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Persistent effect of mTOR inhibition on preneoplastic foci progression and gene expression in a rat model of hepatocellular carcinoma.

ABSTRACT: Hepatocellular carcinoma (HCC) is a heterogeneous disease in which tumor subtypes can be identified based on the presence of adult liver progenitor cells. Having previously identified the mTOR pathway as critical to progenitor cell proliferation in a model of liver injury, we investigated the temporal activation of mTOR signaling in a rat model of hepatic carcinogenesis. The model employed chemical carcinogens and partial hepatectomy to induce progenitor marker-positive HCC. Immunohistochemical staining for phosphorylated ribosomal protein S6 indicated robust mTOR complex 1 (mTORC1) activity in early preneoplastic lesions that peaked during the first week and waned over the subsequent 10 days. Continuous administration of rapamycin by subcutaneous pellet for 70 days markedly reduced the development of focal lesions, but resulted in activation of the PI3K signaling pathway. To test the hypothesis that early mTORC1 activation was critical to the development and progression of preneoplastic foci, we limited rapamycin administration to the 3-week period at the start of the protocol. Focal lesion burden was reduced to a degree indistinguishable from that seen with continuous administration. Short-term rapamycin did not result in the activation of PI3K or mTORC2 pathways. Microarray analysis revealed a persistent effect of short-term mTORC1 inhibition on gene expression that resulted in a genetic signature reminiscent of normal liver. We conclude that mTORC1 activation during the early stages of hepatic carcinogenesis may be critical due to the development of preneoplastic focal lesions in progenitor marker-positive HCC. mTORC1 inhibition may represent an effective chemopreventive strategy for this form of liver cancer.

SUBMITTER: Francois-Vaughan H

PROVIDER: S-EPMC5006212 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Persistent effect of mTOR inhibition on preneoplastic foci progression and gene expression in a rat model of hepatocellular carcinoma.

Francois-Vaughan Heather H Adebayo Adeola O AO Brilliant Kate E KE Parry Nicola M A NMA Gruppuso Philip A PA Sanders Jennifer A JA

Carcinogenesis 20160210 4

Hepatocellular carcinoma (HCC) is a heterogeneous disease in which tumor subtypes can be identified based on the presence of adult liver progenitor cells. Having previously identified the mTOR pathway as critical to progenitor cell proliferation in a model of liver injury, we investigated the temporal activation of mTOR signaling in a rat model of hepatic carcinogenesis. The model employed chemical carcinogens and partial hepatectomy to induce progenitor marker-positive HCC. Immunohistochemical ...[more]

PMID: 26905589

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Project description:Recent publications show that classic hepatoblastoma (HBL) is the result of failure of hepatic stem cells to differentiate into hepatocytes, while hepatocellular carcinoma (HCC) is caused by the dedifferentiation of hepatocytes into cancer stem cells. However, the mechanisms of aggressive HBL and the mechanisms that cause dedifferentiation of hepatocytes into cancer stem cells are unknown. We found that, similar to HCC but opposite to classic HBL, aggressive HBL is the result of dedifferentiation of hepatocytes into cancer stem cells. In both cases of liver cancer, the dephosphorylation of tumor suppressor protein CCAAT/enhancer binding protein α (C/EBPα) at Ser193 (Ser190 in human protein) or mutation of Ser193 to Ala results in a modified protein with oncogenic activities. We have investigated liver cancer in a mouse model C/EBPα-S193A, in a large cohort of human HBL samples, and in Pten/p53 double knockout mice and found that these cancers are characterized by elevation of C/EBPα that is dephosphorylated at Ser190/193. We found that dephosphorylated C/EBPα creates preneoplastic foci with cancer stem cells that give rise to HCC and aggressive HBL. C/EBPα-dependent dedifferentiation of hepatocytes into cancer stem cells includes increased proliferation of hepatocytes, followed by generation of multinucleated hepatocytes and subsequent appearance of hepatocytes with delta-like 1 homolog-positive intranuclear inclusions. We further isolated C/EBPα-dependent multinucleated hepatocytes and found that they possess characteristics of tumor-initiating cells, including elevation of stem cell markers. C/EBPα-dependent cancer stem cells are observed in patients with aggressive HBL and in patients with a predisposition for liver cancer.ConclusionThe earliest steps of adult HCC and aggressive pediatric liver cancer have identical features that include conversion of the tumor suppressor C/EBPα into an oncogenic isoform, which further creates preneoplastic foci where hepatocytes dedifferentiate into cancer cells, giving rise to liver cancer. (Hepatology 2018;67:1857-1871).

Project description:BackgroundHepatocellular carcinoma (HCC) is the sixth most common cancer and the second leading cause of cancer-related deaths worldwide. Despite new technologies in diagnosis and treatment, the incidence and mortality of HCC continue rising. And its pathogenesis is still unclear. As a highly conserved protein of the Golgi apparatus, Golgi phosphoprotein 3 (GOLPH3) has been shown to be involved in tumorigenesis of HCC. This study aimed to explore the exact oncogenic mechanism of GOLPH3 and provide a novel diagnose biomarker and therapeutic strategy for patients with HCC.MethodsFirstly, the expression of GOLPH3 was detected in the HCC tissue specimens and HCC cell lines. Secondly, RNA interference was used for GOLPH3 gene inhibition. Thirdly, cell proliferation was analyzed by MTT; cell apoptosis was analyzed by Annexin-V/PI staining, Hoechst 33,342 staining and caspase 3/7 activity assay. Fourthly, xenograft tumor model was used to study the function of GOLPH3 in tumor growth in vivo. Finally, western blotting and immunohistochemistry were used to investigate the role of GOLHP3 in the mTOR signaling pathway.ResultsData showed that the mRNA and protein expression of GOLPH3 were up-regulated in HCC tumor tissue and cell lines compared with those of control (P < 0.05). Correlation analyses showed that GOLPH3 expression was positively correlated with serum alpha-fetoprotein level (AFP, P = 0.006). Knockdown GOLPH3 expression inhibited proliferation and promoted apoptosis in HCC cell lines. What's more, knockdown GOLPH3 expression led to tumor growth restriction in xenograft tumor model. The expression of phosphorylated mTOR, AKT and S6 K1 were significantly higher in HCC tumor tissue and cell lines compared with those in normal liver tissues (p < 0.05). While the phosphorylated mTOR, AKT and S6 K1 were much lower when diminished GOLPH3 expression in HCC cell lines both in vitro and in vivo.ConclusionThe current study suggests that GOLPH3 contributes to the tumorigenesis of HCC by activating mTOR signaling pathway. GOLPH3 is a promising diagnose biomarker and therapeutic target for HCC. Our study may provide a scientific basis for developing effective approaches to treat the HCC patients with GOLPH3 overexpression.

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Persistent effect of mTOR inhibition on preneoplastic foci progression and gene expression in a rat model of hepatocellular carcinoma.

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Persistent effect of mTOR inhibition on preneoplastic foci progression and gene expression in a rat model of hepatocellular carcinoma.

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