LCK inhibition downregulates YAP activity and is therapeutic in patient-derived models of cholangiocarcinoma.

BACKGROUND & AIMS: There is an unmet need to develop novel, effective medical therapies for cholangiocarcinoma (CCA). The Hippo pathway effector, Yes-associated protein (YAP), is oncogenic in CCA, but has historically been difficult to target therapeutically. Recently, we described a novel role for the LCK proto-oncogene, Src family tyrosine kinase (LCK) in activating YAP through tyrosine phosphorylation. This led to the hypothesis that LCK is a viable therapeutic target in CCA via regulation of YAP activity. METHODS: A novel tyrosine kinase inhibitor with relative selectivity for LCK, NTRC 0652-0, was pharmacodynamically profiled in vitro and in CCA cells. A panel of eight CCA patient-derived organoids were characterized and tested for sensitivity to NTRC 0652-0. Two patient-derived xenograft models bearing fibroblast growth factor receptor 2 (FGFR2)-rearrangements were utilized for in vivo assessment of pharmacokinetics, toxicity, and efficacy. RESULTS: NTRC 0652-0 demonstrated selectivity for LCK inhibition in vitro and in CCA cells. LCK inhibition with NTRC 0652-0 led to decreased tyrosine phosphorylation, nuclear localization, and co-transcriptional activity of YAP, and resulted in apoptotic cell death in CCA cell lines. A subset of tested patient-derived organoids demonstrated sensitivity to NTRC 0652-0. CCAs with FGFR2 fusions were identified as a potentially susceptible and clinically relevant genetic subset. In patient-derived xenograft models of FGFR2 fusion-positive CCA, daily oral treatment with NTRC 0652-0 resulted in stable plasma and tumor drug levels, acceptable toxicity, decreased YAP tyrosine phosphorylation, and significantly decreased tumor growth. CONCLUSIONS: A novel LCK inhibitor, NTRC 0652-0, inhibited YAP signaling and demonstrated preclinical efficacy in CCA cell lines, and patient-derived organoid and xenograft models. IMPACT AND IMPLICATIONS: Although aberrant YAP activation is frequently seen in CCA, YAP targeted therapies are not yet clinically available. Herein we show that a novel LCK-selective tyrosine kinase inhibitor (NTRC 0652-0) effectively inhibits YAP tyrosine phosphorylation and cotranscriptional activity and is well tolerated and cytotoxic in multiple preclinical models. The data suggest this approach may be effective in CCA with YAP dependence or FGFR2 fusions, and these findings warrant further investigation in phase I clinical trials.

Platelet-derived growth factor regulates YAP transcriptional activity via Src family kinase dependent tyrosine phosphorylation.

The Hippo pathway effector YAP is implicated in the pathogenesis of cholangiocarcinoma (CCA). The Hippo pathway relies on signaling cross talk for its regulation. Given the importance of platelet derived growth factor receptor (PDGFR) signaling in CCA biology, our aim was to examine potential YAP regulation by PDGFR. We employed human and mouse CCA specimens and cell lines for these studies. Initially, we confirmed upregulation of PDGFRß and PDGFR ligands in human and mouse CCA specimens and cell lines. YAP, a transcriptional co-activator, was localized to the nucleus in human CCA specimens and a cell line, as well as patient derived xenografts (PDX). PDGFR pharmacologic inhibition led to a redistribution of YAP from the nucleus to cytosol and downregulation of YAP target genes in a human CCA cell line. siRNA silencing of PDGFR-ß similarly downregulated YAP target genes. YAP activation (nuclear localization and target gene expression) was regulated by Src family kinases (SFKs) downstream of PDGFR. SFK activity resulted in phosphorylation of YAP on tyrosine357 (YAPY357 ). The importance of YAPY357 phosphorylation in regulating YAP activation was confirmed utilizing the SB-1 cell line, a mouse cell line expressing YAP S127A precluding canonical serine phosphorylation. PDGFR inhibition decreased cellular abundance of the survival protein Mcl-1, a known YAP target gene, and accordingly increased cell death in CCA cells in vitro and in vivo. These preclinical data demonstrate that a PDGFR-SFK cascade regulates YAP activation via tyrosine phosphorylation in CCA. Inhibiting this cascade may provide a viable therapeutic strategy for this human malignancy.

A Hippo and Fibroblast Growth Factor Receptor Autocrine Pathway in Cholangiocarcinoma.

Herein, we have identified cross-talk between the Hippo and fibroblast growth factor receptor (FGFR) oncogenic signaling pathways in cholangiocarcinoma (CCA). Yes-associated protein (YAP) nuclear localization and up-regulation of canonical target genes was observed in CCA cell lines and a patient-derived xenograft (PDX). Expression of FGFR1, -2, and -4 was identified in human CCA cell lines, driven, in part, by YAP coactivation of TBX5. In turn, FGFR signaling in a cell line with minimal basal YAP expression induced its cellular protein expression and nuclear localization. Treatment of YAP-positive CCA cell lines with BGJ398, a pan-FGFR inhibitor, resulted in a decrease in YAP activation. FGFR activation of YAP appears to be driven largely by FGF5 activation of FGFR2, as siRNA silencing of this ligand or receptor, respectively, inhibited YAP nuclear localization. BGJ398 treatment of YAP-expressing cells induced cell death due to Mcl-1 depletion. In a YAP-associated mouse model of CCA, expression of FGFR 1, 2, and 4 was also significantly increased. Accordingly, BGJ398 treatment was tumor-suppressive in this model and in a YAP-positive PDX model. These preclinical data suggest not only that the YAP and Hippo signaling pathways culminate in an Mcl-1-regulated tumor survival pathway but also that nuclear YAP expression may be a biomarker to employ in FGFR-directed therapy.

Lipid-Induced Signaling Causes Release of Inflammatory Extracellular Vesicles From Hepatocytes.

BACKGROUND & AIMS: Hepatocyte cellular dysfunction and death induced by lipids and macrophage-associated inflammation are characteristics of nonalcoholic steatohepatitis (NASH). The fatty acid palmitate can activate death receptor 5 (DR5) on hepatocytes, leading to their death, but little is known about how this process contributes to macrophage-associated inflammation. We investigated whether lipid-induced DR5 signaling results in the release of extracellular vesicles (EVs) from hepatocytes, and whether these can induce an inflammatory macrophage phenotype. METHODS: Primary mouse and human hepatocytes and Huh7 cells were incubated with palmitate, its metabolite lysophosphatidylcholine, or diluent (control). The released EV were isolated, characterized, quantified, and applied to macrophages. C57BL/6 mice were placed on chow or a diet high in fat, fructose, and cholesterol to induce NASH. Some mice also were given the ROCK1 inhibitor fasudil; 2 weeks later, serum EVs were isolated and characterized by immunoblot and nanoparticle-tracking analyses. Livers were collected and analyzed by histology, immunohistochemistry, and quantitative polymerase chain reaction. RESULTS: Incubation of primary hepatocytes and Huh7 cells with palmitate or lysophosphatidylcholine increased their release of EVs, compared with control cells. This release was reduced by inactivating mediators of the DR5 signaling pathway or rho-associated, coiled-coil-containing protein kinase 1 (ROCK1) inhibition. Hepatocyte-derived EVs contained tumor necrosis factor-related apoptosis-inducing ligand and induced expression of interleukin 1ß and interleukin 6 messenger RNAs in mouse bone marrow-derived macrophages. Activation of macrophages required DR5 and receptor-interacting protein kinase 1. Administration of the ROCK1 inhibitor fasudil to mice with NASH reduced serum levels of EVs; this reduction was associated with decreased liver injury, inflammation, and fibrosis. CONCLUSIONS: Lipids, which stimulate DR5, induce release of hepatocyte EVs, which activate an inflammatory phenotype in macrophages. Strategies to inhibit ROCK1-dependent release of EVs by hepatocytes might be developed for the treatment of patients with NASH.

Mixed lineage kinase 3 mediates release of C-X-C motif ligand 10-bearing chemotactic extracellular vesicles from lipotoxic hepatocytes.

UNLABELLED: Mixed lineage kinase 3 (MLK3) deficiency reduces macrophage-associated inflammation in a murine model of nonalcoholic steatohepatitis (NASH). However, the mechanistic links between MLK3 activation in hepatocytes and macrophage-driven inflammation in NASH are uncharted. Herein, we report that MLK3 mediates the release of (C-X-C motif) ligand 10 (CXCL10)-laden extracellular vesicles (EVs) from lipotoxic hepatocytes, which induce macrophage chemotaxis. Primary mouse hepatocytes (PMHs) and Huh7 cells were treated with palmitate or lysophosphatidylcholine (LPC). Released EVs were isolated by differential ultracentrifugation. LPC treatment of PMH or Huh7 cells induced release of EVs, which was prevented by either genetic or pharmacological inhibition of MLK3. Mass spectrometry identified the potent chemokine, CXCL10, in the EVs, which was markedly enriched in EVs isolated from LPC-treated hepatocytes versus untreated cells. Green fluorescent protein (GFP)-tagged CXCL10 was present in vesicular structures and colocalized with the red fluorescent protein (RFP)-tagged EV marker, CD63, after LPC treatment of cotransfected Huh-7 cells. Either genetic deletion or pharmacological inhibition of MLK3 prevented CXCL10 enrichment in EVs. Treatment of mouse bone-marrow-derived macrophages with lipotoxic hepatocyte-derived EVs induced macrophage chemotaxis, an effect blocked by incubation with CXCL10-neutralizing antisera. MLK3-deficient mice fed a NASH-inducing diet had reduced concentrations of total plasma EVs and CXCL10 containing EVs compared to wild-type mice. CONCLUSIONS: During hepatocyte lipotoxicity, activated MLK3 induces the release of CXCL10-bearing vesicles from hepatocytes, which are chemotactic for macrophages.

TRAIL receptor deletion in mice suppresses the inflammation of nutrient excess.

BACKGROUND & AIMS: Low-grade chronic inflammation is a cardinal feature of the metabolic syndrome, yet its pathogenesis is not well defined. The purpose of this study was to examine the role of TRAIL receptor (TR) signaling in the pathogenesis of obesity-associated inflammation using mice with the genetic deletion of TR. METHODS: TR knockout (TR(-/-)) mice and their littermate wild-type (WT) mice were fed a diet high in saturated fat, cholesterol and fructose (FFC) or chow. Metabolic phenotyping, liver injury, and liver and adipose tissue inflammation were assessed. Chemotaxis and activation of mouse bone marrow-derived macrophages (BMDMϕ) was measured. RESULTS: Genetic deletion of TR completely repressed weight gain, adiposity and insulin resistance in FFC-fed mice. Moreover, TR(-/-) mice suppressed steatohepatitis, with essentially normal serum ALT, hepatocyte apoptosis and liver triglyceride accumulation. Gene array data implicated inhibition of macrophage-associated hepatic inflammation in the absence of the TR. In keeping with this, there was diminished accumulation and activation of inflammatory macrophages in liver and adipose tissue. TR(-/-) BMDMϕ manifest reduced chemotaxis and diminished activation of nuclear factor-κ B signaling upon activation by palmitate and lipopolysaccharide. CONCLUSIONS: These data advance the concept that macrophage-associated hepatic and adipose tissue inflammation of nutrient excess requires TR signaling.

A small molecule MST1/2 inhibitor accelerates murine liver regeneration with improved survival in models of steatohepatitis.

Dysfunctional liver regeneration following surgical resection remains a major cause of postoperative mortality and has no therapeutic options. Without targeted therapies, the current treatment paradigm relies on supportive therapy until homeostasis can be achieved. Pharmacologic acceleration of regeneration represents an alternative therapeutic avenue. Therefore, we aimed to generate a small molecule inhibitor that could accelerate liver regeneration with an emphasis on diseased models, which represent a significant portion of patients who require surgical resection and are often not studied. Utilizing a clinically approved small molecule inhibitor as a parent compound, standard medicinal chemistry approaches were utilized to generate a small molecule inhibitor targeting serine/threonine kinase 4/3 (MST1/2) with reduced off-target effects. This compound, mCLC846, was then applied to preclinical models of murine partial hepatectomy, which included models of diet-induced metabolic dysfunction-associated steatohepatitis (MASH). mCLC846 demonstrated on target inhibition of MST1/2 and reduced epidermal growth factor receptor inhibition. The inhibitory effects resulted in restored pancreatic beta-cell function and survival under diabetogenic conditions. Liver-specific cell-line exposure resulted in Yes-associated protein activation. Oral delivery of mCLC846 perioperatively resulted in accelerated murine liver regeneration and improved survival in diet-induced MASH models. Bulk transcriptional analysis of regenerating liver remnants suggested that mCLC846 enhanced the normal regenerative pathways and induced them following liver resection. Overall, pharmacological acceleration of liver regeneration with mCLC846 was feasible, had an acceptable therapeutic index, and provided a survival benefit in models of diet-induced MASH.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) protein-induced lysosomal translocation of proapoptotic effectors is mediated by phosphofurin acidic cluster sorting protein-2 (PACS-2).

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of liver cancer cell lines requires death receptor-5 (DR5)-dependent permeabilization of lysosomal membranes. Ligated DR5 triggers recruitment of the proapoptotic proteins Bim and Bax to lysosomes, releasing cathepsin B into the cytosol where it mediates mitochondria membrane permeabilization and activation of executioner caspases. Despite the requirement for lysosome membrane permeabilization during TRAIL-induced apoptosis, little is known about the mechanism that controls recruitment of Bim and Bax to lysosomal membranes. Here we report that TRAIL induces recruitment of the multifunctional sorting protein phosphofurin acidic cluster sorting protein-2 (PACS-2) to DR5-positive endosomes in Huh-7 cells where it forms an immunoprecipitatable complex with Bim and Bax on lysosomal membranes. shRNA-targeted knockdown of PACS-2 prevents recruitment of Bim or Bax to lysosomes, blunting the TRAIL-induced lysosome membrane permeabilization. Consistent with the reduced lysosome membrane permeabilization, shRNA knockdown of PACS-2 in Huh-7 cells reduced TRAIL-induced apoptosis and increased clonogenic cell survival. The determination that recombinant PACS-2 bound Bim but not Bax in vitro and that shRNA knockdown of Bim blocked Bax recruitment to lysosomes suggests that TRAIL/DR5 triggers endosomal PACS-2 to recruit Bim and Bax to lysosomes to release cathepsin B and induce apoptosis. Together, these findings provide insight into the lysosomal pathway of apoptosis.

Degradation of cIAPs contributes to hepatocyte lipoapoptosis.

Hepatocyte apoptosis is a hallmark of nonalcoholic steatohepatitis. We have previously observed that the saturated free fatty acids (FFAs) induce hepatocyte apoptosis in part via a death receptor 5 (DR5)-mediated signaling pathway. Cellular inhibitor of apoptosis protein 1 and 2 (cIAP-1 and cIAP-2) proteins are potent inhibitors of death receptor-mediated apoptosis. However, the role of the cIAPs in FFA-mediated hepatocyte apoptosis is unexplored. Our aim was to determine whether cIAPs are dysregulated during hepatocyte lipoapoptosis. cIAP proteins underwent rapid cellular elimination following treatment with the saturated FFAs palmitate (PA) and stearate. In contrast, PA did not decrease cIAP-1 and cIAP-2 mRNA expression in the cells. Degradation of cIAPs was dependent on their E3-ligase activity, suggesting that cIAPs undergo autoubiquitination that leads to proteasomal degradation. Huh-7 cells stably expressing shRNA targeting cIAP-1, but not cIAP-2, displayed enhanced sensitivity to PA-mediated apoptosis. Incubation with the SMAC mimetic JP1584, which induces rapid degradation of cIAPs, also enhanced PA-mediated apoptosis. Hepatocytes isolated from DR5 knockout mice exhibited reduced apoptosis following treatment with PA plus JP1584, implying that degradation of cIAPs sensitizes to DR5-mediated cell death pathways. A decrease of cIAP-1 was also observed in tissue from patients with nonalcoholic steatohepatitis compared with normal obese subjects. Collectively, these results implicate proteasomal degradation of cIAPs by FFA as a mechanism contributing to hepatocyte lipoapoptosis.

miR-25 targets TNF-related apoptosis inducing ligand (TRAIL) death receptor-4 and promotes apoptosis resistance in cholangiocarcinoma.

UNLABELLED: It has been established that microRNA expression and function contribute to phenotypic features of malignant cells, including resistance to apoptosis. Although targets and functional roles for a number of microRNAs have been described in cholangiocarcinoma, many additional microRNAs dysregulated in this tumor have not been assigned functional roles. In this study, we identify elevated miR-25 expression in malignant cholangiocarcinoma cell lines as well as patient samples. In cultured cells, treatment with the Smoothened inhibitor, cyclopamine, reduced miR-25 expression, suggesting Hedgehog signaling stimulates miR-25 production. Functionally, miR-25 was shown to protect cells against TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Correspondingly, antagonism of miR-25 in culture sensitized cells to apoptotic death. Computational analysis identified the TRAIL Death Receptor-4 (DR4) as a potential novel miR-25 target, and this prediction was confirmed by immunoblot, cell staining, and reporter assays. CONCLUSION: These data implicate elevated miR-25 levels in the control of tumor cell apoptosis in cholangiocarcinoma. The identification of the novel miR-25 target DR4 provides a mechanism by which miR-25 contributes to evasion of TRAIL-induced cholangiocarcinoma apoptosis.

Death receptor 5 signaling promotes hepatocyte lipoapoptosis.

Nonalcoholic steatohepatitis is characterized by hepatic steatosis, elevated levels of circulating free fatty acids (FFA), endoplasmic reticulum (ER) stress, and hepatocyte lipoapoptosis. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptor 5 (DR5) is significantly elevated in patients with nonalcoholic steatohepatitis, and steatotic hepatocytes demonstrate increased sensitivity to TRAIL-mediated cell death. Nonetheless, a role for TRAIL and/or DR5 in mediating lipoapoptotic pathways is unexplored. Here, we examined the contribution of DR5 death signaling to lipoapoptosis by free fatty acids. The toxic saturated free fatty acid palmitate induces an increase in DR5 mRNA and protein expression in Huh-7 human hepatoma cells leading to DR5 localization into lipid rafts, cell surface receptor clustering with subsequent recruitment of the initiator caspase-8, and ultimately cellular demise. Lipoapoptosis by palmitate was not inhibited by a soluble human recombinant DR5-Fc chimera protein suggesting that DR5 cytotoxic signaling is ligand-independent. Hepatocytes from murine TRAIL receptor knock-out mice (DR(-/-)) displayed reduced palmitate-mediated lipotoxicity. Likewise, knockdown of DR5 or caspase-8 expression by shRNA technology attenuated palmitate-induced Bax activation and apoptosis in Huh-7 cells, without altering induction of ER stress markers. Similar observations were verified in other cell models. Finally, knockdown of CHOP, an ER stress-mediated transcription factor, reduced DR5 up-regulation and DR5-mediated caspase-8 activation upon palmitate treatment. Collectively, these results suggest that ER stress-induced CHOP activation by palmitate transcriptionally up-regulates DR5, likely resulting in ligand-independent cytotoxic signaling by this death receptor.

A hedgehog survival pathway in 'undead' lipotoxic hepatocytes.

BACKGROUND & AIMS: Ballooned hepatocytes in non-alcoholic steatohepatitis (NASH) generate sonic hedgehog (SHH). This observation is consistent with a cellular phenotype in which the cell death program has been initiated but cannot be executed. Our aim was to determine whether ballooned hepatocytes have potentially disabled the cell death execution machinery, and if so, can their functional biology be modeled in vitro. METHODS: Immunohistochemistry was performed on human NASH specimens. In vitro studies were performed using HuH-7 cells with shRNA targeted knockdown of caspase 9 (shC9 cells) or primary hepatocytes from caspase 3(-/-) mice. RESULTS: Ballooned hepatocytes in NASH display diminished expression of caspase 9. This phenotype was modeled using shC9 cells; these cells were resistant to lipoapoptosis by palmitate (PA) or lysophosphatidylcholine (LPC) despite lipid droplet formation. During lipid loading by either PA or LPC, shC9 cells activate JNK which induces SHH expression via AP-1. An autocrine hedgehog survival signaling pathway was further delineated in both shC9 and caspase 3(-/-) cells during lipotoxic stress. CONCLUSIONS: Ballooned hepatocytes in NASH downregulate caspase 9, a pivotal caspase executing the mitochondrial pathway of apoptosis. Hepatocytes engineered to reduce caspase 9 expression are resistant to lipoapoptosis, in part, due to a hedgehog autocrine survival signaling pathway.

Mechanisms of lysophosphatidylcholine-induced hepatocyte lipoapoptosis.

Isolated hepatocytes undergo lipoapoptosis, a feature of hepatic lipotoxicity, on treatment with saturated free fatty acids (FFA) such as palmitate (PA). However, it is unknown if palmitate is directly toxic to hepatocytes or if its toxicity is indirect via the generation of lipid metabolites such as lysophosphatidylcholine (LPC). PA-mediated hepatocyte lipoapoptosis is associated with endoplasmic reticulum (ER) stress, c-Jun NH(2)-terminal kinase (JNK) activation, and a JNK-dependent upregulation of the potent proapoptotic BH3-only protein PUMA (p53 upregulated modulator of apoptosis). Our aim was to determine which of these mechanisms of lipotoxicity are activated by PA-derived LPC. We employed Huh-7 cells and isolated murine and human primary hepatocytes. Intracellular LPC concentrations increase linearly as a function of the exogenous, extracellular PA, stearate, or LPC concentration. Incubation of Huh-7 cells or primary hepatocytes with LPC induced cell death by apoptosis in a concentration-dependent manner. Substituting LPC for PA resulted in caspase-dependent cell death that was accompanied by activating phosphorylation of JNK with c-Jun phosphorylation and an increase in PUMA expression. LPC also induced ER stress as manifest by eIF2α phosphorylation and CAAT/enhancer binding homologous protein (CHOP) induction. LPC cytotoxicity was attenuated by pharmacological inhibition of JNK or glycogen synthase kinase-3 (GSK-3). Similarly, short-hairpin RNA (shRNA)-targeted knockdown of CHOP protected Huh-7 cells against LPC-induced toxicity. The LPC-induced PUMA upregulation was prevented by JNK inhibition or shRNA-targeted knockdown of CHOP. Finally, genetic deficiency of PUMA rendered murine hepatocytes resistant to LPC-induced apoptosis. We concluded that LPC-induced lipoapoptosis is dependent on mechanisms largely indistinguishable from PA. These data suggest that FFA-mediated cytotoxicity is indirect via the generation of the toxic metabolite, LPC.

Myofibroblast-derived PDGF-BB promotes Hedgehog survival signaling in cholangiocarcinoma cells.

UNLABELLED: Cholangiocarcinoma (CCA) cells paradoxically express the death ligand, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and, therefore, are dependent upon potent survival signals to circumvent TRAIL cytotoxicity. CCAs are also highly desmoplastic cancers with a tumor microenvironment rich in myofibroblasts (MFBs). Herein, we examine a role for MFB-derived CCA survival signals. We employed human KMCH-1, KMBC, HuCCT-1, TFK-1, and Mz-ChA-1 CCA cells, as well as human primary hepatic stellate and myofibroblastic LX-2 cells, for these studies. In vivo experiments were conducted using a syngeneic rat orthotopic CCA model. Coculturing CCA cells with myofibroblastic human primary hepatic stellate cells or LX-2 cells significantly decreased TRAIL-induced apoptosis in CCA cells, a cytoprotective effect abrogated by neutralizing platelet-derived growth factor (PDGF)-BB antiserum. Cytoprotection by PDGF-BB was dependent upon Hedgehog (Hh) signaling, because it was abolished by the smoothened (SMO; the transducer of Hh signaling) inhibitor, cyclopamine. PDGF-BB induced cyclic adenosine monophosphate-dependent protein kinase-dependent trafficking of SMO to the plasma membrane, resulting in glioma-associated oncogene (GLI)2 nuclear translocation and activation of a consensus GLI reporter gene-based luciferase assay. A genome-wide messenger RNA expression analysis identified 67 target genes to be commonly up- (50 genes) or down-regulated (17 genes) by both Sonic hedgehog and PDGF-BB in a cyclopamine-dependent manner in CCA cells. Finally, in a rodent CCA in vivo model, cyclopamine administration increased apoptosis in CCA cells, resulting in tumor suppression. CONCLUSIONS: MFB-derived PDGF-BB protects CCA cells from TRAIL cytotoxicity by a Hh-signaling-dependent process. These results have therapeutical implications for the treatment of human CCA.

SHP2 inhibition enhances Yes-associated protein-mediated liver regeneration in murine partial hepatectomy models.

Disrupted liver regeneration following hepatectomy represents an "undruggable" clinical challenge associated with poor patient outcomes. Yes-associated protein (YAP), a transcriptional coactivator that is repressed by the Hippo pathway, is instrumental in liver regeneration. We have previously described an alternative, Hippo-independent mechanism of YAP activation mediated by downregulation of protein tyrosine phosphatase nonreceptor type 11 (PTPN11, also known as SHP2) inhibition. Herein, we examined the effects of YAP activation with a selective SHP1/SHP2 inhibitor, NSC-87877, on liver regeneration in murine partial hepatectomy models. In our studies, NSC-87877 led to accelerated hepatocyte proliferation, improved liver regeneration, and decreased markers of injury following partial hepatectomy. The effects of NSC-87877 were lost in mice with hepatocyte-specific Yap/Taz deletion, and this demonstrated dependence on these molecules for the enhanced regenerative response. Furthermore, administration of NSC-87877 to murine models of nonalcoholic steatohepatitis was associated with improved survival and decreased markers of injury after hepatectomy. Evaluation of transcriptomic changes in the context of NSC-87877 administration revealed reduction in fibrotic signaling and augmentation of cell cycle signaling. Cytoprotective changes included downregulation of Nr4a1, an apoptosis inducer. Collectively, the data suggest that SHP2 inhibition induces a pro-proliferative and cytoprotective enhancement of liver regeneration dependent on YAP.

Glycogen synthase kinase-3 (GSK-3) inhibition attenuates hepatocyte lipoapoptosis.

BACKGROUNDS & AIMS: Saturated free fatty acids induce hepatocyte lipoapoptosis, a key pathologic feature of non-alcoholic steatohepatitis. The saturated free fatty acid palmitate induces hepatocyte lipoapoptosis via an endoplasmic reticulum stress pathway resulting in c-Jun-N-terminal (JNK) activation. Glycogen synthase kinase (GSK)-3 is a serine/threonine kinase which may also promote JNK activation. Thus, our aim was to determine if GSK-3 inhibition suppresses palmitate induced JNK activation and lipoapoptosis. METHODS: For these studies, we employed mouse primary hepatocytes, Huh-7 and Hep3B cell lines. RESULTS: Palmitate-induced GSK-3 activation was identified by phosphorylation of its substrate glycogen synthase. GSK-3 pharmacologic inhibition, by GSK-3 inhibitor IX and enzastaurin, significantly reduced PA-mediated lipoapoptosis. More importantly, Huh-7 cells, in which either GSK-3α or GSK-3ß isoforms were stably and selectively knocked down by shRNA, displayed resistance to palmitate-induced cytotoxicity. GSK-3 pharmacological inhibitors and shRNA-targeted knockdown of GSK-3α or GSK-3ß also suppressed JNK activation by palmitate. JNK activation, in part, promotes lipoapotosis by inducing expression of the pro-apoptotic effector p53-upregulated modulator of apoptosis (PUMA). Consistent with this concept, GSK-3 pharmacologic inhibition also reduced PUMA cellular protein levels during exposure to palmitate. On the other hand, the GSK-3 inhibitors did not prevent PA induction of ER stress. CONCLUSIONS: Our results suggest that GSK-3 activation promotes a JNK-dependent cytotoxic signaling cascade culminating in lipoapoptosis.

A smac mimetic reduces TNF related apoptosis inducing ligand (TRAIL)-induced invasion and metastasis of cholangiocarcinoma cells.

UNLABELLED: Cholangiocarcinoma (CCA) cells paradoxically express tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a death ligand that, failing to kill CCA cells, instead promotes their tumorigenicity and especially the metastatic behaviors of cell migration and invasion. Second mitochondria-derived activator of caspase (smac) mimetics are promising cancer therapeutic agents that enhance proapoptotic death receptor signaling by causing cellular degradation of inhibitor of apoptosis (IAP) proteins. Our aim was to examine the in vitro and in vivo effects of the smac mimetic JP1584 in CCA. Despite JP1584-mediated loss of cellular inhibitor of apoptosis-1 (cIAP-1) and cIAP-2, TRAIL failed to induce apoptosis in KMCH-1, TFK-1, and BDEneu CCA cells; a finding consistent with a downstream block in death signaling. Because cIAP-1 and cIAP-2 also promote nuclear factor kappa B (NF-kappaB) activation by the canonical pathway, the effect of JP1584 on this signaling pathway was examined. Treatment with JP1584 inhibited TRAIL-induced NF-kappaB activation as well as TRAIL-mediated up-regulation of the NF-kappaB target gene, matrix metalloproteinase 7 (MMP7). JP1584 also reduced TRAIL-mediated CCA cell migration and invasion in vitro. Finally, in a syngeneic rat orthotopic CCA model, JP1584 administration reduced MMP7 messenger RNA levels and extrahepatic metastases. CONCLUSION: : Although the smac mimetic JP1584 does not sensitize cells to apoptosis, it reduces TRAIL-induced CCA cell metastatic behavior. These data support the emerging concept that IAPs are prometastatic and represent targets for antimetastatic therapies.

Mcl-1 degradation during hepatocyte lipoapoptosis.

The mechanisms of free fatty acid-induced lipoapoptosis are incompletely understood. Here we demonstrate that Mcl-1, an anti-apoptotic member of the Bcl-2 family, was rapidly degraded in hepatocytes in response to palmitate and stearate by a proteasome-dependent pathway. Overexpression of a ubiquitin-resistant Mcl-1 mutant in Huh-7 cells attenuated palmitate-mediated Mcl-1 loss and lipoapoptosis; conversely, short hairpin RNA-targeted knockdown of Mcl-1 sensitized these cells to lipoapoptosis. Palmitate-induced Mcl-1 degradation was attenuated by the novel protein kinase C (PKC) inhibitor rottlerin. Of the two human novel PKC isozymes, PKCdelta and PKC, only activation of PKC was observed by phospho-immunoblot analysis. As compared with Jurkat cells, a smaller PKC polypeptide and mRNA were expressed in hepatocytes consistent with an alternative splice variant. Short hairpin RNA-mediated knockdown of PKC reduced Mcl-1 degradation and lipoapoptosis. Likewise, genetic deletion of Pkc also attenuated Mcl-1 degradation and cytotoxicity by palmitate in primary hepatocytes. During treatment with palmitate, rottlerin inhibited phosphorylation of Mcl-1 at Ser(159), a phosphorylation site previously implicated in Mcl-1 turnover. Consistent with these results, an Mcl-1 S159A mutant was resistant to degradation and improved cell survival during palmitate treatment. Collectively, these results implicate PKC-dependent destabilization of Mcl-1 as a mechanism contributing to hepatocyte lipoapoptosis.

JNK1-dependent PUMA expression contributes to hepatocyte lipoapoptosis.

Free fatty acids (FFA) induce hepatocyte lipoapoptosis by a c-Jun N-terminal kinase (JNK)-dependent mechanism. However, the cellular processes by which JNK engages the core apoptotic machinery during lipotoxicity, especially activation of BH3-only proteins, remain incompletely understood. Thus, our aim was to determine whether JNK mediates induction of BH3-only proteins during hepatocyte lipoapoptosis. The saturated FFA palmitate, but not the monounsaturated FFA oleate, induces an increase in PUMA mRNA and protein levels. Palmitate induction of PUMA was JNK1-dependent in primary murine hepatocytes. Palmitate-mediated PUMA expression was inhibited by a dominant negative c-Jun, and direct binding of a phosphorylated c-Jun containing the activator protein 1 complex to the PUMA promoter was identified by electrophoretic mobility shift assay and a chromatin immunoprecipitation assay. Short hairpin RNA-targeted knockdown of PUMA attenuated Bax activation, caspase 3/7 activity, and cell death. Similarly, the genetic deficiency of Puma rendered murine hepatocytes resistant to lipoapoptosis. PUMA expression was also increased in liver biopsy specimens from patients with non-alcoholic steatohepatitis as compared with patients with simple steatosis or controls. Collectively, the data implicate JNK1-dependent PUMA expression as a mechanism contributing to hepatocyte lipoapoptosis.

Transcriptional suppression of mir-29b-1/mir-29a promoter by c-Myc, hedgehog, and NF-kappaB.

MicroRNAs regulate pathways contributing to oncogenesis, and thus the mechanisms causing dysregulation of microRNA expression in cancer are of significant interest. Mature mir-29b levels are decreased in malignant cells, and this alteration promotes the malignant phenotype, including apoptosis resistance. However, the mechanism responsible for mir-29b suppression is unknown. Here, we examined mir-29 expression from chromosome 7q32 using cholangiocarcinoma cells as a model for mir-29b downregulation. Using 5' rapid amplification of cDNA ends, the transcriptional start site was identified for this microRNA locus. Computational analysis revealed the presence of two putative E-box (Myc-binding) sites, a Gli-binding site, and four NF-kappaB-binding sites in the region flanking the transcriptional start site. Promoter activity in cholangiocarcinoma cells was repressed by transfection with c-Myc, consistent with reports in other cell types. Treatment with the hedgehog inhibitor cyclopamine, which blocks smoothened signaling, increased the activity of the promoter and expression of mature mir-29b. Mutagenesis analysis and gel shift data are consistent with a direct binding of Gli to the mir-29 promoter. Finally, activation of NF-kappaB signaling, via ligation of Toll-like receptors, also repressed mir-29b expression and promoter function. Of note, activation of hedgehog, Toll-like receptor, and c-Myc signaling protected cholangiocytes from TRAIL-induced apoptosis. Thus, in addition to c-Myc, mir-29 expression can be suppressed by hedgehog signaling and inflammatory pathways, both commonly activated in the genesis of human malignancies.