Amplification and/or activation of the c-Myc protooncogene 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 the mTORC1 complex, strongly inhibits c-Myc liver tumor formation. Also, p70S6K/ribosomal protein S6 (RPS6) and eukaryotic translation initiation factor 4E-binding protein 1/eukaryotic translation initiation factor 4E (4EBP1/eIF4E) signaling cascades downstream of mTORC1 are required for c-Myc-driven tumorigenesis. Intriguingly, microarray expression analysis revealed the upregulation of multiple amino acid transporters, including 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 HCC 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 mTOR pathway or amino acid transporters may be an effective and novel therapeutic option for the treatment of HCC with activated c-Myc signaling.

Activation of the AKT/mTOR cascade and overexpression of c-Met have been implicated in the development of human hepatocellular carcinoma (HCC). To elucidate the functional crosstalk between the two pathways, we generated a model characterized by the combined expression of activated AKT and c-Met in the mouse liver. Co-expression of AKT and c-Met triggered rapid liver tumor development and mice required to be euthanized within 8 weeks after hydrodynamic injection. At the molecular level, liver tumors induced by AKT/c-Met display activation of AKT/mTOR and Ras/MAPK cascades as well as increased lipogenesis and glycolysis. Since a remarkable lipogenic phenotype characterizes liver lesions from AKT/c-Met mice, we determined the requirement of lipogenesis in AKT/c-Met driven hepatocarcinogenesis using conditional Fatty Acid Synthase (FASN) knockout mice. Of note, hepatocarcinogenesis induced by AKT/c-Met was fully inhibited by FASN ablation. In human HCC samples, coordinated expression of FASN, activated AKT, and c-Met proteins was detected in a subgroup of biologically aggressive tumors. Altogether, our study demonstrates that co-activation of AKT and c-Met induces HCC development that depends on the mTORC1/FASN pathway. Suppression of mTORC1 and/or FASN might be highly detrimental for the growth of human HCC subsets characterized by concomitant induction of the AKT and c-Met cascades.

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. 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 antitumor efficacy in vivo. Multiple human ICC cell lines were used for in vitro experiments. Hematoxylin and eosin staining, immunohistochemistry and immunoblotting were applied for 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 Altogether, our 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 regimen, especially in the subset 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 versus 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.

The recent epidemic of obesity has been associated with a sharp rise in the incidence of non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanism(s) remains poorly described and effective therapeutic approaches against NAFLD are lacking. The results establish that microRNA-378 facilitates the development of hepatic inflammation and fibrosis and suggests the therapeutic potential of microRNA-378 inhibitor for the treatment of NAFLD.

Different pyruvate kinase isoforms are expressed in a tissue-specific manner, with pyruvate kinase M2 (PKM2) suggested to be the predominant isoform in proliferating cells and cancer cells. Due to differential regulation of enzymatic activities, PKM2 but not PKM1 has been thought to favor cell proliferation. However, the role of PKM2 in tumorigenesis has been recently challenged. Here we report that increased glucose catabolism through glycolysis and increased pyruvate kinase activity in c-MYC-driven liver tumors are associated with increased expression of both PKM1 and PKM2 isoforms and decreased expression of the liver-specific isoform of pyruvate kinase, PKL. Depletion of PKM2 at the time of c-MYC over-expression in murine livers did not affect c-MYC induced tumorigenesis and resulted in liver tumor formation with decreased pyruvate kinase activity and decreased catabolism of glucose into alanine and the Krebs cycle. An increased PKM1/PKM2 ratio by ectopic PKM1 expression further decreased glucose flux into serine biosynthesis and increased flux into lactate and the Krebs cycle, resulting in reduced total levels of serine. However, these changes also did not affect c-MYC-induced liver tumor development. These results suggest that increased expression of PKM2 is not required to support c-MYC-induced tumorigenesis in the liver and that various PKM1/PKM2 ratios and pyruvate kinase activities can sustain glucose catabolism required for this process.

The current clinical practice is based on the assumption of strong correlation between diffuse glutamine synthetase expression and β-catenin activation in hepatocellular adenoma and hepatocellular carcinoma. This high correlation is based on limited data, and may represent an oversimplification as glutamine synthetase staining patterns show wide variability in clinical practice. Standardized criteria for interpreting diverse glutamine synthetase patterns, and the association between each pattern and β-catenin mutations is not clearly established. This study examines the correlation between glutamine synthetase staining patterns and β-catenin mutations in 15 typical hepatocellular adenomas, 5 atypical hepatocellular neoplasms and 60 hepatocellular carcinomas. Glutamine synthetase staining was classified into one of three patterns: (a) diffuse homogeneous: moderate to strong cytoplasmic staining in more than 90% of lesional cells, without a map-like pattern, (b) diffuse heterogeneous: moderate to strong staining in 50–90% of lesional cells, without a map-like pattern, and (c) patchy: moderate to strong staining in <50% of lesional cells (often perivascular), or weak staining irrespective of extent, and all other staining patterns (including negative cases). Sanger sequencing of CTNNB1 exon 3 was performed in all cases. Of hepatocellular tumors with diffuse glutamine synthetase staining (homogeneous or heterogeneous), an exon 3 β-catenin mutation was detected in 33% (2/6) of typical hepatocellular adenoma, 75% (3/4) of atypical hepatocellular neoplasm and 17% (8/47) of hepatocellular carcinomas. An exon 3 mutation was also observed in 15% (2/13) of hepatocellular carcinomas with patchy glutamine synthetase staining. The results show a modest correlation between diffuse glutamine synthetase immunostaining and exon 3 β-catenin mutations in hepatocellular adenoma and hepatocellular carcinoma with discrepancy rates exceeding 50% in both hepatocellular adenoma and hepatocellular carcinoma. The interpretation of β-catenin activation based on glutamine synthetase staining should be done with caution, and the undetermined significance of various glutamine synthetase patterns should be highlighted in pathology reports.

Background & Aims Activating mutations of PIK3CA occur in various tumor types, including human hepatocellular carcinoma. The mechanisms whereby PIK3CA contributes to hepatocarcinogenesis remain poorly understood. Methods PIK3CA mutants H1047R or E545K were hydrodynamically transfected, either alone or in combination with NRasV12 or c-Met genes, in the mouse liver. Results Overexpression of H1047R or E545K alone was able to induce AKT/mTOR signaling in the mouse liver, leading to hepatic steatosis. However, none of the mice developed liver tumors over long term. In contrast, H1047R or E545K cooperated with NRasV12 or c-Met rapidly induce liver tumor formation in mice. At the molecular level, all the tumor nodules displayed activation of AKT/mTOR and Ras/MAPK cascades. Ablation of AKT2 significantly inhibited hepatic steatosis induced by H1047R or E545K and carcinogenesis induced by H1047R/c-Met or E545K/c-Met. Furthermore, tumorigenesis induced by H1047R/c-Met was abolished in conditional Raptor knockout mice. Conclusions In conclusion, both H1047R and E545K are able to activate the AKT/mTOR pathway. An intact AKT2/mTORC1 cascade is required for tumorigenesis induced by H1047R/c-Met or E545K/c-Met in the liver.

The elucidation of molecular events that confer tamoxifen resistance to estrogen receptor α (ER) positive breast cancer is of major scientific and therapeutic importance. Here, we report that LEM4 overexpression renders ER+ breast cancer cells resistant to tamoxifen by activating the cyclin D-CDK4/6 axis and the ERα signaling. We show that LEM4 overexpression accelerates tumor growth. Interaction with LEM4 stabilizes CDK4 and Rb, promotes Rb phosphorylation and the G1/S phase transition. LEM4 depletion or combined tamoxifen and PD0332991 treatment significantly reverses tamoxifen resistance. Furthermore, LEM4 interacts with and stabilizes both Aurora-A and ERα, promotes Aurora-A mediated phosphorylation of ERα-Ser167, leading to increase in ERα DNA-binding and transactivation activity. Elevated levels of LEM4 correlates with poorer relapse-free survival in patients with ER+ breast cancer undergoing endocrine therapy. Thus, LEM4 represents a prognostic marker and an attractive target for breast cancer therapeutics. Functional antagonism of LEM4 could overcome tamoxifen resistance.