Patrick L. Splinter

A Cellular Micro-RNA, let-7i, Regulates Toll-like Receptor 4 Expression and Contributes to Cholangiocyte Immune Responses against Cryptosporidium parvum Infection

Toll-like receptors (TLRs) are important pathogen recognition molecules and are key to epithelial immune responses to microbial infection. However, the molecular mechanisms that regulate TLR expression in epithelia are obscure. Micro-RNAs play important roles in a wide range of biological events through post-transcriptional suppression of target mRNAs. Here we report that human biliary epithelial cells (cholangiocytes) express let-7 family members, micro-RNAs with complementarity to TLR4 mRNA. We found that let-7 regulates TLR4 expression via post-transcriptional suppression in cultured human cholangiocytes. Infection of cultured human cholangiocytes with Cryptosporidium parvum, a parasite that causes intestinal and biliary disease, results in decreased expression of primary let-7i and mature let-7 in a MyD88/NF-κB-dependent manner. The decreased let-7 expression is associated with C. parvum-induced up-regulation of TLR4 in infected cells. Moreover, experimentally induced suppression or forced expression of let-7i causes reciprocal alterations in C. parvum-induced TLR4 protein expression, and consequently, infection dynamics of C. parvum in vitro. These results indicate that let-7i regulates TLR4 expression in cholangiocytes and contributes to epithelial immune responses against C. parvum infection. Furthermore, the data raise the possibility that micro-RNA-mediated post-transcriptional pathways may be critical to host-cell regulatory responses to microbial infection in general.

The Water Channel Aquaporin-8 Is Mainly Intracellular in Rat Hepatocytes, and Its Plasma Membrane Insertion Is Stimulated by Cyclic AMP

We previously found that water transport across hepatocyte plasma membranes occurs mainly via a non-channel mediated pathway. Recently, it has been reported that mRNA for the water channel, aquaporin-8 (AQP8), is present in hepatocytes. To further explore this issue, we studied protein expression, subcellular localization, and regulation of AQP8 in rat hepatocytes. By subcellular fractionation and immunoblot analysis, we detected anN-glycosylated band of ∼34 kDa corresponding to AQP8 in hepatocyte plasma and intracellular microsomal membranes. Confocal immunofluorescence microscopy for AQP8 in cultured hepatocytes showed a predominant intracellular vesicular localization. Dibutyryl cAMP (Bt2cAMP) stimulated the redistribution of AQP8 to plasma membranes. Bt2cAMP also significantly increased hepatocyte membrane water permeability, an effect that was prevented by the water channel blocker dimethyl sulfoxide. The microtubule blocker colchicine but not its inactive analog lumicolchicine inhibited the Bt2cAMP effect on both AQP8 redistribution to cell surface and hepatocyte membrane water permeability. Our data suggest that in rat hepatocytes AQP8 is localized largely in intracellular vesicles and can be redistributed to plasma membranes via a microtubule-depending, cAMP-stimulated mechanism. These studies also suggest that aquaporins contribute to water transport in cAMP-stimulated hepatocytes, a process that could be relevant to regulated hepatocyte bile secretion.

Multiple TLRs Are Expressed in Human Cholangiocytes and Mediate Host Epithelial Defense Responses to Cryptosporidium parvum via Activation of NF-κB

Infection of epithelial cells by Cryptosporidium parvum triggers a variety of host-cell innate and adaptive immune responses including release of cytokines/chemokines and up-regulation of antimicrobial peptides. The mechanisms that trigger these host-cell responses are unclear. Thus, we evaluated the role of TLRs in host-cell responses during C. parvum infection of cultured human biliary epithelia (i.e., cholangiocytes). We found that normal human cholangiocytes express all known TLRs. C. parvum infection of cultured cholangiocytes induces the selective recruitment of TLR2 and TLR4 to the infection sites. Activation of several downstream effectors of TLRs including IL-1R-associated kinase, p-38, and NF-κB was detected in infected cells. Transfection of cholangiocytes with dominant-negative mutants of TLR2 and TLR4, as well as the adaptor molecule myeloid differentiation protein 88 (MyD88), inhibited C. parvum-induced activation of IL-1R-associated kinase, p-38, and NF-κB. Short-interfering RNA to TLR2, TLR4, and MyD88 also blocked C. parvum-induced NF-κB activation. Moreover, C. parvum selectively up-regulated human β-defensin-2 in directly infected cells, and inhibition of TLR2 and TLR4 signals or NF-κB activation were each associated with a reduction of C. parvum-induced human β-defensin-2 expression. A significantly higher number of parasites were detected in cells transfected with a MyD88 dominant-negative mutant than in the control cells at 48–96 h after initial exposure to parasites, suggesting MyD88-deficient cells were more susceptible to infection. These findings demonstrate that cholangiocytes express a variety of TLRs, and suggest that TLR2 and TLR4 mediate cholangiocyte defense responses to C. parvum via activation of NF-κB.

Cholangiocyte cilia express TRPV4 and detect changes in luminal tonicity inducing bicarbonate secretion

Cholangiocytes, epithelial cells lining the biliary tree, have primary cilia extending from their apical membrane into the ductal lumen. Although important in disease, cilia also play a vital role in normal cellular functions. We reported that cholangiocyte cilia are sensory organelles responding to mechanical stimuli (i.e., luminal fluid flow) by alterations in intracellular Ca2+ and cAMP. Because cholangiocyte cilia are also ideally positioned to detect changes in composition and tonicity of bile, we hypothesized that cilia also function as osmosensors. TRPV4, a Ca2+-permeable ion channel, has been implicated in signal transduction of osmotic stimuli. Using purified rat cholangiocytes and perfused intrahepatic bile duct units (IBDUs), we found that TRPV4 is expressed on cholangiocyte cilia, and that hypotonicity induces an increase in intracellular Ca2+ in a TRPV4-, ciliary-, and extracellular calcium-dependent manner. The osmosensation of luminal tonicity by ciliary TRPV4 induces bicarbonate secretion, the main determinant of ductal bile formation, by a mechanism involving apical ATP release. Furthermore, the activation of TRPV4 in vivo, by its specific agonist, 4αPDD, induces an increase in bile flow as well as ATP release and bicarbonate secretion. Our results suggest that cholangiocyte primary cilia play an important role in ductal bile formation by acting as osmosensors.

MicroRNA15a modulates expression of the cell-cycle regulator Cdc25A and affects hepatic cystogenesis in a rat model of polycystic kidney disease

Hyperproliferation of bile duct epithelial cells due to cell-cycle dysregulation is a key feature of cystogenesis in polycystic liver diseases (PCLDs). Recent evidence suggests a regulatory role for microRNAs (miRNAs) in a variety of biological processes, including cell proliferation. We therefore hypothesized that miRNAs may be involved in the regulation of selected components of the cell cycle and might contribute to hepatic cystogenesis. We found that the cholangiocyte cell line PCK-CCL, which is derived from the PCK rat, a model of autosomal recessive polycystic kidney disease (ARPKD), displayed global changes in miRNA expression compared with normal rat cholangiocytes (NRCs). More specific analysis revealed decreased levels of 1 miRNA, miR15a, both in PCK-CCL cells and in liver tissue from PCK rats and patients with a PCLD. The decrease in miR15a expression was associated with upregulation of its target, the cell-cycle regulator cell division cycle 25A (Cdc25A). Overexpression of miR15a in PCK-CCL cells decreased Cdc25A levels, inhibited cell proliferation, and reduced cyst growth. In contrast, suppression of miR15a in NRCs accelerated cell proliferation, increased Cdc25A expression, and promoted cyst growth. Taken together, these results suggest that suppression of miR15a contributes to hepatic cystogenesis through dysregulation of Cdc25A.

MicroRNA-513 Regulates B7-H1 Translation and Is Involved in IFN-γ-Induced B7-H1 Expression in Cholangiocytes

Biliary epithelial cells (cholangiocytes) respond to proinflammatory cytokines such as IFN-γ and actively participate in the regulation of biliary inflammatory response in the liver. B7-H1 (also known as CD274 or PD-L1) is a member of the B7 costimulatory molecules and plays a critical immunoregulatory role in cell-mediated immune responses. In this study, we show that resting human cholangiocytes in culture express B7-H1 mRNA, but not B7-H1 protein. IFN-γ induces B7-H1 protein expression and alters the microRNA (miRNA) expression profile in cholangiocytes. Of those IFN-γ-down-regulated miRNAs, we identified microRNA-513 (miR-513) with complementarity to the 3′-untranslated region of B7-H1 mRNA. Targeting of the B7-H1 3′-untranslated region by miR-513 results in translational repression. Transfection of cholangiocytes with an antisense oligonucleotide to miR-513 induces B7-H1 protein expression. Additionally, transfection of miR-513 precursor decreases IFN-γ-induced B7-H1 protein expression and consequently influences B7-H1-associated apoptotic cell death in cocultured Jurkat cells. Thus, miR-513 regulates B7-H1 translation and is involved in IFN-γ-induced B7-H1 expression in human cholangiocytes, suggesting a role for miRNA-mediated gene silencing in the regulation of cholangiocyte response to IFN-γ.

Cholangiocyte primary cilia are chemosensory organelles that detect biliary nucleotides via P2Y12 purinergic receptors

Cholangiocytes, the epithelial cells lining intrahepatic bile ducts, contain primary cilia, which are mechano- and osmosensory organelles detecting changes in bile flow and osmolality and transducing them into intracellular signals. Here, we asked whether cholangiocyte cilia are chemosensory organelles by testing the expression of P2Y purinergic receptors and components of the cAMP signaling cascade in cilia and their involvement in nucleotide-induced cAMP signaling in the cells. We found that P2Y(12) purinergic receptor, adenylyl cyclases (i.e., AC4, AC6, and AC8), and protein kinase A (i.e., PKA RI-beta and PKA RII-alpha regulatory subunits), exchange protein directly activated by cAMP (EPAC) isoform 2, and A-kinase anchoring proteins (i.e., AKAP150) are expressed in cholangiocyte cilia. ADP, an endogenous agonist of P2Y(12) receptors, perfused through the lumen of isolated rat intrahepatic bile ducts or applied to the ciliated apical surface of normal rat cholangiocytes (NRCs) in culture induced a 1.9- and 1.5-fold decrease of forskolin-induced cAMP levels, respectively. In NRCs, the forskolin-induced cAMP increase was also lowered by 1.3-fold in response to ATP-gammaS, a nonhydrolyzed analog of ATP but was not affected by UTP. The ADP-induced changes in cAMP levels in cholangiocytes were abolished by chloral hydrate (a reagent that removes cilia) and by P2Y(12) siRNAs, suggesting that cilia and ciliary P2Y(12) are involved in nucleotide-induced cAMP signaling. In conclusion, cholangiocyte cilia are chemosensory organelles that detect biliary nucleotides through ciliary P2Y(12) receptors and transduce corresponding signals into a cAMP response.

Up‐regulation of microRNA 506 leads to decreased Cl−/HCO3− anion exchanger 2 expression in biliary epithelium of patients with primary biliary cirrhosis

Cl−/HCO  3− anion exchanger 2 (AE2) participates in intracellular pH homeostasis and secretin‐stimulated biliary bicarbonate secretion. AE2/SLC4A2 gene expression is reduced in liver and blood mononuclear cells from patients with primary biliary cirrhosis (PBC). Our previous findings of hepatic and immunological features mimicking PBC in Ae2‐deficient mice strongly suggest that decreased AE2 expression might be involved in the pathogenesis of PBC. Here, we tested the potential role of microRNA 506 (miR‐506) — predicted as candidate to target AE2 mRNA — for the decreased expression of AE2 in PBC. Real‐time quantitative polymerase chain reaction showed that miR‐506 expression is increased in PBC livers versus normal liver specimens. In situ hybridization in liver sections confirmed that miR‐506 is up‐regulated in the intrahepatic bile ducts of PBC livers, compared with normal and primary sclerosing cholangitis livers. Precursor‐mediated overexpression of miR‐506 in SV40‐immortalized normal human cholangiocytes (H69 cells) led to decreased AE2 protein expression and activity, as indicated by immunoblotting and microfluorimetry, respectively. Moreover, miR‐506 overexpression in three‐dimensional (3D)‐cultured H69 cholangiocytes blocked the secretin‐stimulated expansion of cystic structures developed under the 3D conditions. Luciferase assays and site‐directed mutagenesis demonstrated that miR‐506 specifically may bind the 3′untranslated region (3′UTR) of AE2 messenger RNA (mRNA) and prevent protein translation. Finally, cultured PBC cholangiocytes showed decreased AE2 activity, together with miR‐506 overexpression, compared to normal human cholangiocytes, and transfection of PBC cholangiocytes with anti‐miR‐506 was able to improve their AE2 activity. Conclusion: miR‐506 is up‐regulated in cholangiocytes from PBC patients, binds the 3′UTR region of AE2 mRNA, and prevents protein translation, leading to diminished AE2 activity and impaired biliary secretory functions. In view of the putative pathogenic role of decreased AE2 in PBC, miR‐506 may constitute a potential therapeutic target for this disease. (HEPATOLOGY 2012)

NFκB p50-CCAAT/enhancer-binding protein β (C/EBPβ)-mediated transcriptional repression of microRNA let-7i following microbial infection.

MicroRNAs, central players of numerous cellular processes, regulate mRNA stability or translational efficiency. Although these molecular events are established, the mechanisms regulating microRNA function and expression remain largely unknown. The microRNA let-7i regulates Toll-like receptor 4 expression. Here, we identify a novel transcriptional mechanism induced by the protozoan parasite Cryptosporidium parvum and Gram(−) bacteria-derived lipopolysaccharide (LPS) mediating let-7i promoter silencing in human biliary epithelial cells (cholangiocytes). Using cultured cholangiocytes, we show that microbial stimulus decreased let-7i expression, and promoter activity. Analysis of the mechanism revealed that microbial infection promotes the formation of a NFκB p50-C/EBPβ silencer complex in the regulatory sequence. Chromatin immunoprecipitation assays (ChIP) demonstrated that the repressor complex binds to the let-7i promoter following microbial stimulus and promotes histone-H3 deacetylation. Our results provide a novel mechanism of transcriptional regulation of cholangiocyte let-7i expression following microbial insult, a process with potential implications for epithelial innate immune responses in general.

Engineered measles virus as a novel oncolytic viral therapy system for hepatocellular carcinoma

The oncolytic measles virus Edmonston strain (MV‐Edm), a nonpathogenic virus targeting cells expressing abundant CD46, selectively destroys neoplastic tissue. Clinical development of MV‐Edm would benefit from noninvasive monitoring strategies to determine the speed and extent of the spread of the virus in treated patients and the location of virus‐infected cells. We evaluated recombinant MV‐Edm expressing carcinoembryonic antigen (CEA) or the human sodium iodide symporter (hNIS) for oncolytic potential in hepatocellular carcinoma (HCC) and efficiency in tracking viruses in vivo by noninvasive monitoring. CD46 expression in human HCC and primary hepatocytes was assessed by flow cytometry and immunohistochemistry. Infectivity, syncytium formation, and cytotoxicity of recombinant MV‐Edm in HCC cell lines were evaluated by fluorescence microscopy, crystal violet staining, and the MTS assay. Transgene expression in HCC cell lines after infection with recombinant MV‐Edm in vitro and in vivo was assessed by CEA concentration, 125I‐uptake, and 123I‐imaging studies. Toxicology studies were performed in IfnarKO×CD46 transgenic mice. The CD46 receptor was highly expressed in HCC compared to nonmalignant hepatic tissue. Recombinant MV‐Edm efficiently infected HCC cell lines, resulting in extensive syncytium formation followed by cell death. Transduction of HCC cell lines and subcutaneous HCC xenografts with recombinant MV‐Edm resulted in high‐level expression of transgenes in vitro and in vivo. MV‐Edm was nontoxic in susceptible mice. Intratumoral and intravenous therapy with recombinant MV‐Edm resulted in inhibition of tumor growth and prolongation of survival with complete tumor regression in up to one third of animals. In conclusion, engineered MV‐Edm may be a potent and novel cancer gene therapy system for HCC. MV‐Edm expressing CEA or hNIS elicited oncolytic effects in human HCC cell lines in vitro and in vivo, enabling the spread of the virus to be monitored in a noninvasive manner. (HEPATOLOGY 2006;44:1465–1477.)