in cystic cholangiocytes, reducing their hyperproliferation and apoptosis. Restoration of proteostasis in cystic cholangiocytes with 4-PBA halts hepatic cystogenesis, emerging as a novel therapeutic strategy.

Inhibition of NAE‐dependent protein hyper‐NEDDylation in cystic cholangiocytes halts cystogenesis in experimental models of polycystic liver disease

Inhibition of NAE‐dependent protein hyper‐NEDDylation in cystic cholangiocytes halts cystogenesis in experimental models of polycystic liver disease

Role of TGR5 (GPBAR1) in Liver Disease.

TGR5 (GPBAR1) is a G protein-coupled receptor activated by primary and secondary bile acids, which is expressed in different nonparenchymal cells of the liver, such as sinusoidal endothelial cells, Kupffer cells, cholangiocytes as well as activated hepatic stellate cells. In liver, TGR5 modulates microcirculation, inflammation, regeneration, biliary secretion and proliferation as well as gallbladder filling. Absence of TGR5 renders mice more susceptible toward infectious, inflammatory, metabolic as well as cholestatic liver injuries. It is unknown whether TGR5 plays a role in the pathogenesis of human nonalcoholic steatohepatitis and cholestatic liver diseases such as primary sclerosing cholangitis and primary biliary cholangitis. However, overexpression of TGR5 has been detected in human intra- and extrahepatic cholangiocarcinoma as well as in cystic cholangiocytes, where the receptor promotes cell proliferation, anti-apoptosis as well as cyst growth. While TGR5 agonists may improve various aspects of metabolic, inflammatory, and cholestatic liver diseases, TGR5 inhibitors may attenuate disease progression in polycystic liver disease and cholangiocarcinoma.

Combination of a Histone Deacetylase 6 Inhibitor and a Somatostatin Receptor Agonist Synergistically Reduces Hepatorenal Cystogenesis in an Animal Model of Polycystic Liver Disease

Hepatic cystogenesis in polycystic liver disease (PLD) is associated with abnormalities in multiple cellular processes, including elevated cAMP and overexpression of histone deacetylase 6 (HDAC6). Disease progression in polycystic kidney (PCK) rats (an animal model of PLD) is attenuated by inhibition of either cAMP production or HDAC6. Therefore, we hypothesized that concurrent targeting of HDAC6 and cAMP would synergistically reduce cyst growth. Changes in hepatorenal cystogenesis were examined in PCK rats treated with a pan-HDAC inhibitor, panobinostat; three specific HDAC6 inhibitors, ACY-1215, ACY-738, and ACY-241; and a combination of ACY-1215 and the somatostatin receptor analogue, pasireotide. We also assessed effects of ACY-1215 and pasireotide alone and in combination on cell proliferation, cAMP production, and expression of acetylated α-tubulin invitro in cultured cholangiocytes and the length of primary cilia and the frequency of ciliated cholangiocytes invivo in PCK rats. Panobinostat and all three HDAC6 inhibitors decreased hepatorenal cystogenesis in PCK rats. ACY-1215 was more effective than other HDAC inhibitors and was chosen for combinational treatment. ACY-1215+pasireotide combination synergistically reduced cyst growth and increased length of primary cilia in PCK rats. In cultured cystic cholangiocytes, ACY-1215+pasireotide combination concurrently decreased cell proliferation and inhibited cAMP levels. These data suggest that the combination of drugs that inhibit HDAC6 and cAMP may be an effective therapy for PLD.

TGR5 contributes to hepatic cystogenesis in rodents with polycystic liver diseases through cyclic adenosine monophosphate/Gαs signaling.

TGR5 contributes to hepatic cystogenesis by increasing cAMP and enhancing cholangiocyte proliferation; our data suggest that a TGR5 antagonist alone or concurrently with somatostatin receptor agonists represents a potential therapeutic approach in polycystic liver disease. (Hepatology 2017;66:1197-1218).

Ursodeoxycholic acid inhibits hepatic cystogenesis in experimental models of polycystic liver disease

Polycystic liver diseases (PLDs) are genetic disorders characterized by progressive biliary cystogenesis. Current therapies show short-term and/or modest beneficial effects. Cystic cholangiocytes hyperproliferate as a consequence of diminished intracellular calcium levels ([Ca(2+)]i). Here, the therapeutic value of ursodeoxycholic acid (UDCA) was investigated. Effect of UDCA was examined in vitro and in polycystic (PCK) rats. Hepatic cystogenesis and fibrosis, and the bile acid (BA) content were evaluated from the liver, bile, serum, and kidneys by HPLC-MS/MS. Chronic treatment of PCK rats with UDCA inhibits hepatic cystogenesis and fibrosis, and improves their motor behaviour. As compared to wild-type animals, PCK rats show increased BA concentration ([BA]) in liver, similar hepatic Cyp7a1 mRNA levels, and diminished [BA] in bile. Likewise, [BA] is increased in cystic fluid of PLD patients compared to their matched serum levels. In PCK rats, UDCA decreases the intrahepatic accumulation of cytotoxic BA, normalizes their diminished [BA] in bile, increases the BA secretion in bile and diminishes the increased [BA] in kidneys. In vitro, UDCA inhibits the hyperproliferation of polycystic human cholangiocytes via a PI3K/AKT/MEK/ERK1/2-dependent mechanism without affecting apoptosis. Finally, the presence of glycodeoxycholic acid promotes the proliferation of polycystic human cholangiocytes, which is inhibited by both UDCA and tauro-UDCA. UDCA was able to halt the liver disease of a rat model of PLD through inhibiting cystic cholangiocyte hyperproliferation and decreasing the levels of cytotoxic BA species in the liver, which suggests the use of UDCA as a potential therapeutic tool for PLD patients.

Overexpression of Aquaporin 1 on cysts of patients with polycystic liver disease

Polycystic liver disease (PCLD) represents a group of genetic disorders that include autosomal dominant polycystic kidney disease (ADPKD) and isolated polycystic liver disease (iPCLD). There is currently no definitive treatment except for liver transplantation. The aim of this study was to assess the expression level of aquaporin 1 (AQP1) on the PCLD cysts with different sizes and provide the potential therapeutic target. We collected 3 normal bile ducts, and recruited 8 patients with simple liver cyst disease, 24 patients with ADPKD, and 17 patients with iPCLD. AQP1 expression in different types of cyst walls and in normal bile ducts was detected using real time quantitative PCR, western blot and immunofluorescence staining. We also compared AQP1 expression levels in cysts of different sizes. Besides, ionic concentrations, pH and osmolality of cyst fluid were analyzed. The results showed that AQP1 expression in PCLD cysts was significantly higher than that in simple liver cysts and the normal bile ducts. In addition, a comparable increasing trend was found in cysts of smaller sizes to cysts of larger sizes. pH values, the sodium and chloride concentrations were higher in cyst fluid than that in the serum. AQP1 was overexpressed in cystic cholangiocytes. A tendency of increased AQP1 protein expression in correlation with the cyst size was also found. These observations offered a direction into the molecular mechanisms of cyst expansion and maybe provide new treatment strategies to reduce fluid secretion into liver cysts.

Inhibition of metalloprotease hyperactivity in cystic cholangiocytes halts the development of polycystic liver diseases

ObjectivePolycystic liver diseases (PCLDs) are genetic disorders characterised by progressive bile duct dilatation and/or cyst development. Their pathogenesis is a consequence of hyperproliferation, hypersecretion and microRNA alterations in cholangiocytes. Here...

HDAC6 Is Overexpressed in Cystic Cholangiocytes and Its Inhibition Reduces Cystogenesis

Polycystic liver disease (PLD) is a member of the cholangiopathies, a group of liver diseases in which cholangiocytes, the epithelia lining of the biliary tree, are the target cells. PLDs are caused by mutations in genes involved in intracellular signaling pathways, cell cycle regulation, and ciliogenesis, among others. We previously showed that cystic cholangiocytes have abnormal cell cycle profiles and malfunctioning cilia. Because histone deacetylase 6 (HDAC6) plays an important role in both cell cycle regulation and ciliary disassembly, we examined the role of HDAC6 in hepatic cystogenesis. HDAC6 protein was increased sixfold in cystic liver tissue and in cultured cholangiocytes isolated from both PCK rats (an animal model of PLD) and humans with PLD. Furthermore, pharmacological inhibition of HDAC6 by Tubastatin-A, Tubacin, and ACY-1215 decreased proliferation of cystic cholangiocytes in a dose- and time-dependent manner, and inhibited cyst growth in three-dimensional cultures. Importantly, ACY-1215 administered to PCK rats diminished liver cyst development and fibrosis. In summary, we show that HDAC6 is overexpressed in cystic cholangiocytes both invitro and invivo, and its pharmacological inhibition reduces cholangiocyte proliferation and cyst growth. These data suggest that HDAC6 may represent a potential novel therapeutic target for cases of PLD.

Centrosomal Abnormalities Characterize Human and Rodent Cystic Cholangiocytes and Are Associated with Cdc25A Overexpression

Hepatic cystogenesis in polycystic liver diseases is associated with abnormalities of cholangiocyte cilia. Given the crucial association between cilia and centrosomes, we tested the hypothesis that centrosomal defects occur in cystic cholangiocytes of rodents (Pkd2(WS25/-) mice and PCK rats) and of patients with polycystic liver diseases, contributing to disturbed ciliogenesis and cyst formation. We examined centrosomal cytoarchitecture in control and cystic cholangiocytes, the effects of centrosomal abnormalities on ciliogenesis, and the role of the cell-cycle regulator Cdc25A in centrosomal defects by depleting cholangiocytes of Cdc25A invitro and invivo and evaluating centrosome morphology, cell-cycle progression, proliferation, ciliogenesis, and cystogenesis. The cystic cholangiocytes had atypical centrosome positioning, supernumerary centrosomes, multipolar spindles, and extra cilia. Structurally aberrant cilia were present in cystic cholangiocytes during ciliogenesis. Depletion of Cdc25A resulted in i) a decreased number of centrosomes and multiciliated cholangiocytes, ii) an increased fraction of ciliated cholangiocytes with longer cilia, iii) a decreased proportion of cholangiocytes in G1/G0 and S phases of the cell cycle, iv) decreased cell proliferation, and v) reduced cyst growth invitro and invivo. Our data support the hypothesis that centrosomal abnormalities in cholangiocytes are associated with aberrant ciliogenesis and that accelerated cystogenesis is likely due to overexpression of Cdc25A, providing additional evidence that pharmacological targeting of Cdc25A has therapeutic potential in polycystic liver diseases.

Pasireotide is more effective than octreotide in reducing hepatorenal cystogenesis in rodents with polycystic kidney and liver diseases

In polycystic liver (PLD) and kidney (PKD) diseases, increased cyclic adenosine monophosphate (cAMP) levels trigger hepatorenal cystogenesis. A reduction of the elevated cAMP by targeting somatostatin receptors (SSTRs) with octreotide (OCT; a somatostatin analog that preferentially binds to SSTR2) inhibits cyst growth. Here we compare the effects of OCT to pasireotide (PAS; a more potent somatostatin analog with broader receptor specificity) on: (1) cAMP levels, cell cycle, proliferation, and cyst expansion in vitro using cholangiocytes derived from control and PCK rats (a model of autosomal recessive PKD [ARPKD]), healthy human beings, and patients with autosomal dominant PKD (ADPKD); and (2) hepatorenal cystogenesis in vivo in PCK rats and Pkd2(WS25/-) mice (a model of ADPKD). Expression of SSTRs was assessed in control and cystic cholangiocytes of rodents and human beings. Concentrations of insulin-like growth factor 1 (IGF1) and vascular endothelial growth factor (VEGF) (both involved in indirect action of somatostatin analogs), and expression and localization of SSTRs after treatment were evaluated. We found that PAS was more potent (by 30%-45%) than OCT in reducing cAMP and cell proliferation, affecting cell cycle distribution, decreasing growth of cultured cysts in vitro, and inhibiting hepatorenal cystogenesis in vivo in PCK rats and Pkd2(WS25/-) mice. The levels of IGF1 (but not VEGF) were reduced only in response to PAS. Expression of SSTR1 and SSTR2 (but not SSTR3 and SSTR5) was decreased in cystic cholangiocytes compared to control. Although both OCT and PAS increased the immunoreactivity of SSTR2, only PAS up-regulated SSTR1; neither drug affected cellular localization of SSTRs. PAS is more effective than OCT in reducing hepatorenal cystogenesis in rodent models; therefore, it might be more beneficial for the treatment of PKD and PLD.

Altered store operated calcium entry increases cyclic 3',5'-adenosine monophosphate production and extracellular signal-regulated kinases 1 and 2 phosphorylation in polycystin-2-defective cholangiocytes.

Mutations in polycystins (PC1 or PC2/TRPP2) cause progressive polycystic liver disease (PLD). In PC2-defective mice, cyclic 3',5'-adenosine monophosphate/ protein kinase A (cAMP/PKA)-dependent activation of extracellular signal-regulated kinase/ mammalian target of rapamycin (ERK-mTOR) signaling stimulates cyst growth. We investigated the mechanisms connecting PC2 dysfunction to altered Ca(2+) and cAMP production and inappropriate ERK signaling in PC2-defective cholangiocytes. Cystic cholangiocytes were isolated from PC2 conditional-KO (knockout) mice (Pkd2(flox/-) :pCxCreER™; hence, called Pkd2KO) and compared to cholangiocytes from wild-type mice (WT). Our results showed that, compared to WT cells, in PC2-defective cholangiocytes (Pkd2KO), cytoplasmic and ER-Ca(2+) (measured with Fura-2 and Mag-Fluo4) levels are decreased and store-operated Ca(2+) entry (SOCE) is inhibited, whereas the expression of Ca(2+) -sensor stromal interaction molecule 1 (STIM1) and store-operated Ca(2+) channels (e.g., the Orai1 channel) are unchanged. In Pkd2KO cells, ER-Ca(2+) depletion increases cAMP and PKA-dependent ERK1/2 activation and both are inhibited by STIM1 inhibitors or by silencing of adenylyl cyclase type 6 (AC6). These data suggest that PC2 plays a key role in SOCE activation and inhibits the STIM-dependent activation of AC6 by ER Ca(2+) depletion. In PC2-defective cells, the interaction of STIM-1 with Orai channels is uncoupled, whereas coupling to AC6 is maximized. The resulting overproduction of cAMP, in turn, potently activates the PKA/ERK pathway. PLD, because of PC2 deficiency, represents the first example of human disease linked to the inappropriate activation of store-operated cAMP production.