Bortezomib suppresses focal adhesion kinase expression via interrupting nuclear factor-kappa B

The role of proteasomes in tumorigenesis

Protein homeostasis is the basis of normal life activities, and the proteasome family plays an extremely important function in this process. The proteasome 20S is a concentric circle structure with two α rings and two β rings overlapped. The proteasome 20S can perform both ATP-dependent and non-ATP-dependent ubiquitination proteasome degradation by binding to various subunits (such as 19S, 11S, and 200 PA), which is performed by its active subunit β1, β2, and β5. The proteasome can degrade misfolded, excess proteins to maintain homeostasis. At the same time, it can be utilized by tumors to degrade over-proliferate and unwanted proteins to support their growth. Proteasomes can affect the development of tumors from several aspects including tumor signaling pathways such as NF-κB and p53, cell cycle, immune regulation, and drug resistance. Proteasome-encoding genes have been found to be overexpressed in a variety of tumors, providing a potential novel target for cancer therapy. In addition, proteasome inhibitors such as bortezomib, carfilzomib, and ixazomib have been put into clinical application as the first-line treatment of multiple myeloma. More and more studies have shown that it also has different therapeutic effects in other tumors such as hepatocellular carcinoma, non-small cell lung cancer, glioblastoma, and neuroblastoma. However, proteasome inhibitors are not much effective due to their tolerance and singleness in other tumors. Therefore, further studies on their mechanisms of action and drug interactions are needed to investigate their therapeutic potential.

Nuclear factor-κB signaling inhibitors revert multidrug-resistance in breast cancer cells

The emergence of multidrug resistance (MDR) is among the crucial obstacles to breast cancer therapy success. The transcription factor nuclear factor (NF)-κB is correlated to the pathogenesis of breast cancer and resistance to therapy. NF-κB augments the expression of MDR1 gene, which encodes for the membrane transporter P-glycoprotein (P-gp) in cancer cells. Since NF-κB activity is considered to be relatively high in particular when it comes to breast cancer, in the present work, we proposed that the inhibition of NF-κB activity can augment and enhance the sensitivity of breast cancer cells to chemotherapy such as doxorubicin (DOX) by virtue of MDR modulation. Our results demonstrated that the DOX-resistant MCF-7 and MDA-MB-231 clones exhibit higher NF-κB (p65) activity, which is linked to the upregulated expression of ABCB1 and ABCC1 transporter proteins. Combined treatment with NF-kB inhibitors (pentoxifylline and bortezomib) sensitized the resistant breast cancer cells to DOX. Such synergy was compromised by forced overexpression of p65. The DOX/NF-κB inhibitor combinations hampered NF-κB (p65) activation and downregulated MDR efflux transporters' level. Breast cancer cell migration was sharply suppressed in cells co-treated with DOX/NF-κB inhibitors. The same treatments successfully enhanced DOX-mediated induction of apoptosis, which is reflected by the elevated ratio of annexin-V/PI positively stained cells, along with the activation of other apoptotic markers. In conclusion, the data generated from this study provide insights for future translational investigations introducing the use of the clinically approved NF-κB inhibitors as an adjuvant in the treatment protocols of resistant breast cancer to overcome the multidrug resistance and enhance the therapeutic outcomes.

Glycogen synthase kinase 3β in tumorigenesis and oncotherapy (Review)

Glycogen synthase kinase 3β (GSK 3β), a multifunctional serine and threonine kinase, plays a critical role in a variety of cellular activities, including signaling transduction, protein and glycogen metabolism, cell proliferation, cell differentiation, and apoptosis. Therefore, aberrant regulation of GSK 3β results in a broad range of human diseases, such as tumors, diabetes, inflammation and neurodegenerative diseases. Accumulating evidence has suggested that GSK 3β is correlated with tumorigenesis and progression. However, GSK 3β is controversial due to its bifacial roles of tumor suppression and activation. In addition, overexpression of GSK 3β is involved in tumor growth, whereas it contributes to the cell sensitivity to chemotherapy. However, the underlying regulatory mechanisms of GSK 3β in tumorigenesis remain obscure and require further in‑depth investigation. In this review, we comprehensively summarize the roles of GSK 3β in tumorigenesis and oncotherapy, and focus on its potentials as an available target in oncotherapy.

RSRC1 suppresses gastric cancer cell proliferation and migration by regulating PTEN expression

Arginine/serine-rich coiled coil 1 (RSRC1) is a gene which plays a significant role in the constitutive and alternative splicing of mRNA and transcriptional regulation. It has been implicated in various neurological disorders, as well as in cancer. However, its role in gastric cancer (GC) remains unknown. Thus, the present study aimed to investigate the role of RSRC1 in GC. RSRC1 expression in GC tissues was determined by RT-qPCR and immunohistochemical staining. The effects of RSRC1 on cell proliferation and migration were detected using a Cell Counting Kit-8 assay, 5-ethynyl-2′-deoxyuridine (EdU) incorporation assay and a Transwell migration assay. Western blot analysis and RT-qPCR were used to explore the molecular mechanisms of of action of RSRC1 in GC. The results indicated that RSRC1 expression was downregulated in GC tissues compared to paired normal tissues and the reduced expression of RSRC1 was shown to contribute to a poor prognosis of patients with GC. RSRC1 knockdown promoted the proliferation and migration of GC cells. In addition, the knockdown of RSRC1 decreased the expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a potent tumor suppressor gene controlling cellular growth and viability. On the whole, the findings of the present study indicate that RSRC1 functions as a tumor suppressor gene in GC and that it may exert its effects by regulating PTEN expression.

Phytochemical naphtho[1,2-b] furan-4,5‑dione induced topoisomerase II-mediated DNA damage response in human non-small-cell lung cancer

BACKGROUND

Phytochemical naphtho[1,2-b] furan-4,5‑dione (NFD) presenting in Avicennia marina exert anti-cancer effects, but little is known regarding about DNA damage-mediated apoptosis in non-small-cell lung carcinoma (NSCLC).

PURPOSE

To examine whether NFD-induced apoptosis of NSCLC cells is correlated with the induction of DNA damage, and to investigate its underlying mechanism.

STUDY DESIGN

The anti-proliferative effects of NFD were assessed by MTS Assay Kit FACS assay, and in vivo nude mice xenograft assay. The DNA damage related proteins, the Bcl-2 family and pro-apoptotic factors were examined by immunofluorescence assay, q-PCR, and western blotting. The activity of NF-κB p65 in nuclear extracts was detected using a colorimetric DNA-binding ELISA assay. The inhibitory activity of topoisomerase II (TOPO II) was evaluated by molecular docking and TOPO II catalytic assay.

RESULTS

NFD exerted selective cytotoxicity against NSCLC H1299, H1437 and A549 cells rather than normal lung-embryonated cells MRC-5. Remarkably, we found that NFD activated the hull marker and modulator of DNA damage repairs such as γ-H2AX, ATM, ATR, CHK1, and CHK2 probably caused by the accumulation of intracellular reactive oxygen species (ROS) and inhibition of TOPO II activity. Furthermore, the suppression of transcription factor NF-κB by NFD resulted in significantly decreased levels of pro-survival proteins including Bcl-2 family Bcl-2, Bcl-xL and Mcl-1 and the endogenous inhibitors of apoptosis XIAP and survivin in H1299 cells. Moreover, the nude mice xenograft assay further validated the suppression of H1299 growth by NFD, which is the first report for evaluating the anti-cancer effect of NFD in vivo.

CONCLUSION

These findings provide a novel mechanism indicating the inhibition of TOPO II activity and NF-κB signaling by NFD, leading to DNA damage and apoptosis of NSCLC tumor cells.

Cordycepin Suppresses Endothelial Cell Proliferation, Migration, Angiogenesis, and Tumor Growth by Regulating Focal Adhesion Kinase and p53

Focal adhesion kinase (FAK) plays an important role in vascular development, including the regulation of endothelial cell (EC) adhesion, migration, proliferation, and survival. 3'-deoxyadenosine (cordycepin) is known to suppress FAK expression, cell migration, and the epithelial⁻mesenchymal transition in hepatocellular carcinoma (HCC). However, whether cordycepin affects FAK expression and cellular functions in ECs and the specific molecular mechanism remain unclear. In this study, we found that cordycepin suppressed FAK expression and the phosphorylation of FAK (p-FAK) at Tyr397 in ECs. Cordycepin inhibited the proliferation, wound healing, transwell migration, and tube formation of ECs. Confocal microscopy revealed that cordycepin significantly reduced FAK expression and decreased focal adhesion number of ECs. The suppressed expression of FAK was accompanied by induced p53 and p21 expression in ECs. Finally, we demonstrated that cordycepin suppressed angiogenesis in an in vivo angiogenesis assay and reduced HCC tumor growth in a xenograft nude mice model. Our study indicated that cordycepin could attenuate cell proliferation and migration and may result in the impairment of the angiogenesis process and tumor growth via downregulation of FAK and induction of p53 and p21 in ECs. Therefore, cordycepin may be used as a potential adjuvant for cancer therapy.

Spotlight on Bortezomib: potential in the treatment of hepatocellular carcinoma

INTRODUCTION

This study reviews the evidence for the use of Bortezomib (BZB), a first-in-class proteasome inhibitor in advanced Hepatocellular carcinoma (HCC). This review aims to delineate the role of BZB within the management of non-surgical and metastatic HCC, either as an alternative or as an adjunct to the current treatment paradigm.

AREAS COVERED

In addition to BZB pharmacology and mechanism of action, safety and tolerance profiles of the drug obtained from clinical trials are explored. The utility of BZB as a therapeutic agent either alone or in combination with other therapies against HCC, including its application in both preclinical and clinical settings has been reviewed. In particular, we highlight the importance of preclinical evaluation of BZB as a combinatorial agent in synergism with other therapies for the use in the management of HCC.

EXPERT OPINION

There has been much interest surrounding the use of BZB, a first-in-class proteasome inhibitor for HCC therapy. The discernment of outcomes of BZB clinical trials for HCC need to take into consideration the disease-specific factors that can affect survival outcomes including patient selection and aetiological differences. Further preclinical testing of BZB in combination with other therapeutic modalities can be important for eliciting enhanced anti-HCC effects.

RasGRF2 promotes migration and invasion of colorectal cancer cells by modulating expression of MMP9 through Src/Akt/NF-κB pathway

Ras-specific guanine nucleotide-releasing factor 2 (RasGRF2) is a member of the guanine nucleotide exchange factors family which is expressed in a variety of tissues and cancer. However, the role of RasGRF2 in cancer is less reported, especially in colorectal cancer(CRC). Hence, the present study aimed to investigated the function of RasGRF2 and ways in which it affects tumor progression in CRC samples and cell lines. We first measured RasGRF2 mRNA level in 26 paired tumor and nontumor colon tissues after colon cancer surgical resection, and determined RasGRF2 protein level in 97 paired paraffin-embedded colon cancer tissues, and found that levels of RasGRF2 mRNA and protein were increased in colorectal tumor tissues, compared with adjacent non-tumor tissues. We then examined the effects of RasGRF2 knockdown on proliferation, migration and invasion were analyzed in CRC cells (SW480, HCT116 and LS174T). HCT116 cells with RasGRF2 knockdown were injected into the tail vein in nude mice to yield metastatic model, and tumor metastasis was measured as well. We found that knockdown of RasGRF2 in CRC cells reduced their migration and invasion in vitro and metastasis in mice. Furthermore, we explored the underlying molecular mechanism for RasGRF2-mediated CRC migration and invasion. The results showed that knockdown of RasGRF2 in CRC cells impairing the expression of MMP9 and inhibiting the activation of Src/Akt and NF-κB signaling. We conclude that RasGRF2 plays a role in controlling migration and invasion of CRC and modulates the expression of MMP9 through Src/PI 3-kinase and the NF-κB pathways.

Anti-invasive effects of CXCR4 and FAK inhibitors in non-small cell lung carcinomas with mutually inactivated p53 and PTEN tumor suppressors

Non-small cell lung carcinoma (NSCLC) is the most common type of lung cancer. At the time of diagnosis, a large percentage of NSCLC patients have already developed metastasis, responsible for extremely high mortality rates. CXCR4 receptor and focal adhesion kinase (FAK) are known to regulate such invasive cancer behavior. Their expression is downregulated by p53 and PTEN tumor suppressors which are commonly co-inactivated in NSCLC patients and contribute to metastasis. Therefore, targeting CXCR4 or FAK seems to be a promising strategy in suppressing metastatic spread of p53/PTEN deficient NSCLCs. In this study, we first examined the invasive characteristics of NSCLC cells with suppressed p53 and PTEN activity using wound healing, gelatin degradation and invasion assays. Further, changes in the expression of CXCR4 and FAK were evaluated by RT-qPCR and Western Blot analysis. Finally, we tested the ability of CXCR4 and FAK inhibitors (WZ811 and PF-573228, respectively) to suppress the migratory and invasive potential of p53/PTEN deficient NSCLC cells, in vitro and in vivo using metastatic models of human NSCLC. Our results showed that cells with mutually inactive p53 and PTEN have significantly increased invasive potential associated with hyperactivation of CXCR4 and FAK signaling pathways. Treatments with WZ811 and PF-573228 inhibitors significantly reduced migratory and invasive capacity in vitro and showed a trend of improved survival in vivo. Accordingly, we demonstrated that p53/PTEN deficient NSCLCs have extremely invasive phenotype and provided a rationale for the use of CXCR4 or FAK inhibitors for the suppression of NSCLC dissemination.

MAGE-TRIM28 complex promotes the Warburg effect and hepatocellular carcinoma progression by targeting FBP1 for degradation

Hepatocellular carcinoma (HCC) is one of the leading cause of cancer death in the world. Fructose-1,6-biphosphatase (FBP1), a rate-limiting enzyme in gluconeogenesis, has been identified recently as a tumor suppressor in HCC and other cancer types. In this study, we demonstrated that the tripartite motif-containing protein 28 (TRIM28) binds directly to and promotes FBP1 for ubiquitination and degradation. MAGE-A3 and MAGE-C2, which are known to be overexpressed in HCC, can enhance TRIM28-dependent degradation of FBP1 by forming ubiquitin ligase complexes with TRIM28. We further showed that expression of TRIM28 increased glucose consumption and lactate production by promoting FBP1 degradation in HCC cells and that FBP1 is a key mediator of TRIM28-induced HCC growth in culture and in mice. Moreover, we demonstrated that FBP1 and TRIM28 protein levels inversely correlated in HCC patient specimens. Finally, we showed that the proteasome inhibitor bortezomib mitigated the Warburg effect by inhibiting FBP1 degradation in HCC. Collectively, our findings not only identify oncogenic MAGE-TRIM28 complex-mediated proteasome degradation of FBP1 as a key mechanism underlying downregulation of FBP1 proteins in HCC, but also reveal that MAGE-TRIM28-regulated reprogramming of cancer cell metabolism and HCC tumorigenesis is mediated, at least in part, through FBP1 degradation.

Rasfonin promotes autophagy and apoptosis via upregulation of reactive oxygen species (ROS)/JNK pathway

Rasfonin is a fungal secondary metabolite demonstrating with antitumour effects. Reactive oxygen species (ROS) are formed as a natural by-product of the normal metabolism of oxygen and have important roles in cell signalling and homeostasis. Studies reported that many fungal secondary metabolites activated either autophagy or apoptosis through ROS generation. In former study, we revealed that rasfonin induced both autophagy and apoptosis, however, whether it promoted aforementioned processes via upregulation of ROS generation remains explored. In the current work, we demonstrated that rasfonin induced autophagy and apoptosis concomitant with a dramatically ROS production. N-Acetylcysteine (NAC), an often used ROS inhibitor, decreased both autophagic flux and caspase-dependent apoptosis by rasfonin. Flow cytometry analysis revealed NAC was able to reduce rasfonin-dependent apoptosis and necrosis. In methanethiosulfonate (MTS) assay, we observed that NAC significantly blocked rasfonin-induced cell viability loss. In addition, we found that rasfonin increased the phosphorylation of c-Jun NH2-terminal kinase (JNK), which was inhibited by NAC. SP600125, an inhibitor of JNK, reduced rasfonin-dependent autophagic flux and apoptosis. Moreover, we demonstrated that rasfonin inhibited the phosphorylation of both 4E-binding protein 1 (4E-BP1) and S6 kinase 1 (S6K1), two main substrates of mammalian target of rapamycin (mTOR). Collectively, rasfonin activated autophagy and apoptosis through upregulation of ROS/JNK signalling.

The ubiquitin-proteasome system and its potential application in hepatocellular carcinoma therapy

The ubiquitin-proteasome system (UPS) is a complicated tightly controlled system in charge of degrading 80-90% of proteins, and is central to regulating cellular function and keeping protein homeostasis. Therefore, the components of UPS attract considerable attention as potential targets for hepatocellular carcinoma (HCC) therapy. The clinical success of bortezomib in multiple myeloma and mantle cell lymphoma patients has set the precedent for therapeutically targeting this pathway. This review will provide an overview of the UPS in HCC and the current status of therapeutic strategies.

Involvement of 14-3-3 Proteins in Regulating Tumor Progression of Hepatocellular Carcinoma

There are seven mammalian isoforms of the 14-3-3 protein, which regulate multiple cellular functions via interactions with phosphorylated partners. Increased expression of 14-3-3 proteins contributes to tumor progression of various malignancies. Several isoforms of 14-3-3 are overexpressed and associate with higher metastatic risks and poorer survival rates of hepatocellular carcinoma (HCC). 14-3-3β and 14-3-3ζ regulate HCC cell proliferation, tumor growth and chemosensitivity via modulating mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK) and p38 signal pathways. Moreover, 14-3-3ε suppresses E-cadherin and induces focal adhesion kinase (FAK) expression, thereby enhancing epithelial-mesenchymal transition (EMT) and HCC cell migration. 14-3-3ζ forms complexes with αB-crystallin, which induces EMT and is the cause of sorafenib resistance in HCC. Finally, a recent study has indicated that 14-3-3σ induces heat shock protein 70 (HSP70) expression, which increases HCC cell migration. These results suggest that selective 14-3-3 isoforms contribute to cell proliferation, EMT and cell migration of HCC by regulating distinct targets and signal pathways. Targeting 14-3-3 proteins together with specific downstream effectors therefore has potential to be therapeutic and prognostic factors of HCC. In this article, we will overview 14-3-3’s regulation of its downstream factors and contributions to HCC EMT, cell migration and proliferation.

Phosphatase and Tensin Homolog (PTEN) Represses Colon Cancer Progression through Inhibiting Paxillin Transcription via PI3K/AKT/NF-κB Pathway

The tumor suppressor gene phosphatase and tensin homolog (PTEN) is frequently mutated in colon cancer. However, the potential contribution of loss of PTEN to colon cancer progression remains unclear. In this study, we demonstrated that PTEN overexpression or knockdown in Lovo colon cancer cells decreased or increased paxillin expression, respectively. Moreover, paxillin reversed PTEN-mediated inhibition of Lovo cell invasion and migration. Overexpression of PTEN in an orthotropic colon cancer nude mice model inhibited tumor formation and progression. In addition, PTEN protein level was negatively correlated with that of paxillin in human colon cancer tissues. Mechanistically, we identified three NF-κB binding sites on paxillin promoter and confirmed that paxillin was a direct transcriptional target of NF-κB. Our findings reveal a novel mechanism by which PTEN inhibits the progression of colon cancer by inhibiting paxillin expression downstream of PI3K/AKT/NF-κB pathway. Thereby, PTEN/PI3K/AKT/NF-κB/paxillin signaling cascade is an attractive therapeutic target for colon cancer progression.

Receptor-interacting protein kinase 2 promotes triple-negative breast cancer cell migration and invasion via activation of nuclear factor-kappaB and c-Jun N-terminal kinase pathways

Introduction

Metastasis is the main cause of breast cancer morbidity and mortality. Processes that allow for tumor cell migration and invasion are important therapeutic targets. Here we demonstrate that receptor-interacting protein kinase 2 (RIP2), a kinase known to be involved in inflammatory processes, also has novel roles in cancer cell migration and invasion.

Methods

A total of six breast cancer expression databases, including The Cancer Genome Atlas, were assessed for RIP2 expression among various clinical subtypes and its role as a prognostic biomarker. mRNA fluorescence in situ hybridization (FISH) for RIP2 was performed on 17 stage III breast cancers to determine if there was a correlation between RIP2 expression and lymph node involvement. RNA-interference was used to knock-down RIP2 expression in MDA-MB-231, Htb126, SUM149PT, MCF7, T47D, and HCC1428 cells. Cell migration and invasion were measured in vitro by scratch/wound healing and transwell migration assays. A xenograft mouse model was used to assess tumor growth and chemosensitivity to docetaxel in vivo in MDA-MB-231 cells with and without RIP2 small hairpin RNA knockdown. Western blot and immunofluorescence imaging were used to evaluate protein expressions.

Results

Interrogation of expression databases showed that RIP2 expression is significantly over-expressed in triple-negative breast cancers (TNBC: estrogen-receptor (ER) negative, progesterone-receptor (PR) negative, Her2/neu- (Her2) negative), compared to other clinical subtypes. High RIP2 expression correlates with worse progression-free survival using a combined breast cancer expression array dataset consisting of 946 patients. Multivariate analysis shows RIP2 as an independent prognostic biomarker. Knock-down of RIP2 significantly decreases migration in both scratch/wound healing and transwell migration assays in MDA-MB-231, Htb126, SUM149PT, MCF7, and T47D cells and is correlated with decreased Nuclear Factor-kappaB and c-Jun N-terminal kinase (JNK) activation. Finally, RIP2 knock-down leads to increased sensitivity to docetaxel and decreased tumor mass and lung metastases in a xenograft mouse model.

Conclusion

These results highlight RIP2 as a pro-metastasis kinase in patients with advanced breast cancer. These results also illustrate a novel role for this kinase in addition to its known role in inflammation, and suggest that targeting RIP2 may improve outcomes in advanced breast cancer patients, in which it is overexpressed.

PTEN inhibits the invasion and metastasis of gastric cancer via downregulation of FAK expression

The tumor suppressor gene phosphatase and tensin homolog (PTEN) is essential in inhibiting tumor growth and metastasis. However, the mechanism by which PTEN restricts gastric cancer progression and metastasis remains largely elusive. Here we demonstrated that PTEN overexpression or knockdown in gastric cancer cells led to the downregulation or upregulation of focal adhesion kinase (FAK), and decreased or increased cell invasion, respectively. Moreover, FAK overexpression could rescue the inhibition of cell invasion by PTEN. These results were further confirmed in orthotropic gastric cancer nude mice model. In addition, in human gastric cancer tissues, PTEN protein level was conversely correlated with FAK protein level. Mechanistically, we found that PTEN inhibited PI3K/NF-κB pathway and inhibited the DNA binding of NF-κB on FAK promoter. Taken together, our data reveal a novel mechanism that PTEN inhibits the growth and invasion of gastric cancer via the downregulation of FAK expression and suggest that exploiting PTEN/PI3K/NF-κB/FAK axis is a promising approach to treat gastric cancer metastasis.

Bortezomib effect on E2F and cyclin family members in human hepatocellular carcinoma cell lines

AIM: To evaluate the effects of the proteasome inhibitor bortezomib (BZB) on E2Fs and related genes in hepatocellular carcinoma (HCC) cells.

METHODS: The mRNA levels of the E2F family members (pro-proliferative: E2F1-3 and anti-proliferative: E2F4-8) and of their related genes cyclins and cyclin-dependent kinases (cdks) were evaluated in two HCC cell lines following a single BZB administration. mRNA levels of the epithelial-mesenchymal transition (EMT) genes were also measured in both cell lines after BZB treatment. The BZB concentration (40 nmol/L) used was chosen to stay well below the maximal amount/cm² recommended for in vivo application, and 2 d incubation was chosen as this time point has been found optimal to detect BZB effects in our previous studies. The HCC cell lines, HepG2 and JHH6, were chosen as they display different phenotypes, hepatocyte-like for HepG2 and undifferentiated for JHH6, thus representing an in vitro model of low and high aggressive forms of HCC, respectively. The mRNA levels of the target genes were measured by two-color microarray-based gene expression analysis, performed according to Agilent Technologies protocol and using an Agilent Scan B. For the E2F family members, mRNA levels were quantified by real-time reverse transcription polymerase chain reaction (RT-PCR). Using small interfering RNA’s, the effects of E2F8 depletion on cell number was also evaluated.

RESULTS: After BZB treatment, microarray analysis of the undifferentiated JHH6 revealed a significant decrease in the expression of the pro-proliferative E2F member E2F2. Quantitative RT-PCR data were in keeping with the microarray analysis, and showed a significant increase and decrease in E2F8 and E2F2 mRNA levels, respectively. In contrast, BZB treatment of the hepatocyte-like HCC cell line HepG2 had a significant impact on mRNA levels of 5 of the 8 E2F members. In particular, mRNA levels of the pro-proliferative E2F members E2F1, E2F2, and of the anti-proliferative member E2F8, decreased over 80%. Notably, a reduction in E2F8 expression in HepG2 and JHH6 cells following siRNA treatment had no impact on cell proliferation. As observed with JHH6, BZB treatment of HepG2 cells induced a significant increase in mRNA levels of an anti-proliferative E2F member, E2F6 in this case. As was observed with E2F’s, more dramatic changes in mRNA levels of the E2F related genes cyclins and Cdks and EMT genes were observed after BZB treatment of HepG2 compared to JHH6.

CONCLUSION: The differential expression of E2Fs and related genes induced by BZB in diverse HCC cell phenotypes contribute to bortezomib’s mechanism of action in hepatocellular carcinoma.

Asiatic acid, a triterpene, inhibits cell proliferation through regulating the expression of focal adhesion kinase in multiple myeloma cells

The aim of the present study was to investigate whether asiatic acid (AA), a pentacyclic triterpene derived from Centella asiatica, exerts anti-proliferative effects on multiple myeloma RPMI 8226 cells and to determine the molecular mechanism underlying the anticancer action of AA. The study sought to analyze the potential role of AA on the proliferation of the RPMI 8226 cells using a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium assay. Cell cycle arrest was detected by flow cytometry, and the expression levels of focal adhesion kinase (FAK) in the myeloma cells induced by AA were analyzed using the western blotting and immunoprecipitation methods. The results indicated that AA significantly inhibited cell proliferation in a time- and dose-dependent manner and led to G₂/M phase arrest at concentrations of 35 and 40 μmol/l in the RPMI 8226 cells. The expression levels of FAK and p-FAK were distinctly decreased following AA treatment (at the concentration of 40 μmol/l) for 24 h compared with that of the control groups. Taken together, these results demonstrated that AA was able to regulate cell cycle progression in RPMI 8226 cells, thereby significantly inhibiting cell growth. Furthermore, AA decreased the expression levels of FAK, indicating that the antitumor mechanism of AA may be associated with the inhibition of signal transduction mediated by FAK.

Cordycepin regulates GSK-3β/β-catenin signaling in human leukemia cells

BACKGROUND

Leukemia stem cells (LSCs) are a limitless cell source for the initiation and maintenance of leukemia. Activation of the Wnt/β-catenin pathway is required for the survival and development of LSCs. Therefore, targeting β-catenin is considered a therapeutic strategy for the treatment of leukemia. The goal of this study was to explore whether cordycepin, an active component of the traditional medicine Cordyceps sinensis, regulates β-catenin expression in leukemia cells.

METHODOLOGY AND PRINCIPAL FINDINGS

In this study, we found that cordycepin significantly suppressed cell proliferation in all malignant cancer cells, including U937, K562, A549, HepG2, SK-Hep1 and MCF7 in a dose-dependent manner. However, cordycepin reduced β-catenin levels in U937, K562 and THP1 leukemia cells and had no effect on other solid cancer cells. In addition, treatment with cordycepin significantly suppressed leukemia colony formation in soft agar assay. Cordycepin enhanced proteasome-dependent degradation and inhibited nuclear translocation of β-catenin in leukemia cells. Cordycepin-reduced β-catenin stability was restored by the addition of a pharmacological inhibitor of GSK-3β, indicating that cordycepin-suppressed β-catenin stability is mediated by the activation of GSK-3β. Furthermore, cordycepin abolished the effect of Wnt3a-induced β-catenin in leukemia cells. In addition, cordycepin-impaired β-catenin is regulated by Akt activation but is not significantly influenced by AMPK or mTOR signal pathways.

SIGNIFICANCE

Our findings show for the first time that codycepin selectively reduces β-catenin stability in leukemia but not in other solid tumor cells. This suppressive effect is mediated by regulating GSK-3β. A synergistic combination of cordycepin with other treatments should be used as a novel strategy to eradicate leukemia via elimination of LSCs.

14-3-3ε overexpression contributes to epithelial-mesenchymal transition of hepatocellular carcinoma

Background

14-3-3ε is implicated in regulating tumor progression, including hepatocellular carcinoma (HCC). Our earlier study indicated that elevated 14-3-3ε expression is significantly associated with higher risk of metastasis and lower survival rates of HCC patients. However, the molecular mechanisms of how 14-3-3ε regulates HCC tumor metastasis are still unclear.

Methodology and Principal Findings

In this study, we show that increased 14-3-3ε expression induces HCC cell migration and promotes epithelial-mesenchymal transition (EMT), which is determined by the reduction of E-cadherin expression and induction of N-cadherin and vimentin expression. Knockdown with specific siRNA abolished 14-3-3ε-induced cell migration and EMT. Furthermore, 14-3-3ε selectively induced Zeb-1 and Snail expression, and 14-3-3ε-induced cell migration was abrogated by Zeb-1 or Snail siRNA. In addition, the effect of 14-3-3ε-reduced E-cadherin was specifically restored by Zeb-1 siRNA. Positive 14-3-3ε expression was significantly correlated with negative E-cadherin expression, as determined by immunohistochemistry analysis in HCC tumors. Analysis of 14-3-3ε/E-cadherin expression associated with clinicopathological characteristics revealed that the combination of positive 14-3-3ε and negative E-cadherin expression is significantly correlated with higher incidence of HCC metastasis and poor 5-year overall survival. In contrast, patients with positive 14-3-3ε and positive E-cadherin expression had better prognostic outcomes than did those with negative E-cadherin expression.

Significance

Our findings show for the first time that E-cadherin is one of the downstream targets of 14-3-3ε in modulating HCC tumor progression. Thus, 14-3-3ε may act as an important regulator in modulating tumor metastasis by promoting EMT as well as cell migration, and it may serve as a novel prognostic biomarker or therapeutic target for HCC.

FAK and p53 protein interactions

Focal Adhesion Kinase plays a major role in cell adhesion, motility, survival, proliferation, metastasis, angiogenesis and lymphangiogenesis. In 2004, we have cloned the promoter sequence of FAK and found that p53 inhibits its activity (BBA, v. 1678, 2004). In 2005, we were the first group to show that FAK and p53 proteins directly interact in the cells (JBC, v. 280, 2005). We have shown that FAK and p53 proteins interact in the cytoplasm and in the nucleus by immunoprecipitation, pull-down and confocal microscopy assays. We have shown that FAK inhibited activity of p53 with the transcriptional targets: p21, Bax and Mdm-2 through protein-protein interactions. We identified the 7 amino-acid site in p53 that is involved in interaction with FAK protein. The present review will discuss the interaction of FAK and p53 proteins and discuss the mechanism of FAK-p53 loop regulation: inhibition of FAK promoter activity by p53 protein and also inhibition of p53 transcriptional activity by FAK protein.

The interaction between ER and NFκB in resistance to endocrine therapy

Endocrine therapy is a commonly used treatment for estrogen receptor (ER)-positive breast cancer. Although endocrine therapy has a favorable outcome in many patients, development of resistance is common. Recent studies have shown that NFκB, a transcription factor regulating a wide variety of cellular processes, might play a role in the development of endocrine resistance. The precise interaction between ER and NFκB and how this contributes to the attenuated responsiveness of ER-positive breast cancer cells to hormonal treatment remains unclear. This review provides an overview of the mechanisms of action for both transcription factors and focuses on the current knowledge explaining how ER and NFκB affect each other's activity and how this cross-talk might contribute to the development of an endocrine resistance phenotype in breast cancer cells.

Glycogen synthase kinase 3 beta: can it be a target for oral cancer

Despite progress in treatment approaches for oral cancer, there has been only modest improvement in patient outcomes in the past three decades. The frequent treatment failure is due to the failure to control tumor recurrence and metastasis. These failures suggest that new targets should be identified to reverse oral epithelial dysplastic lesions. Recent developments suggest an active role of glycogen synthase kinase 3 beta (GSK3 β) in various human cancers either as a tumor suppressor or as a tumor promoter. GSK3β is a Ser/Thr protein kinase, and there is emerging evidence that it is a tumor suppressor in oral cancer. The evidence suggests a link between key players in oral cancer that control transcription, accelerated cell cycle progression, activation of invasion/metastasis and anti-apoptosis, and regulation of these factors by GSK3β. Moreover, the major upstream kinases of GSK3β and their oncogenic activation by several etiological agents of oral cancer support this hypothesis. In spite of all this evidence, a detailed analysis of the role of GSK3β in oral cancer and of its therapeutic potential has yet to be conducted by the scientific community. The focus of this review is to discuss the multitude of roles of GSK3β, its possible role in controlling different oncogenic events and how it can be targeted in oral cancer.