Inhibition of growth and metastasis of human hepatocellular carcinoma by antisense oligonucleotide targeting signal transducer and activator of transcription 3

S-glutathionylation impairs signal transducer and activator of transcription 3 activation and signaling

S-glutathionylation is a physiological, reversible protein modification of cysteine residues with glutathione in response to mild oxidative stress. Because the key cell growth regulator signal transducer and activator of transcription (STAT) 3 is particularly susceptible to redox regulation, we hypothesized that oxidative modification of cysteine residues of STAT3 by S-glutathionylation may occur. Herein, we show that the cysteine residues of STAT3 are modified by a thiol-alkylating agent and are the targets of S-glutathionylation. STAT3 protein thiol reactivity was reversibly attenuated with concomitant increase in the S-glutathionylation of STAT3 upon treatment of human HepG2 hepatoma cells with pyrrolidine dithiocarbamate, glutathione disulfide, or diamide. Under these conditions there was a marked reduction in IL-6-dependent STAT3 signaling, including decreased STAT3 tyrosine phosphorylation, loss in nuclear accumulation of STAT3, and impaired expression of target genes, such as fibrinogen-gamma. In a cell-free system, diamide induced glutathionylation of STAT3, which was decreased upon addition of glutaredoxin (GRX)-1, a deglutathionylation enzyme, or the reducing agent, dithiothreitol. Glutathionylated STAT3 was a poor Janus protein tyrosine kinase 2 substrate in vitro, and it exhibited low DNA-binding activity. Cellular GRX-1 activity was inhibited by diamide and pyrrolidine dithiocarbamate treatment; however, ectopic expression of GRX-1 was accompanied by a modest increase in phosphorylation, nuclear translocation, and DNA-binding ability of STAT3 in response to IL-6. These results are the first to show S-glutathionylation of STAT3, a modification that may exert regulatory function in STAT3 signaling.

Inhibition of invasion and metastasis of hepatocellular carcinoma cells via targeting RhoC in vitro and in vivo

PURPOSE

Hepatocellular carcinoma (HCC) is one of the most deadly human cancers because of its high incidence of metastasis. Our previous work identified a strong correlation between increased expression of RhoC and HCC metastasis. Here, we investigate to define the role of RhoC in HCC metastasis. Furthermore, we sought to determine whether inhibition of the expression of RhoC might block the metastasis of HCC in vivo.

EXPERIMENTAL DESIGN

A stable retroviral small interfering RNA approach was employed to selectively knockdown the expression of RhoC in vitro and in vivo. Invasion and migration assay, MTT and fluorescence-activated cell sorting analysis, Rho activity assay, and immunofluorescence staining were carried out to characterize RhoC in vitro. An anti-RhoC retroviral gene delivery BALB/c nude mice model was established to investigate whether knockdown of the expression of RhoC might inhibit the metastasis of HCC in vivo.

RESULTS

We confirmed the correlation of RhoC expression and metastatic potentials of HCC cell lines. We also showed that suppression of RhoC expression resulted in inhibition of invasion and migration without an apparent effect on cell survival and proliferation in HCCLM3 cells. Furthermore, a similar effect of RhoC on autotaxin-induced invasion of HCCLM3 cells was also observed. Significantly, we successfully adopted an HCC metastatic mouse model that allowed us to show that knockdown of the RhoC expression resulted in inhibition of metastasis of HCC in vivo for the first time.

CONCLUSIONS

Our results show a critical role of RhoC in metastasis of HCC, implicating RhoC as a potential therapeutic target to block HCC metastasis.

RhoC is essential for angiogenesis induced by hepatocellular carcinoma cells via regulation of endothelial cell organization

The angiogenesis induced by tumor cells is essential for metastasis of hepatocellular carcinoma. Available information suggests that RhoC participates in angiogenesis through regulation of vascular endothelial growth factor expression in tumor cells. For its broad functions in cell migration and cytoskeletal organization, we hypothesized that RhoC regulating angiogenesis does not exclusively depend on regulation of vascular endothelial growth factor expression. To address this question, in the present study, we used a retroviral small interfering RNA approach to selectively knockdown the expression of RhoC in a neovascularization model in vivo and in vitro. Our present results indicate that RhoC is the downstream regulator of vascular endothelial growth factor in endothelial cells and is essential for angiogenesis induced by vascular endothelial growth factor, notwithstanding that RhoC regulates the expression of vascular endothelial growth factor in tumor cells. Furthermore, we show that knockdown of RhoC is associated with the inhibition of invasion and migration but not apoptosis of endothelial cells. Knockdown of RhoC results in inhibition of endothelial cell organization through restraining the reorganization of F-actin filaments, which represses endothelial cell network and sprout formation. In conclusion, our results demonstrate that knockdown of RhoC inhibits angiogenesis induced by tumor cells not only through effecting the release of vascular endothelial growth factor, but also through inhibiting endothelial cell migration and organization, which implies that it blocks tumor metastasis by specifically inhibiting RhoC in endothelial cells.

Cultured rat hepatocytes upregulate Akt and ERK in an ErbB-2-dependent manner

Epidermal growth factor (EGF) stimulates freshly plated adult hepatocytes to synthesize DNA, but only after they pass through a lag phase of 40 h following EGF exposure. The longer the cells are maintained, they become more responsive to EGF and the lag phase shortens. Maximal EGF-mediated stimulation of DNA synthesis requires the induction of ErbB2, which is not normally expressed in adult hepatocytes. We used immunological methods to demonstrate increased expression during culture of two gene families required for EGF to stimulate hepatocyte DNA synthesis: Akt and ERK 1/2. Both families showed hyperexpression in culture particularly when cells were exposed to insulin and EGF. Unlike CDK-2 and cyclin D1, integral mediators of the G1/S phase transition, ERK 1/2 and Akt appeared in the absence of EGF, particularly when insulin was present. This hyperexpression, which high concentrations of dexamethasone reversed, increased basal and growth factor-stimulated phosphorylation of Akt and ERK 1/2. Pharmacological blockade of phosphatidylinositol kinase suppressed the Akt increase whereas pharmacological blockade or small interfering RNA downregulation of ErbB2 inhibited both Akt and ERK 1/2 expression. All three Akt isoforms contributed to the increase in total Akt. EGF but not insulin specifically upregulated Akt 2 and 3. Since Akt and ERK 1/2 are also hyperexpressed in poorly differentiated hepatomas, their dysregulation in cancer may involve transcriptional mechanisms normally operative in cultured hepatocytes. We hypothesize that the induction and activation of ErbB2 increases the expression of these kinases, enhancing the responsiveness of hepatocytes to EGF as they adapt to culture.

ENMD-1198, a novel tubulin-binding agent reduces HIF-1alpha and STAT3 activity in human hepatocellular carcinoma(HCC) cells, and inhibits growth and vascularization in vivo

Background

Hepatocellular carcinoma (HCC) represents a highly vascularized tumor entity and the process of angiogenesis is essential for the growth of HCC. Importantly, the pro-angiogenic transcription factors HIF-1α and STAT3 have been implicated in HCC progression, thus representing interesting targets for molecular targeted therapy. We hypothesized that therapeutic inhibition of HIF-1α could be achieved by using a novel tubulin-binding agent (ENMD-1198). ENMD-1198 is an analog of 2-methoxyestradiol (2ME2) with antiproliferative and antiangiogenic activity.

Methods

The human HCC cell lines HUH-7 and HepG2 were used for experiments. Effects of ENMD-1198 on constitutive and inducible (hypoxia, growth factors) activation of signaling cascades, including HIF-1α and STAT3, were investigated by Western blotting. Changes in VEGF expression were determined by real-time PCR. Effects of ENMD-1198 on cancer cell migration and invasion were evaluated in in vitro-assays. The growth-inhibitory effects of ENMD-1198 (200 mg/kg/day) were determined in a subcutaneous tumor model (HUH-7).

Results

ENMD-1198 inhibited the phosphorylation of MAPK/Erk, PI-3K/Akt and FAK. Moreover, activation of HIF-1α and STAT3 was dramatically reduced by ENMD-1198, which resulted in lower VEGF mRNA expression (P < 0.05). In addition, tumor cell migratory and invasive properties were significantly inhibited (P < 0.05, for both). In vivo, treatment with ENMD-1198 led to a significant reduction in tumor growth, tumor vascularization, and numbers of proliferating tumor cells (P < 0.05 for all).

Conclusion

The novel microtubule destabilizing agent ENMD-1198 is suitable for inhibiting HIF-1α and STAT3 in human HCC cells and leads to reduced tumor growth and vascularization in vivo. Hence, inhibition of HIF-1α and STAT3 could prove valuable for therapy of hepatocellular carcinoma.

Ups and downs: the STAT1:STAT3 seesaw of Interferon and gp130 receptor signalling

Downstream of cytokine or growth factor receptors, STAT3 counteracts inflammation and promotes cell survival/proliferation and immune tolerance while STAT1 inhibits proliferation and favours innate and adaptive immune responses. STAT1 and STAT3 activation are reciprocally regulated and perturbation in their balanced expression or phosphorylation levels may re-direct cytokine/growth factor signals from proliferative to apoptotic, or from inflammatory to anti-inflammatory. Here we review the functional canonical and non-canonical effects of STAT1/3 activation and discuss the hypothesis that perturbation of their expression and/or activation levels may provide novel therapeutic strategies in different clinical settings and particularly in cancer.

Stat3 promotes metastatic progression of prostate cancer

There are currently no effective therapies for metastatic prostate cancer because the molecular mechanisms that underlie the metastatic spread of primary prostate cancer are unclear. Transcription factor Stat3 is constitutively active in malignant prostate epithelium, and its activation is associated with high histological grade and advanced cancer stage. In this work, we hypothesized that Stat3 stimulates metastatic progression of prostate cancer. We show that Stat3 is active in 77% of lymph node and 67% of bone metastases of clinical human prostate cancers. Importantly, adenoviral gene delivery of wild-type Stat3 (AdWTStat3) to DU145 human prostate cancer cells increased the number of lung metastases by 33-fold in an experimental metastasis assay compared with controls. Using various methods to inhibit Stat3, we demonstrated that Stat3 promotes human prostate cancer cell migration. Stat3 induced the formation of lamellipodia in both DU145 and PC-3 cells, further supporting the concept that Stat3 promotes a migratory phenotype of human prostate cancer cells. Moreover, Stat3 caused the rearrangement of cytoplasmic actin stress fibers and microtubules in both DU145 and PC-3 cells. Finally, inhibition of the Jak2 tyrosine kinase decreased both activation of Stat3 and prostate cancer cell motility. Collectively, these data indicate that transcription factor Stat3 is involved in metastatic behavior of human prostate cancer cells and may provide a therapeutic target to prevent metastatic spread of primary prostate cancer.

Growth inhibition of human hepatocellular carcinoma cells by blocking STAT3 activation with decoy-ODN

More and more studies show that signal transducer and activator of transcription 3 (STAT3) is frequently constitutively activated in a wide number of malignancies and named as an attractive molecular target for tumor treatment. Here, we employed STAT3-decoy ODN, which specifically block over-activated STAT3, to treat human hepatocellular carcinoma (HCC) cells, and evaluated the cellular proliferation ability and investigated the molecular mechanisms in vitro. The results demonstrated that the proliferation of HCC cells was suppressed significantly by STAT3-decoy ODN, being associated with the increased apoptosis and cell arrest at G0/G1 to S phase transition. Further investigates showed the expression of STAT3-regulated genes including bcl-x1, cyclin D1 and c-myc, which involved in cell apoptosis and cell cycle progression, were down-regulated significantly both at transcription and translation levels. These data suggested that STAT3 may be potentially used as a molecular target in HCC therapy.

Jak inhibitor induces S phase cell-cycle arrest and augments TRAIL-induced apoptosis in human hepatocellular carcinoma cells

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in various cancers and plays a crucial role in oncogensis, including the activation of genes encoding apoptosis inhibitors and cell-cycle regulators. We investigated the biological significance of the Janus kinase (Jak)-STAT pathway in human hepatocellular carcinoma (HCC). Constitutive activation of STAT3 was seen in 49.4% of human HCC specimens and in HCC cell lines. Jak inhibitor AG490 inhibited activation of STAT3 and markedly reduced cell viability without significant apoptosis. AG490 also induced S phase cell-cycle arrest with down-regulation of cyclin D1, A, E and up-regulation of p21, p27, phospho-Chk2. AG490 also inhibited caspase inhibitory proteins, such as XIAP and survivin, and augmented TRAIL-induced apoptosis. Our study suggests that the Jak-STAT pathway plays an important role in cell-cycle progression and resistance to apoptosis. Inhibition of the Jak-STAT pathway may thus be a therapeutic target for HCC.

Signal transducer and activator of transcription 3 activation promotes invasive growth of colon carcinomas through matrix metalloproteinase induction

Signal transducer and activator of transcription 3 (STAT3) is aberrantly activated in colorectal carcinomas (CRCs). Here, we define the relationship between STAT3 function and the malignant properties of colon carcinoma cells. Elevated activation of STAT3 enhances invasive growth of the CRC cell lines. To address mechanisms through which STAT3 influences invasiveness, the protease mRNA expression pattern of CRC biopsies was analyzed and correlated with the STAT3 activity status. These studies revealed a striking coincidence of STAT3 activation and strong expression of matrix metalloproteinases MMP-1, -3, -7, and -9. Immunohistological examination of CRC tumor specimens showed a clear colocalization of MMP-1 and activated STAT3. Experimentally induced STAT3 activity in CRC cell lines enhanced both the level of MMP-1 mRNA and secreted MMP-1 enzymatic activity. A direct connection of STAT3 activity and transcription from the MMP-1 promoter was shown by reporter gene experiments. Moreover, high-affinity binding of STAT3 to STAT recognition elements in both the MMP-1 and MMP-3 promoter was demonstrated. Xenograft tumors arising from implantation of CRC cells into nude mice showed simultaneous appearance and colocalization of p-Y-STAT3 and MMP-1 expression. Our results link aberrant activity of STAT3 in CRC to malignant tumor progression through upregulated expression of MMPs.