Tg737 inhibition results in malignant transformation in fetal liver stem/progenitor cells by promoting cell-cycle progression and differentiation arrest

Differentiation-inducing therapeutic effect of Notch inhibition in reversing malignant transformation of liver normal stem cells via MET

Background

Liver cancer stem cells (LCSCs) are the key factors for cancer metastasis, recurrent, and drug resistance. LCSCs are originated from either hepatocytes dedifferentiation or differentiation arresting of liver normal stem cells (LNSCs). Differentiation-inducing therapy is a novel strategy in solid tumors. Furthermore, Notch signaling pathway has been proved to play important role in the process of hepatocytes differentiation. In previous study, a malignant transformation cellular model of LNSCs has been built up, and in this study we are trying to illustrate whether inhibition of Notch can reverse this malignant tendency and drive these malignant cells back to differentiate into mature hepatocytes.

Results

Inhibition of Notch signaling pathway can down-regulate the stemness-related cancer markers, lower the proliferative status, alleviate the invasive characteristic, or attenuate the metastasis tendency. What is more, it can help the malignantly transformed cells to regain the mature hepatic function of glucagon synthesis, urea metabolism, albumin production, and indocyanine-green (ICG) clearance.

Materials and Methods

HOX transcript antisense RNA (HOTAIR) expression was enhanced in LNSCs via lentivirus transduction to set up the malignant transformation cellular model. Then, a Notch inhibitor was applied to induce malignantly transformed cells differentiate into mature hepatocytes, and malignant abilities of proliferation, invasiveness, tumorigenesis as well as mature hepatocyte function were observed and compared.

Conclusions

The data demonstrate that the anti-tumor effects of Notch inhibition may lie not only on killing the cancer cells or LCSCs directly, it can also induce the LCSCs differentiation into mature hepatocytes via mesenchymal-epithelial transition (MET) progress or downgrade the malignancy.

Tg737 regulates epithelial-mesenchymal transition and cancer stem cell properties via a negative feedback circuit between Snail and HNF4α during liver stem cell malignant transformation

Determining the origin of liver cancer stem cells is important for treating hepatocellular carcinoma. Tg737 deficiency plays an important role in the malignant transformation of liver stem cells, but the underlying mechanism remains unclear. Here we established a chemical-induced mouse hepatoma model and found that Tg737 and hepatocyte nuclear factor 4-alpha (HNF4α) expression decreased and epithelial-mesenchymal transition (EMT)-related marker expression increased during liver cancer development. To investigate the underlying mechanism, we knocked down Tg737 in WB-F344 (WB) rat hepatic oval cells. Loss of Tg737 resulted in nuclear β-catenin accumulation and activation of the Wnt/β-catenin pathway, which further promoted EMT and the malignant phenotype. XAV939, a β-catenin inhibitor, attenuated WB cell malignant transformation due to Tg737 knockdown. To clarify the relationships of Tg737, the β-catenin pathway, and HNF4α, we inhibited Snail and overexpressed HNF4α after Tg737 knockdown in WB cells and found that Snail and HNF4α comprise a negative feedback circuit. Taken together, the results showed that Tg737 regulates a Wnt/β-catenin/Snail-HNF4α negative feedback circuit, thereby blocking EMT and the malignant transformation of liver stem cells to liver cancer stem cells.

MicroRNA-548a-5p promotes proliferation and inhibits apoptosis in hepatocellular carcinoma cells by targeting Tg737

AIM: To investigate whether Tg737 is regulated by microRNA-548a-5p (miR-548a-5p), and correlates with hepatocellular carcinoma (HCC) cell proliferation and apoptosis.

METHODS: Assays of loss of function of Tg737 were performed by the colony formation assay, CCK assay and cell cycle assay in HCC cell lines. The interaction between miR-548a-5p and its downstream target, Tg737, was evaluated by a dual-luciferase reporter assay and quantitative real-time polymerase chain reaction. Tg737 was then up-regulated in HCC cells to evaluate its effect on miR-548a-5p regulation. HepG2 cells stably overexpressing miR-548a-5p or miR-control were also subcutaneously inoculated into nude mice to evaluate the effect of miR-548a-5p up-regulation on in vivo tumor growth. As the final step, the effect of miR-548a-5p on the apoptosis induced by cisplatin was evaluated by flow cytometry.

RESULTS: Down-regulation of Tg737, which is a target gene of miR-548a-5p, accelerated HCC cell proliferation, and miR-548a-5p promoted HCC cell proliferation in vitro and in vivo. Like the down-regulation of Tg737, overexpression of miR-548a-5p in HCC cell lines promoted cell proliferation, increased colony forming ability and hampered cell apoptosis. In addition, miR-548a-5p overexpression increased HCC cell growth in vivo. MiR-548a-5p down-regulated Tg737 expression through direct contact with its 3’ untranslated region (UTR), and miR-548a-5p expression was negatively correlated with Tg737 levels in HCC specimens. Restoring Tg737 (without the 3’UTR) significantly hampered miR-548a-5p induced cell proliferation, and rescued the miR-548a-5p induced cell proliferation inhibition and apoptosis induced by cisplatin.

CONCLUSION: MiR-548a-5p negatively regulates the tumor inhibitor gene Tg737 and promotes tumorigenesis in vitro and in vivo, indicating its potential as a novel therapeutic target for HCC.

New frontiers: discovering cilia-independent functions of cilia proteins

In most vertebrates, mitotic spindles and primary cilia arise from a common origin, the centrosome. In non-cycling cells, the centrosome is the template for primary cilia assembly and, thus, is crucial for their associated sensory and signaling functions. During mitosis, the duplicated centrosomes mature into spindle poles, which orchestrate mitotic spindle assembly, chromosome segregation, and orientation of the cell division axis. Intriguingly, both cilia and spindle poles are centrosome-based, functionally distinct structures that require the action of microtubule-mediated, motor-driven transport for their assembly. Cilia proteins have been found at non-cilia sites, where they have distinct functions, illustrating a diverse and growing list of cellular processes and structures that utilize cilia proteins for crucial functions. In this review, we discuss cilia-independent functions of cilia proteins and re-evaluate their potential contributions to "cilia" disorders.

Role of liver stem cells in hepatocarcinogenesis

Liver cancer is an aggressive disease with a high mortality rate. Management of liver cancer is strongly dependent on the tumor stage and underlying liver disease. Unfortunately, most cases are discovered when the cancer is already advanced, missing the opportunity for surgical resection. Thus, an improved understanding of the mechanisms responsible for liver cancer initiation and progression will facilitate the detection of more reliable tumor markers and the development of new small molecules for targeted therapy of liver cancer. Recently, there is increasing evidence for the “cancer stem cell hypothesis”, which postulates that liver cancer originates from the malignant transformation of liver stem/progenitor cells (liver cancer stem cells). This cancer stem cell model has important significance for understanding the basic biology of liver cancer and has profound importance for the development of new strategies for cancer prevention and treatment. In this review, we highlight recent advances in the role of liver stem cells in hepatocarcinogenesis. Our review of the literature shows that identification of the cellular origin and the signaling pathways involved is challenging issues in liver cancer with pivotal implications in therapeutic perspectives. Although the dedifferentiation of mature hepatocytes/cholangiocytes in hepatocarcinogenesis cannot be excluded, neoplastic transformation of a stem cell subpopulation more easily explains hepatocarcinogenesis. Elimination of liver cancer stem cells in liver cancer could result in the degeneration of downstream cells, which makes them potential targets for liver cancer therapies. Therefore, liver stem cells could represent a new target for therapeutic approaches to liver cancer in the near future.

Notch inhibition promotes fetal liver stem/progenitor cells differentiation into hepatocytes via the inhibition of HNF-1β

In a previous study, the Notch pathway inhibited with N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (also called DAPT) was shown to promote the differentiation of fetal liver stem/progenitor cells (FLSPCs) into hepatocytes and to impair cholangiocyte differentiation. The precise mechanism for this, however, was not elucidated. Two mechanisms are possible: Notch inhibition might directly up-regulate hepatocyte differentiation via HGF (hepatocyte growth factor) and HNF (hepatocyte nuclear factor)-4α or might impair cholangiocyte differentiation thereby indirectly rendering hepatocyte differentiation as the dominant state. In this study, HGF and HNF expression was detected after the Notch pathway was inhibited. Although our initial investigation indicated that the inhibition of Notch induced hepatocyte differentiation with an efficiency similar to the induction via HGF, the results of this study demonstrate that Notch inhibition does not induce significant up-regulation of HGF or HNF-4α in FLSPCs. This suggests that Notch inhibition induces hepatocyte differentiation without the influence of HGF or HNF-4α. Moreover, significant down-regulation of HNF-1β was observed, presumably dependent on an impairment of cholangiocyte differentiation. To confirm this presumption, HNF-1β was blocked in FLSPCs and was followed by hepatocyte differentiation. The expression of markers of mature cholangiocyte was impaired and hepatocyte markers were elevated significantly. The data thus demonstrate that the inhibition of cholangiocyte differentiation spontaneously induces hepatocyte differentiation and further suggest that hepatocyte differentiation from FLSPCs occurs at the expense of the impairment of cholangiocyte differentiation, probably being enhanced partially via HNF-1β down-regulation or Notch inhibition.

Stages based molecular mechanisms for generating cholangiocytes from liver stem/progenitor cells

Except for the most organized mature hepatocytes, liver stem/progenitor cells (LSPCs) can differentiate into many other types of cells in the liver including cholangiocytes. In addition, LSPCs are demonstrated to be able to give birth to other kinds of extra-hepatic cell types such as insulin-producing cells. Even more, under some bad conditions, these LSPCs could generate liver cancer stem like cells (LCSCs) through malignant transformation. In this review, we mainly concentrate on the molecular mechanisms for controlling cell fates of LSPCs, especially differentiation of cholangiocytes, insulin-producing cells and LCSCs. First of all, to certificate the cell fates of LSPCs, the following three features need to be taken into account to perform accurate phenotyping: (1) morphological properties; (2) specific markers; and (3) functional assessment including in vivo transplantation. Secondly, to promote LSPCs differentiation, systematical attention should be paid to inductive materials (such as growth factors and chemical stimulators), progressive materials including intracellular and extracellular signaling pathways, and implementary materials (such as liver enriched transcriptive factors). Accordingly, some recommendations were proposed to standardize, optimize, and enrich the effective production of cholangiocyte-like cells out of LSPCs. At the end, the potential regulating mechanisms for generation of cholangiocytes by LSPCs were carefully analyzed. The differentiation of LSPCs is a gradually progressing process, which consists of three main steps: initiation, progression and accomplishment. It’s the unbalanced distribution of affecting materials in each step decides the cell fates of LSPCs.

Interpretation of interlocking key issues of cancer stem cells in malignant solid tumors

OBJECTIVE

In this review, several interlinking issues related to cancer stem cells (CSCs) in malignant solid tumors are sequentially discussed.

METHODS

A literature search was performed using PubMed, Web of Science and the Cochrane library, combining the words CSCs, solid tumor, isolation, identification, origination, therapy, target and epithelial-mesenchymal transition.

RESULTS

Because a primary problem is the isolation of CSCs, we first analyzed the advantages and disadvantages of recently used methods, which were mostly based on the physical or immunochemical characteristics of CSCs. Once CSCs are isolated, they should be identified by their stem cell properties. Here, we suggest how to establish a standard identification strategy. We also focused on the origination hypotheses of CSCs. The supporting molecular mechanisms for each theory were thoroughly analyzed and integrated. Especially, epithelial- mesenchymal transition is an increasingly recognized mechanism to generate CSCs that are endowed with a more invasive and metastatic phenotype. Finally, we discuss putative strategies of eliminating CSCs as effective cancer therapies.

CONCLUSION

After several interlocking issues of CSCs are thoroughly clarified, these CSCs in solid malignant tumors may specifically be targeted, which raises a new hope for eliminating these tumors.

Tg737 signaling is required for hypoxia-enhanced invasion and migration of hepatoma cells

BACKGROUND

Although hypoxia is known to promote hepatoma cell invasion and migration, little is known regarding the molecular mechanisms of this process. Our previous research showed that loss of Tg737 is associated with hepatoma cell invasion and migration; therefore, we hypothesized that the Tg737 signal might be required for hypoxia-enhanced invasion and migration.

METHODS

We established in vitro normoxic or hypoxic models to investigate the role of Tg737 in the hypoxia-enhanced invasion and migration of hepatoma cells. The hepatoma cell lines HepG2 and MHCC97-H were subjected to normoxic or hypoxic conditions, and the cell adhesion, invasion, and migration capabilities were tested. The expression of Tg737 under normoxia or hypoxia was detected using western blot assays; cell viability was determined using flow cytometry. Furthermore, we created HepG2 and MHCC97-H cells that over expressed Tg737 prior to incubation under hypoxia and investigated their metastatic characteristics. Finally, we analyzed the involvement of critical molecular events known to regulate invasion and migration.

RESULTS

In this study, Tg737 expression was significantly inhibited in HepG2 and MHCC97-H cells following exposure to hypoxia. The down regulation of Tg737 expression corresponded to significantly decreased adhesion and increased invasion and migration. Hypoxia also decreased the expression/secretion of polycystin-1, increased the secretion of interleukin-8 (IL-8), and increased the levels of active and total transforming growth factor β 1 (TGF-β1), critical regulators of cell invasion and migration. Moreover, the decrease in adhesiveness and the increase in the invasive and migratory capacities of hypoxia-treated hepatoma cells were attenuated by pcDNA3.1-Tg737 transfection prior to hypoxia. Finally, following the up regulation of Tg737, the expression/secretion of polycystin-1 increased, and the secretion of IL-8 and the levels of active and total TGF-β1 decreased correspondingly.

CONCLUSIONS

These data provide evidence that Tg737 contributes to hypoxia-induced invasion and migration, partially through the polycystin-1, IL-8, and TGF-β1 pathway. Taken together, this work suggests that Tg737 is involved in the invasion and migration of hepatoma cells under hypoxia, with the involvement of the polycystin-1, IL-8, and TGF-β1 signaling pathway. Tg737 is a potential therapeutic target for inhibiting the high invasion and migration potential of hepatoma cells in hypoxic regions.

Tissue-specific transplantation antigen P35B (TSTA3) immune response-mediated metabolism coupling cell cycle to postreplication repair network in no-tumor hepatitis/cirrhotic tissues (HBV or HCV infection) by biocomputation

We constructed the low-expression tissue-specific transplantation antigen P35B (TSTA3) immune response-mediated metabolism coupling cell cycle to postreplication repair network in no-tumor hepatitis/cirrhotic tissues (HBV or HCV infection) compared with high-expression (fold change ≥ 2) human hepatocellular carcinoma in GEO data set, by using integration of gene regulatory network inference method with gene ontology analysis of TSTA3-activated up- and downstream networks. Our results showed TSTA3 upstream-activated CCNB2, CKS1B, ELAVL3, GAS7, NQO1, NTN1, OCRL, PLA2G1B, REG3A, SSTR5, etc. and TSTA3 downstream-activated BAP1, BRCA1, CCL20, MCM2, MS4A2, NTN1, REG1A, TP53I11, VCAN, SLC16A3, etc. in no-tumor hepatitis/cirrhotic tissues. TSTA3-activated network enhanced the regulation of apoptosis, cyclin-dependent protein kinase activity, cell migration, insulin secretion, transcription, cell division, cell proliferation, DNA replication, postreplication repair, cell differentiation, T-cell homeostasis, neutrophil-mediated immunity, neutrophil chemotaxis, interleukin-8 production, inflammatory response, immune response, B-cell activation, humoral immune response, actin filament organization, xenobiotic metabolism, lipid metabolism, phospholipid metabolism, leukotriene biosynthesis, organismal lipid catabolism, phosphatidylcholine metabolism, arachidonic acid secretion, activation of phospholipase A2, deoxyribonucleotide biosynthesis, heterophilic cell adhesion, activation of MAPK activity, signal transduction by p53 class mediator resulting in transcription of p21 class mediator, G-protein-coupled receptor protein signaling pathway, response to toxin, acute-phase response, DNA damage response, intercellular junction assembly, cell communication, and cell recognition, as a result of inducing immune response-mediated metabolism coupling cell cycle to postreplication repair in no-tumor hepatitis/cirrhotic tissues.