The Hippo pathway effector TAZ induces intrahepatic cholangiocarcinoma in mice and is ubiquitously activated in the human disease

Background

Intrahepatic cholangiocarcinoma (iCCA) is a highly aggressive primary liver tumor with increasing incidence worldwide, dismal prognosis, and few therapeutic options. Mounting evidence underlines the role of the Hippo pathway in this disease; however, the molecular mechanisms whereby the Hippo cascade contributes to cholangiocarcinogenesis remain poorly defined.

Methods

We established novel iCCA mouse models via hydrodynamic transfection of an activated form of transcriptional coactivator with PDZ-binding motif (TAZ), a Hippo pathway downstream effector, either alone or combined with the myristoylated AKT (myr-AKT) protooncogene, in the mouse liver. Hematoxylin and eosin staining, immunohistochemistry, electron microscopy, and quantitative real-time RT-PCR were applied to characterize the models. In addition, in vitro cell line studies were conducted to address the growth-promoting roles of TAZ and its paralog YAP.

Results

Overexpression of TAZ in the mouse liver triggered iCCA development with very low incidence and long latency. In contrast, co-expression of TAZ and myr-AKT dramatically increased tumor frequency and accelerated cancer formation in mice, with 100% iCCA incidence and high tumor burden by 10 weeks post hydrodynamic injection. AKT/TAZ tumors faithfully recapitulated many of the histomolecular features of human iCCA. At the molecular level, the development of the cholangiocellular lesions depended on the binding of TAZ to TEAD transcription factors. In addition, inhibition of the Notch pathway did not hamper carcinogenesis but suppressed the cholangiocellular phenotype of AKT/TAZ tumors. Also, knockdown of YAP, the TAZ paralog, delayed cholangiocarcinogenesis in AKT/TAZ mice without affecting the tumor phenotype. Furthermore, human preinvasive and invasive iCCAs and mixed hepatocellular carcinoma/iCCA displayed widespread TAZ activation and downregulation of the mechanisms protecting TAZ from proteolysis.

Conclusions

Overall, the present data underscore the crucial role of TAZ in cholangiocarcinogenesis

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02394-2.

Corrigendum: Pathogenetic, Prognostic, and Therapeutic Role of Fatty Acid Synthase in Human Hepatocellular Carcinoma

[This corrects the article DOI: 10.3389/fonc.2019.01412.].

CD90 is regulated by notch1 and hallmarks a more aggressive intrahepatic cholangiocarcinoma phenotype

BACKGROUND

Intrahepatic Cholangiocarcinoma (iCCA) is characterized by a strong stromal reaction playing a role in tumor progression. Thymus cell antigen 1 (THY1), also called Cluster of Differentiation 90 (CD90), is a key regulator of cell-cell and cell-matrix interaction. In iCCA, CD90 has been reported to be associated with a poor prognosis. In an iCCA PDX model, we recently found that CD90 was downregulated in mice treated with the Notch γ-secretase inhibitor Crenigacestat. The study aims to investigate the role of CD90 in relation to the NOTCH pathway.

METHODS

THY1/CD90 gene and protein expression was evaluated in human iCCA tissues and xenograft models by qRT-PCR, immunohistochemistry, and immunofluorescence. Notch1 inhibition was achieved by siRNA. THY1/CD90 functions were investigated in xenograft models built with HuCCT1 and KKU-M213 cell lines, engineered to overexpress or knockdown THY1, respectively.

RESULTS

CD90 co-localized with EPCAM, showing its epithelial origin. In vitro, NOTCH1 silencing triggered HES1 and THY1 down-regulation. RBPJ, a critical transcriptional regulator of NOTCH signaling, exhibited putative binding sites on the THY1 promoter and bound to the latter, implying CD90 as a downstream NOTCH pathway effector. In vivo, Crenigacestat suppressed iCCA growth and reduced CD90 expression in the PDX model. In the xenograft model, Crenigacestat inhibited tumor growth of HuCCT1 cells transfected to overexpress CD90 and KKU-M213 cells constitutively expressing high levels of CD90, while not affecting the growth of HuCCT1 control cells and KKU-M213 depleted of CD90. In an iCCA cohort, patients with higher expression levels of NOTCH1/HES1/THY1 displayed a significantly shorter survival.

CONCLUSIONS

iCCA patients with higher NOTCH1/HES1/THY1 expression have the worst prognosis, but they are more likely to benefit from Notch signaling inhibition. These findings represent the scientific rationale for testing NOTCH1 inhibitors in clinical trials, taking the first step toward precision medicine for iCCA.

TAZ is indispensable for c-MYC-induced hepatocarcinogenesis

BACKGROUND & AIMS

Mounting evidence implicates the Hippo downstream effectors Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) in hepatocellular carcinoma (HCC). We investigated the functional contribution of YAP and/or TAZ to c-MYC-induced liver tumor development.

METHODS

The requirement for YAP and/or TAZ in c-Myc-driven hepatocarcinogenesis was analyzed using conditional Yap, Taz, and Yap;Taz knockout (KO) mice. An hepatocyte-specific inducible TTR-CreER^T2 KO system was applied to evaluate the role of YAP and TAZ during tumor progression. Expression patterns of YAP, TAZ, c-MYC, and BCL2L12 were analyzed in human HCC samples.

RESULTS

We found that the Hippo cascade is inactivated in c-Myc-induced mouse HCC. Intriguingly, TAZ mRNA levels and activation status correlated with c-MYC activity in human and mouse HCC, but YAP mRNA levels did not. We demonstrated that TAZ is a direct transcriptional target of c-MYC. In c-Myc induced murine HCCs, ablation of Taz, but not Yap, completely prevented tumor development. Mechanistically, TAZ was required to avoid c-Myc-induced hepatocyte apoptosis during tumor initiation. The anti-apoptotic BCL2L12 gene was identified as a novel target regulated specifically by YAP/TAZ, whose silencing strongly suppressed c-Myc-driven murine hepatocarcinogenesis. In c-Myc murine HCC lesions, conditional knockout of Taz, but not Yap, led to tumor regression, supporting the requirement of TAZ for c-Myc-driven HCC progression.

CONCLUSIONS

TAZ is a pivotal player at the crossroad between the c-MYC and Hippo pathways in HCC. Targeting TAZ might be beneficial for the treatment of patients with HCC and c-MYC activation.

LAY SUMMARY

The identification of novel treatment targets and approaches for patients with hepatocellular carcinoma is crucial to improve survival outcomes. We identified TAZ as a transcriptional target of c-MYC which plays a critical role in c-MYC-dependent hepatocarcinogenesis. TAZ could potentially be targeted for the treatment of patients with c-MYC-driven hepatocellular carcinoma.

RASSF1A independence and early galectin-1 upregulation in PIK3CA-induced hepatocarcinogenesis: new therapeutic venues

Aberrant activation of the phosphoinositide 3‐kinase (PI3K)/AKT/mTOR and Ras/mitogen‐activated protein kinase (MAPK) pathways is a hallmark of hepatocarcinogenesis. In a subset of hepatocellular carcinomas (HCCs), PI3K/AKT/mTOR signaling dysregulation depends on phosphatidylinositol‐4,5‐bisphosphate 3‐kinase, catalytic subunit alpha (PIK3CA) mutations, while RAS/MAPK activation is partly attributed to promoter methylation of the tumor suppressor Ras association domain‐containing protein 1 (RASSF1A). To evaluate a possible cocarcinogenic effect of PIK3CA activation and RASSF1A knockout, plasmids expressing oncogenic forms of PIK3CA (E545K or H1047R mutants) were delivered to the liver of RASSF1A knockout and wild‐type mice by hydrodynamic tail vein injection combined with sleeping beauty‐mediated somatic integration. Transfection of either PIK3CA E545K or H1047R mutants sufficed to induce HCCs in mice irrespective of RASSF1A mutational background. The related tumors displayed a lipogenic phenotype with upregulation of fatty acid synthase and stearoyl‐CoA desaturase‐1 (SCD1). Galectin‐1, which was commonly upregulated in preneoplastic lesions and tumors, emerged as a regulator of SCD1. Co‐inhibitory treatment with PIK3CA inhibitors and the galectin‐1 inhibitor OTX008 resulted in synergistic cytotoxicity in human HCC cell lines, suggesting novel therapeutic venues.

Cabozantinib-based combination therapy for the treatment of hepatocellular carcinoma

OBJECTIVE

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer with limited treatment options. Cabozantinib, an orally bioavailable multikinase inhibitor is now approved by Food and Drug Administration (FDA) for HCC patients. We evaluated the therapeutic efficacy of cabozantinib, either alone or in combination, in vitro and in vivo.

DESIGN

Human HCC cell lines and HCC mouse models were used to assess the therapeutic efficacy and targeted molecular pathways of cabozantinib, either alone or in combination with the pan-mTOR inhibitor MLN0128 or the checkpoint inhibitor anti-PD-L1 antibody.

RESULTS

Cabozantinib treatment led to stable disease in c-Met/β-catenin and Akt/c-Met mouse HCC while possessing limited efficacy on Akt/Ras and c-Myc liver tumours. Importantly, cabozantinib effectively inhibited c-MET and ERK activity, leading to decreased PKM2 and increased p21 expression in HCC cells and in c-Met/β-catenin and Akt/c-Met HCC. However, cabozantinib was ineffective in inhibiting the Akt/mTOR cascade. Intriguingly, a strong inhibition of angiogenesis by cabozantinib occurred regardless of the oncogenic drivers. However, cabozantinib had limited impact on other tumour microenvironment parameters, including tumour infiltrating T cells, and did not induce programmed death-ligand 1 (PD-L1) expression. Combining cabozantinib with MLN0128 led to tumour regression in c-Met/β-catenin mice. In contrast, combined treatment with cabozantinib and the checkpoint inhibitor anti-PD-L1 antibody did not provide any additional therapeutic benefit in the four mouse HCC models tested.

CONCLUSION

c-MET/ERK/p21/PKM2 cascade and VEGFR2-induced angiogenesis are the primary targets of cabozantinib in HCC treatment. Combination therapies with cabozantinib and mTOR inhibitors may be effective against human HCC.

Overexpression of Mothers Against Decapentaplegic Homolog 7 Activates the Yes-Associated Protein/NOTCH Cascade and Promotes Liver Carcinogenesis in Mice and Humans

BACKGROUND AND AIMS

Mothers against decapentaplegic homolog (SMAD) 7 is an antagonist of TGF-β signaling. In the present investigation, we sought to determine the relevance of SMAD7 in liver carcinogenesis using in vitro and in vivo approaches.

APPROACH AND RESULTS

We found that SMAD7 is up-regulated in a subset of human HCC samples with poor prognosis. Gene set enrichment analysis revealed that SMAD7 expression correlates with activated yes-associated protein (YAP)/NOTCH pathway and cholangiocellular signature genes in HCCs. These findings were substantiated in human HCC cell lines. In vivo, overexpression of Smad7 alone was unable to initiate HCC development, but it significantly accelerated c-Myc/myeloid cell leukemia 1 (MCL1)-induced mouse HCC formation. Consistent with human HCC data, c-Myc/MCL1/Smad7 liver tumors exhibited an increased cholangiocellular gene expression along with Yap/Notch activation and epithelial-mesenchymal transition (EMT). Intriguingly, blocking of the Notch signaling did not affect c-Myc/MCL1/Smad7-induced hepatocarcinogenesis while preventing cholangiocellular signature expression and EMT, whereas ablation of Yap abolished c-Myc/MCL1/Smad7-driven HCC formation. In mice overexpressing a myristoylated/activated form of AKT, coexpression of SMAD7 accelerated carcinogenesis and switched the phenotype from HCC to intrahepatic cholangiocarcinoma (iCCA) lesions. In human iCCA, SMAD7 expression was robustly up-regulated, especially in the most aggressive tumors, and directly correlated with the levels of YAP/NOTCH targets as well as cholangiocellular and EMT markers.

CONCLUSIONS

The present data indicate that SMAD7 contributes to liver carcinogenesis by activating the YAP/NOTCH signaling cascade and inducing a cholangiocellular and EMT signature.

Current challenges to underpinning the genetic basis for cholangiocarcinoma

AREAS COVERED

This review provides an overview regarding the current scenario and knowledge of the CCA genomic landscape and the potentially actionable molecular aberrations in each CCA subtype.

EXPERT OPINION

The establishment and advances of high-throughput methodologies applied to genetic and epigenetic profiling are changing many cancer types' therapeutic landscape , including CCA.The large body of data generated must be interpreted appropriately and eventually implemented in clinical practice. The following advancements toward precision medicine in CCA management will require designing better clinical trials with improved methods to stratify biliary tumor patients.

Distinct and Overlapping Roles of Hippo Effectors YAP and TAZ During Human and Mouse Hepatocarcinogenesis

BACKGROUND & AIMS

Yes-associated protein (YAP) and its paralog transcriptional co-activator with post synaptic density protein, drosophila disc large tumor suppressor and zonula occludens-1-binding motif (TAZ) are 2 co-activators downstream of Hippo tumor-suppressor cascade. Both have been implicated in the development of hepatocellular carcinoma (HCC). However, whether YAP and TAZ have distinct or overlapping functions during hepatocarcinogenesis remains unknown.

METHODS

Expression patterns of YAP and TAZ were analyzed in human HCC samples. The requirement of Yap and/or Taz in protein kinase B (Akt)/ neuroblastoma RAS viral oncogene homolog (NRas) -driven liver tumorigenesis was analyzed using conditional Yap, Taz, and Yap;Taz knockout mice. Transcriptional programs regulated by YAP and/or TAZ were identified via RNA sequencing.

RESULTS

We found that in human HCC samples, an almost ubiquitous activation of YAP or TAZ occurs, underlying their role in this tumor type. Intriguingly, 70% of HCC samples showed only nuclear YAP or TAZ immunoreactivity. In the Akt/NRas liver tumor model, where nuclear Yap and Taz can be detected readily, deletion of Yap or Taz alone only mildly delayed liver tumor development, whereas their concomitant ablation strongly inhibited tumor cell proliferation and significantly suppressed Akt/NRas-driven hepatocarcinogenesis. In HCC cell lines, silencing of either YAP or TAZ led to decreased expression of both overlapping and distinct sets of genes, with the most prominent gene signatures related to cell-cycle progression and DNA replication.

CONCLUSIONS

YAP and TAZ have overlapping and distinct roles in hepatocarcinogenesis. HCCs may display unique activation of YAP or TAZ, thus relying on either YAP or TAZ for their growth.

Pivotal Role of Fatty Acid Synthase in c-MYC Driven Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a deadly form of liver malignancy with limited treatment options. Amplification and/or overexpression of c-MYC is one of the most frequent genetic events in human HCC. The mammalian target of Rapamycin Complex 1 (mTORC1) is a major functional axis regulating various aspects of cellular growth and metabolism. Recently, we demonstrated that mTORC1 is necessary for c-Myc driven hepatocarcinogenesis as well as for HCC cell growth in vitro. Among the pivotal downstream effectors of mTORC1, upregulation of Fatty Acid Synthase (FASN) and its mediated de novo lipogenesis is a hallmark of human HCC. Here, we investigated the importance of FASN on c-Myc-dependent hepatocarcinogenesis using in vitro and in vivo approaches. In mouse and human HCC cells, we found that FASN suppression by either gene silencing or soluble inhibitors more effectively suppressed proliferation and induced apoptosis in the presence of high c-MYC expression. In c-Myc/Myeloid cell leukemia 1 (MCL1) mouse liver tumor lesions, FASN expression was markedly upregulated. Most importantly, genetic ablation of Fasn profoundly delayed (without abolishing) c-Myc/MCL1 induced HCC formation. Liver tumors developing in c-Myc/MCL1 mice depleted of Fasn showed a reduction in proliferation and an increase in apoptosis when compared with corresponding lesions from c-Myc/MCL1 mice with an intact Fasn gene. In human HCC samples, a significant correlation between the levels of c-MYC transcriptional activity and the expression of FASN mRNA was detected. Altogether, our study indicates that FASN is an important effector downstream of mTORC1 in c-MYC induced HCC. Targeting FASN may be helpful for the treatment of human HCC, at least in the tumor subset displaying c-MYC amplification or activation.

Transcriptomic and Proteomic Analysis of Clear Cell Foci (CCF) in the Human Non-Cirrhotic Liver Identifies Several Differentially Expressed Genes and Proteins with Functions in Cancer Cell Biology and Glycogen Metabolism

Clear cell foci (CCF) of the liver are considered to be pre-neoplastic lesions of hepatocellular adenomas and carcinomas. They are hallmarked by glycogen overload and activation of AKT (v-akt murine thymoma viral oncogene homolog)/mTOR (mammalian target of rapamycin)-signaling. Here, we report the transcriptome and proteome of CCF extracted from human liver biopsies by laser capture microdissection. We found 14 genes and 22 proteins differentially expressed in CCF and the majority of these were expressed at lower levels in CCF. Using immunohistochemistry, the reduced expressions of STBD1 (starch-binding domain-containing protein 1), USP28 (ubiquitin-specific peptidase 28), monad/WDR92 (WD repeat domain 92), CYB5B (Cytochrome b5 type B), and HSPE1 (10 kDa heat shock protein, mitochondrial) were validated in CCF in independent specimens. Knockout of Stbd1, the gene coding for Starch-binding domain-containing protein 1, in mice did not have a significant effect on liver glycogen levels, indicating that additional factors are required for glycogen overload in CCF. Usp28 knockout mice did not show changes in glycogen storage in diethylnitrosamine-induced liver carcinoma, demonstrating that CCF are distinct from this type of cancer model, despite the decreased USP28 expression. Moreover, our data indicates that decreased USP28 expression is a novel factor contributing to the pre-neoplastic character of CCF. In summary, our work identifies several novel and unexpected candidates that are differentially expressed in CCF and that have functions in glycogen metabolism and tumorigenesis.

The Hippo Effector Transcriptional Coactivator with PDZ-Binding Motif Cooperates with Oncogenic β-Catenin to Induce Hepatoblastoma Development in Mice and Humans

Hepatoblastoma (HB) is the most common pediatric liver tumor. Though Wnt/β-catenin and Hippo cascades are implicated in HB development, studies on crosstalk between β-catenin and Hippo downstream effector transcriptional coactivator with PDZ-binding motif (TAZ) in HB are lacking. Expression levels of TAZ and β-catenin in human HB specimens were assessed by immunohistochemistry. Functional interplay between TAZ and β-catenin was determined by overexpression of an activated form of TAZ (TAZS89A), either alone or combined with an oncogenic form of β-catenin (ΔN90-β-catenin), in mouse liver via hydrodynamic transfection. Activation of TAZ often co-occurred with that of β-catenin in clinical specimens. Although the overexpression of TAZS89A alone did not induce hepatocarcinogenesis, concomitant overexpression of TAZS89A and ΔN90-β-catenin triggered the development of HB lesions exhibiting both epithelial and mesenchymal features. Mechanistically, TAZ/β-catenin-driven HB development required TAZ interaction with transcriptional enhanced associate domain factors. Blockade of the Notch cascade did not inhibit TAZ/β-catenin-dependent HB formation in mice but suppressed the mesenchymal phenotype. Neither Yes-associated protein nor heat shock factor 1 depletion affected HB development in TAZ/β-catenin mice. In human HB cell lines, silencing of TAZ resulted in decreased cell growth, which was further reduced when TAZ knockdown was associated with suppression of either β-catenin or Yes-associated protein. Overall, our study identified TAZ as a crucial oncogene in HB development and progression.

Cholesterol biosynthesis supports the growth of hepatocarcinoma lesions depleted of fatty acid synthase in mice and humans

OBJECTIVE

Increased de novo fatty acid (FA) synthesis and cholesterol biosynthesis have been independently described in many tumour types, including hepatocellular carcinoma (HCC).

DESIGN

We investigated the functional contribution of fatty acid synthase (Fasn)-mediated de novo FA synthesis in a murine HCC model induced by loss of Pten and overexpression of c-Met (sgPten/c-Met) using liver-specific Fasn knockout mice. Expression arrays and lipidomic analysis were performed to characterise the global gene expression and lipid profiles, respectively, of sgPten/c-Met HCC from wild-type and Fasn knockout mice. Human HCC cell lines were used for in vitro studies.

RESULTS

Ablation of Fasn significantly delayed sgPten/c-Met-driven hepatocarcinogenesis in mice. However, eventually, HCC emerged in Fasn knockout mice. Comparative genomic and lipidomic analyses revealed the upregulation of genes involved in cholesterol biosynthesis, as well as decreased triglyceride levels and increased cholesterol esters, in HCC from these mice. Mechanistically, loss of Fasn promoted nuclear localisation and activation of sterol regulatory element binding protein 2 (Srebp2), which triggered cholesterogenesis. Blocking cholesterol synthesis via the dominant negative form of Srebp2 (dnSrebp2) completely prevented sgPten/c-Met-driven hepatocarcinogenesis in Fasn knockout mice. Similarly, silencing of FASN resulted in increased SREBP2 activation and hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase (HMGCR) expression in human HCC cell lines. Concomitant inhibition of FASN-mediated FA synthesis and HMGCR-driven cholesterol production was highly detrimental for HCC cell growth in culture.

CONCLUSION

Our study uncovers a novel functional crosstalk between aberrant lipogenesis and cholesterol biosynthesis pathways in hepatocarcinogenesis, whose concomitant inhibition might represent a therapeutic option for HCC.

Inhibition of MELK Protooncogene as an Innovative Treatment for Intrahepatic Cholangiocarcinoma

Background and Objectives: Intrahepatic cholangiocarcinoma (iCCA) is a pernicious tumor characterized by a dismal outcome and scarce therapeutic options. To substantially improve the prognosis of iCCA patients, a better understanding of the molecular mechanisms responsible for development and progression of this disease is imperative. In the present study, we aimed at elucidating the role of the maternal embryonic leucine zipper kinase (MELK) protooncogene in iCCA. Materials and Methods: We analyzed the expression of MELK and two putative targets, Forkhead Box M1 (FOXM1) and Enhancer of Zeste Homolog 2 (EZH2), in a collection of human iCCA by real-time RT-PCR and immunohistochemistry (IHC). The effects on iCCA growth of both the multi-kinase inhibitor OTSSP167 and specific small-interfering RNA (siRNA) against MELK were investigated in iCCA cell lines. Results: Expression of MELK was significantly higher in tumors than in corresponding non-neoplastic liver counterparts, with highest levels of MELK being associated with patients' shorter survival length. In vitro, OTSSP167 suppressed the growth of iCCA cell lines in a dose-dependent manner by reducing proliferation and inducing apoptosis. These effects were amplified when OTSSP167 administration was coupled to the DNA-damaging agent doxorubicin. Similar results, but less remarkable, were obtained when MELK was silenced by specific siRNA in the same cells. At the molecular level, siRNA against MELK triggered downregulation of MELK and its targets. Finally, we found that MELK is a downstream target of the E2F1 transcription factor. Conclusion: Our results indicate that MELK is ubiquitously overexpressed in iCCA, where it may represent a prognostic indicator and a therapeutic target. In particular, the combination of OTSSP167 (or other, more specific MELK inhibitors) with DNA-damaging agents might be a potentially effective therapy for human iCCA.

Pathogenetic, Prognostic, and Therapeutic Role of Fatty Acid Synthase in Human Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common solid tumors worldwide, characterized by clinical aggressiveness, resistance to conventional chemotherapy, and high lethality. Consequently, there is an urgent need to better delineate the molecular pathogenesis of HCC to develop new preventive and therapeutic strategies against this deadly disease. Noticeably, emerging evidence indicates that proteins involved in lipid biosynthesis are important mediators along the development and progression of HCC in humans and rodents. Here, we provide a comprehensive overview of: (a) The pathogenetic relevance of lipogenic proteins involved in liver carcinogenesis, with a special emphasis on the master fatty acid regulator, fatty acid synthase (FASN); (b) The molecular mechanisms responsible for unrestrained activation of FASN and related fatty acid biosynthesis in HCC; (c) The findings in experimental mouse models of liver cancer and their possible clinical implications; (d) The existing potential therapies targeting FASN. A consistent body of data indicates that elevated levels of lipogenic proteins, including FASN, characterize human hepatocarcinogenesis and are predictive of poor prognosis of HCC patients. Pharmacological or genetic blockade of FASN is highly detrimental for the growth of HCC cells in both in vitro and in vivo models. In conclusion, FASN is involved in the molecular pathogenesis of HCC, where it plays a pivotal role both in tumor onset and progression. Thus, targeted inhibition of FASN and related lipogenesis could be a potentially relevant treatment for human HCC.

The mTORC2-Akt1 Cascade Is Crucial for c-Myc to Promote Hepatocarcinogenesis in Mice and Humans

Hepatocellular carcinoma (HCC) is a deadly form of liver cancer with limited treatment options. The c-Myc transcription factor is a pivotal player in hepatocarcinogenesis, but the mechanisms underlying c-Myc oncogenic activity in the liver remain poorly delineated. Mammalian target of rapamycin complex 2 (mTORC2) has been implicated in cancer by regulating multiple AGC kinases, especially AKT proteins. In the liver, AKT1 and AKT2 are widely expressed. While AKT2 is the major isoform downstream of activated phosphoinositide 3-kinase and loss of phosphatase and tensin homolog-induced HCC, the precise function of AKT1 in hepatocarcinogenesis is largely unknown. In the present study, we demonstrate that mTORC2 is activated in c-Myc-driven mouse HCC, leading to phosphorylation/activation of Akt1 but not Akt2. Ablation of Rictor inhibited c-Myc-induced HCC formation in vivo. Mechanistically, we discovered that loss of Akt1, but not Akt2, completely prevented c-Myc HCC formation in mice. Silencing of Rictor or Akt1 in c-Myc HCC cell lines inhibited phosphorylated forkhead box o1 expression and strongly suppressed cell growth in vitro. In human HCC samples, c-MYC activation is strongly correlated with phosphorylated AKT1 expression. Higher expression of RICTOR and AKT1, but not AKT2, is associated with poor survival of patients with HCC. In c-Myc mice, while rapamycin, an mTORC1 inhibitor, had limited efficacy at preventing c-Myc-driven HCC progression, the dual mTORC1 and mTORC2 inhibitor MLN0128 effectively promoted tumor regression by inducing apoptosis and necrosis. Conclusion: Our study indicates the functional contribution of mTORC2/Akt1 along c-Myc-induced hepatocarcinogenesis, with AKT1 and AKT2 having distinct roles in HCC development and progression; targeting both mTORC1 and mTORC2 may be required for effective treatment of human HCC displaying c-Myc amplification or overexpression.

Loss of Fbxw7 synergizes with activated Akt signaling to promote c-Myc dependent cholangiocarcinogenesis

BACKGROUND & AIMS

The ubiquitin ligase F-box and WD repeat domain-containing 7 (FBXW7) is recognized as a tumor suppressor in many cancer types due to its ability to promote the degradation of numerous oncogenic target proteins. Herein, we aimed to elucidate its role in intrahepatic cholangiocarcinoma (iCCA).

METHODS

Herein, we first confirmed that FBXW7 gene expression was reduced in human iCCA specimens. To identify the molecular mechanisms by which FBXW7 dysfunction promotes cholangiocarcinogenesis, we generated a mouse model by hydrodynamic tail vein injection of Fbxw7ΔF, a dominant negative form of Fbxw7, either alone or in association with an activated/myristylated form of AKT (myr-AKT). We then confirmed the role of c-MYC in human iCCA cell lines and its relationship to FBXW7 expression in human iCCA specimens.

RESULTS

FBXW7 mRNA expression is almost ubiquitously downregulated in human iCCA specimens. While forced overexpression of Fbxw7ΔF alone did not induce any appreciable abnormality in the mouse liver, co-expression with AKT triggered cholangiocarcinogenesis and mice had to be euthanized by 15 weeks post-injection. At the molecular level, a strong induction of Fbxw7 canonical targets, including Yap, Notch2, and c-Myc oncoproteins, was detected. However, only c-MYC was consistently confirmed as a FBXW7 target in human CCA cell lines. Most importantly, selected ablation of c-Myc completely impaired iCCA formation in AKT/Fbxw7ΔF mice, whereas deletion of either Yap or Notch2 only delayed tumorigenesis in the same model. In human iCCA specimens, an inverse correlation between the expression levels of FBXW7 and c-MYC transcriptional activity was observed.

CONCLUSIONS

Downregulation of FBXW7 is ubiquitous in human iCCA and cooperates with AKT to induce cholangiocarcinogenesis in mice via c-Myc-dependent mechanisms. Targeting c-MYC might represent an innovative therapy against iCCA exhibiting low FBXW7 expression.

LAY SUMMARY

There is mounting evidence that FBXW7 functions as a tumor suppressor in many cancer types, including intrahepatic cholangiocarcinoma, through its ability to promote the degradation of numerous oncoproteins. Herein, we have shown that the low expression of FBXW7 is ubiquitous in human cholangiocarcinoma specimens. This low expression is correlated with increased c-MYC activity, leading to tumorigenesis. Our findings suggest that targeting c-MYC might be an effective treatment for intrahepatic cholangiocarcinoma.

Modification of the base excision repair enzyme MBD4 by the small ubiquitin-like molecule SUMO1

The base excision repair DNA N-glycosylase MBD4 (also known as MED1), an interactor of the DNA mismatch repair protein MLH1, plays a central role in the maintenance of genomic stability of CpG sites by removing thymine and uracil from G:T and G:U mismatches, respectively. MBD4 is also involved in DNA damage response and transcriptional regulation. The interaction with other proteins is likely critical for understanding MBD4 functions. To identify novel proteins that interact with MBD4, we used tandem affinity purification (TAP) from HEK-293 cells. The MBD4-TAP fusion and its co-associated proteins were purified sequentially on IgG and calmodulin affinity columns; the final eluate was shown to contain MLH1 by western blotting, and MBD4-associated proteins were identified by mass spectrometry. Bands with molecular weight higher than that expected for MBD4 (˜66 kD) yielded peptides corresponding to MBD4 itself and the small ubiquitin-like molecule-1 (SUMO1), suggesting that MBD4 is sumoylated in vivo. MBD4 sumoylation was validated by co-immunoprecipitation in HEK-293 and MCF7 cells, and by an in vitrosumoylation assay. Sequence and mutation analysis identified three main sumoylation sites: MBD4 is sumoylated preferentially on K137, with additional sumoylation at K215 and K377. Patterns of MBD4 sumoylation were altered, in a DNA damage-specific way, by the anti-metabolite 5-fluorouracil, the alkylating agent N-Methyl-N-nitrosourea and the crosslinking agent cisplatin. MCF7 extract expressing sumoylated MBD4 displays higher thymine glycosylase activity than the unmodified species. Of the 67 MBD4 missense mutations reported in The Cancer Genome Atlas, 14 (20.9%) map near sumoylation sites. These results indicate that MBD4 is sumoylated in vivo in a DNA damage-specific manner, and suggest that sumoylation serves to regulate its repair activity and could be compromised in cancer. This study expands the role played by sumoylation in fine-tuning DNA damage response and repair.

SNAI1 Promotes the Cholangiocellular Phenotype, but not Epithelial-Mesenchymal Transition, in a Murine Hepatocellular Carcinoma Model

Hepatocellular carcinoma (HCC) is the most common type of liver cancer and has limited treatment options. Snail family transcriptional repressor 1 (SNAI1) is a master regulator of epithelial-mesenchymal transition (EMT) and has been implicated in HCC initiation and progression. However, the precise role of SNAI1 and the way it contributes to hepatocarcinogenesis have not been investigated in depth, especially in vivo. Here, we analyzed the functional relevance of SNAI1 in promoting hepatocarcinogenesis in the context of the AKT/c-Met-driven mouse liver tumor model (AKT/c-Met/SNAI1). Overexpression of SNAI1 did not accelerate AKT/c-Met-induced HCC development or induce metastasis in mice. Elevated SNAI1 expression rather led to the formation of cholangiocellular (CCA) lesions in the mouse liver, a phenotype that was paralleled by increased activation of Yap and Notch. Ablation of Yap strongly inhibited AKT/c-Met/SNAI-induced HCC and CCA development, whereas inhibition of the Notch pathway specifically blocked the CCA-like phenotype in mice. Intriguingly, overexpression of SNAI1 failed to induce EMT, indicated by strong E-cadherin expression and lack of vimentin expression by AKT/c-Met/SNAI tumor cells. SNAI1 mRNA levels strongly correlated with the expression of CCA markers, including SOX9, CK19, and EPCAM, but not with EMT markers such as E-CADHERIN and ZO-1, in human HCC samples. Overall, our findings suggest SNAI1 regulates the CCA-like phenotype in hepatocarcinogenesis via regulation of Yap and Notch. SIGNIFICANCE: These findings report a new function of SNAI1 to promote cholangiocellular transdifferentiation instead of epithelial-mesenchymal transition in hepatocellular carcinoma.

A novel preclinical model of cholangiocarcinoma based on human aberrant FBXW7 expression

e15624

Background: Pre-clinical models that mimic human genetic events occurring in intrahepatic cholangiocarcinoma (iCCA) are limited. The ubiquitin ligase F-box and WD repeat domain-containing 7 (FBXW7) is recognized as a tumor suppressor in many cancer types. Methods: Firstly, we determined the FBXW7 mutation frequency (n = 120) and mRNA expression (n = 87) in a collection of human iCCA. Based on the preliminary findings in human data, we generated a mouse model by hydrodynamic tail vein injection of activated/myristylated (myr-)AKT with Fbxw7ΔF, a dominant negative form of Fbxw7. Subsequently, we investigated the role of established targets of Fbxw7, namely Notch2, Yap, and c-Myc in this novel mouse model and in human CCA cell lines. Results: FBXW7 mRNA expression is almost ubiquitously downregulated (71/82; 86.6%) in human iCCA specimens, while only 0.8% of samples showed FBXW7 somatic mutations. In vivo, co-expression of AKT and Fbxw7ΔF triggered the development of iCCA lesions and mice were euthanized by 15 weeks post-injection due to high tumor burden. At the molecular level, a strong induction of FBXW7 canonical targets, including Yap, Notch2, and c-Myc oncoproteins, was detected. However, only c-Myc was consistently confirmed as a FBXW7 target in human CCA cell lines. Interestingly, selected ablation of c-Myc completely impaired iCCA formation in AKT/Fbxw7ΔF mice, whereas deletion of either Yap or Notch2 delayed cholangiocarcinogenesis in the same model. Furthermore, in human iCCA specimens, a strong, inverse correlation between the expression levels of FBXW7 and c-Myc was observed. Conclusions: Downregulation of FBXW7 is almost ubiquitous in human iCCA and cooperates with AKT to induce cholangiocarcinogenesis in mice. This pre-clinical mouse model could be used to test novel therapeutics targeting c-Myc, Notch2, and/or Yap.

MicroRNA-203 impacts on the growth, aggressiveness and prognosis of hepatocellular carcinoma by targeting MAT2A and MAT2B genes

Hepatocellular carcinoma (HCC) is characterized by the down-regulation of the liver-specific methyladenosyltransferase 1A (MAT1A) gene, encoding the S-adenosylmethionine synthesizing isozymes MATI/III, and the up-regulation of the widely expressed methyladenosyltransferase 2A (MAT2A), encoding MATII isozyme, and methyladenosyltransferase 2B (MAT2B), encoding a β-subunit without catalytic action that regulates MATII enzymatic activity. Different observations showed hepatocarcinogenesis inhibition by miR-203. We found that miR-203 expression in HCCs is inversely correlated with HCC proliferation and aggressiveness markers, and with MAT2A and MAT2B levels. MiR-203 transfection in HepG2 and Huh7 liver cancer cells targeted the 3'-UTR of MAT2A and MAT2B, inhibiting MAT2A and MAT2B mRNA levels and MATα2 and MATβ2 protein expression. These molecular events were paralleled by an increase in SAM content and were associated with growth restraint and apoptosis, inhibition of cell migration and invasiveness, and suppression of the expression of CD133 and LIN28B stemness markers. In contrast, MAT2B transfection in the same cell lines led to a rise of both MATβ2 and MATα2 expression, associated with increases in cell growth, migration, invasion and overexpression of stemness markers and p-AKT. Altogether, our results indicate that the miR-203 oncosuppressor activity may at least partially depend on its inhibition of MAT2A and MAT2B and show, for the first time, an oncogenic activity of MAT2B linked to AKT activation.

Functional role of SGK3 in PI3K/Pten driven liver tumor development

Background

Hepatocellular carcinoma (HCC) is a leading cause of cancer related deaths worldwide. The PI3K cascade is one of the major signaling pathways underlying HCC development and progression. Activating mutations of PI3K catalytic subunit alpha (PIK3CA) and/or loss of Pten often occur in human HCCs. Serum and glucocorticoid kinase 3 (SGK3) belongs to the SGK family of AGK kinases and functions in parallel to AKT downstream of PI3K. Previous studies have shown that SGK3 may be the major kinase responsible for the oncogenic potential of PIK3CA helical domain mutants, such as PIK3CA(E545K), but not kinase domain mutants, such as PIK3CA(H1047R).

Methods

We investigated the functional contribution of SGK3 in mediating activated PIK3CA mutant or loss of Pten induced HCC development using Sgk3 knockout mice.

Results

We found that ablation of Sgk3 does not affect PIK3CA(H1047R) or PIK3CA(E545K) induced lipogenesis in the liver. Using PIK3CA(H1047R)/c-Met, PIK3CA(E545K)/c-Met, and sgPten/c-Met murine HCC models, we also demonstrated that deletion of Sgk3 moderately delays PIK3CA(E545K)/c-Met driven HCC, while not affecting PIK3CA(H1047R)/c-Met or sgPten/c-Met HCC formation in mice. Similarly, in human HCC cell lines, silencing of SGK3 reduced PIK3CA(E545K) -but not PIK3CA(H1047R)- induced accelerated tumor cell proliferation.

Conclusion

Altogether, our data suggest that SGK3 plays a role in transducing helical domain mutant PIK3CA signaling during liver tumor development.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5551-2) contains supplementary material, which is available to authorized users.

TEA Domain Transcription Factor 4 Is the Major Mediator of Yes-Associated Protein Oncogenic Activity in Mouse and Human Hepatoblastoma

Hepatoblastoma (HB) is the most common type of pediatric liver cancer. Activation of yes-associated protein (YAP) has been implicated in HB molecular pathogenesis. The transcriptional co-activator Yap regulates downstream gene expression through interaction with the TEA domain (TEAD) proteins. Nonetheless, YAP also displays functions that are independent of its transcriptional activity. The underlying molecular mechanisms by which Yap promotes HB development remain elusive. In the current study, we demonstrated that blocking TEAD function via the dominant-negative form of TEAD2 abolishes Yap-driven HB formation in mice and restrains human HB growth in vitro. When TEAD2 DNA-binding domain was fused with virus protein 16 transcriptional activation domain, it synergized with activated β-catenin to promote HB formation in vivo. Among TEAD genes, silencing of TEAD4 consistently inhibited tumor growth and Yap target gene expression in HB cell lines. Furthermore, TEAD4 mRNA expression was significantly higher in human HB lesions when compared with corresponding nontumorous liver tissues. Human HB specimens also exhibited strong nuclear immunoreactivity for TEAD4. Altogether, data demonstrate that TEAD-mediated transcriptional activity is both sufficient and necessary for Yap-driven HB development. TEAD4 is the major TEAD isoform and Yap partner in human HB. Targeting TEAD4 may represent an effective treatment option for human HB.

TGF-β as Multifaceted Orchestrator in HCC Progression: Signaling, EMT, Immune Microenvironment, and Novel Therapeutic Perspectives

Therapeutic attempts to treat hepatocellular carcinoma (HCC) frequently result in a poor response or treatment failure. The efficacy of approved drugs and survival expectancies is affected by an ample degree of variability that can be explained at least in part by the enormous between-patient cellular and molecular heterogeneity of this neoplasm. Transforming growth factor-β (TGF-β) is hyperactivated in a large fraction of HCCs, where it influences complex interactive networks covering multiple cell types and a plethora of other local soluble ligands, ultimately establishing several malignancy traits. This cytokine boosts the invasiveness of cancerous epithelial cells through promoting the epithelial-to-mesenchymal transition program, but also skews the phenotype of immune cells toward a tumor-supporting status. Here, we discuss recent strategies pursued to offset TGF-β-dependent processes that promote metastatic progression and immune surveillance escape in solid cancers, including HCC. Moreover, we report findings indicating that TGF-β reduces the expression of the proinflammatory factors CCL4 and interleukin-1β (IL-1β in human ex vivo treated HCC tissues. While this is consistent with the anti-inflammatory properties of TGF-β, whether it is an outright tumor promoter or suppressor is still a matter of some debate. Indeed, IL-1β has also been shown to support angiogenesis and cell invasiveness in some cancers. In addition, we describe an inhibitory effect of TGF-β on the secretion of CCL2 and CXCL1 by HCC-derived fibroblasts, which suggests the existence of an indirect stroma-mediated functional link between TGF-β and downstream immunity.

Oncogenic potential of N-terminal deletion and S45Y mutant β-catenin in promoting hepatocellular carcinoma development in mice

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide with limited treatment options. Mutation of β-catenin is one of the most frequent genetic events along hepatocarcinogenesis. β-catenin mutations can be in the form of point mutation or large N-terminal deletion. Studies suggested that different β-catenin mutations might have distinct oncogenic potential.

METHODS

We tested the oncogenic activity of β-cateninS45Y, one of the most frequent point mutations of β-catenin, and ∆N90-β-catenin, a form of β-catenin with a large N-terminal deletion, in promoting HCC development in mice. Thus, we co-expressed β-cateninS45Y or ∆N90-β-catenin together with c-Met into the mouse liver using hydrodynamic injection.

RESULTS

We found that both β-catenin mutations were able to induce HCC formation in combination with c-Met at the same latency and efficiency. Tumors showed similar histological features and proliferation rates. However, immunohistochemistry showed predominantly nuclear staining of β-catenin in c-Met/∆N90-β-catenin HCC, but membrane immunoreactivity in c-Met/β-cateninS45Y HCC. qRT-PCR analysis demonstrated that both ∆N90-β-catenin and β-cateninS45Y induced the same effectors, although at somewhat different levels. In cultured cells, both ∆N90-β-catenin and β-cateninS45Y were capable of inducing TCF/LEF reporter expression, promoting proliferation, and inhibiting apoptosis.

CONCLUSIONS

Our study suggests that β-cateninS45Y and ∆N90-β-catenin, in combination with the c-Met proto-oncogene, have similar oncogenic potential. Furthermore, nuclear staining of β-catenin does not always characterize β-catenin activity.

Focal adhesion kinase activation limits efficacy of Dasatinib in c-Myc driven hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a deadly malignancy with limited treatment options. Recently, it was found that Dasatinib treatment led to synthetic lethality in c-Myc high-expressing human cancer cells due to inhibition of p-Lyn. Overexpression of c-Myc is frequently seen in human HCC. We investigated the sensitivity to Dasatinib in vitro using HCC cell lines and in vivo using c-Myc mouse HCC model. We found that HCC cell line responsiveness to Dasatinib varied significantly. However, there was no correlation between c-Myc expression and IC₅₀ to Dasatinib. In c-Myc-induced HCC in mice, tumors continued to grow despite Dasatinib treatment, although the eventual tumor burden was lower in Dasatinib treatment cohort. Molecular analyses revealed that Dasatinib was effective in inhibiting p-Src, but not p-Lyn, in HCC. Importantly, we found that in HCC cell lines as well as c-Myc mouse HCC, Dasatinib treatment induced up regulation of activated/phosphorylated (p)-focal adhesion kinase(FAK). Concomitant treatment of HCC cell lines with Dasatinib and FAK inhibitor prevented Dasatinib-induced FAK activation, leading to stronger growth restraint. Altogether, our results suggest that Dasatinib may have limited efficacy as single agent for HCC treatment. Combined treatment with Dasatinib with FAK inhibitor might represent a novel therapeutic approach against HCC.

Oncogene-dependent addiction to carbohydrate-responsive element binding protein in hepatocellular carcinoma

Metabolic reprogramming is a hallmark of many cancer types, including hepatocellular carcinoma (HCC). Identifying the critical players in this process might be crucial for the generation of novel and effective anti-neoplastic therapies. In the present investigation, we determined the importance of carbohydrate responsive element binding protein (ChREBP), a central player in the regulation of lipid and glucose metabolism in the liver, on the development of HCC in in vitro and in vivo models. We found that genetic deletion of ChREBP (that will be referred to as ChREBPKO mice) strongly delays or impairs hepatocarcinogenesis driven by AKT or AKT/c-Met overexpression in mice, respectively. In contrast, HCC development was found to be completely unaffected by ChREBP depletion in mice co-expressing AKT and N-Ras protooncogenes. In mouse and human HCC cell lines, suppression of ChREBP via specific small interfering RNAs (siRNAs) resulted in decreased proliferation and induction of apoptosis. Of note, these cellular events were strongly augmented by concomitant inhibition of the mitogen-activated protein kinase (MAPK) pathway. The present data indicate that ChREBP activity might be required or dispensable for HCC growth, depending on the oncogenes involved. In particular, the activation of Ras/MAPK signaling might represent a possible mechanism of resistance to ChREBP depletion in this tumor type. Additional studies are needed to unravel the molecular mechanisms rendering HCC cells insensitive to ChREBP suppression.

Combined CDK4/6 and Pan-mTOR Inhibition Is Synergistic Against Intrahepatic Cholangiocarcinoma

PURPOSE

Intrahepatic cholangiocarcinoma (ICC) is an aggressive cancer type, lacking effective therapies and associated with a dismal prognosis. Palbociclib is a selective CDK4/6 inhibitor, which has been shown to suppress cell proliferation in many experimental cancer models. Recently, we demonstrated that pan-mTOR inhibitors, such as MLN0128, effectively induce apoptosis, although have limited efficacy in restraining proliferation of ICC cells. Here, we tested the hypothesis that palbociclib, due to its antproliferative properties in many cancer types, might synergize with MLN0128 to impair ICC growth.

EXPERIMENTAL DESIGN

Human ICC cell lines and the AKT/YapS127A ICC mouse model were used to test the therapeutic efficacy of palbociclib and MLN0128, either alone or in combination.

RESULTS

Administration of palbociclib suppressed in vitro ICC cell growth by inhibiting cell-cycle progression. Concomitant administration of palbociclib and MLN0128 led to a pronounced, synergistic growth constraint of ICC cell lines. Furthermore, while treatment with palbociclib or MLN0128 alone resulted in tumor growth reduction in AKT/YapS127A mice, a remarkable tumor regression was achieved when the two drugs were administered simultaneously. Mechanistically, palbociclib was found to potentiate MLN0128 mTOR inhibition activity, whereas MLN0128 prevented the upregulation of cyclin D1 induced by palbociclib treatment.

CONCLUSIONS

Our study indicates the synergistic activity of palbociclib and MLN0128 in inhibiting ICC cell proliferation. Thus, combination of CDK4/6 and mTOR inhibitors might represent a novel, promising, and effective therapeutic approach against human ICC.See related commentary by Malumbres, p. 6.

Hippo Cascade Controls Lineage Commitment of Liver Tumors in Mice and Humans

Primary liver cancer consists mainly of hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). A subset of human HCCs expresses a ICC-like gene signature and is classified as ICC-like HCC. The Hippo pathway is a critical regulator of normal and malignant liver development. However, the precise function(s) of the Hippo cascade along liver carcinogenesis remain to be fully delineated. The role of the Hippo pathway in a murine mixed HCC/ICC model induced by activated forms of AKT and Ras oncogenes (AKT/Ras) was investigated. The authors demonstrated the inactivation of Hippo in AKT/Ras liver tumors leading to nuclear localization of Yap and TAZ. Coexpression of AKT/Ras with Lats2, which activates Hippo, or the dominant negative form of TEAD2 (dnTEAD2), which blocks Yap/TAZ activity, resulted in delayed hepatocarcinogenesis and elimination of ICC-like lesions in the liver. Mechanistically, Notch2 expression was found to be down-regulated by the Hippo pathway in liver tumors. Overexpression of Lats2 or dnTEAD2 in human HCC cell lines inhibited their growth and led to the decreased expression of ICC-like markers, as well as Notch2 expression. Altogether, this study supports the key role of the Hippo cascade in regulating the differentiation status of liver tumors.

Efficacy of MEK inhibition in a K-Ras-driven cholangiocarcinoma preclinical model

Intrahepatic cholangiocarcinoma (iCCA) is a deadly malignancy with limited treatment options. Gain-of-function mutations in K-Ras is a very frequent alteration, occurring in ~15 to 25% of human iCCA patients. Here, we established a new iCCA model by expressing activated forms of Notch1 (NICD) and K-Ras (K-Ras^V12D) in the mouse liver (K-Ras/NICD mice). Furthermore, we investigated the therapeutic potential of MEK inhibitors in vitro and in vivo using human CCA cell lines and K-Ras/NICD mice, respectively. Treatment with U0126, PD901, and Selumetinib MEK inhibitors triggered growth restraint in all CCA cell lines tested, with the most pronounced growth suppressive effects being observed in K-Ras mutant cells. Growth inhibition was due to reduction in proliferation and massive apoptosis. Furthermore, treatment of K-Ras/NICD tumor-bearing mice with PD901 resulted in stable disease. At the molecular level, PD901 efficiently inhibited ERK activation in K-Ras/NICD tumor cells, mainly leading to increased apoptosis. Altogether, our study demonstrates that K-Ras/NICD mice represent a novel and useful preclinical model to study K-Ras-driven iCCA development and the effectiveness of MEK inhibitors in counteracting this process. Our data support the usefulness of MEK inhibitors for the treatment of human iCCA.

Pan-mTOR inhibitor MLN0128 is effective against intrahepatic cholangiocarcinoma in mice

BACKGROUND & AIMS

Intrahepatic cholangiocarcinoma (ICC) is a lethal malignancy without effective treatment options. MLN0128, a second generation pan-mTOR inhibitor, shows efficacy for multiple tumor types. We evaluated the therapeutic potential of MLN0128 vs. gemcitabine/oxaliplatin in a novel ICC mouse model.

METHODS

We established a novel ICC mouse model via hydrodynamic transfection of activated forms of AKT (myr-AKT) and Yap (YapS127A) protooncogenes (that will be referred to as AKT/YapS127A). Genetic approaches were applied to study the requirement of mTORC1 and mTORC2 in mediating AKT/YapS127A driven tumorigenesis. Gemcitabine/oxaliplatin and MLN0128 were administered in AKT/YapS127A tumor-bearing mice to study their anti-tumor efficacy in vivo. Multiple human ICC cell lines were used for in vitro experiments. Hematoxylin and eosin staining, immunohistochemistry and immunoblotting were applied for the characterization and mechanistic study.

RESULTS

Co-expression of myr-AKT and YapS127A promoted ICC development in mice. Both mTORC1 and mTORC2 complexes were required for AKT/YapS127A ICC development. Gemcitabine/oxaliplatin had limited efficacy in treating late stage AKT/YapS127A ICC. In contrast, partial tumor regression was achieved when MLN0128 was applied in the late stage of AKT/YapS127A cholangiocarcinogenesis. Furthermore, when MLN0128 was administered in the early stage of AKT/YapS127A carcinogenesis, it led to disease stabilization. Mechanistically, MLN0128 efficiently inhibited AKT/mTOR signaling both in vivo and in vitro, inducing strong ICC cell apoptosis and only marginally affecting proliferation.

CONCLUSIONS

This study suggests that mTOR kinase inhibitors may be beneficial for the treatment of ICC, even in tumors that are resistant to standard of care chemotherapeutics, such as gemcitabine/oxaliplatin-based regimens, especially in the subset of tumors exhibiting activated AKT/mTOR cascade. Lay summary: We established a novel mouse model of intrahepatic cholangiocarcinoma (ICC). Using this new preclinical model, we evaluated the therapeutic potential of mTOR inhibitor MLN0128 vs. gemcitabine/oxaliplatin (the standard chemotherapy for ICC treatment). Our study shows the anti-neoplastic potential of MLN0128, suggesting that it may be superior to gemcitabine/oxaliplatin-based chemotherapy for the treatment of ICC, especially in the tumors exhibiting activated AKT/mTOR cascade.

Hepatocellular glycogenotic foci after combined intraportal pancreatic islet transplantation and knockout of the carbohydrate responsive element binding protein in diabetic mice

Aims

The intraportal pancreatic islet transplantation (IPIT) model of diabetic rats is an insulin mediated model of hepatocarcinogenesis characterized by the induction of clear cell foci (CCF) of altered hepatocytes, which are pre-neoplastic lesions excessively storing glycogen (glycogenosis) and exhibiting activation of the AKT/mTOR protooncogenic pathway. In this study, we transferred the IPIT model to the mouse and combined it with the knockout of the transcription factor carbohydrate responsive element binding protein (chREBP).

Methods

C57BL/6J Wild-type (WT) and chREBP-knockout (chREBP-KO) mice (n = 297) were matched to 16 groups (WT/ chREBP-KO, experimental/control, streptozotocine-induced diabetic/not diabetic, one/four weeks). Experimental groups received the intraportal transplantation of 70 pancreatic islets. Liver and pancreatic tissue was examined using histology, morphometry, enzyme- and immunohistochemistry and electron microscopy.

Results

CCF emerged in the liver acini downstream of the transplanted islets. In comparison to WT lesions, CCF of chREBP-KO mice displayed more glycogen accumulation, reduced activity of the gluconeogenic enzyme glucose-6-phosphatase, decreased glycolysis, lipogenesis and reduced levels of the AKT/mTOR cascade members. Proliferative activity of CCF was ∼two folds higher in WT mice than in chREBP-KO mice.

Conclusions

The IPIT model is applicable to mice, as murine CCF resemble preneoplastic liver lesions from this hepatocarcinogenesis model in the rat in terms of morphological, metabolic and molecular alterations and proliferative activity, which is diminished after chREBP knockout. chREBP appears to be an essential component of AKT/mTOR mediated cell proliferation and the metabolic switch from a glycogenotic to lipogenic phenotype in precursor lesions of hepatocarcinogenesis.

Tankyrase inhibitors suppress hepatocellular carcinoma cell growth via modulating the Hippo cascade

Previous data indicate that Tankyrase inhibitors exert anti-growth functions in many cancer cell lines due to their ability to inactivate the YAP protooncogene. In the present manuscript, we investigated the effect of Tankyrase inhibitors on the growth of hepatocellular carcinoma (HCC) cell lines and the molecular mechanisms involved. For this purpose, we performed cell proliferation assay by colony-forming ability in seven human HCC cells subjected to XAV-939 and G007-LK Tankyrase inhibitors. Noticeably, the two Tankyrase inhibitors suppressed the HCC cell growth in a dose-dependent manner. Furthermore, we found that Tankyrase inhibitors synergized with MEK and AKT inhibitors to suppress HCC cell proliferation. At the molecular level, Tankyrase inhibitors significantly decreased YAP protein levels, reduced the expression of YAP target genes, and inhibited YAP/TEAD luciferase reporter activity. In addition, Tankyrase inhibitors administration was accompanied by upregulation of Angiomotin-like 1 (AMOTL1) and Angiomotin-like 2 (AMOTL2) proteins, two major negative regulators of YAP. Altogether, the present data indicate that XAV-939 and G007-LK Tankyrase inhibitors could suppress proliferation of hepatocellular carcinoma cells and downregulate YAP/TAZ by stabilizing AMOTL1 and AMOTL2 proteins, thus representing new potential anticancer drugs against hepatocellular carcinoma.

Central role of mTORC1 downstream of YAP/TAZ in hepatoblastoma development

Hepatoblastoma (HB) is the most common type of liver malignancy in children. Recent studies suggest that activation of Yes-associated protein (YAP) is a major molecular event in HB development, as activated YAP synergizes with mutant β-catenin to promote HB formation in mice (YAP/β-catenin). However, how YAP regulates HB development remains poorly defined. Similarly, de-regulation of mammalian target of rapamycin complex 1 (mTORC1) signaling has been implicated in multiple tumor types, but its functional role in HB development is scarcely understood. In the present study, we found that mTORC1 is activated in human HB cells and YAP/β-catenin-induced mouse HB tumor tissues. mTOR inhibitor MLN0128 significantly inhibits human HB cell growth in vitro. Furthermore, ablation of Raptor, the unique subunit of mTORC1, strongly delayed YAP/β-catenin-induced HB development in mice. At the molecular level, we found that expression of the amino acid transporter SLC38A1 is induced in mouse HB tissues, and amino acid deprivation leads to mTORC1 suppression in HB cell lines. Silencing of YAP and/or its paralog, transcriptional co-activator with PDZ binding motif (TAZ), decreased SLC38A1 expression as well as mTORC1 activation in HB cells. Furthermore, a frequent and concomitant upregulation of mTORC1 and SLC38A1 was detected in a collection of human HB specimens. Altogether, our study demonstrates the key role of mTORC1 in HB development. YAP and TAZ promote HB development via inducing SLC38A1 expression, whose upregulation leads to mTORC1 activation. Targeting mTOR pathway or amino acid transporters may represent novel therapeutic strategies for the treatment of human HB.

A functional mammalian target of rapamycin complex 1 signaling is indispensable for c-Myc-driven hepatocarcinogenesis

Amplification and/or activation of the c-Myc proto-oncogene is one of the leading genetic events along hepatocarcinogenesis. The oncogenic potential of c-Myc has been proven experimentally by the finding that its overexpression in the mouse liver triggers tumor formation. However, the molecular mechanism whereby c-Myc exerts its oncogenic activity in the liver remains poorly understood. Here, we demonstrate that the mammalian target of rapamycin complex 1 (mTORC1) cascade is activated and necessary for c-Myc-dependent hepatocarcinogenesis. Specifically, we found that ablation of Raptor, the unique member of mTORC1, strongly inhibits c-Myc liver tumor formation. Also, the p70 ribosomal S6 kinase/ribosomal protein S6 and eukaryotic translation initiation factor 4E-binding protein 1/eukaryotic translation initiation factor 4E signaling cascades downstream of mTORC1 are required for c-Myc-driven tumorigenesis. Intriguingly, microarray expression analysis revealed up-regulation of multiple amino acid transporters, including solute carrier family 1 member A5 (SLC1A5) and SLC7A6, leading to robust uptake of amino acids, including glutamine, into c-Myc tumor cells. Subsequent functional studies showed that amino acids are critical for activation of mTORC1 as their inhibition suppressed mTORC1 in c-Myc tumor cells. In human hepatocellular carcinoma specimens, levels of c-Myc directly correlate with those of mTORC1 activation as well as of SLC1A5 and SLC7A6.

CONCLUSION

Our current study indicates that an intact mTORC1 axis is required for c-Myc-driven hepatocarcinogenesis; thus, targeting the mTOR pathway or amino acid transporters may be an effective and novel therapeutic option for the treatment of hepatocellular carcinoma with activated c-Myc signaling. (Hepatology 2017;66:167-181).

Inhibition of HSF1 suppresses the growth of hepatocarcinoma cell lines in vitro and AKT-driven hepatocarcinogenesis in mice

Upregulation of the heat shock transcription factor 1 (HSF1) has been described as a frequent event in many cancer types, but its oncogenic role in hepatocellular carcinoma (HCC) remains poorly delineated. In the present study, we assessed the function(s) of HSF1 in hepatocarcinogenesis via in vitro and in vivo approaches. In particular, we determined the importance of HSF1 on v-Akt murine thymoma viral oncogene homolog (AKT)-induced liver cancer development in mice. We found that knockdown of HSF1 activity via specific siRNA triggered growth restraint by suppressing cell proliferation and inducing massive cell apoptosis in human HCC cell lines. At the molecular level, HSF1 inhibition was accompanied by downregulation of the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) cascade and related metabolic pathways. Most importantly, overexpression of a dominant negative form of HSF1 (HSF1dn) in the mouse liver via hydrodynamic gene delivery led to the inhibition of mouse hepatocarcinogenesis driven by overexpression of AKT. In human liver cancer specimens, we detected that HSF1 is progressively induced from human non-tumorous surrounding livers to HCC, reaching the highest expression in the tumors characterized by the poorest outcome (as defined by the length of patients’ survival). In conclusion, HSF1 is an independent prognostic factor in liver cancer and might represent an innovative therapeutic target in HCC subsets characterized by activation of the AKT/mTOR pathway.

Role of the Notch signaling in cholangiocarcinoma

INTRODUCTION

Cholangiocarcinoma (CCA) is an emerging cancer entity of the liver, associated with poor outcome and characterized by resistance to conventional chemotherapeutic treatments. In the last decade, many signaling pathways associated with CCA development and progression have been identified and are currently under intense investigation. Cumulating evidence indicates that the Notch cascade, a highly-conserved pathway in most multicellular organisms, is a critical player both in liver malignant transformation and tumor aggressiveness, thus representing a potential therapeutic target in this pernicious disease. Areas covered: In the present review article, we comprehensively summarize and critically discuss the current knowledge on the Notch pathway, its specific and key roles in cholangiocarcinogenesis, the treatment strategies aimed at suppressing this signaling cascade in cancer, and the encouraging results coming from preclinical trials. Expert opinion: The Notch pathway represents a major driver of carcinogenesis and a promising therapeutic target in human CCA. A better understanding of the molecular mechanisms triggered by the Notch pathway as well as its functional crosstalk with other signaling cascade will be highly helpful for the design of innovative therapies against human CCA.

Oncogene dependent requirement of fatty acid synthase in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the most frequent primary tumor of the liver, is an aggressive cancer type with limited treatment options. Cumulating evidence underlines a crucial role of aberrant lipid biosynthesis (a process known as de novo lipogenesis) along carcinogenesis. Previous studies showed that suppression of fatty acid synthase (FASN), the major enzyme responsible for de novo lipogenesis, is highly detrimental for the in vitro growth of HCC cell lines. To assess whether de novo lipogenesis is required for liver carcinogenesis, we have generated various mouse models of liver cancer by stably overexpressing candidate oncogenes in the mouse liver via hydrodynamic gene delivery. We found that overexpression of FASN in the mouse liver is unable to malignantly transform hepatocytes. However, genetic deletion of FASN totally suppresses hepatocarcinogenesis driven by AKT and AKT/c-Met protooncogenes in mice. On the other hand, liver tumor development is completely unaffected by FASN depletion in mice co-expressing β-catenin and c-Met. Our data indicate that tumors might be either addicted to or independent from de novo lipogenesis for their growth depending on the oncogenes involved. Additional investigation is required to unravel the molecular mechanisms whereby some oncogenes render cancer cells resistant to inhibition of de novo lipogenesis.

Both de novo synthetized and exogenous fatty acids support the growth of hepatocellular carcinoma cells

BACKGROUND & AIMS

Although it is well established that fatty acids (FA) are indispensable for the proliferation and survival of cancer cells in hepatocellular carcinoma (HCC), inhibition of Fatty Acid Synthase (FASN) cannot completely repress HCC cell growth in culture. Thus, we hypothesized that uptake of exogenous FA by cancer cells might play an important role in the development and progression of HCC. Lipoprotein lipase (LPL) is the enzyme that catalyses the hydrolysis of triglycerides into free fatty acids (FFA) and increases the cellular uptake of FA.

METHODS

We used immunohistochemistry and quantitative reverse transcription real-time polymerase chain reaction to evaluate LPL expression in human and mouse HCC samples. Using lipoprotein-deficient medium as well as siRNAs against LPL and/or FASN, we investigated whether human HCC cells depend on both endogenous and exogenous fatty acids for survival in vitro.

RESULTS

We found that LPL is upregulated in mouse and human HCC samples. High expression of LPL in human HCC samples is associated with poor prognosis. In HCC cell lines, silencing of FASN or LPL or culturing the cells in lipoprotein-deficient medium significantly decreased cell proliferation. Importantly, when FASN suppression was coupled to concomitant LPL depletion, the growth restraint of cell lines was further augmented.

CONCLUSIONS

The present study strongly suggests that both de novo synthetized and exogenous FA play a major role along hepatocarcinogenesis. Thus, combined suppression of LPL and FASN might be highly beneficial for the treatment of human HCC.

Jagged 1 is a major Notch ligand along cholangiocarcinoma development in mice and humans

Intrahepatic cholangiocarcinoma (ICC) is a rare yet deadly malignancy with limited treatment options. Activation of the Notch signalling cascade has been implicated in cholangiocarcinogenesis. However, while several studies focused on the Notch receptors required for ICC development, little is known about the upstream inducers responsible for their activation. Here, we show that the Jagged 1 (Jag1) ligand is almost ubiquitously upregulated in human ICC samples when compared with corresponding non-tumorous counterparts. Furthermore, we found that while overexpression of Jag1 alone does not lead to liver tumour development, overexpression of Jag1 synergizes with activated AKT signalling to promote liver carcinogenesis in AKT/Jag1 mice. Histologically, tumours consisted exclusively of ICC, with hepatocellular tumours not occurring in AKT/Jag1 mice. Furthermore, tumours from AKT/Jag1 mice exhibited extensive desmoplastic reaction, an important feature of human ICC. At the molecular level, we found that both AKT/mTOR and Notch cascades are activated in AKT/Jag1 ICC tissues, and that the Notch signalling is necessary for ICC development in AKT/Jag1 mice. In human ICC cell lines, silencing of Jag1 via specific small interfering RNA reduces proliferation and increases apoptosis. Finally, combined inhibition of AKT and Notch pathways is highly detrimental for the in vitro growth of ICC cell lines. In summary, our study demonstrates that Jag1 is an important upstream inducer of the Notch signalling in human and mouse ICC. Targeting Jag1 might represent a novel therapeutic strategy for the treatment of this deadly disease.

The Epidermal Growth Factor Receptor (EGFR) Inhibitor Gefitinib Reduces but Does Not Prevent Tumorigenesis in Chemical and Hormonal Induced Hepatocarcinogenesis Rat Models

Activation of the epidermal growth factor receptor (EGFR) signaling pathway promotes the development of hepatocellular adenoma (HCA) and carcinoma (HCC). The selective EGFR inhibitor Gefitinib was found to prevent hepatocarcinogenesis in rat cirrhotic livers. Thus, Gefitinib might reduce progression of pre-neoplastic liver lesions to HCC. In short- and long-term experiments, administration of N-Nitrosomorpholine (NNM) or intrahepatic transplantation of pancreatic islets in diabetic (PTx), thyroid follicles in thyroidectomized (TTx) and ovarian fragments in ovariectomized (OTx) rats was conducted for the induction of foci of altered hepatocytes (FAH). Gefitinib was administered for two weeks (20 mg/kg) or three and nine months (10 mg/kg). In NNM-treated rats, Gefitinib administration decreased the amount of FAH when compared to controls. The amount of HCA and HCC was decreased, but development was not prevented. Upon all transplantation models, proliferative activity of FAH was lower after administration of Gefitinib in short-term experiments. Nevertheless, the burden of HCA and HCC was not changed in later stages. Thus, EGFR inhibition by Gefitinib diminishes chemical and hormonal also induced hepatocarcinogenesis in the initiation stage in the non-cirrhotic liver. However, progression to malignant hepatocellular tumors was not prevented, indicating only a limited relevance of the EGFR signaling cascade in later stages of hepatocarcinogenesis.

Differential requirement for de novo lipogenesis in cholangiocarcinoma and hepatocellular carcinoma of mice and humans

Hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC) are the most prevalent types of primary liver cancer. These malignancies have limited treatment options, resulting in poor patient outcomes. Metabolism reprogramming, including increased de novo lipogenesis, is one of the hallmarks of cancer. Fatty acid synthase (FASN) catalyzes the de novo synthesis of long-chain fatty acids from acetyl-coenzyme A and malonyl-coenzyme A. Increased FASN expression has been reported in multiple tumor types, and inhibition of FASN expression has been shown to have tumor-suppressing activity. Intriguingly, we found that while FASN is up-regulated in human HCC samples, its expression is frequently low in human ICC specimens. Similar results were observed in mouse ICC models induced by different oncogenes. Ablating FASN in the mouse liver did not affect activated AKT and Notch (AKT/Notch intracellular domain 1) induced ICC formation in vivo. Furthermore, while both HCC and ICC lesions develop in mice following hydrodynamic injection of AKT and neuroblastoma Ras viral oncogene homolog oncogenes (AKT/Ras), deletion of FASN in AKT/Ras mice triggered the development almost exclusively of ICCs. In the absence of FASN, ICC cells might receive lipids for membrane synthesis through exogenous fatty acid uptake. In accordance with the latter hypothesis, ICC cells displayed high expression of fatty acid uptake-related proteins and robust long-chain fatty acid uptake.

CONCLUSION

Our data demonstrate that FASN dependence is not a universal feature of liver tumors: while HCC development is highly dependent of FASN and its mediated lipogenesis, ICC tumorigenesis can be insensitive to FASN deprivation; our study supports novel therapeutic approaches to treat this pernicious tumor type with the inhibition of exogenous fatty acid uptake. (Hepatology 2016;63:1900-1913).

Quantification of liver proton-density fat fraction in 7.1T preclinical MR systems: Impact of the fitting technique

PURPOSE

To investigate the feasibility of estimating the proton-density fat fraction (PDFF) using a 7.1T magnetic resonance imaging (MRI) system and to compare the accuracy of liver fat quantification using different fitting approaches.

MATERIALS AND METHODS

Fourteen leptin-deficient ob/ob mice and eight intact controls were examined in a 7.1T animal scanner using a 3D six-echo chemical shift-encoded pulse sequence. Confounder-corrected PDFF was calculated using magnitude (magnitude data alone) and combined fitting (complex and magnitude data). Differences between fitting techniques were compared using Bland-Altman analysis. In addition, PDFFs derived with both reconstructions were correlated with histopathological fat content and triglyceride mass fraction using linear regression analysis.

RESULTS

The PDFFs determined with the use of both reconstructions correlated very strongly (r = 0.91). However, small mean bias between reconstructions demonstrated divergent results (3.9%; confidence interval [CI] 2.7-5.1%). For both reconstructions, there was linear correlation with histopathology (combined fitting: r = 0.61; magnitude fitting: r = 0.64) and triglyceride content (combined fitting: r = 0.79; magnitude fitting: r = 0.70).

CONCLUSION

Liver fat quantification using the PDFF derived from MRI performed at 7.1T is feasible. PDFF has strong correlations with histopathologically determined fat and with triglyceride content. However, small differences between PDFF reconstruction techniques may impair the robustness and reliability of the biomarker at 7.1T. J. Magn. Reson. Imaging 2016;44:1425-1431.

PI3K/AKT/mTOR pathway plays a major pathogenetic role in glycogen accumulation and tumor development in renal distal tubules of rats and men

Activation of the PI3K/AKT/mTOR pathway is a crucial molecular event in human clear cell renal cell carcinoma (ccRCC), and is also upregulated in diabetic nephropathy. In diabetic rats metabolic changes affect the renal distal tubular epithelium and lead to glycogen-storing Armanni-Ebstein lesions (AEL), precursor lesions of RCC in the diabetes induced nephrocarcinogenesis model. These lesions resemble human sporadic clear cell tubules (CCT) and tumor cells of human ccRCC.

Human sporadic CCT were examined in a collection of 324 nephrectomy specimen, in terms of morphologic, metabolic and molecular alterations, and compared to preneoplastic CCT and RCC developed in the rat following streptozotocin-induced diabetes or N-Nitrosomorpholine administration. Diabetic and non-diabetic rats were subjected to the dual PI3K/mTOR inhibitor, NVP/BEZ235.

Human sporadic CCT could be detected in 17.3% of kidney specimens. Human and rat renal CCT display a strong induction of the PI3K/AKT/mTOR pathway and related metabolic alterations. Proteins involved in glycolysis and de novo lipogenesis were upregulated. In in vivo experiments, dual inhibition of PI3K and mTOR resulted in a reduction of proliferation of rat diabetes related CCT and increased autophagic activity.

The present data indicate that human sporadic CCT exhibit a pattern of morphologic and metabolic alterations similar to preneoplastic lesions in the rat model. Activation of the PI3K/AKT/mTOR pathway in glycogenotic tubuli is a remarkable molecular event and suggests a preneoplastic character of these lesions also in humans.

PI3K/AKT/mTOR-dependent stabilization of oncogenic far-upstream element binding proteins in hepatocellular carcinoma cells

Transcription factors of the far-upstream element-binding protein (FBP) family represent cellular pathway hubs, and their overexpression in liver cancer (hepatocellular carcinoma [HCC]) stimulates tumor cell proliferation and correlates with poor prognosis. Here we determine the mode of oncogenic FBP overexpression in HCC cells. Using perturbation approaches (kinase inhibitors, small interfering RNAs) and a novel system for rapalog-dependent activation of AKT isoforms, we demonstrate that activity of the phosphatidylinositol-4,5-biphosphate 3-kinase/AKT pathway is involved in the enrichment of nuclear FBP1 and FBP2 in liver cancer cells. In human HCC tissues, phospho-AKT significantly correlates with nuclear FBP1/2 accumulation and expression of the proliferation marker KI67. Mechanistic target of rapamycin (mTOR) inhibition or blockade of its downstream effector eukaryotic translation initiation factor 4E activity equally reduced FBP1/2 concentrations. The mTORC1 inhibitor rapamycin diminishes FBP enrichment in liver tumors after hydrodynamic gene delivery of AKT plasmids. In addition, the multikinase inhibitor sorafenib significantly reduces FBP levels in HCC cells and in multidrug resistance 2-deficient mice that develop HCC due to severe inflammation. Both FBP1/2 messenger RNAs are highly stable, with FBP2 being more stable than FBP1. Importantly, inhibition of phosphatidylinositol-4,5-biphosphate 3-kinase/AKT/mTOR signaling significantly diminishes FBP1/2 protein stability in a caspase-3/-7-dependent manner.

CONCLUSION

These data provide insight into a transcription-independent mechanism of FBP protein enrichment in liver cancer; further studies will have to show whether this previously unknown interaction between phosphatidylinositol-4,5-biphosphate 3-kinase/AKT/mTOR pathway activity and caspase-mediated FBP stabilization allows the establishment of interventional strategies in FBP-positive HCCs.

Inactivation of fatty acid synthase impairs hepatocarcinogenesis driven by AKT in mice and humans

BACKGROUND & AIMS

Cumulating evidence underlines the crucial role of aberrant lipogenesis in human hepatocellular carcinoma (HCC). Here, we investigated the oncogenic potential of fatty acid synthase (FASN), the master regulator of de novo lipogenesis, in the mouse liver.

METHODS

FASN was overexpressed in the mouse liver, either alone or in combination with activated N-Ras, c-Met, or SCD1, via hydrodynamic injection. Activated AKT was overexpressed via hydrodynamic injection in livers of conditional FASN or Rictor knockout mice. FASN was suppressed in human hepatoma cell lines via specific small interfering RNA.

RESULTS

Overexpression of FASN, either alone or in combination with other genes associated with hepatocarcinogenesis, did not induce histological liver alterations. In contrast, genetic ablation of FASN resulted in the complete inhibition of hepatocarcinogenesis in AKT-overexpressing mice. In human HCC cell lines, FASN inactivation led to a decline in cell proliferation and a rise in apoptosis, which were paralleled by a decrease in the levels of phosphorylated/activated AKT, an event controlled by the mammalian target of rapamycin complex 2 (mTORC2). Downregulation of AKT phosphorylation/activation following FASN inactivation was associated with a strong inhibition of rapamycin-insensitive companion of mTOR (Rictor), the major component of mTORC2, at post-transcriptional level. Finally, genetic ablation of Rictor impaired AKT-driven hepatocarcinogenesis in mice.

CONCLUSIONS

FASN is not oncogenic per se in the mouse liver, but is necessary for AKT-driven hepatocarcinogenesis. Pharmacological blockade of FASN might be highly useful in the treatment of human HCC characterized by activation of the AKT pathway.

SKP2 cooperates with N-Ras or AKT to induce liver tumor development in mice

Mounting evidence indicates that S-Phase Kinase-Associated Protein 2 (SKP2) is overexpressed in human hepatocellular carcinoma (HCC). However, the role of SKP2 in hepatocarcinogenesis remains poorly delineated. To elucidate the function(s) of SKP2 in HCC, we stably overexpressed the SKP2 gene in the mouse liver, either alone or in combination with activated forms of N-Ras (N-RasV12), AKT1 (myr-AKT1), or β-catenin (ΔN90-β-catenin) protooncogenes, via hydrodynamic gene delivery. We found that forced overexpression of SKP2, N-RasV12 or ΔN90-β-catenin alone as well as co-expression of SKP2 and ΔN90-β-catenin did not induce liver tumor development. Overexpression of myr-AKT1 alone led to liver tumor development after long latency. In contrast, co-expression of SKP2 with N-RasV12 or myr-AKT1 resulted in early development of multiple hepatocellular tumors in all SKP2/N-RasV12 and SKP2/myr-AKT1 mice. At the molecular level, preneoplastic and neoplastic liver lesions from SKP2/N-RasV12 and SKP2/myr-AKT1 mice exhibited a strong induction of AKT/mTOR and Ras/MAPK pathways. Noticeably, the tumor suppressor proteins whose levels have been shown to be downregulated by SKP2-dependent degradation in various tumor types, including p27, p57, Dusp1, and Rassf1A were not decreased in liver lesions from SKP2/N-RasV12 and SKP2/myr-AKT1 mice. In human HCC specimens, nuclear translocation of SKP2 was associated with activation of the AKT/mTOR and Ras/MAPK pathways, but not with β-catenin mutation or activation. Altogether, the present data indicate that SKP2 cooperates with N-Ras and AKT proto-oncogenes to promote hepatocarcinogenesis in vivo.