Deregulated expression of Notch receptors in human hepatocellular carcinoma

Novel therapeutic strategies for targeting liver cancer stem cells

The cancer stem cell (CSC) hypothesis was first proposed over 40 years ago. Advances in CSC isolation were first achieved in hematological malignancies, with the first CSC demonstrated in acute myeloid leukemia. However, using similar strategies and technologies, and taking advantage of available surface markers, CSCs have been more recently demonstrated in a growing range of epithelial and other solid organ malignancies, suggesting that the majority of malignancies are dependent on such a compartment.

Primary liver cancer consists predominantly of hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). It is believed that hepatic progenitor cells (HPCs) could be the origin of some HCCs and ICCs. Furthermore, stem cell activators such as Wnt/β-catenin, TGF-β, Notch and Hedgehog signaling pathways also expedite tumorigenesis, and these pathways could serve as molecular targets to assist in designing cancer prevention strategies. Recent studies indicate that additional factors such as EpCAM, Lin28 or miR-181 may also contribute to HCC progression by targeting HCC CSCs. Various therapeutic drugs that directly modulate CSCs have been examined in vivo and in vitro. However, CSCs clearly have a complex pathogenesis, with a considerable crosstalk and redundancy in signaling pathways, and hence targeting single molecules or pathways may have a limited benefit for treatment. Many of the key signaling molecules are shared by both CSCs and normal stem cells, which add further challenges for designing molecularly targeted strategies specific to CSCs but sparing normal stem cells to avoid side effects. In addition to the direct control of CSCs, many other factors that are needed for the maintenance of CSCs, such as angiogenesis, vasculogenesis, invasion and migration, hypoxia, immune evasion, multiple drug resistance, and radioresistance, should be taken into consideration when designing therapeutic strategies for HCC.

Here we provide a brief review of molecular signaling in liver CSCs and present insights into new therapeutic strategies for targeting liver CSCs.

Notch signaling proteins: legitimate targets for cancer therapy

Proteins and small peptides (growth factors and hormones) are key molecules in maintaining cellular homeostasis. To that end, Notch signaling pathway proteins are known to play critical roles in maintaining the balance between cell proliferation, differentiation and apoptosis, and thus it has been suggested that Notch may be responsible for the development and progression of human malignancies. Therefore, the Notch signaling pathway proteins may present novel therapeutic targets, which could have promising therapeutic impact on eradicating human malignancies. This review describes the role of Notch signaling pathway proteins in cancer and how its deregulation is involved in tumor development and progression leading to metastasis and the ultimate demise of patients diagnosed with cancer. Further, we summarize the role of several Notch inhibitors especially "natural agents" that could represent novel therapeutic strategies targeting Notch signaling toward better treatment outcome of patients diagnosed with cancer.

Rosuvastatin counteracts vessel arterialisation and sinusoid capillarisation, reduces tumour growth, and prolongs survival in murine hepatocellular carcinoma

Background and Aims. An arterial blood supply and phenotypic changes of the sinusoids characterise the liver vasculature in human hepatocellular carcinoma (HCC). We investigated the effects of rosuvastatin on liver vessel anomalies, tumour growth and survival in HCC. Methods. We treated transgenic mice developing HCC, characterized by vessel anomalies similar to those of human HCC, with rosuvastatin. Results. In the rosuvastatin group, the survival time was longer (P < .001), and liver weight (P < .01) and nodule surface (P < .01) were reduced. Rosuvastatin decreased the number of smooth muscle actin-positive arteries (P < .05) and prevented the sinusoid anomalies, with decreased laminin expression (P < .001), activated hepatic stellate cells (P < .001), and active Notch4 expression. Furthermore, rosuvastatin inhibited endothelial cell but not tumour hepatocyte functions. Conclusions. Rosuvastatin reduced the vessel anomalies and tumour growth and prolonged survival in HCC. These results represent new mechanisms of the effects of statin on tumour angiogenesis and a potential target therapy in HCC.

Up-regulated expression of Notch1 and Jagged1 in human colon adenocarcinoma

Deregulated expression of Notch molecules is observed in many malignant tumors, however, the expression of Notch1 and Jagged1 in colon adenocarcinoma is still unknown. This study is to investigate the expression of Notch1 and Jagged1 in human colon adenocarcinoma. Sixty-five human colon adenocarcinoma and 60 adjacent nontumor colon tissue sections were detected by immunohistochemistry. Ten paired fresh surgical human colon adenocarcinoma and adjacent nontumor colon samples were analyzed by Western blot and RT-PCR. Both Notch1 and Jagged1 were expressed in the cytoplasm of neoplastic cells of colon adenocarcinoma tissue. The protein and mRNA levels of both molecules were higher in colon adenocarcinoma than in adjacent nontumor tissue. Moreover, Notch1 was positively correlated with tumor stage. This investigation demonstrates that Notch1 and Jagged1 are up-regulated in human colon adenocarcinoma and suggests that Notch1/Jagged1 signaling might play a role in the development of colon adenocarcinoma.

Epigenetic regulation of cancer stem cells in liver cancer: current concepts and clinical implications

The two dominant models of carcinogenesis postulate stochastic (clonal evolution) or hierarchic organization of tumor (cancer stem cell model). According to the latter, at the germinal center of tumor evolution is a cancer stem cell (CSC) which, similar to normal adult stem cells, possesses the capacity of self-renewal and a differentiation potential. Over the past few years, compelling evidence has emerged in support of the hierarchic cancer model for many solid tumors including hepatocellular cancers. The CSCs are posited to be responsible not only for tumor initiation but also for the generation of distant metastasis and relapse after therapy. These characteristics are particularly relevant for a multi-resistant tumor entity like human hepatocellular carcinoma and may herald a paradigm shift in the management of this deadly disease. Identification and detailed characterization of liver CSCs is therefore imperative for improving prevention approaches, enhancing early detection, and extending the limited treatment options. Despite the current progress in understanding the contribution of CSCs to the generation of heterogeneity of tumors, the molecular complexity and exact regulation of CSCs is poorly understood. This review focuses on the genetic and epigenetic mechanisms that regulate and define the unique CSC properties with an emphasis on key regulatory pathways of liver CSCs and their clinical significance.

Over-activated Notch-1 protects gastric carcinoma BGC-823 cells from TNFalpha-induced apoptosis

BACKGROUND/AIM

The role of Notch-1 in human gastric carcinoma, one of the most common carcinomas of the human digestive tract, remains poorly characterised. Here, we investigated the effect and mechanism of Notch-1 activation on TNFalpha-induced apoptosis of human gastric carcinoma BGC-823 cells.

METHODS

Cell viabililty was measured by MTT assay. Apoptosis was detected by flow cytometry assay. Notch-1, Hes-1, caspase-3 p20 and NF-kappaB p65 expressions were assayed by Western blotting. NF-kappaB activation was tested by electrophoretic mobility shift assay (EMSA), and caspase-3 activation was tested by colorimetric assay.

RESULTS

BGC-823 cells underwent apoptosis following stimulation with TNFalpha. We found that Notch-1 was over-activated by overexpressing exogenous intracellular domain of Notch (ICN) via retrovirus-mediated gene transfer, and over-activated Notch-1 reduced the TNFalpha-induced growth suppression and apoptosis in BGC-823 cells. Down-regulation of Notch-1 by siRNA targeting Notch-1 enhanced TNFalpha-induced apoptosis in BGC-823 cells. As the molecular mechanism involved, we showed over-activated Notch-1 partially suppressed TNFalpha-induced activation of caspase-3. However, TNFalpha-induced activation of NF-kappaB was not affected by over-activated Notch-1.

CONCLUSIONS

Our data indicate that over-activated Notch-1 significantly protects BGC-823 cells from TNFalpha-induced apoptosis, and this effect is mediated, at least in part, by decreasing activation of caspase-3 independent of NF-kappaB.

Significance of HBx gene up-regulated expression of DNA repair enzyme hMTH1 in the HepG2 cells

AIM: To explore the role of oxidative DNA damage repair enzyme hMTH1 in the HBx-induced hepatocellular carcinoma.

METHODS: 8-OHdG levels were determined using HPLC/ECD in the HepG2/HBx and in HepG2 and HepG2/pcDNA3.1 of the control cells. Using the β-actin as the interior control, real-time quantitative polymerase chain reaction (qPCR) was employed to examine the expression of DNA repair enzyme hMTH1 of hydrolyze 8-OHdG.

RESULTS: The 8-OHdG level was significantly higher in the HepG2/HBx than in HepG2 and HepG2/pcDNA3.1 (36.5 ± 6.25 vs 8.52 ± 1.65, 9.12 ± 2.69 fmol 8-OHdG/mg DNA, both P < 0.05), and the expression of DNA repair enzyme hMTH1 mRNA was significantly higher than the control cells (1.213 ± 0.100 vs 0.087 ± 0.026, 0.112 ± 0.052 hMTH1/β-actin mRNA×100, both P < 0.05).

CONCLUSION: HBx gene may increase the level of oxidative DNA-adduct 8-OHdG by promoting the oxidative stress in HepG2 cells, thus reactivity increases the expression of DNA repair enzyme hMTH1.

Selective ablation of Notch3 in HCC enhances doxorubicin's death promoting effect by a p53 dependent mechanism

BACKGROUND/AIMS

The functional roles of endogenous Notch3 and Notch1 for protecting human hepatocellular carcinoma (HCC) lines against doxorubicin-induced death have been investigated. We previously reported aberrant Notch3 and Notch4 up-regulation in HCC and we have extended these observations to include Notch1.

METHODS

Notch1 expression was assessed by immunohistochemistry and immunoblotting. Notch3 and Notch1 expression were ablated in multiple HCC lines by stable retroviral transduction of short hairpin RNAs (shRNAs). Effects on doxorubicin sensitivity were evaluated with respect to cell growth, expression of specific cell cycle effectors and multiple apoptotic parameters.

RESULTS

Notch3 depletion increased p53 expression, doxorubicin uptake, DNA damage, the apoptosis inducing effects of doxorubicin and also impeded the cell cycle progression of HCC cells. Ablating p53 expression in Notch3 knockdown (KD) cells largely abolished their enhanced doxorubicin sensitivity; and Notch3 KD in p53(-/-) Hep3B cells failed to influence their response to doxorubicin. Although up-regulated in most HCC, Notch1 (unlike Notch3) did not contribute to the doxorubicin resistance of HCC lines.

CONCLUSIONS

Our in vitro results represent the first evidence that Notch3 silencing in combination with chemotherapeutics could conceivably provide a novel strategy for HCC treatment that deserves further exploration.

The effects of HBx gene on the expression of DNA repair enzymes hOGG1 and hMYHalpha mRNA in HepG2 cells

To observe the alteration in the expression of DNA repair enzymes hOGG1 and hMYHalpha and the change in 8-OHdG levels in the HBx gene-transfected cells HepG2/HBx and to explore the mechanisms of the HBV-associated hepatocellular carcinoma, the gene-transfected cells HepG2/HBx which stably expressed HBx was established, and the effect of HBx on the cell cycle and proliferation of HepG2 was examined. By using the beta-actin as the interior control, real-time polymerase chain reaction (Real-time qPCR) was employed to quantitatively detect the expression of DNA repair enzymes hOGG1 and hMYHalpha in the HepG2/HBx, the control cells HepG2 and HepG2 transfected with pcDNA3.1 vector (HepG2/pDNA3.1). The 8-OHdG levels were determined by HPLC/ECD in the established gene-transfected cells HepG2/HBx and the control cells HepG2 and HepG2/pcDNA3.1. Our results showed that the expression of DNA repair enzyme hMYHalpha in the HepG2/HBx (0.021+/-0.007) was significantly lower than that of HepG2 (0.099+/-0.041) (P<0.05) and HepG2/pDNA3.1 (0.121+/-0.005) (P<0.05). However, the no significant differences existed in the expression of DNA repair enzyme hOGG1 among the three cell strains (P>0.05). The 8-OHdG level in the HepG2/HBx was significantly higher than that in HepG2 and HepG2/pcDNA3.1 (P<0.05). It is concluded that HBx gene may inhibit the expression of DNA repair enzyme hMYHalpha mRNA to impair the ability to repair the intracellular DNA oxidative damage, to increase the oxidative DNA-adduct 8-OHdG and to affect the nucleotide excision repair function, thus participate in the occurrence and development of hepatocellular carcinoma.

Effects of down-regulation of p21 by HBx gene on HepG2 cell proliferation and apoptosis

AIM: To establish gene-transfected cell strain HepG2/HBx and study the effect of HBx on cell cycle, proliferation and apoptosis of HepG2 cells as well as the potential regulative role of p21.

METHODS: HBx was transfected into HepG2 cells and G418 selection was used to obtain the positive clones of HepG2/HBx cells. Then HBx mRNA expression and protein expression were detected using RT-PCR and western blot analysis respectively. MTT assay and flow cytometry were adopted to measure the proliferation, cell cycle and apoptosis of HepG2/HBx, HepG2 and HepG2/pcDNA3.1 (HepG2 cells transfected with pcDNA3.1) cells. Semi-quantified RT-PCR was used to evaluate the expression of p21 and p53 in three groups.

RESULTS: The expression of mRNA and protein of HBx in HepG2/HBx cells was confirmed by RT-PCR and western blot respectively. The proliferation of HepG2/HBx cells was accelerated. The proportion of HepG2/HBx cells decreased significantly in G₀/G₁ phase (43.34% ± 3.11% vs 57.69 ± 4.28%, P < 0.01), but increased remarkably in S phase (28.69% ± 1.17% vs 22.41% ± 1.99%, P < 0.05) and the apoptosis rate of HepG2/HBx cells was at a significantly lower level (1.19% ± 0.06% vs 5.43% ± 0.42%, P < 0.001). Compared with HepG2 and HepG2/pcDNA3.1 cells, the expression of p21 mRNA in HepG2/HBx was down-regulated (0.16 ± 0.05 vs 0.78 ± 0.15, P < 0.001), while there was no significant difference in the expression of p53 gene.

CONCLUSION: The HBx gene down-regulates the expression of p21 mRNA, which may play an important role in accelerating cell cycle, improving growth and inhibiting apoptosis of HepG2 cells.