Inhibition of STAT3 signaling leads to apoptosis of leukemic large granular lymphocytes and decreased Mcl-1 expression

Celecoxib induces apoptosis and cell-cycle arrest in nasopharyngeal carcinoma cell lines via inhibition of STAT3 phosphorylation

AIM

To investigate the mechanisms underlying the anticancer effect of celecoxib on nasopharyngeal carcinoma (NPC).

METHODS

NPC cell lines, HNE1 and CNE1-LMP1, were treated with various concentrations of celecoxib for 48 h. The antiproliferative effect of celecoxib was assessed using MTT assay. Both cell cycle profiles and apoptosis were analyzed using flow cytometry. Western blot was used to measure the levels of signal transducer and activator of transcription 3 (STAT3), phosphorylated STAT3(Y705) (pSTAT3(Y705)), COX-2, Survivin, Mcl-1, Bcl-2 and Cyclin D1.

RESULTS

Celecoxib (10-75 μmol/L) inhibited the proliferation of the NPC cell lines in a dose-dependent manner. Celecoxib (25 and 50 μmol/L) induced apoptosis and cell-cycle arrest at the G(0)/G(1) checkpoint in the NPC cell lines, which was associated with significantly reduced STAT3 phosphorylation. The genes downstream of STAT3 (ie, Survivin, Mcl-1, Bcl-2 and Cyclin D1) were significantly down-regulated after exposure to celecoxib (25 and 50 μmol/L).

CONCLUSION

The anticancer effects of celecoxib on NPC cell lines results from inducing apoptosis and cell cycle arrest, which may be partly mediated through the STAT3 pathway.

Resveratrol suppresses tumorigenicity and enhances radiosensitivity in primary glioblastoma tumor initiating cells by inhibiting the STAT3 axis

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor. Patients diagnosed with GBM have a poor prognosis, and it has been reported that tumor malignancy and GBM recurrence are promoted by STAT3 signaling. As resveratrol (RV), a polyphenol in grapes, is reported to be a potent and non-toxic cancer-preventive compound, the aim of this study was to investigate the therapeutic effect and molecular mechanisms of RV on GBM-derived radioresistant tumor initiating cells (TIC). Firstly, our results showed that primary GBM-CD133(+) TIC presented high tumorigenic and radiochemoresistant properties as well as increased protein levels of phosphorylated STAT3. We consistently observed that treatment with shRNA-STAT3 (sh-STAT3) or AG490, a STAT3 inhibitor, significantly inhibited the cancer stem-like cell properties and radioresistance of GBM-CD133(+) in vitro and in vivo. Furthermore, treatment of GBM-CD133(+) with 100 µM RV induced apoptosis and enhanced radiosensitivity by suppressing STAT3 signaling. Microarray results suggested that RV or AG490 inhibited the stemness gene signatures of GBM-CD133(+) and facilitated the differentiation of GBM-CD133(+) into GBM-CD133(-) or astrocytoma cells. Finally, xenotransplant experiments indicated that RV or sh-STAT3 therapy could significantly improve the survival rate and synergistically enhance the radiosensitivity of radiation-treated GBM-TIC. In summary, RV can reduce in vivo tumorigenicity and enhance the sensitivity of GBM-TIC to radiotherapies through the STAT3 pathway.

Role of STAT3 in Transformation and Drug Resistance in CML

Chronic myeloid leukemia (CML) is initially driven by the bcr-abl fusion oncoprotein. The identification of bcr-abl led to the discovery and rapid translation into the clinic of bcr-abl kinase inhibitors. Although, bcr-abl inhibitors are efficacious, experimental evidence indicates that targeting bcr-abl is not sufficient for elimination of minimal residual disease found within the bone marrow (BM). Experimental evidence indicates that the failure to eliminate the leukemic stem cell contributes to persistent minimal residual disease. Thus curative strategies will likely need to focus on strategies where bcr-abl inhibitors are given in combination with agents that specifically target the leukemic stem cell or the leukemic stem cell niche. One potential target to be exploited is the Janus kinase (JAK)/signal transducers and activators of transcription 3 (STAT3) pathway. Recently using STAT3 conditional knock-out mice it was shown that STAT3 is critical for initiating the disease. Interestingly, in the absence of treatment, STAT3 was not shown to be required for maintenance of the disease, suggesting that STAT3 is required only in the tumor initiating stem cell population (Hoelbl et al., 2010). In the context of the BM microenvironment, STAT3 is activated in a bcr-abl independent manner by the cytokine milieu. Activation of JAK/STAT3 was shown to contribute to cell survival even in the event of complete inhibition of bcr-abl activity within the BM compartment. Taken together, these studies suggest that JAK/STAT3 is an attractive therapeutic target for developing strategies for targeting the JAK-STAT3 pathway in combination with bcr-abl kinase inhibitors and may represent a viable strategy for eliminating or reducing minimal residual disease located in the BM in CML.

Overexpression of phospholipase D enhances Bcl-2 expression by activating STAT3 through independent activation of ERK and p38MAPK in HeLa cells

The purpose of this study was to identify the role of phospholipase D (PLD) isozymes in Bcl-2 expression. Overexpression of PLD1 or PLD2 increased Bcl-2 expression and phosphatidic acid (PA), the product of PLDs, also upregulated Bcl-2 expression. Treatment with PA activated the phospholipase A(2) (PLA(2))/G(i)/ERK1/2, RhoA/Rho-associated kinase (ROCK)/p38 MAPK, and Rac1/p38 MAPK pathways. PA-induced phosphorylation of ERK1/2 was attenuated by a PLA(2) inhibitor (mepacrine) and, a G(i) protein inhibitor (pertussis toxin, PTX). On the other hand, p38 MAPK phosphorylation was attenuated by a dominant negative Rac1 and a specific Rho-kinase inhibitor (Y-27632). These results suggest that PLA(2)/G(i) acts at the upstream of ERK1/2, while Rac1 and RhoA/ROCK act upstream of p38 MAPK. We next, tried to determine which transcription factor is involved in PLD-related Bcl-2 expression. When signal transducer and activator of transcription 3 (STAT3) activity was blocked by a STAT3 specific siRNA, PA-induced Bcl-2 expression was remarkably decreased, suggesting that STAT3 is an essential transcription factor linking PLD to Bcl-2 upregulation. Taken together, these findings indicate that PLD acts as an important regulator in Bcl-2 expression by activating STAT3 involving the phosphorylation of Ser727 through the PLA(2)/G(i)/ERK1/2, RhoA/ROCK/p38 MAPK, and Rac1/p38 MAPK pathways.

Cryptotanshinone activates p38/JNK and inhibits Erk1/2 leading to caspase-independent cell death in tumor cells

Cryptotanshinone (CPT), a natural compound isolated from the plant Salvia miltiorrhiza Bunge, is a potential anticancer agent. However, the underlying mechanism is not well understood. Here, we show that CPT induced caspase-independent cell death in human tumor cells (Rh30, DU145, and MCF-7). Besides downregulating antiapoptotic protein expression of survivin and Mcl-1, CPT increased phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-jun N-terminal kinase (JNK), and inhibited phosphorylation of extracellular signal-regulated kinases 1/2 (Erk1/2). Inhibition of p38 with SB202190 or JNK with SP600125 attenuated CPT-induced cell death. Similarly, silencing p38 or c-Jun also in part prevented CPT-induced cell death. In contrast, expression of constitutively active mitogen-activated protein kinase kinase 1 (MKK1) conferred resistance to CPT inhibition of Erk1/2 phosphorylation and induction of cell death. Furthermore, we found that all of these were attributed to CPT induction of reactive oxygen species (ROS). This is evidenced by the findings that CPT induced ROS in a concentration- and time-dependent manner; CPT induction of ROS was inhibited by N-acetyl-L-cysteine (NAC), a ROS scavenger; and NAC attenuated CPT activation of p38/JNK, inhibition of Erk1/2, and induction of cell death. The results suggested that CPT induction of ROS activates p38/JNK and inhibits Erk1/2, leading to caspase-independent cell death in tumor cells.

Honokiol inhibits signal transducer and activator of transcription-3 signaling, proliferation, and survival of hepatocellular carcinoma cells via the protein tyrosine phosphatase SHP-1

The activation of signal transducers and activators of transcription 3 (STAT3) has been closely linked with the proliferation, survival, invasion, and angiogenesis of hepatocellular carcinoma (HCC) and represents an attractive target for therapy. In the present report, we investigated whether honokiol mediates its effect through interference with the STAT3 activation pathway. The effect of honokiol on STAT3 activation, associated protein kinases, and phosphatase, STAT3-regulated gene products and apoptosis was investigated using both functional proteomics tumor pathway technology platform and different HCC cell lines. We found that honokiol inhibited both constitutive and inducible STAT3 activation in a dose- and time-dependent manner in HCC cells. The suppression was mediated through the inhibition of activation of upstream kinases c-Src, Janus-activated kinase 1, and Janus-activated kinase 2. Vanadate treatment reversed honokiol-induced down-regulation of STAT3, suggesting the involvement of a tyrosine phosphatase. Indeed, we found that honokiol induced the expression of tyrosine phosphatase SHP-1 that correlated with the down-regulation of constitutive STAT3 activation. Moreover, deletion of SHP-1 gene by siRNA abolished the ability of honokiol to inhibit STAT3 activation. The inhibition of STAT3 activation by honokiol led to the suppression of various gene products involved in proliferation, survival, and angiogenesis. Finally, honokiol inhibited proliferation and significantly potentiated the apoptotic effects of paclitaxel and doxorubicin in HCC cells. Overall, the results suggest that honokiol is a novel blocker of STAT3 activation and may have a great potential for the treatment of HCC and other cancers.

Inhibition of phosphorylated STAT3 by cucurbitacin I enhances chemoradiosensitivity in medulloblastoma-derived cancer stem cells

INTRODUCTION

CD133 (PROM1) is a potential marker for cancer stem cells (CSCs), including those found in brain tumors. Recently, medulloblastoma (MB)-derived CD133-positive cells were found to have CSC-like properties and were proposed to be important contributors to tumorigenicity, cancer progression, and chemoradioresistance. However, the biomolecular pathways and therapeutic targets specific to MB-derived CSCs remain unresolved.

MATERIALS AND METHODS

In the present study, we isolated CD133(+) cells from MB cell lines and determined that they showed increased tumorigenicity, radioresistance, and higher expression of both embryonic stem cell-related and drug resistance-related genes compared to CD133(-) cells. Bioinformatics analysis suggested that the STAT3 pathway might be important in MB and CD133(+) cells. To evaluate the effects of inhibiting the STAT3 pathway, MB-derived CD133(+/-) cells were treated with the potent STAT3 inhibitor, cucurbitacin I. Treatment with cucurbitacin I significantly suppressed the CSC-like properties and stemness gene signature of MB-derived CD133(+) cells. Furthermore, cucurbitacin I treatment increased the apoptotic sensitivity of MB-derived CD133(+) cells to radiation and chemotherapeutic drugs. Notably, cucurbitacin I demonstrated synergistic effects with ionizing radiation to inhibit tumorigenicity in MB-CD133(+)-inoculated mice.

RESULTS

These results indicate that the STAT3 pathway plays a key role in mediating CSC properties in MB-derived CD133(+) cells. Targeting STAT3 with cucurbitacin I may therefore represent a novel therapeutic approach for treating malignant brain tumors.

Reciprocal activation between PLK1 and Stat3 contributes to survival and proliferation of esophageal cancer cells

BACKGROUND & AIMS

Aberrant activation of the signal transducer and activator of transcription (Stat)3 and overexpression of polo-like kinase (PLK)1 each have been associated with cancer pathogenesis. The mechanisms and significance of dysregulation of Stat3 and PLK1 in carcinogenesis and cancer progression are unclear. We investigated the relationship between Stat3 and PLK1 and the effects of their dysregulation in esophageal squamous cell carcinoma (ESCC) cells.

METHODS

We used immunoblot, quantitative reverse-transcription polymerase chain reaction, immunochemistry, chromatin immunoprecipitation, mobility shift, and reporter assays to investigate the relationship between Stat3 and PLK1. We used colony formation, fluorescence-activated cell sorting, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, and xenograft tumor assays to determine the effects of increased activation of Stat3 and PLK1 in proliferation and survival of ESCC cells.

RESULTS

Stat3 directly activated transcription of PLK1 in esophageal cancer cells and mouse embryonic fibroblast cell NIH3T3. PLK1 then potentiated the expression of Stat3; β-catenin was involved in PLK1-dependent transcriptional activation of Stat3. This mutual regulation between Stat3 and PLK1 was required for proliferation of esophageal cancer cells and resistance to apoptosis in culture and as tumor xenografts in mice. Furthermore, phosphorylation of Stat3 and overexpression of PLK1 were correlated in a subset of ESCC.

CONCLUSIONS

Stat3 and PLK1 control each other's transcription in a positive feedback loop that contributes to the development of ESCC. Increased activity of Stat3 and overexpression of PLK1 promote survival and proliferation of ESCC cells in culture and in mice.

Crosstalk of Sp1 and Stat3 signaling in pancreatic cancer pathogenesis

Pancreatic cancer progression is attributed to genetic and epigenetic alterations and a chaotic tumor microenvironment. Those diverse "upstream signal" factors appear to converge on specific sets of central nuclear regulators, namely, transcription factors. Specificity Protein 1 (Sp1) and signal transducer and activator of transcription 3 (Stat3) are central transcription factors that regulate a number of pathways important to tumorigenesis, including tumor cell-cycle progression, apoptosis, angiogenesis, metastasis, and evasion of the immune system. Recently, researchers demonstrated many types of crosstalk of Sp1 and Stat3 in tumor signal transduction and that these factors function cooperatively to activate targeted genes and promote tumorigenesis in pancreatic cancer. Therefore, targeting both Sp1 and Stat3 is a potential preventive and therapeutic strategy for pancreatic cancer.

Diindolylmethane suppresses ovarian cancer growth and potentiates the effect of cisplatin in tumor mouse model by targeting signal transducer and activator of transcription 3 (STAT3)

BACKGROUND

Signal transducer and activator of transcription 3 (STAT3) is activated in majority of ovarian tumors and confers resistance to cisplatin treatment in patients with ovarian cancer. We have reported previously that diindolylmethane (DIM) inhibits the growth of ovarian cancer cells. However, to date the exact mechanism by which DIM induces growth suppressive effects has not been clear. In this report the mode of action of DIM is investigated.

METHODS

Six human ovarian cancer cell lines and an ovarian tumor xenograft animal model were used to study the effect of diindolylmethane alone or in combination with cisplatin.

RESULTS

Diindolylmethane treatment induced apoptosis in all six ovarian cancer cell lines. Phosphorylation of STAT3 at Tyr-705 and Ser-727 was reduced by DIM in a concentration-dependent manner. In addition, diindolylmethane treatment inhibited nuclear translocation, DNA binding, and transcriptional activity of STAT3. Interleukin (IL)-6-induced phosphorylation of STAT3 at Tyr-705 was significantly blocked by DIM. Overexpression of STAT3 by gene transfection blocked DIM-induced apoptosis. In addition, DIM treatment reduced the levels of IL-6 in ovarian cancer cells and in the tumors. DIM treatment also inhibited cell invasion and angiogenesis by suppressing hypoxia-inducible factor 1α (HIF-1α) and vascular epithelial growth factor (VEGF). Importantly, diindolylmethane treatment potentiated the effects of cisplatin in SKOV-3 cells by targeting STAT3. Oral administration of 3 mg diindolylmethane per day and subsequent administration of cisplatin substantially inhibited in vivo tumor growth. Western blotting analysis of tumor lysates indicated increased apoptosis and reduced STAT3 activation.

CONCLUSIONS

These findings provide a rationale for further clinical investigation of DIM alone or in combination for chemoprevention and/or chemotherapy of ovarian cancer.

Dietary compounds as potent inhibitors of the signal transducers and activators of transcription (STAT) 3 regulatory network

Signal transducers and activators of transcription (STAT) proteins were described as a family of latent cytosolic transcription factors whose activation is dependent on phosphorylation via growth factor- and cytokine-membrane receptors including interferon and interleukin, or by non-receptor intracellular tyrosine kinases, including Src. A vast majority of natural substances are capable of modulating mitogenic signals, cell survival, apoptosis, cell cycle regulation, angiogenesis as well as processes involved in metastasis development. The inhibition of STAT3 phosphorylation by natural and dietary compounds leads to decreased protein expression of STAT3 targets essentially involved in regulation of the cell cycle and apoptotic cell death. This review details the cell signaling pathways involving STAT transcription factors as well as the corresponding compounds from nature able to interfere with this regulatory system in human cancer.

Autophagy-mediated HMGB1 release antagonizes apoptosis of gastric cancer cells induced by vincristine via transcriptional regulation of Mcl-1

Autophagy-associated release of HMGB1 is known to protect cancer cells from many chemotherapeutics. However, the detailed molecular mechanism(s) responsible remains largely undefined. We show in this study that HMGB1 released into the extracellular space protects gastric cancer cells from apoptosis induced by the microtubule-targeting drug vincristine through transcriptional upregulation of Mcl-1. Extracellular HMGB1 appeared essential for autophagy-mediated inhibition of apoptosis, in that siRNA knockdown of HMGB1 or inhibition of its release abolished the protective effect of autophagy. Strikingly, vincristine upregulated the Mcl-1 mRNA expression through a transcriptional increase, but did not alter the expression levels of the Mcl-1 protein. Inhibition of HMGB1 release blocked the increase in the Mcl-1 transcript and caused reduction in Mcl-1 at the protein level, indicating that HMGB1-mediated signaling was necessary for transcriptional upregulation of Mcl-1. This seemed critical for maintaining sufficient Mcl-1 protein expression required for survival of gastric cancer cells exposed to vincristine. The effect of extracellular HMGB1 on transcriptional regulation of Mcl-1 was confirmed in gastric cancer cells treated with recombinant HMGB1. Taken together, these results identify HMGB1-mediated upregulation of Mcl-1 transcription as an important mechanism by which autophagy protects gastric cancer cells from apoptosis induced by vincristine.

The curcumin analogue hydrazinocurcumin exhibits potent suppressive activity on carcinogenicity of breast cancer cells via STAT3 inhibition

Curcumin, the active component of turmeric, has been shown to protect against carcinogenesis and prevent tumor development in cancer. In our study, we tested the efficacy of a synthetic curcumin analogue, known as hydrazinocurcumin (HC), in breast cancer cells. The results demonstrated that compared to curcumin, HC was more effective in inhibiting STAT3 phosphorylation and downregulation of an array of STAT3 downstream targets which contributed to suppression of cell proliferation, loss of colony formation, depression of cell migration and invasion as well as induction of cell apoptosis. It was concluded that HC is a potent agent in the inhibition of STAT3 with more favorable pharmacological activity than curcumin, and HC may have translational potential as an effective cancer therapeutic or preventive agent for human breast carcinoma.

Dynamical and structural analysis of a T cell survival network identifies novel candidate therapeutic targets for large granular lymphocyte leukemia

The blood cancer T cell large granular lymphocyte (T-LGL) leukemia is a chronic disease characterized by a clonal proliferation of cytotoxic T cells. As no curative therapy is yet known for this disease, identification of potential therapeutic targets is of immense importance. In this paper, we perform a comprehensive dynamical and structural analysis of a network model of this disease. By employing a network reduction technique, we identify the stationary states (fixed points) of the system, representing normal and diseased (T-LGL) behavior, and analyze their precursor states (basins of attraction) using an asynchronous Boolean dynamic framework. This analysis identifies the T-LGL states of 54 components of the network, out of which 36 (67%) are corroborated by previous experimental evidence and the rest are novel predictions. We further test and validate one of these newly identified states experimentally. Specifically, we verify the prediction that the node SMAD is over-active in leukemic T-LGL by demonstrating the predominant phosphorylation of the SMAD family members Smad2 and Smad3. Our systematic perturbation analysis using dynamical and structural methods leads to the identification of 19 potential therapeutic targets, 68% of which are corroborated by experimental evidence. The novel therapeutic targets provide valuable guidance for wet-bench experiments. In addition, we successfully identify two new candidates for engineering long-lived T cells necessary for the delivery of virus and cancer vaccines. Overall, this study provides a bird's-eye-view of the avenues available for identification of therapeutic targets for similar diseases through perturbation of the underlying signal transduction network.

T-LGL leukemia is a blood cancer characterized by an abnormal increase in the abundance of a type of white blood cell called T cell. Since there is no known curative therapy for this disease, identification of potential therapeutic targets is of utmost importance. Experimental identification of manipulations capable of reversing the disease condition is usually a long, arduous process. Mathematical modeling can aid this process by identifying potential therapeutic interventions. In this work, we carry out a systematic analysis of a network model of T cell survival in T-LGL leukemia to get a deeper insight into the unknown facets of the disease. We identify the T-LGL status of 54 components of the system, out of which 36 (67%) are corroborated by previous experimental evidence and the rest are novel predictions, one of which we validate by follow-up experiments. By deciphering the structure and dynamics of the underlying network, we identify component perturbations that lead to programmed cell death, thereby suggesting several novel candidate therapeutic targets for future experiments.

γ-Tocotrienol is a novel inhibitor of constitutive and inducible STAT3 signalling pathway in human hepatocellular carcinoma: potential role as an antiproliferative, pro-apoptotic and chemosensitizing agent

BACKGROUND AND PURPOSE

Activation of signal transducer and activator of transcription 3 (STAT3) play a critical role in the survival, proliferation, angiogenesis and chemoresistance of tumour cells. Thus, agents that suppress STAT3 phosphorylation have potential as cancer therapies. In the present study, we investigated whether the apoptotic, antiproliferative and chemosensitizing effects of γ-tocotrienol are associated with its ability to suppress STAT3 activation in hepatocellular carcinoma (HCC).

EXPERIMENTAL APPROACH

The effect of γ-tocotrienol on STAT3 activation, associated protein kinases and phosphatase, STAT3-regulated gene products, cellular proliferation and apoptosis in HCC cells was investigated.

KEY RESULTS

γ-Tocotrienol inhibited both the constitutive and inducible activation of STAT3 with minimum effect on STAT5. γ-Tocotrienol also inhibited the activation of Src, JAK1 and JAK2 implicated in STAT3 activation. Pervanadate reversed the γ-tocotrienol-induced down-regulation of STAT3, suggesting the involvement of a protein tyrosine phosphatase. Indeed, we found that γ-tocotrienol induced the expression of the tyrosine phosphatase SHP-1 and deletion of the SHP-1 gene by small interfering RNA abolished the ability of γ-tocotrienol to inhibit STAT3 activation. γ-Tocotrienol also down-regulated the expression of STAT3-regulated gene products, including cyclin D1, Bcl-2, Bcl-xL, survivin, Mcl-1 and vascular endothelial growth factor. Finally, γ-tocotrienol inhibited proliferation, induced apoptosis and significantly potentiated the apoptotic effects of chemotherapeutic drugs (paclitaxel and doxorubicin) used for the treatment of HCC.

CONCLUSIONS AND IMPLICATIONS

Overall, these results suggest that γ-tocotrienol is a novel blocker of the STAT3 activation pathway, with a potential role in future therapies for HCC and other cancers.

Pathophysiologic mechanisms and management of neutropenia associated with large granular lymphocytic leukemia

Large granular lymphocyte (LGL) syndrome includes a spectrum of clonal T cell and natural killer cell chronic lymphoproliferative disorders. These conditions are thought to arise from chronic antigenic stimulation, while the long-term survival of the abnormal LGLs appears to be sustained by resistance to apoptosis and/or impaired survival signaling. T-cell LGL (T-LGL) leukemia is the most common LGL disorder in the Western world. Despite its indolent course, the disease is often associated with neutropenia, the pathogenesis of which is multifactorial, comprising both humoral and cytotoxic mechanisms. This article addresses the pathogenesis of T-LGL leukemia and natural killer cell chronic lymphoproliferative disorder, as well as that of T-LGL leukemia-associated neutropenia. Furthermore, as symptomatic neutropenia represents an indication for initiating treatment, available therapeutic options are also discussed.

Hyperactive EGF receptor, Jaks and Stat3 signaling promote enhanced colony-forming ability, motility and migration of cisplatin-resistant ovarian cancer cells

We present evidence that the cisplatin-resistant human ovarian cancer lines, A2780S/CP1 (S/CP1), A2780S/CP3 (S/CP3) and A2780S/CP5 (S/CP5), derived by subjecting the sensitive A2780S ovarian cancer line to multiple rounds of cisplatin treatments followed by recovery and are resistant to 1, 3 and 5 μM cisplatin, respectively, have increased colony-forming ability and altered morphology that is consistent with enhanced motility, migration and invasiveness in vitro. The malignant phenotype progresses with increasing resistance and is associated with hyperactive epidermal growth factor receptor (EGFR)/extracellular signal-regulated kinase (Erk)1/2 and janus kinases (Jaks), aberrant signal transducer and activator of transcription (Stat) 3 activation promoted by EGFR and Jaks, and epithelial-mesenchymal transition (EMT) in vitro. Survivin and FLIP anti-apoptotic factors, vascular endothelial growth factor (VEGF) and matrix metalloproteinase activities are also elevated in the resistant cells. Accordingly, the ectopic expression of constitutively-active Stat3C in the sensitive A2780S cells diminished cisplatin sensitivity. The inhibition of EGFR or Stat3 activity repressed Survivin, VEGF and Vimentin expression and the colony-forming potential, viability, motility and migration of the resistant cells, and sensitized them to cisplatin. Analysis of human ovarian cancer patients' tumor tissues shows aberrantly-active EGFR and Stat3 that in certain cases correlate with Vimentin over-expression. Intra-peritoneal mouse xenograft studies revealed, compared with the sensitive A2780S line that had low tumor incidence restricted to the ovary, a high tumor incidence for the resistant S/CP3 and S/CP5 lines that formed tumor nodules at several locations on the small intestine and colon, and which responded poorly to cisplatin, but were sensitive to concurrent treatment with cisplatin and EGFR or Stat3 inhibitor. Hyperactive EGFR signaling through Stat3 and the Jak-Stat3 activity together promote ovarian cancer progression to cisplatin resistance and therefore represent targets for preventing the development of cisplatin resistance and the recurrent disease during cisplatin therapy in ovarian cancer.

Therapeutic efficacy of FTY720 in a rat model of NK-cell leukemia

NK-cell leukemia is a clonal expansion of NK cells. The illness can occur in an aggressive or chronic form. We studied cell lines from human and rat NK-cell leukemias (aggressive NK-cell leukemia) as well as samples from patients with chronic NK-cell leukemia to investigate pathogenic mechanisms. Here we report that Mcl-1 was overexpressed in leukemic NK cells and that knockdown of Mcl-1 induced apoptosis in these leukemic cells. In vitro treatment of human and rat NK leukemia cells with FTY720 led to caspase-dependent apoptosis and decreased Mcl-1 expression in a time- and-dose-dependent manner. These biologic effects could be inhibited by blockade of reactive oxygen species generation and the lysosomal degradation pathway. Lipidomic analyses after FTY720 treatment demonstrated elevated levels of sphingosine, which mediated apoptosis of leukemic NK cells in vitro. Importantly, systemic administration of FTY720 induced complete remission in the syngeneic Fischer rat model of NK-cell leukemia. Therapeutic efficacy was associated with decreased expression of Mcl-1 in vivo. These data demonstrate that therapeutic benefit of FTY720 may result from both altered sphingolipid metabolism as well as enhanced degradation of a key component of survival signaling.

Signal transducer and activator of transcription 3 pathway mediates genipin-induced apoptosis in U266 multiple myeloma cells

It has drawn a lot of attention to target signal transducer and activator of transcription 3 (STAT3) as a potential strategy for cancer therapeutics. Using several myelogenous cell lines, the effect of genipin (an active compound of Gardenia fruit) on the STAT3 pathway and apoptosis was investigated. Genipin suppressed the constitutive STAT3 activation in U266 and U937 cells and stimulated Src homology 2 domain-containing phosphatase 1 (SHP-1), which dephosphorylates and inactivates STAT3. Specifically, genipin blocked STAT3 activation via repressing the activation of c-Src, but not Janus kinase 1 (JAK1). Genipin also downregulated the expression of STAT3 target genes including Bcl-2, Bcl-x(L) , Survivin, Cyclin D1, and VEGF. Conversely, protein tyrosine phosphatase inhibitor pervanadate blocked genipin induced STAT3 inactivation. Using DNA fragmentation or TUNEL assays, we demonstrated the apoptotic effect of genipin on U266, MM.1S, and U937 cells. Furthermore, genipin effectively potentiated the cytotoxic effect of chemotherapeutic agents, such as bortezomib, thalidomide, and paclitaxel in U266 cells. Our data suggest that through regulation of Src and SHP-1, genipin antagonizes STAT3 for the induction of apoptosis in myeloma cells.

Signal transducer and activator of transcription 3 (STAT3): a promising target for anticancer therapy

Signal transducer and activator of transcription 3 (STAT3) is an oncogenic protein whose inhibition is sought for the prevention and treatment of cancer. In this review, the validated therapeutic strategy to block aberrant activity of STAT3 in many tumor cell lines is evaluated by presenting the most promising inhibitors to date. The compounds are discussed in classes based on their different mechanisms of action, which are critically explained. In addition, their future clinical development as anticancer agents is considered. Furthermore, the efforts devoted to the comprehension of the structure-activity relationships and to the identification of the biological effects are brought to attention. The synthetic and technological approaches recently developed to overcome the difficulties in the obtainment of clinically suitable drugs are also presented.

Prognostic significance of nuclear pSTAT3 in oral cancer

BACKGROUND

Aberrant nuclear accumulation of proteins influences tumor development and may predict biologic aggressiveness and disease prognosis. This study determined the prognostic significance of pSTAT3 (phosphorylayed signal transducer and activator of transcription 3) in oral squamous cell carcinomas (OSCCs).

METHODS AND RESULTS

Using immunohistochemistry, a significant increase in nuclear accumulation of pSTAT3 was observed in 49 of 90 leukoplakias (54.4%) and 63/94 OSCCs (67%) (p(trend) < .001). Increased pSTAT3 was associated with tumor stage (p = .01), nodal metastasis (p = .0018), and tobacco consumption (p = .004). Kaplan-Meier analysis demonstrated that OSCC with increased nuclear pSTAT3 showed significantly reduced disease-free survival (13 months), compared with the patients with no nuclear pSTAT3 expression (64 months, p = .019). Cox regression analysis revealed nuclear pSTAT3 as the most significant predictor of poor prognosis (p = .024, hazard ratio [HR] = 2.7).

CONCLUSIONS

Increased nuclear accumulation of pSTAT3 occurs in early premalignant stages and is a marker for poor prognosis of OSCC.

T-cell and natural killer-cell large granular lymphocyte leukemia neoplasias

Large granular lymphocyte (LGL) leukemia is a rare disorder of cytotoxic lymphocytes. LGL cells play an integral role in the immune system and are divided into two major lineages of CD3(-)natural killer (NK) cells and CD3(+) T cells that circulate throughout the blood in search of infected cells, in which they will make contact through a receptor ligand and induce cell death. LGL cells are also programmed to undergo apoptosis after contact with an infected target cell; however, they continue to survive in individuals with LGL leukemia. This unchecked proliferation and cytotoxicity of LGLs in patients results in autoimmunity or malignancy. Rheumatoid arthritis is the most common autoimmune condition seen in individuals with LGL leukemia; however, LGL leukemia is associated with a wide spectrum of other autoimmune diseases. Patients may also suffer from other hematological conditions including hemolytic anemia, pure red cell aplasia, and neutropenia, which lead to recurrent bacterial infections. Currently, the only established treatment involves a low dose of an immunosuppressive regimen with methotrexate, in which 40-50% of patients are either resistant or do not respond. In order to establish new therapeutics it is important to understand the current state of LGL leukemia both in the clinic and in basic research.

B7-H3 silencing increases paclitaxel sensitivity by abrogating Jak2/Stat3 phosphorylation

In many types of cancer, the expression of the immunoregulatory protein B7-H3 has been associated with poor prognosis. Previously, we observed a link between B7-H3 and tumor cell migration and invasion, and in present study, we have investigated the role of B7-H3 in chemoresistance in breast cancer. We observed that silencing of B7-H3, via stable short hairpin RNA or transient short interfering RNA transfection, increased the sensitivity of multiple human breast cancer cell lines to paclitaxel as a result of enhanced drug-induced apoptosis. Overexpression of B7-H3 made the cancer cells more resistant to the drug. Next, we investigated the mechanisms behind B7-H3-mediated paclitaxel resistance and found that the level of Stat3 Tyr705 phosphorylation was decreased in B7-H3 knockdown cells along with the expression of its direct downstream targets Mcl-1 and survivin. The phosphorylation of Janus kinase 2 (Jak2), an upstream molecule of Stat3, was also significantly decreased. In contrast, reexpression of B7-H3 in B7-H3 knockdown and low B7-H3 expressing cells increased the phosphorylation of Jak2 and Stat3. In vivo animal experiments showed that B7-H3 knockdown tumors displayed a slower growth rate than the control xenografts. Importantly, paclitaxel treatment showed a strong antitumor activity in the mice with B7-H3 knockdown tumors, but only a marginal effect in the control group. Taken together, our data show that in breast cancer cells, B7-H3 induces paclitaxel resistance, at least partially by interfering with Jak2/Stat3 pathway. These results provide novel insight into the function of B7-H3 and encourage the design and testing of approaches targeting this protein and its partners.

Pleiotropic action of AP-1 in v-Src-transformed cells

The activation of AP-1 is a hallmark of cell transformation by tyrosine kinases. In this study, we characterize the role of AP-1 proteins in the transformation of chicken embryo fibroblasts (CEF) by v-Src. In normal CEF, the expression of a dominant negative mutant of c-Jun (TAM67) induced senescence. In contrast, three distinct phenotypes were observed when TAM67 was expressed in v-Src-transformed CEF. While senescent cells were also present, the inhibition of AP-1 caused apoptosis in a fraction of the v-Src-transformed cells. In addition, cells containing lipid-rich vesicles accumulated, suggesting that a subpopulation of the v-Src-transformed cells underwent differentiation in response to the inhibition of AP-1. JunD and Fra-2 were the main components of this factor, while c-Jun accounted for a minor fraction of AP-1 in v-Src-transformed CEF. The downregulation of c-Jun expression by short hairpin RNA (shRNA) induced senescence in normal and v-Src-transformed cells. In contrast, a high incidence of apoptosis was caused by the downregulation of JunD, suggesting that it is required for the survival of v-Src-transformed CEF. Levels of the p53 tumor suppressor were elevated under conditions of JunD inhibition. Repression of p53 by shRNA enhanced the survival and anchorage-independent proliferation of v-Src-transformed CEF with JunD/AP-1 inhibition. The inhibition of Fra-2 had no visible phenotype in normal CEF but caused the appearance of lipid-rich vesicles in v-Src-transformed CEF. Therefore, AP-1 facilitated transformation by acting as a survival factor, by inhibiting premature entry into senescence, and by blocking the differentiation of v-Src-transformed CEF.

Ets-1 mediates upregulation of Mcl-1 downstream of XBP-1 in human melanoma cells upon ER stress

Past studies have shown that upregulation of the anti-apoptotic Bcl-2 family protein Mcl-1 is a major adaptive mechanism of melanoma cells to endoplasmic reticulum (ER) stress, and has an important role in resistance of the cells to apoptosis. In this study, we show that the increase in transcription of Mcl-1 in melanoma cells triggered by pharmacological ER stress inducers is mediated by the transcription factor Ets-1. By incremental deletion analysis of the Mcl-1 promoter, we identified a DNA fragment containing an Ets-1 binding site that is transcriptionally responsive to ER stress. Mutations in the Ets-1 binding site or knockdown of Ets-1 inhibited the increase in Mcl-1, indicating that Ets-1 has a critical role in transcriptional upregulation of Mcl-1. Similar to Mcl-1, Ets-1 was transcriptionally upregulated by ER stress. This was mediated by the IRE1α/XBP-1 branch of the unfolded protein response, as upregulation of Ets-1 was inhibited in melanoma cell lines deficient in IRE1α or XBP-1 established by short hairpin RNA knockdown. Activation of the PI3k/Akt pathway downstream of XBP-1 was also involved, in that inhibition of the pathway blocked upregulation of Ets-1. Inhibition of Ets-1 enhanced ER stress-induced apoptosis in melanoma cell lines and in fresh melanoma isolates, recapitulating the effect of inhibition of Mcl-1. These results reveal a key mechanism by which Mcl-1 is transcriptionally upregulated in melanoma cells by ER stress, and identify Ets-1 as a potential target for inhibition to sensitize melanoma cells to apoptosis.

Thymoquinone inhibits proliferation, induces apoptosis and chemosensitizes human multiple myeloma cells through suppression of signal transducer and activator of transcription 3 activation pathway

BACKGROUND AND PURPOSE

Constitutive activation of the signal transducer and activator of transcription 3 (STAT3) pathway is frequently encountered in several human cancers including multiple myeloma (MM). Thus, agents that suppress STAT3 phosphorylation have a potential for treatment of MM. In the present report, we investigated whether thymoquinone (TQ), the main component isolated from the medicinal plant Nigella sativa, modulated the STAT3 signalling pathway in MM cells.

EXPERIMENTAL APPROACH

The effect of TQ on both constitutive and IL-6-induced STAT3 activation, associated protein kinases, STAT3-regulated gene products involved in proliferation, survival and angiogenesis, cellular proliferation and apoptosis in MM cells, was investigated.

KEY RESULTS

We found that TQ inhibited both constitutive and IL-6-inducible STAT3 phosphorylation which correlated with the inhibition of c-Src and JAK2 activation. Vanadate reversed the TQ-induced down-regulation of STAT3 activation, suggesting the involvement of a protein tyrosine phosphatase. Indeed, we found that TQ can induce the expression of Src homology-2 phosphatase 2 that correlated with suppression of STAT3 activation. TQ also down-regulated the expression of STAT3-regulated gene products, such as cyclin D1, Bcl-2, Bcl-xL, survivin, Mcl-1 and vascular endothelial growth factor. Finally, TQ induced the accumulation of cells in sub-G1 phase, inhibited proliferation and induced apoptosis, as indicated by poly ADP ribose polymerase cleavage. TQ also significantly potentiated the apoptotic effects of thalidomide and bortezomib in MM cells.

CONCLUSIONS AND IMPLICATIONS

Our study has identified STAT3 signalling as a target of TQ and has thus raised its potential application in the prevention and treatment of MM and other cancers.

c-Abl regulates Mcl-1 gene expression in chronic lymphocytic leukemia cells

Chronic lymphocytic leukemia (CLL) is a malignancy characterized by clonal expansion of mature B cells that are resistant to apoptosis. This resistance to apoptosis partly results from Mcl-1 expression because high levels of this protein in CLL cells correlate with poor disease prognosis and resistance to chemotherapy. Thus, understanding the mechanism(s) regulating Mcl-1 expression in CLL cells may be useful in the development of new therapies for this incurable disease. In the present study, we show a strong relationship between c-Abl and Mcl-1 expression in CLL cells. We show that treatment of CLL cells with Abl-specific siRNA or with imatinib, to inhibit c-Abl activity, results in the down-regulation of Mcl-1 protein and mRNA. A major regulator of Mcl-1 gene expression is STAT3. Our data show that CLL cells expressing high levels of c-Abl also show elevated levels of phospho-STAT3, and that STAT3 phosphorylation in CLL cells is dependent on c-Abl activity. However, STAT3 phosphorylation by c-Abl requires activation of nuclear factor-κB, secretion of autocrine interleukin-6, and active protein kinase C. Taken together, our data demonstrate the mechanism involved in c-Abl regulation of Mcl-1 expression in CLL cells, and suggest that c-Abl inhibition has therapeutic application in the treatment of this disease.

How I treat LGL leukemia

Large granular lymphocyte (LGL) leukemia is characterized by a clonal expansion of either CD3(+) cytotoxic T or CD3(-) NK cells. Prominent clinical features of T-LGL leukemia include neutropenia, anemia and rheumatoid arthritis (RA). The terminal effector memory phenotype (CD3(+)/CD45RA(+)/CD62L(-)CD57(+)) of T-LGL suggests a pivotal chronic antigen-driven immune response. LGL survival is then promoted by platelet-derived growth factor and interleukin-15, resulting in global dysregulation of apoptosis and resistance to normal pathways of activation-induced cell death. These pathogenic features explain why treatment of T-LGL leukemia is based on immunosuppressive therapy. The majority of these patients eventually need treatment because of severe or symptomatic neutropenia, anemia, or RA. No standard therapy has been established because of the absence of large prospective trials. The authors use low-dose methotrexate initially for T-LGL leukemia patients with neutropenia and/or RA. We recommend either methotrexate or oral cyclophosphamide as initial therapy for anemia. If treatment is not successful, patients are switched to either the other agent or cyclosporine. The majority of patients experience an indolent clinical course. Deaths infrequently occur because of infections related to severe neutropenia. As there are no curative therapeutic modalities for T-LGL leukemia, new treatment options are needed.

Cucurbitacin I suppressed stem-like property and enhanced radiation-induced apoptosis in head and neck squamous carcinoma--derived CD44(+)ALDH1(+) cells

Head and neck squamous cell carcinoma (HNSCC) is a prevalent cancer worldwide. Signal transducers and activators of transcription 3 (STAT3) signaling is reported to promote tumor malignancy and recurrence in HNSCC. Cucurbitacins, triterpenoid derivatives, are strong STAT3 inhibitors with anticancer properties. Recent studies have shown aldehyde dehydrogenase 1 (ALDH1) to be a marker of cancer stem cells (CSC) in HNSCC. The aim of this study was to investigate the therapeutic effect of cucurbitacin I in HNSCC-derived CSCs. Using immunohistochemical analysis, we firstly showed that CD44, ALDH1, and phosphorylated STAT3 (p-STAT3) were higher in high-grade HNSCCs, and that triple positivity for CD44/ALDH1/p-STAT3 indicated a worse prognosis for HNSCC patients. Secondly, CD44(+)ALDH1(+) cells isolated from seven HNSCC patients showed greater tumorigenicity, radioresistance, and high expression of stemness (Bmi-1/Oct-4/Nanog) and epithelial-mesenchymal-transitional (Snail/Twist) genes as p-STAT3 level increased. Furthermore, we found that cucurbitacin I (JSI-124) can effectively inhibit the expression of p-STAT3 and capacities for tumorigenicity, sphere formation, and radioresistance in HNSCC-CD44(+)ALDH1(+). Notably, 150 nmol/L cucurbitacin I effectively blocked STAT3 signaling and downstream survivin and Bcl-2 expression, and it induced apoptosis in HNSCC-CD44(+)ALDH1(+). Moreover, microarray data indicated that 100 nmol/L cucurbitacin I facilitated CD44(+)ALDH1(+) cells to differentiate into CD44⁻ALDH1⁻ and enhanced the radiosensitivity of HNSCC-CD44(+)ALDH1(+). Xenotransplant experiments revealed that cucurbitacin I combined with radiotherapy significantly suppressed tumorigenesis and lung metastasis and further improved the survival rate in HNSCC-CD44(+)ALDH1(+)-transplanted immunocompromised mice. Taken together, our data show that cucurbitacin I, STAT3 inhibitor, reduces radioresistant, distant-metastatic, and CSC-like properties of HNSCC-CD44(+)ALDH1(+) cells. The potential of cucurbitacin I as a radiosensitizer should be verified in future anti-CSC therapy.

Inhibition of the Signal Transducers and Activators of Transcription (STAT) 3 Signalling Pathway by AG490 in Laryngeal Carcinoma Cells

Signal transducers and activators of transcription (STAT) are important in the development of laryngeal carcinomas and are potential novel molecular targets for therapy to improve survival of patients with this cancer. This study was designed to investigate the influence of the janus activated kinase (JAK)/STAT inhibitor AG490 on proliferation and apoptosis of Hep-2 human laryngeal cancer cells and whether there was any inhibition by AG490 of the JAK/STAT3 signalling pathway. AG490 inhibited cell proliferation in dose-and time-dependent manners and induced apoptosis in Hep-2 cells, with the number of apoptotic cells increasing with time. AG490 inhibited G1 to S cell cycle transition and induced G1 cell cycle arrest as well as significantly down-regulating STAT3, phosphorylated STAT3 and survivin in Hep-2 cells. This study showed that AG490 significantly inhibited proliferation and induced apoptosis of laryngeal carcinoma cells through down-regulation of STAT3 and survivin, suggesting a potential target for laryngeal carcinoma treatment.

Silencing STAT3 with short hairpin RNA enhances radiosensitivity of human laryngeal squamous cell carcinoma xenografts in vivo

Short hairpin RNA (shRNA) targeting signal transducer and activator of transcription 3 (STAT3) potentiate the radiosensitivity of human laryngeal squamous carcinoma cells in vitro. In the present study, we investigated the inhibitory effect of STAT3 shRNA plus radiotherapy on nude mouse laryngeal squamous cell carcinoma xenografts. The xenotransplanted tumors were treated with STAT3 shRNA, with or without radiation, following a planned scheme. The inhibition rate for tumor growth was calculated and the tumor growth curve was plotted. In addition, the expression of p-STAT3, B cell lymphoma 2 (Bcl-2), p53, vascular endothelial growth factor (VEGF) protein and intratumoral microvessel density (MVD) was determined by immunohistochemistry. Flow cytometry was used to detect the rate of cell apoptosis. The results revealed that STAT3 shRNA transfection plus radiotherapy significantly minimized tumor volume and increased the rate of tumor inhibition. p-STAT3 protein expression and intratumoral MVD were observed to be down-regulated, whereas apoptosis was increased. There was a positive correlation between the expression of p-STAT3 and Bcl-2, and also between the expression of p53 and VEGF, and MVD. These findings indicate that STAT3 shRNA potentiate the radiosensitivity of laryngeal carcinoma xenografts in vivo by regulating downstream signaling proteins in the STAT3 pathway.

Fluacrypyrim, a novel STAT3 activation inhibitor, induces cell cycle arrest and apoptosis in cancer cells harboring constitutively-active STAT3

STAT3 protein has an important role in oncogenesis and is a promising anticancer target. Herein, we demonstrate that a novel small molecule fluacrypyrim (FAPM) inhibits the growth of leukemia cells by a predominant G1 arrest with significant decrease of the protein and mRNA levels of cyclin D1. As cyclin D1 is transcriptionally regulated by STAT3, FAPM is then shown to markedly inhibit the STAT3 phosphorylation with marginal effect on the other signal transducers and activators of transcription, and without effect on phosphoinositide-3-kinase and mitogen-activated protein kinase pathways. Further analysis shows that FAPM significantly increases the protein tyrosine phosphatases (PTPs) activity in a dose-dependent manner, and the inhibition of PTP activation by sodium pervanadate reverses FAPM-induced suppression of STAT3 tyrosine phosphorylation, indicating an important role of PTP in the action of FAPM. Finally, FAPM treatment results in selective suppression of STAT3-mediated transcriptional activity and its downstream effectors, and subsequent induction of growth arrest and apoptosis in STAT3-dependent cancer cell lines. This study therefore identifies FAPM as a potent STAT3 activation inhibitor with possible therapeutic potential against malignancies with constitutive STAT3 activation.

Targeting of survivin by nanoliposomal ceramide induces complete remission in a rat model of NK-LGL leukemia

The natural killer (NK) type of aggressive large granular lymphocytic (LGL) leukemia is a fatal illness that pursues a rapid clinical course. There are no effective therapies for this illness, and pathogenetic mechanisms remain undefined. Here we report that the survivin was highly expressed in both aggressive and chronic leukemic NK cells but not in normal NK cells. In vitro treatment of human and rat NK-LGL leukemia cells with cell-permeable, short-chain C₆-ceramide (C₆) in nanoliposomal formulation led to caspase-dependent apoptosis and diminished survivin protein expression, in a time- and dose-dependent manner. Importantly, systemic intravenous delivery of nanoliposomal ceramide induced complete remission in the syngeneic Fischer F344 rat model of aggressive NK-LGL leukemia. Therapeutic efficacy was associated with decreased expression of survivin in vivo. These data suggest that in vivo targeting of survivin through delivery of nanoliposomal C₆-ceramide may be a promising therapeutic approach for a fatal leukemia.

The rGel/BLyS fusion toxin inhibits STAT3 signaling via down-regulation of interleukin-6 receptor in diffuse large B-cell lymphoma

Aberrant signal transducer and activator of transcription (STAT)3 signaling participates in the development and progress of human cancers. We previously generated a highly cytotoxic fusion toxin designated rGel/BLyS for receptor-mediated delivery of the rGel toxin to malignant B-cells. In this study, we examined this fusion toxin for its ability to impact STAT3 signaling in diffuse large B-cell lymphoma (DLBCL). The activated B cell-like DLBCL lines were found to express higher levels of interleukin-6 receptor (IL-6R) and STAT3 than did the germinal center B cell-like DLBCL lines. Treatment of DLBCL cells with rGel/BLyS resulted in down-regulation of IL-6R and inhibited STAT3 phosphorylation, STAT3-DNA binding activity, and IL-6-inducible STAT3 reporter gene activity. In agreement with these results, we additionally found that rGel/BLyS down-regulated levels of several STAT3 targets (c-Myc, p21, Mcl-1, and Bcl-x(L)) and p-SYK, a positive regulator of STAT3. Inhibition of IL-6R-mediated STAT3 signaling by rGel/BLyS led to growth inhibition, triggered accumulation of cells in the sub-G(1) phase of the cell cycle, and induced apoptosis. Our results indicate that rGel/BLyS is an excellent candidate for the treatment of aggressive DLBCL which is resistant to conventional chemotherapeutic regimens and STAT3 signaling pathway may be an attractive therapeutic target for non-Hodgkin's lymphoma.

Growth factor signaling pathways as targets for prevention of epithelial carcinogenesis

Growth factor receptor (GFR) signaling controls epithelial cell growth by responding to various endogenous or exogenous stimuli and subsequently activating downstream signaling pathways including Stat3, PI3K/Akt/mTOR, MAPK, and c-Src. Environmental chemical toxicants and UVB irradiation cause enhanced and prolonged activation of GFR signaling and downstream pathways that contributes to epithelial cancer development including skin cancer. Recent studies, especially those with tissue-specific transgenic mouse models, have demonstrated that GFRs and their downstream signaling pathways contribute to all three stages of epithelial carcinogenesis by regulating a wide variety of biological functions including proliferation, apoptosis, angiogenesis, cell adhesion, and migration. Inhibiting these signaling pathways early in the carcinogenic process results in reduced cell proliferation and survival, leading to decreased tumor formation. Collectively, these studies suggest that GFR signaling and subsequent downstream signaling pathways are potential targets for the prevention of epithelial cancers including skin cancer.

Inhibition of STAT3 signaling blocks the anti-apoptotic activity of IL-6 in human liver cancer cells

Interleukin-6 (IL-6) is a multifunctional cytokine, which may block apoptosis during inflammation to protect cells under very toxic conditions. However, IL-6 also activates STAT3 in many types of human cancer. Recent studies demonstrate that high levels of IL-6 are associated with hepatocellular carcinoma, the most common type of liver cancer. Here we reported that IL-6 promoted survival of human liver cancer cells through activating STAT3 in response to doxorubicin treatment. Endogenous IL-6 levels in SNU-449 cells were higher than in Hep3B cells. Meanwhile, SNU-449 cells were more resistant to doxorubicin than Hep3B cells. Addition of IL-6 induced STAT3 activation in Hep3B cells and led to protection against doxorubicin. In contrast, neutralizing IL-6 with anti-IL-6 antibody decreased survival of SNU-449 cells in response to doxorubicin. To elucidate the mechanism of the anti-apoptotic function of IL-6, we investigated if STAT3 mediated this drug resistance. Targeting STAT3 with STAT3 siRNA reduced the protection of IL-6 against doxorubicin-induced apoptosis, indicating that STAT3 signaling contributed to the anti-apoptotic effect of IL-6. Moreover, we further explored if a STAT3 small molecule inhibitor could abolish this anti-apoptotic effect. LLL12, a STAT3 small molecule inhibitor, blocked IL-6-induced STAT3 phosphorylation, resulting in attenuation of the anti-apoptotic activity of IL-6. Finally, neutralization of endogenous IL-6 with anti-IL-6 antibody or blockade of STAT3 with LLL12 lowered the recovery in SNU-449 cells after doxorubicin treatment. Therefore, our results demonstrated that targeting STAT3 signaling could interrupt the anti-apoptotic function of IL-6 in human liver cancer cells.

The small heat shock protein 27 is a key regulator of CD8+ CD57+ lymphocyte survival

Differences in CD8(+)CD57(-) and CD8(+)CD57(+) lymphocyte lifespan have been documented. Lower numbers and shorter lifespan are characteristic of CD8(+)CD57(+) in normal individuals. However, CD8(+)CD57(+) are expanded in certain disease states including T cell large granular leukemia and other hematologic malignancies. The mechanisms responsible for the differences in CD8(+)CD57(-) and CD8(+)CD57(+) lifespan remain elusive. In this study, we demonstrate that the small heat shock protein (Hsp) 27 is a key regulator of CD8(+)CD57(+) lymphocyte lifespan. We found that Hsp27 expression is significantly lower in CD8(+)CD57(+) than in CD8(+)CD57(-) lymphocytes. In contrast, Hsp60 and Hsp70 are expressed at comparable levels. Unlike other antiapoptotic Bcl-2-like molecules, the expression of Hsp27 tightly correlates with CD8(+)CD57(+) and CD8(+)CD57(-) lifespan. We demonstrate that Hsp27 overexpression in CD8(+)CD57(+) lymphocytes to levels found normally in CD8(+)CD57(-) lymphocytes decreased apoptosis. Accordingly, silencing of Hsp27 in CD8(+)CD57(-) lymphocytes increased apoptosis. Collectively these results demonstrate that Hsp27 is a critical regulator of normal CD8(+)CD57(+) lifespan supporting its use as a marker of lifespan in this lineage, and suggest a mechanism responsible for the decreased apoptosis and clonal expansion characteristic of certain disease states.

MICA polymorphism identified by whole genome array associated with NKG2D-mediated cytotoxicity in T-cell large granular lymphocyte leukemia

BACKGROUND

Large granular lymphocyte leukemia is a semi-autonomous clonal proliferation of cytotoxic T cells accompanied by immune cytopenias and various autoimmune conditions. Due to the rarity of this disease and its association with autoimmune diseases, a theoretical germline or somatic mutation might have significant penetrance, thus enabling detection, even from samples of suboptimal size, through genome-wide association studies.

DESIGN AND METHODS

To investigate a non-mendelian genetic predisposition to large granular lymphocyte leukemia, we used a step-wise method for gene discovery. First, a modified 'random forests' technique was used for candidate gene identification: this was followed by traditional allele-specific polymerase chain reaction, sequencing modalities, and mechanistic assays.

RESULTS

Our analysis found an association with MICA, a non-peptide-presenting, tightly regulated, stress-induced MHC-like molecule and cognate receptor for NKG2D, found abundantly on large granular lymphocyte leukemia cells. Sequencing of germline DNA revealed a higher frequency of MICA*00801/A5.1 in patients with large granular lymphocyte leukemia than in matched controls (64% versus 41%, P<0.001, homozygous 40% versus 15%, P<0.001). Flow cytometry was employed to determine the expression of MICA within hematologic compartments, showing that the signal intensity of MICA was increased in granulocytes from neutropenic patients with large granular lymphocyte leukemia in comparison with that in controls (P=0.033). Furthermore, neutrophil counts were inversely correlated with MICA expression (R(2)=0.50, P=0.035). Finally, large granular lymphocyte leukemia cells were able to selectively kill MICA(+) Ba/F3 lymphocytes transfected with human MICA*019 in a dose-dependent manner compared to naïve cells (P<0.001), an effect mitigated by administration of an anti-NKG2D antibody (P=0.033).

CONCLUSIONS

Our results illustrate that MICA-NKG2D played a role in disease pathogenesis in the majority of patients in our cohort of cases of large granular lymphocyte leukemia and further investigation into this signaling axis may provide potent therapeutic targets.

INCB16562, a JAK1/2 selective inhibitor, is efficacious against multiple myeloma cells and reverses the protective effects of cytokine and stromal cell support

Cytokines in the bone marrow of multiple myeloma patients activate Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathways in tumor cells and promote tumor growth, survival, and drug resistance. INCB16562 was developed as a novel, selective, and orally bioavailable small-molecule inhibitor of JAK1 and JAK2 markedly selective over JAK3. The specific cellular activity of the inhibitor was demonstrated by its potent and dose-dependent inhibition of cytokine-dependent JAK/STAT signaling and cell proliferation in the absence of effects on Bcr-Abl-expressing cells. Treatment of myeloma cells with INCB16562 potently inhibited interleukin-6 (IL-6)-induced phosphorylation of STAT3. Moreover, the proliferation and survival of myeloma cells dependent on IL-6 for growth, as well as the IL-6-induced growth of primary bone marrow-derived plasma cells from a multiple myeloma patient, were inhibited by INCB16562. Induction of caspase activation and apoptosis was observed and attributed, at least in part, to the suppression of Mcl-1 expression. Importantly, INCB16562 abrogated the protective effects of recombinant cytokines or bone marrow stromal cells and sensitized myeloma cells to cell death by exposure to dexamethasone, melphalan, or bortezomib. Oral administration of INCB16562 antagonized the growth of myeloma xenografts in mice and enhanced the antitumor activity of relevant agents in combination studies. Taken together, these data suggest that INCB16562 is a potent JAK1/2 inhibitor and that mitigation of JAK/STAT signaling by targeting JAK1 and JAK2 will be beneficial in the treatment of myeloma patients, particularly in combination with other agents.

IL-15 triggers an antiapoptotic pathway in human intraepithelial lymphocytes that is a potential new target in celiac disease-associated inflammation and lymphomagenesis

Enteropathy-associated T cell lymphoma is a severe complication of celiac disease (CD). One mechanism suggested to underlie its development is chronic exposure of intraepithelial lymphocytes (IELs) to potent antiapoptotic signals initiated by IL-15, a cytokine overexpressed in the enterocytes of individuals with CD. However, the signaling pathway by which IL-15 transmits these antiapoptotic signals has not been firmly established. Here we show that the survival signals delivered by IL-15 to freshly isolated human IELs and to human IEL cell lines derived from CD patients with type II refractory CD (RCDII) - a clinicopathological entity considered an intermediary step between CD and enteropathy-associated T cell lymphoma - depend on the antiapoptotic factors Bcl-2 and/or Bcl-xL. The signals also required IL-15Rbeta, Jak3, and STAT5, but were independent of PI3K, ERK, and STAT3. Consistent with these data, IELs from patients with active CD and RCDII contained increased amounts of Bcl-xL, phospho-Jak3, and phospho-STAT5. Furthermore, incubation of patient duodenal biopsies with a fully humanized human IL-15-specific Ab effectively blocked Jak3 and STAT5 phosphorylation. In addition, treatment with this Ab induced IEL apoptosis and wiped out the massive IEL accumulation in mice overexpressing human IL-15 in their gut epithelium. Together, our results delineate the IL-15-driven survival pathway in human IELs and demonstrate that IL-15 and its downstream effectors are meaningful therapeutic targets in RCDII.

Cytokine-induced tumor suppressors: a GRIM story

Cytokines belonging to the IFN family are potent growth suppressors. In a number of clinical and preclinical studies, vitamin A and its derivatives like retinoic acid (RA) have been shown to exert synergistic growth-suppressive effects on several tumor cells. We have employed a genome-wide expression-knockout approach to identify the genes critical for IFN/RA-induced growth suppression. A number of novel genes associated with Retinoid-Interferon-induced Mortality (GRIM) were isolated. In this review, we will describe the molecular mechanisms of actions of one, GRIM-19, which participates in multiple pathways for exerting growth control and/or cell death. This protein is emerging as a new tumor suppressor. In addition, GRIM-19 appears to participate in innate immune responses as its activity is modulated by several viruses and bacteria. Thus, GRIMs seem to couple with multiple biological responses by acting at critical nodes.

Identification of beta-escin as a novel inhibitor of signal transducer and activator of transcription 3/Janus-activated kinase 2 signaling pathway that suppresses proliferation and induces apoptosis in human hepatocellular carcinoma cells

The activation of signal transducer and activator of transcription 3 (STAT3) has been linked with the proliferation, survival, invasion, and angiogenesis of a variety of human cancer cells, including hepatocellular carcinoma (HCC). Agents that can suppress STAT3 activation have potential for the prevention and treatment of HCC. In this study, we tested an agent, beta-escin, for its ability to suppress STAT3 activation. We found that beta-escin, a pentacyclic triterpenoid, inhibited both constitutive and interleukin-6-inducible STAT3 activation in a dose- and time-dependent manner in HCC cells. The suppression was mediated through the inhibition of activation of upstream kinases c-Src, Janus-activated kinase 1, and Janus-activated kinase 2. Vanadate treatment reversed the beta-escin-induced down-regulation of STAT3, suggesting the involvement of a tyrosine phosphatase. Indeed, we found that beta-escin induced the expression of tyrosine phosphatase Src homology phosphatase 1 that correlated with the down-regulation of constitutive STAT3 activation. beta-Escin also down-regulated the expression of STAT3-regulated gene products, such as cyclin D1, Bcl-2, Bcl-xL, survivin, Mcl-1, and vascular endothelial growth factor. Finally, beta-escin inhibited proliferation and also substantially potentiated the apoptotic effects of paclitaxel and doxorubicin in HCC cells. Overall, these results suggest that beta-escin is a novel blocker of STAT3 activation that may have potential in the suppression of proliferation and chemosensitization in HCC.

Sorafenib inhibits STAT3 activation to enhance TRAIL-mediated apoptosis in human pancreatic cancer cells

Signal transducers and activators of transcription 3 (STAT3) is constitutively active in human pancreatic cancer cells and can promote cell growth and apoptosis resistance that contribute to tumorigenesis. We determined if sorafenib, a multikinase inhibitor, can induce apoptosis by targeting STAT3 signaling to enhance apoptosis induction by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Human pancreatic cancer cell lines (PANC-1 and BxPC-3) were preincubated with sorafenib (Nexavar) alone or followed by TRAIL. Apoptosis was determined by Annexin V labeling, caspase cleavage, and Bax/Bak activation. Protein expression was analyzed by immunoblotting. Knockdown of STAT3, Mcl-1, and Bim were achieved by lentiviral small hairpin RNA. Adenoviral dominant-negative or retroviral constitutively active (CA) STAT3 were also used. Sorafenib inhibited constitutive STAT3 phosphorylation (Tyr(705)) and suppressed Mcl-1 and Bcl-x(L) proteins in a dose- and time-dependent manner. CA-STAT3 overexpression was shown to attenuate caspase-3 cleavage and suppression of Mcl-1 by sorafenib. STAT3 knockdown or a DN STAT3 was shown to downregulate Mcl-1 and Bcl-x(L) and to sensitize cells to TRAIL-mediated apoptosis. Treatment with sorafenib enhanced TRAIL-induced Annexin V staining and release of mitochondrial cytochrome c and AIF. Because the BH3-only Bim protein is a potent inducer of mitochondrial apoptosis, Bim knockdown was shown to attenuate caspase-3, caspase-9 cleavage, and Bax/Bak activation by sorafenib plus TRAIL. The suppression of STAT3 by genetic means or using sorafenib was shown to downregulate Mcl-1 and Bcl-x(L) and to sensitize cells to TRAIL-mediated apoptosis. These data indicate that targeting STAT3 may enhance treatment efficacy against pancreatic cancer.