Cyclin D1 is transcriptionally regulated by and required for transformation by activated signal transducer and activator of transcription 3

Benzyl isothiocyanate inhibits oncogenic actions of leptin in human breast cancer cells by suppressing activation of signal transducer and activator of transcription 3

Molecular effects of obesity, a well-established risk factor for breast cancer progression, are mediated by adipocytokine leptin. Given the important role of leptin in breast cancer growth and metastasis, novel strategies to antagonize biological effects of this adipocytokine are much desired. We showed previously that benzyl isothiocyanate (BITC), a constituent of edible cruciferous vegetables (e.g. garden cress), confers significant protection against mammary carcinogenesis in a transgenic mouse model. The present study provides first evidence for the efficacy of BITC against oncogenic effects of leptin. The BITC treatment circumvented leptin-induced clonogenicity and anchorage-independent growth of MDA-MB-231 and MCF-7 human breast cancer cells. Leptin-stimulated migration and invasion of these cells was also inhibited in the presence of BITC. Analysis of the underlying molecular mechanisms revealed that BITC treatment suppressed leptin-induced Stat3 phosphorylation and cyclin D1 transactivation. The BITC-mediated inhibition of MDA-MB-231 xenograft growth correlated with a modest yet significant decrease in levels of Tyr705 phosphorylated Stat3. The BITC treatment efficiently inhibited Stat3 and SRC1 recruitment to cyclin D1 promoter in a chromatin immunoprecipitation analysis. Furthermore, overexpression of constitutively active Stat3 imparted significant protection against BITC-mediated inhibition of cyclin D1 transactivation, whereas RNA interference of Stat3 resulted in a significant increase in BITC-mediated inhibition of cyclin D1 transactivation in the presence of leptin. These results indicate that Stat3 plays an important role in BITC-mediated inhibition of leptin-induced cyclin D1 transactivation. In conclusion, BITC could potentially be a rational therapeutic strategy for breast carcinoma in obese patients with high leptin levels.

Notch induces cyclin-D1-dependent proliferation during a specific temporal window of neural differentiation in ES cells

The Notch signaling pathway controls cell fate choices at multiple steps during cell lineage progression. To produce the cell fate choice appropriate for a particular stage in the cell lineage, Notch signaling needs to interpret the cell context information for each stage and convert it into the appropriate cell fate instruction. The molecular basis for this temporal context-dependent Notch signaling output is poorly understood, and to study this, we have engineered a mouse embryonic stem (ES) cell line, in which short pulses of activated Notch can be produced at different stages of in vitro neural differentiation. Activation of Notch signaling for 6h specifically at day 3 during neural induction in the ES cells led to significantly enhanced cell proliferation, accompanied by Notch-mediated activation of cyclin D1 expression. A reduction of cyclin-D1-expressing cells in the developing CNS of Notch signaling-deficient mouse embryos was also observed. Expression of a dominant negative form of cyclin D1 in the ES cells abrogated the Notch-induced proliferative response, and, conversely, a constitutively active form of cyclin D1 mimicked the effect of Notch on cell proliferation. In conclusion, the data define a novel temporal context-dependent function of Notch and a critical role for cyclin D1 in the Notch-induced proliferation in ES cells.

Progesterone receptor induces ErbB-2 nuclear translocation to promote breast cancer growth via a novel transcriptional effect: ErbB-2 function as a coactivator of Stat3

Progesterone receptor (PR) and ErbB-2 bidirectional cross talk participates in breast cancer development. Here, we identified a new mechanism of the PR and ErbB-2 interaction involving the PR induction of ErbB-2 nuclear translocation and the assembly of a transcriptional complex in which ErbB-2 acts as a coactivator of Stat3. We also highlighted that the function of ErbB-2 as a Stat3 coactivator drives progestin-induced cyclin D1 promoter activation. Notably, PR is also recruited together with Stat3 and ErbB-2 to the cyclin D1 promoter, unraveling a new and unexpected nonclassical PR genomic mechanism. The assembly of the nuclear Stat3/ErbB-2 transcriptional complex plays a key role in the proliferation of breast tumors with functional PR and ErbB-2. Our findings reveal a novel therapeutic intervention for PR- and ErbB-2-positive breast tumors via the specific blockage of ErbB-2 nuclear translocation.

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.

The cdk5 kinase regulates the STAT3 transcription factor to prevent DNA damage upon topoisomerase I inhibition

The STAT3 transcription factors are cytoplasmic proteins that induce gene activation in response to growth factor stimulation. Following tyrosine phosphorylation, STAT3 proteins dimerize, translocate to the nucleus, and activate specific target genes involved in cell-cycle progression. Despite its importance in cancer cells, the molecular mechanisms by which this protein is regulated in response to DNA damage remain to be characterized. In this study, we show that STAT3 is activated in response to topoisomerase I inhibition. Following treatment, STAT3 is phosphorylated on its C-terminal serine 727 residue but not on its tyrosine 705 site. We also show that topoisomerase I inhibition induced the up-regulation of the cdk5 kinase, a protein initially described in neuronal stress responses. In co-immunoprecipitations, cdk5 was found to associate with STAT3, and pulldown experiments indicated that it associates with the C-terminal activation domain of STAT3 upon DNA damage. Importantly, the cdk5-STAT3 pathway reduced DNA damage in response to topoisomerase I inhibition through the up-regulation of Eme1, an endonuclease involved in DNA repair. ChIP experiments indicated that STAT3 can be found associated with the Eme1 promoter when phosphorylated only on its serine 727 residue and not on tyrosine 705. We therefore propose that the cdk5-STAT3 oncogenic pathway plays an important role in the expression of DNA repair genes and that these proteins could be used as predictive markers of tumors that will fail to respond to chemotherapy.

RNA interference against hepatic epidermal growth factor receptor has suppressive effects on liver regeneration in rats

Liver regeneration after a two-thirds partial hepatectomy (PHx) is a complex process requiring interaction and cooperation of many growth factors and cytokines and cross talk between multiple pathways. Along with hepatocyte growth factor and its receptor MET (HGF-MET), the epidermal growth factor receptor (EGFR) signaling pathway is activated within 60 minutes after PHx. To investigate the role of EGFR in liver regeneration, we used two EGFR-specific short hairpin silencing RNAs to inhibit EGFR expression in regenerating normal rat liver. Suppression of EGFR mRNA and protein was evident in treated rats. There was also a demonstrable decrease but not complete elimination of bromo-deoxyuridine incorporation and mitoses at 24 hours after PHx. In addition, we observed up-regulation of MET and Src as well as activation of the ErbB-3-ErbB-2-PI3K-Akt pathway and down-regulation of STAT 3, cyclin D1, cyclin E1, p21, and C/EBP beta. The decrease in the ratio of C/EBP alpha to C/EBP beta known to occur after PHx was offset in shEGFR-treated rats. Despite suppression of hepatocyte proliferation lasting into day 3 after PHx, liver weight restoration occurred. Interestingly, hepatocytes in shEGFR-treated rats were considerably larger when compared with ScrRNA-treated controls. The data indicate that although the MET and EGFR pathways are similar, the contributions made by MET and EGFR are unique and are not compensated by each other or other cytokines.

Stat3 is required for anchorage-independent growth and metastasis but not for mammary tumor development downstream of the ErbB-2 oncogene

The oncogenic transcription factor Stat3 is constitutively active in a high percentage of human tumors including mammary adenocarcinomas and is reported to participate in the ErbB-2 oncogene signaling. In order to assess the role of signal transducer and activator of transcription 3 (Stat3) in mammary tumorigenesis downstream of ErbB-2, we generated mice expressing the activated rat ErbB-2 (neu) but lacking Stat3 in the mammary epithelium. Stat3 is apparently not required for neu-driven mammary tumorigenesis as tumors developed similarly in both Stat3-sufficient and Stat3-deficient glands. However, short hairpin RNA (shRNA)-mediated Stat3 silencing in a neu-overexpressing tumor-derived cell line completely abolished both neu-driven anchorage-independent growth and lung metastasis. Our data suggest that Stat3 might be a useful therapeutic target in breast tumors showing amplification and/or overexpression of the ErbB-2 oncogene, which normally display aggressive, metastatic behavior.

STAT3 is required for proliferation and maintenance of multipotency in glioblastoma stem cells

Signal transducer and activator of transcription 3 (STAT3) regulates diverse cellular processes, including cell growth, differentiation, and apoptosis, and is frequently activated during tumorigenesis. Recently, putative glioblastoma stem cells (GBM-SCs) were isolated and characterized. These cells can self-renew indefinitely in culture, are highly tumorigenic, and retain the ability to differentiate in culture. We have found that treatment of GBM-SCs with two chemically distinct small molecule inhibitors of STAT3 DNA-binding inhibits cell proliferation and the formation of new neurospheres from single cells. Genetic knockdown of STAT3 using a short hairpin RNA also inhibits GBM-SC proliferation and neurosphere formation, confirming that these effects are specific to STAT3. Although STAT3 inhibition can induce apoptosis in serum-derived GBM cell lines, this effect was not observed in GBM-SCs grown in stem cell medium. Markers of neural stem cell multipotency also decrease upon STAT3 inhibition, suggesting that STAT3 is required for maintenance of the stem-like characteristics of these cells. Strikingly, even a transient inhibition of STAT3 leads to irreversible growth arrest and inhibition of neurosphere formation. These data suggest that STAT3 regulates the growth and self-renewal of GBM-SCs and is thus a potential target for cancer stem cell-directed therapy of glioblastoma multiforme.

STAT3 is constitutively phosphorylated on serine 727 residues, binds DNA, and activates transcription in CLL cells

Chronic lymphocytic leukemia (CLL) is the most common leukemia in the Western hemisphere, but its pathogenesis is still poorly understood. Constitutive tyrosine phosphorylation (p) of signal transducer and activator of transcription (STAT) 3 occurs in several solid tumors and hematologic malignancies. In CLL, however, STAT3 is constitutively phosphorylated on serine 727, not tyrosine 705, residues. Because the biologic significance of serine pSTAT3 in CLL is not known, we studied peripheral blood cells of 106 patients with CLL and found that, although tyrosine pSTAT3 was inducible, serine pSTAT3 was constitutive in all patients studied, regardless of blood count, disease stage, or treatment status. In addition, we demonstrated that constitutive serine pSTAT3 translocates to the nucleus by the karyopherin-beta nucleocytoplasmic system and binds DNA. Dephosphorylation of inducible tyrosine pSTAT3 did not affect STAT3-DNA binding, suggesting that constitutive serine pSTAT3 binds DNA. Furthermore, infection of CLL cells with lentiviral STAT3-small hairpin RNA reduced the expression of several STAT3-regulated survival and proliferation genes and induced apoptosis, suggesting that constitutive serine pSTAT3 initiates transcription in CLL cells. Taken together, our data suggest that constitutive phosphorylation of STAT3 on serine 727 residues is a hallmark of CLL and that STAT3 be considered a therapeutic target in this disease.

Tanshinone IIA inhibits constitutive STAT3 activation, suppresses proliferation, and induces apoptosis in rat C6 glioma cells

Signal transducer and activator of transcription 3 (STAT3) is usually constitutively activated in a variety of malignancies. Thus, STAT3 may be a promising target for treatment of tumor cells. Recently, Tanshinone IIA (Tan IIA), a major active constituent from the root of Salvia miltiorrhiza Bunge, was reported to have apoptosis inducing effects on a large variety of cancer cells. In this study, we evaluate the anti-proliferation and apoptosis inducing effects of Tan IIA on C6 glioma cells. Cell growth and proliferation were measured by MTT assay, cell apoptosis was observed by flow cytometry and DNA-fragmentation analysis. Further more, we investigated inhibitory effects of Tan IIA on STAT3 activity and its downstream targets: Bcl-XL, cyclin D1. Alteration of STAT3 activity was examined by measuring their DNA binding activity and tyrosine phosphorylation. Changes in the expression levels of Bcl-XL and cyclin D1 were examined by Western blot analysis. We found that the cellular growth were inhibited and cell apoptosis were observed after the treatment with Tan IIA. The STAT3 activity was significantly reduced by Tan IIA parallel with a significant attenuation of expression of Bcl-XL and cyclin D1. These results suggest that Tan IIA may serve as an effective adjunctive reagent in the treatment of glioma for its targeting of constitutive STAT3 signaling.

Self-regulation of Stat3 activity coordinates cell-cycle progression and neural crest specification

A complex set of extracellular signals is required for neural crest (NC) specification. However, how these signals function to coordinate cell-cycle progression and differentiation remains poorly understood. Here, we report in Xenopus a role for the transcription factor signal transducers and activators of transcription-3 (Stat3) in this process downstream of FGF signalling. Depletion of Stat3 inhibits NC gene expression and cell proliferation, whereas overexpression expands the NC domain and promotes cell proliferation. Stat3 is phosphorylated and activated in ectodermal cells by FGFs through binding with FGFR4. Stat3 activation is also modulated by Hairy2 and Id3 proteins that, respectively, facilitate and disrupt Stat3-FGFR4 complex formation. Furthermore, distinct levels of Stat3 activity control Hairy2 and Id3 transcription, leading to Stat3 self-regulation. Finally, high Stat3 activity maintains cells in an undifferentiated state, whereas low activity promotes cell proliferation and NC differentiation. Together, our data suggest that Stat3, downstream of FGFs and under the positive and negative feedback regulation of Hairy2 and Id3, plays an essential role in the coordination of cell-cycle progression and differentiation during NC specification.

Enhanced Stat3 activation in POMC neurons provokes negative feedback inhibition of leptin and insulin signaling in obesity

Leptin-stimulated Stat3 activation in proopiomelanocortin (POMC)-expressing neurons of the hypothalamus plays an important role in maintenance of energy homeostasis. While Stat3 activation in POMC neurons is required for POMC expression, the role of elevated basal Stat3 activation as present in the development of obesity has not been directly addressed. Here, we have generated and characterized mice expressing a constitutively active version of Stat3 (Stat3-C) in POMC neurons (Stat3-C(POMC) mice). On normal chow diet, these animals develop obesity as a result of hyperphagia and decreased POMC expression accompanied by central leptin and insulin resistance. This unexpected finding coincides with POMC-cell-specific, Stat3-mediated upregulation of SOCS3 expression inhibiting both leptin and insulin signaling as insulin-stimulated PIP(3) (phosphatidylinositol-3,4,5 triphosphate) formation and protein kinase B (AKT) activation in POMC neurons as well as with the fact that insulin's ability to hyperpolarize POMC neurons is largely reduced in POMC cells of Stat3-C(POMC) mice. These data indicate that constitutive Stat3 activation is not sufficient to promote POMC expression but requires simultaneous PI3K (phosphoinositide 3-kinase)-dependent release of FOXO1 repression. In contrast, upon exposure to a high-fat diet, food intake and body weight were unaltered in Stat3-C(POMC) mice compared with control mice. Taken together, these experiments directly demonstrate that enhanced basal Stat3 activation in POMC neurons as present in control mice upon high-fat feeding contributes to the development of hypothalamic leptin and insulin resistance.

All-trans retinoic acid suppresses Stat3 signaling during skin carcinogenesis

Squamous cell carcinoma (SCC) of the skin is the most clinically aggressive form of nonmelanoma skin cancer. We have determined the effects of all-trans retinoic acid (ATRA), a naturally occurring chemopreventive retinoid, on signal transducer and activator of transcription 3 (Stat3) signaling during the development of skin SCC. Stat3 is a transcription factor that plays a critical role in cell proliferation and survival, and it is constitutively active in several malignant cell types. We have previously shown that Stat3 is required for the initiation, promotion, and progression of skin SCC. ATRA is a highly efficient suppressor of tumor formation in the two-stage mouse skin carcinogenesis model and we have shown that this effect correlates with the suppression of the B-Raf/Mek/Erk signaling pathway. In this study, we have determined the pattern of Stat3 phosphorylation throughout the course of the two-stage protocol, both in the presence and absence of ATRA. We have used both SENCAR mice and K5.Stat3C transgenic mice, which express the Stat3C protein, a constitutively active form of Stat3, in the skin. Using Western blotting and immunohistochemical staining with phosphospecific antibodies, we show that coadministration of ATRA suppressed the 12-O-tetradecanoylphorbol-13-acetate-induced phosphorylation of Stat3 in both models, but was only able to suppress tumor formation in the SENCAR mice. Surprisingly, ATRA actually enhanced tumor formation in 12-O-tetradecanoylphorbol-13-acetate-treated K5.Stat3C mice. We hypothesize that ATRA blocks tumor formation, at least in part, by targeting events upstream of Stat3, such as the B-Raf/Mek/Erk pathway, and that in the K5.Stat3C mice, in which Stat3 activity is constitutive, it cannot suppress tumor formation.

Association of interleukin-6 signalling with the muscle stem cell response following muscle-lengthening contractions in humans

Background

The regulation of muscle stem cells in humans in response to muscle injury remains largely undefined. Recently, interleukin-6 (IL-6) has been implicated in muscle stem cell (satellite cell)-mediated muscle hypertrophy in animals; however, the role of IL-6 in the satellite cell (SC) response following muscle-lengthening contractions in humans has not been studied.

Methodology/Principal Findings

Eight subjects (age 22±1 y; 79±8 kg) performed 300 maximal unilateral lengthening contractions (3.14 rad.s⁻¹) of the knee extensors. Blood and muscle samples were collected before and at 4, 24, 72, and 120 hours post intervention. IL-6, IL-6 receptor (IL-6Rα), cyclin D1, suppressor of cytokine signling-3 (SOCS3) mRNA were measured using quantitative RT-PCR and serum IL-6 protein was measured using an ELISA kit. JAK2 and STAT3 phosphorylated and total protein was measured using western blotting techniques. Immunohistochemical analysis of muscle cross-sections was performed for the quantification of SCs (Pax7⁺ cells) as well as the expression of phosphorylated STAT3, IL-6, IL-6Rα, and PCNA across all time-points. The SC response, as defined by an amplification of Pax7⁺ cells, was rapid, increasing by 24 h and peaking 72 h following the intervention. Muscle IL-6 mRNA increased following the intervention, which correlated strongly (R² = 0.89, p<0.002) with an increase in serum IL-6 concentration. SC IL-6Rα protein was expressed on the fiber, but was also localized to the SC, and IL-6⁺ SC increased rapidly following muscle-lengthening contractions and returned to basal levels by 72 h post-intervention, demonstrating an acute temporal expression of IL-6 with SC. Phosphorylated STAT3 was evident in SCs 4 h after lengthening contraction, and the downstream genes, cyclin D1 and SOCS3 were significantly elevated 24 hours after the intervention.

Conclusions/Significance

The increased expression of STAT3 responsive genes and expression of IL-6 within SCs demonstrate that IL-6/STAT3 signaling occurred in SCs, correlating with an increase in SC proliferation, evidenced by increased Pax7⁺/PCNA⁺ cell number in the early stages of the time-course. Collectively, these data illustrate that IL-6 is an important signaling molecule associated with the SC response to acute muscle-lengthening contractions in humans.

Inhibition of ataxia telangiectasia mutated kinase activity enhances TRAIL-mediated apoptosis in human melanoma cells

The aim of the present study was to elucidate the effects of ataxia telangiectasia mutated (ATM) kinase on the regulation of the extrinsic tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 2/DR5-mediated death pathway in human melanoma cells. We revealed that total ATM protein levels were high in some human melanoma lines compared with normal cells. The basal levels of active form ATM phospho-Ser(1981) were also detectable in many melanoma lines and could be further up-regulated by gamma-irradiation. Pretreatment of several melanoma lines just before gamma-irradiation with the inhibitor of ATM kinase KU-55933 suppressed p53 and nuclear factor-kappaB (NF-kappaB) activation but notably increased radiation-induced DR5 surface expression, down-regulated cFLIP (caspase-8 inhibitor) levels, and substantially enhanced exogenous TRAIL-induced apoptosis. Furthermore, gamma-irradiation in the presence of KU-55933 rendered TRAIL-resistant HHMSX melanoma cells susceptible to TRAIL-mediated apoptosis. In addition, suppression of ATM expression by the specific short hairpin RNA also resulted in down-regulation of cFLIP levels, up-regulation of surface DR5 expression, and TRAIL-mediated apoptosis in melanoma cells. Besides p53 and NF-kappaB, crucial regulators of DR5 expression, transcription factor STAT3 is known to negatively regulate DR5 expression. Suppression of Ser(727) and Tyr(705) phosphorylation of STAT3 by KU-55933 reduced STAT3 transacting activity accompanied by elevation in DR5 expression. Dominant-negative STAT3beta also efficiently up-regulated the DR5 surface expression and down-regulated cFLIP levels in melanoma cells in culture and in vivo. Taken together, our data show the existence of an ATM-dependent STAT3-mediated antiapoptotic pathway, which on suppression sensitizes human melanoma cells to TRAIL-mediated apoptosis.

Cyclin D1 downregulation is important for permanent cell cycle exit and initiation of differentiation induced by anchorage-deprivation in human keratinocytes

To understand the relationship between permanent cell cycle exit and differentiation the immortalized keratinocyte cell line, SIK and the squamous cell carcinoma, SCC9 were compared during differentiation induced by anchorage-deprivation. The SIK cells when placed in suspension culture promptly lost almost all ability to reinitiate growth by 2 days concomitantly expressing the differentiation specific proteins, transglutaminase (TGK) and involucrin. These cells rapidly underwent G1 cell cycle arrest with complete disappearance of phosphorylated RB. In contrast SCC9 cells neither showed TGK expression nor increase in involucrin. They decreased their colony-forming ability much more slowly, which coordinated well with a gradual decrease in phosphorylated RB, demonstrating the significant resistance to loss of colony-forming ability and cell cycle exit. In accordance, cyclin D1, a positive regulator of cyclin-dependent kinase (CDK) 4/6 which phosphorylates RB decreased drastically in anchorage deprived SIK but not in SCC9 cells. Endogenous cyclin D1 knockdown in SCC9 cells by siRNA enhanced loss of the colony-forming ability during anchorage-deprivation. Conversely enforced expression of cyclin D1 in SIK cells and in another immortalized keratinocyte cell line, HaCaT, partly prevented loss of their colony-forming abilities. Cyclin D1 overexpression antagonized Keratin 10 expression in suspended HaCaT cells. The result demonstrates the importance of cyclin D1 down regulation for proper initiation of keratinocyte differentiation.

Constitutive activation and targeted disruption of signal transducer and activator of transcription 3 (Stat3) in mouse epidermis reveal its critical role in UVB-induced skin carcinogenesis

In this study, the potential role of Stat3 in UVB-induced skin carcinogenesis was examined using skin-specific gain and loss of function transgenic mice, i.e., K5.Stat3C and K5Cre.Stat3^fl/fl mice, respectively. The epidermis of Stat3-deficient mice was highly sensitive to UVB-induced apoptosis, whereas the epidermis of K5.Stat3C mice was more resistant to UVB-induced apoptosis. In particular, the status of Stat3 influenced the survival of UV-photoproduct cells, including those located in the bulge region of hair follicles. K5.Stat3C mice exhibited significantly increased epidermal proliferation and hyperplasia in response to UVB irradiation, whereas Stat3-deficient mice showed reduced epidermal proliferation and hyperplasia. Expression of target genes regulated by Stat3, such as cyclin D1 and Bcl-x_L, was increased in epidermis of both control and UVB-irradiated K5.Stat3C mice, and downregulated in epidermis of both control and UVB-irradiated K5Cre.Stat3^fl/fl mice. Following UVB irradiation, the formation of skin tumors in K5.Stat3C mice was accelerated and both the incidence and multiplicity of skin tumors was significantly greater than wild-type controls. In contrast, Stat3-deficient mice were resistant to UVB skin carcinogenesis. These results demonstrate that Stat3 plays an important role in the development of UVB-induced skin tumors through its effects on both survival and proliferation of keratinocytes during carcinogenesis.

Sorafenib triggers antiproliferative and pro-apoptotic signals in human esophageal adenocarcinoma cells

BACKGROUND AND PURPOSE

Current therapies offer scant benefit to patients with advanced esophageal adenocarcinoma. We investigated the effects of Sorafenib, a multifunctional kinase inhibitor, on several growth regulatory pathways that control cell growth and survival in SEG-1 cells derived from Barrett's adenocarcinoma.

METHODS

SEG-1 cells were exposed to acidified medium or taurocholic acid, with and without pre-incubation with Sorafenib. Cyclin D1 and E, c-Myc, and Bcl-2 expression levels as well as STAT3 activations were determined by Western blotting. Cyclin D1 mRNA was measured by real-time PCR. Apoptosis was assessed by TUNEL assay.

RESULTS

Sorafenib significantly inhibited SEG-1 cell proliferation stimulated by acid or bile acid treatments and reduced cell survival. This drug significantly reduced the up-regulations of cyclin D1, cyclin E, c-Myc, and Bcl-2 as well as the activation of STAT3 in SEG-1 cells.

CONCLUSIONS

These results support a rational basis for future clinical studies to assess the therapeutic benefit of Sorafenib in esophageal adenocarcinoma.

The function of Stat3 in tumor cells and their microenvironment

Stat3 was initially recognized as a transcription factor and mediates the nuclear action of many different cytokines and growth factors. In addition to its roles in normal cell function, the inappropriate activation of Stat3 in tumor cells has attracted the attention of tumor biologists and has led to the consideration of Stat3 as a drug target. The induction of Stat3 activity under physiological circumstances is transient and many different levels of activation and deactivation have been defined. In addition to kinases and phosphatases, the SOCS proteins and the PIAS proteins have been recognized as negatively regulating components, which fine-tune the extent and the duration of Stat3 function. Its nuclear cytoplasmic shuttling is exquisitely regulated and adds to the complexity of Stat3 action. Newly discovered associations with cytoplasmic molecules suggest functions outside the conventional transcriptional regulation context. High molecular weight transcription complexes suggest that Stat3 might assume roles in transcriptional induction as well as in transcriptional suppression. The aberrant activation in tumor cells and the central function of Stat3 in the communication between cells of the immune system and tumor cells are of great interest for translational research projects and innovative drug development.

BCR-ABL1-induced expression of HSPA8 promotes cell survival in chronic myeloid leukaemia

In order to determine new signal transduction pathways implicated in chronic myeloid leukaemia (CML), we performed a gene expression profile comparison between CD34+ cells from CML patients and healthy donors. Functional studies were performed using the Mo7e and Mo7e-p210 cell lines. Expression of CCND1 (Cyclin D1), as well as the chaperone HSPA8, which is important for regulation of CCND1, were significantly upregulated in CD34+ CML cells. Upregulation of HSPA8 was dependent, at least in part, on STAT5 (signal transducer and activator of transcrition 5)-dependent transcriptional activation, as demonstrated by chromatin immunoprecipitation. The presence of HSPA8 in the nuclear protein fraction as well as its binding to CCND1 suggests that it may contribute to stabilization of the CCND1/CDK4 complex, which, in turn, may participate in proliferation of CML cells. Treatment of CML cells with the specific HSPA8 inhibitor 15-deoxyspergualin induced inhibition of CML cell viability but did not induce apoptosis. In conclusion, our studies suggest that STAT5-mediated activation of HSPA8 induces nuclear translocation and activation of the CCND1/CDK4 complex leading to increased proliferation of CML cells, deciphering a new pathway implicated in CML and supporting a potential role of chaperone inhibitors in the treatment of CML.

Epidermal growth factor receptor controls flat dysplastic aberrant crypt foci development and colon cancer progression in the rat azoxymethane model

PURPOSE

Colonic carcinogenesis deranges growth-regulating epidermal growth factor receptors (EGFR). We previously showed that EGFR signals were up-regulated in human aberrant crypt foci (ACF), putative colon cancer precursors. The azoxymethane model of colon cancer recapitulates many aspects of human colonic tumors. Recent studies indicate that flat dysplastic ACF with increased beta-catenin are tumor precursors in this model. We asked, therefore, if EGFR signals are required for flat dysplastic ACF development and cancer progression.

EXPERIMENTAL DESIGN

Rats received azoxymethane or saline, and standard chow or chow supplemented with gefitinib, an EGFR inhibitor, for 44 weeks. EGFR signals were quantified in normal colon, flat ACF, and tumors by computerized analysis of immunostains and Western blots. K-ras mutations were assessed by PCR and mRNA for egfr ligands by quantitative real-time PCR.

RESULTS

EGFR inhibition with gefitinib decreased the incidence of flat dysplastic ACF from 66% to 36% and tumors from 71% to 22% (P < 0.05). This inhibitor also reduced the overexpressions of cyclin D1 and Cox-2 in flat ACF. Furthermore, in flat ACF, EGFR blockade decreased the up-regulation of c-Jun, FosB, phosphorylated active signal transducers and activators of transcription 3, and CCAAT/enhancer binding protein-beta, potential regulators of cyclin D1 and Cox-2. In colonic tumors, EGFR blockade significantly decreased angiogenesis, proliferation, and progression while also increasing apoptosis (P < 0.05). Gefitinib also inhibited the activations of extracellular signal-regulated kinase, Src, and AKT pathways in tumors.

CONCLUSIONS

We have shown for the first time that EGFR promotes the development of flat dysplastic ACF and the progression of malignant colonic tumors. Furthermore, we have mechanistically identified several transcription factors and their targets as EGFR effectors in colonic carcinogenesis.

Expression of seven gastric cancer-associated genes and its relevance for Wnt, NF-kappaB and Stat3 signaling

The aim of the current study was to profile c-Myc, standard CD44 (CD44s), CD44v6, cyclin D1, survivin, MMP-7 and VEGF expression patterns in different gastric samples and to elucidate their relevance for Wnt, NF-kappaB and/or Stat3 activation using multiple experimental approaches. The results revealed that 87.1% (27/31) of gastric cancers and 8.7% (2/23) of noncancerous lesions (chronic gastritis and intestinal metaplasia) showed Wnt activation (Wnt(+)) that was closely related to the expression of the seven genes. Some Wnt(-) noncancerous lesions also expressed the above-mentioned genes, higher frequencies of survivin (7/8), VEGF (7/8), cyclin D1 (6/8) and c-Myc (5/8) but not CD44s (2/8), CD44v6 (3/8) and MMP-7 (2/8) being detected in the NF-kappaB(+) samples. Stat3 was activated in 37/54 gastric tissues, and in 3/4 VEGF, 4/6 c-Myc, 4/8 survivin, 2/4 MMP-7, 1/2 CD44v6, and 4/9 cyclin D1(+) but Wnt(-)/NF-kappaB(-) samples. These findings showed a close correlation in GCs between Wnt, NF-kappaB and Stat3 signaling and expression of the seven genes, the importance of NF-kappaB and Stat3 activation in regulating c-Myc, survivin, cyclin D1 and VEGF in noncancerous lesions, and the potential coordinative effects of these three signalings on GC formation presumably by promoting the transcription of their common target genes.

Targeting the cytoplasmic and nuclear functions of signal transducers and activators of transcription 3 for cancer therapy

Signal transducers and activators of transcription (STAT) are a highly conserved family of transcription factors that are activated by phosphorylation in the cytoplasm, after which they translocate to the nucleus to regulate gene expression. Among the seven STATs, STAT3 is of particular interest due to its constitutive phosphorylation in a large proportion of human cancers and its ability to induce neoplastic transformation. Inhibition of STAT3 can reverse tumor growth in experimental systems while having few effects in normal cells. These findings have implicated STAT3 as a potentially important target for therapeutic intervention. In addition to its well-described role as a transcription factor, STAT3 has been found recently to have important effects in the cytoplasm. Collectively, these functions of STAT3 directly contribute to tumorigenesis, invasion, and metastasis. Given the potential importance of STAT3 as a target for cancer therapy, molecules have been developed that can block STAT3 function at a variety of steps. These drugs show promise as anticancer agents in model systems of a variety of common human cancers. Thus, elucidating the functions of STAT3 and developing agents to inhibit this protein remain important scientific and clinical challenges.

Signal transducer and activator of transcription 3 (Stat3) in epithelial carcinogenesis

Signal transducer and activator of transcription 3 (Stat3) is one of a family of cytoplasmic proteins that participate in normal cellular responses to cytokines and growth factors as transcription factors. Stat3 modulates various physiological functions including cell survival, cell-cycle regulation, and angiogenesis through regulation of gene expression, and its constitutive activation is associated with a number of human epithelial cancers. Recent studies with skin-specific gain and loss of Stat3 function transgenic mice have shown that Stat3 plays critical roles in skin carcinogenesis. Multistage skin carcinogenesis bioassays performed with these transgenic mice clearly demonstrate that Stat3 is required for both tumor initiation and promotion through regulation of genes involved in survival and proliferation, respectively. Stat3 also plays a role in malignant progression of skin tumors by regulating genes that are involved in angiogenesis and invasion. Further studies have revealed that Stat3 plays a critical role in epidermal cell proliferation and survival following exposure to ultraviolet B (UVB) irradiation. In addition, Stat3 is constitutively active in UVB-induced skin tumors from both mice and humans. Collectively, these studies suggest that Stat3 may be a potential target for both the prevention and treatment of human epithelial cancers including skin cancer.

Stat3 is tyrosine-phosphorylated through the interleukin-6/glycoprotein 130/Janus kinase pathway in breast cancer

Introduction

Signal transducer and activator of transcription 3 (Stat3) is constitutively tyrosine-phosphorylated in approximately 50% of primary breast carcinomas. A number of different mechanisms responsible for Stat3 activation, including abnormal activation of receptor tyrosine kinases, Src, and Janus kinases (Jaks), have been implicated in breast cancer.

Methods

We examined six breast cancer-derived cell lines expressing high or low levels of tyrosine-phosphorylated Stat3 (pStat3) as well as primary breast cancer specimens.

Results

Inhibition of Src or EGFR (epidermal growth factor receptor) tyrosine kinases had no effect on pStat3 levels, whereas pan-Jak inhibitor P6 resulted in complete abrogation of Stat3 phosphorylation and inhibition of growth. Jaks are required for cytokine signaling, and the glycoprotein 130 (gp130) receptor-associated Jaks are known mediators of Stat3 phosphorylation. Blockade of the gp130 receptor or sequestration of the interleukin-6 (IL-6) ligand led to a decrease of pStat3 levels. Conditioned media from those cell lines expressing high levels of pStat3 contained IL-6 and were capable of stimulating Stat3 phosphorylation. We examined IL-6 levels in primary breast tumors and found a positive correlation between pStat3 and IL-6 expression.

Conclusion

In summary, a principal mechanism of Stat3 activation in breast cancer is through the IL-6/gp130/Jak pathway.

Loss of signal transducer and activator of transcription 5 leads to hepatosteatosis and impaired liver regeneration

Growth hormone controls many facets of a cell's biology through the transcription factors Stat5a and Stat5b (Stat5). However, whole body deletion of these genes from the mouse does not provide portentous information on cell-specific cytokine signaling. To explore liver-specific functions of Stat5, the entire Stat5 locus was deleted in hepatocytes using Cre-mediated recombination. Notably, Stat5-mutant mice developed fatty livers and displayed impaired proliferation of hepatocytes upon partial hepatectomy (PHx). Loss of Stat5 led to molecular consequences beyond the reduced expression of Stat5 target genes, such as those encoding suppressor of cytokine signaling 2 (SOCS2), Cish, and insulin-like growth factor 1 (IGF-1). In particular, circulating growth hormone levels were increased and correlated with insulin resistance and increased insulin levels. Aberrant growth hormone (GH)-induced activation of the transcription factors Stat1 and Stat3 was observed in mutant livers. To test whether some of the defects observed in liver-specific Stat5 deficient mice were due to aberrant Stat1 expression and activation, we generated Stat1(-/-) mice with a hepatocyte-specific deletion of Stat5. Concomitant loss of both Stat5 and Stat1 restored cell proliferation upon PHx but did not reverse fatty liver development. Thus the molecular underpinnings of some defects observed in the absence of Stat5 are the consequence of a deregulated activation of other signal transducers and activators of transcription (STAT) family members.

CONCLUSION

Aberrant cytokine-Stat5 signaling in hepatocytes alters their physiology through increased activity of Stat1 and Stat3. Such cross-talk between different pathways could add to the complexity of syndromes observed in disease.

Expression of DNA Methyltransferase 1 Is Activated by Hepatitis B Virus X Protein via a Regulatory Circuit Involving the p16INK4a-Cyclin D1-CDK 4/6-pRb-E2F1 Pathway

DNA methyltransferase 1 (DNMT1) is responsible for copying DNA methylation patterns to the daughter strands during DNA replication. Its expression is frequently up-regulated in human tumors, including hepatocellular carcinoma, but the mechanism of overexpression and its biological significance remain unclear. Here, we show that hepatitis B virus X protein (HBx) activates DNMT1 expression via a regulatory circuit involving the p16(INK4a)-cyclin D1-cyclin-dependent kinase (CDK) 4/6-retinoblastoma protein (pRb)-E2F1 pathway. HBx induced DNA hypermethylation of p16(INK4a) promoter to repress its expression, which subsequently led to activation of G1-CDKs, phosphorylation of pRb, activation of E2F1, and finally transcriptional activation of DNMT1. Inhibition of DNMT1 activity by either treatment with 5'-Aza-2'dC or introduction of DNMT1 small interfering RNA not only abolished the DNA methylation-mediated p16(INK4a) repression but also impaired DNMT1 expression itself, suggesting a cross-talk between DNMT1 and p16(INK4a). The up-regulation of cyclin D1 by HBx is likely to serve as an initiative impulse for the circuit because it was absolutely required for the activation of DNMT1 expression. We also observed that accumulated DNMT1 via this pathway inactivates E-cadherin expression through promoter hypermethylation. Considering that the pRb-E2F1 pathway is commonly activated in human tumors, activation of this circuit might be widespread and a potential therapeutic target.

Effect of AG490 combined with gemcitabine on the growth of human pancreatic cancer cells

AIM: To investigate the effect of Janus kinase (JAK) specific inhibitor AG490 combined with gemcitabine on the proliferation of human pancreatic cancer cell line SW1990 and STAT3 signal transduction pathway as well as their mechanisms.

METHODS: Human pancreatic cancer cell line SW1990 was divided into control group, AG490-treated group, gemcitabine-treated group and AG490 + gemcitabine-treated group. After 48 h, the proliferation of SW1990 cells was detected by MTT assay. Flow cytometry was used to examine cell apoptosis. The expression of STAT3, Cyclin D1, Bcl-xL and Bax were detected by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively.

RESULTS: The proliferation of SW1990 cells was significantly lower in AG490 or gemcitabine group than that in control group (2.20 ± 0.25, 2.30 ± 0.220 vs 3.78 ± 0.42, P < 0.05), but the apoptosis rate was markedly higher (35.40% ± 3.08%, 34.64% ± 1.38% vs 16.49% ± 1.45%, P < 0.05). Moreover, the proliferation (1.49 ± 0.15) and apoptosis (43.80% ± 1.57%) had notable difference between AG490+gemcitabine group and AG490 or gemcitabine group. After 48 h, AG490 remarkably down-regulated the expression of p-STAT3 (13.83% ± 0.64% vs 79.87% ± 1.43%, P < 0.05), and the expression of Cyclin D1 (mRNA: 15.63% ± 0.59% vs 43.83% ± 0.64%, P < 0.05; protein: 17.50% ± 0.92% 49.87% ± 1.27%, P < 0.05), Bcl-xL (mRNA: 13.93% ± 0.21% vs 75.70% ± 0.46%, P < 0.05; protein: 34.17% ± 1.70% vs 83.93% ± 0.80%, P < 0.05) and Survivin (mRNA: 58.27% ± 0.42% vs 82.93% ± 1.68%, P < 0.05; protein: 13.23% ± 1.03% vs 18.60 ± 1.08%, P < 0.05) were also decreased in comparison with that in control group; however, Bax expression was increased (mRNA: 10.33% ± 1.18% vs 5.43% ± 0.70%, P < 0.05; protein: 13.07% ± 1.04% vs 6.23% ± 2.40%, P < 0.05). There was no difference between gemcitabine and control group.

CONCLUSION: Blockade of STAT3 signal pathway inhibits the proliferation and promotes the apoptosis of SW1990 cells. AG490 combined with gemcitabine shows a synergic effect, which provides a new therapeutic approach for pancreatic cancer therapy.

Eps8 facilitates cellular growth and motility of colon cancer cells by increasing the expression and activity of focal adhesion kinase

In an attempt to study the role of Eps8 in human carcinogenesis, we observe that ectopic overexpression of Eps8 in SW480 cells (low Eps8 expression) increases cell proliferation. By contrast, expressing eps8 small interference RNA in SW620 and WiDr cells (high Eps8 expression) reduces their proliferation rate. Interestingly, attenuation of Eps8 decreases Src Pi-Tyr-416, Shc Pi-Tyr-317, and serum-induced FAK Pi-Tyr-397 and Pi-Tyr-861. Remarkably, by virtue of mammalian target of rapamycin/STAT3 Pi-Ser-727, Eps8 modulates FAK expression required for cell proliferation. Within 62% of colorectal tumor specimens examined, >2-fold enhancement of Eps8 as compared with their normal counterparts is observed, especially for those from the advanced stage. In agreement with the modulation of FAK by Eps8, the concomitant expression of these two proteins in tumor specimens is observed. Notably, Eps8 attenuation also impedes the motility of SW620 and WiDr cells, which can be rescued by ectopically expressed FAK. This finding discloses the indispensability of Eps8 and FAK in cell locomotion. These results provide a novel mechanism for Eps8-mediated FAK expression and activation in colon cancer cells.

leptin-induced growth stimulation of breast cancer cells involves recruitment of histone acetyltransferases and mediator complex to CYCLIN D1 promoter via activation of Stat3

Numerous epidemiological studies documented that obesity is a risk factor for breast cancer development in postmenopausal women. Leptin, the key player in the regulation of energy balance and body weight control also acts as a growth factor on certain organs in both normal and disease state. In this study, we analyzed the role of leptin and the molecular mechanism(s) underlying its action in breast cancer cells that express both short and long isoforms of leptin receptor. Leptin increased MCF7 cell population in the S-phase of the cell cycle along with a robust increase in CYCLIN D1 expression. Also, leptin induced Stat3-phosphorylation-dependent proliferation of MCF7 cells as blocking Stat3 phosphorylation with a specific inhibitor, AG490, abolished leptin-induced proliferation. Using deletion constructs of CYCLIN D1 promoter and chromatin immunoprecipitation assay, we show that leptin induced increase in CYCLIN D1 promoter activity is mediated through binding of activated Stat3 at the Stat binding sites and changes in histone acetylation and methylation. We also show specific involvement of coactivator molecules, histone acetyltransferase SRC1, and mediator complex in leptin-mediated regulation of CYCLIN D1 promoter. Importantly, silencing of SRC1 and Med1 abolished the leptin induced increase in CYCLIN D1 expression and MCF7 cell proliferation. Intriguingly, recruitment of both SRC1 and Med1 was dependent on phosphorylated Stat3 as AG490 treatment inhibited leptin-induced recruitment of these coactivators to CYCLIN D1 promoter. Our data suggest that CYCLIN D1 may be a target gene for leptin mediated growth stimulation of breast cancer cells and molecular mechanisms involve activated Stat3-mediated recruitment of distinct coactivator complexes.

Constitutively activated Stat3 induces tumorigenesis and enhances cell motility of prostate epithelial cells through integrin beta 6

The persistent activation of signal transducer and activator of transcription 3 (Stat3) is a common feature of prostate cancer. However, little is known about the Stat3 targets that may mediate prostate tumorigenesis. The introduction of an activating mutant form of Stat3 (Stat3-C) into immortalized prostate epithelial cells resulted in tumorigenesis. Stat3-C-expressing cells had decreased E-cadherin levels, increased numbers of lamellipodia and stress fibers, and enhanced migratory capacities compared to vector control-expressing cells, with a concomitant increase in the expression of integrin beta6 and its ligand, fibronectin (FN). Exogenously added FN increased cellular migration, with a concomitant loss of E-cadherin expression. The blockade of integrin alphavbeta6 in Stat3-C-expressing cells inhibited migration, increased E-cadherin levels, and reduced colony formation in soft agar. These results demonstrate the sufficiency of constitutively activated Stat3 in mediating prostate tumorigenesis and identify novel Stat3 targets that are involved in promoting cell migration and transformation.

Deregulation and cross talk among Sonic hedgehog, Wnt, Hox and Notch signaling in chronic myeloid leukemia progression

Deciphering the BCR-ABL-independent signaling exploited in chronic myeloid leukemia (CML) progression is an important aspect in cancer stem-cell biology. CML stem-cell compartment is dynamic as it progresses to terminal blast crisis where myeloid and lymphoid blasts fail to differentiate. We demonstrate cross-regulation of signaling network involving Sonic hedgehog (Shh), Wnt, Notch and Hox for the inexorable blastic transformation of CD34(+) CML cells. Significant upregulation in Patched1, Frizzled2, Lef1, CyclinD1, p21 (P < or =0.0002) and downregulation of HoxA10 and HoxB4 (P< or =0.0001) transcripts in CD34(+) cells distinguish blast crisis from chronic CML. We report Shh-dependent Stat3 activation orchestrates these mutually interconnected signaling pathways. Stimulation of CD34(+) CML cells with either soluble Shh or Wnt3a did not activate Akt or p44/42-mitogen activated protein kinase (MAPK) pathways. Interestingly, unlike dominant negative Stat3beta, introduction of constitutive active Stat3 in CD34(+) CML cells induces cross-regulation in gene expression. Additionally, Shh and Wnt3a-dependent regulation of cyclin-dependent kinase inhibitors (CDKI) in CML suggests their role in the network. Taken together, our findings propose that deregulation in the form of hyperactive Shh and Wnt with repressed Notch and Hox pathways involving Stat3, Gli3, beta-catenin, CyclinD1, Hes1, HoxA10 and p21 might act synergistically to form an important hub in CML progression.

Insulin Receptor Substrate-1 Regulates the Transformed Phenotype of BT-20 Human Mammary Cancer Cells

Although originating from a human breast cancer, BT-20 cells do not form colonies in soft agar. BT-20 cells do not express insulin receptor substrate-1 (IRS-1), which is known to promote both normal and abnormal growth and to inhibit differentiation. Stable expression of IRS-1 confers to BT-20 cells the ability to form colonies in soft agar. BT-20 cells form tumors in xenografts in mice, but the size of tumors is twice as large when the cells express IRS-1. The increased transformed phenotype is characterized by occupancy of the rDNA and cyclin D1 promoters by IRS-1 and the activation of the cyclin D1, c-myc, and rDNA promoters. In addition, the retinoblastoma protein, which is detectable in the rDNA promoter of quiescent BT-20/IRS-1 cells, is replaced by IRS-1 after insulin-like growth factor-I stimulation. Our results indicate that in BT-20 human mammary cancer cells, expression of IRS-1 activates promoters involved in cell growth and cell proliferation, resulting in a more transformed phenotype. Targeting of IRS-1 could be effective in inhibiting the proliferation of mammary cancer cells. [Cancer Res 2007;67(5):2124–30]

The STAT3 oncogene as a predictive marker of drug resistance

Constitutive activation of STAT3 (signal transducer and activator of transcription) has been reported in several primary cancers and tumor cell lines where it induces cell transformation through a combined inhibition of apoptosis and cell-cycle activation. Several studies have suggested that STAT3 prevents cell-cycle arrest and cell death through upregulation of survival proteins and downregulation of tumor suppressors. As a consequence of anti-apoptotic and proliferative lesions, we propose that this oncogenic pathway is also involved in intrinsic drug resistance and that STAT3-expressing tumors are resistant to chemotherapeutic agents. If this hypothesis is correct, the detection of the activated form of this protein should help to define subsets of tumors that fail to respond to chemotherapy. Furthermore, interfering with the STAT3 oncogenic pathway might restore the sensitivity to anticancer drugs.

Stromal and epithelial caveolin-1 both confer a protective effect against mammary hyperplasia and tumorigenesis: Caveolin-1 antagonizes cyclin D1 function in mammary epithelial cells

Here, we investigate the role of caveolin-1 (Cav-1) in breast cancer onset and progression, with a focus on epithelial-stromal interactions, ie, the tumor microenvironment. Cav-1 is highly expressed in adipocytes and is abundant in mammary fat pads (stroma), but it remains unknown whether loss of Cav-1 within mammary stromal cells affects the differentiated state of mammary epithelia via paracrine signaling. To address this issue, we characterized the development of the mammary ductal system in Cav-1-/- mice and performed a series of mammary transplant studies, using both wild-type and Cav-1-/- mammary fat pads. Cav-1-/- mammary epithelia were hyperproliferative in vivo, with dramatic increases in terminal end bud area and mammary ductal thickness as well as increases in bromodeoxyuridine incorporation, extracellular signal-regulated kinase-1/2 hyperactivation, and up-regulation of STAT5a and cyclin D1. Consistent with these findings, loss of Cav-1 dramatically exacerbated mammary lobulo-alveolar hyperplasia in cyclin D1 Tg mice, whereas overexpression of Cav-1 caused reversion of this phenotype. Most importantly, Cav-1-/- mammary stromal cells (fat pads) promoted the growth of both normal mammary ductal epithelia and mammary tumor cells. Thus, Cav-1 expression in both epithelial and stromal cells provides a protective effect against mammary hyperplasia as well as mammary tumorigenesis.

Cyclin D1 Overexpression and Response to Bortezomib Treatment in a Breast Cancer Model

BACKGROUND

Cyclin D1 is frequently overexpressed in breast cancer, and its overexpression is, surprisingly, associated with improved survival. One potential mechanism for this association involves signal transducer and activator of transcription 3 (STAT3).

METHODS

Cyclin D1 and STAT3 expression were assessed in human tumors using microarray analysis and in breast cancer cell lines HBL100, T47D, MCF7, MDA-MB-453, and BT20 and in HBL100 and T47D cells stably overexpressing cyclin D1 using immunoblot analysis. Cyclin D1 protein was stabilized by treatment with the proteasome inhibitor bortezomib, and the effects on STAT3 expression in vitro was determined by using immunoblotting and on xenograft tumor growth and apoptosis in vivo was determined by using terminal deoxyuridine nick-end labeling assays. All statistical tests were two-sided.

RESULTS

Tumors with high cyclin D1 expression (n = 17) had low STAT3 expression (mean = 274 arbitrary units), and those with low cyclin D1 expression (n = 31) had high STAT3 expression (mean = 882 arbitrary units) (P<.001). In HBL100 and T47D parental and cyclin D1-overexpressing cells, cyclin D1 overexpression was also inversely associated with STAT3 expression, and cyclin D1 directly reduced the expression of STAT3. Stabilization of cyclin D1 protein by bortezomib treatment further amplified the cyclin D1-dependent repression of STAT3 in vitro and slowed tumor growth in vivo (week 7: untreated mean = 185.7 mm3 versus treated mean = 136.2 mm3, difference = 49.5 mm3, 95% confidence interval [CI] = 18 to 81 mm3, P = .007; week 8: untreated mean = 240.2 mm3 versus treated mean = 157.3 mm3, difference = 82.9 mm3, 95% CI = 9.1 to 156.7 mm3, P = .0014; and week 9: untreated mean = 256.4 mm3 versus treated mean = 170.2 mm3, difference = 86.2 mm3, 95% CI = 22.8 to 149.6 mm3, P = .006) and increased apoptosis (untreated mean = 19% versus treated mean = 54%, difference = 35%, 95% CI = 24.7% to 45.4%; P = .013) of xenograft tumors.

CONCLUSIONS

Cyclin D1 repression of STAT3 expression may explain the association between cyclin D1 overexpression and improved outcome in breast cancer. In addition, bortezomib can amplify the proapoptotic function of cyclin D1, raising the possibility that cyclin D1 levels may be a marker for predicting the response to this novel drug.

The structure of IL2 bound to the three chains of the IL2 receptor and how signaling occurs

The interleukin-2 molecule and receptor were the first of the interleukins to be discovered and characterized at the molecular level. Now after 20 years of effort, two groups have succeeded in determining the structure of IL2 bound to the external domains of the three receptor chains in a quaternary complex. What do we know now that we did not know before this structural information was available, and how do these new data help us to develop new therapies?

KLF8 transcription factor participates in oncogenic transformation

Kruppel-like factor 8 (KLF8) is a member of the family of KLF transcription factors. Several KLF members have been shown to play a role in oncogenesis. We have previously demonstrated that KLF8 mediates cell cycle progression downstream of focal adhesion kinase (FAK) by upregulating cyclin D1. FAK plays a critical role in transformation and tumorigenesis and is aberrantly upregulated in many types of human cancer. Little is known about the function of KLF8 in these regards. Here we provide evidence suggesting a novel role of KLF8 in oncogenic transformation. We show that KLF8 expression is elevated in several types of human cancer cells and primary tumor tissues. Induced expression of ectopic KLF8 causes serum-independent growth and morphological transformation in NIH3T3 cells and enhances anchorage-independent growth of v-Src-transformed cells. In contrast, expression of a dominant-negative mutant of KLF8 dramatically suppresses the transformed phenotypes induced by v-Src. In addition, the KLF8-enhanced transformation in the v-Src cells was prevented by ablating cyclin D1 expression. Overall, these results indicate that KLF8 is required for v-Src-induced transformation and may play a role in tumor progression of human cancer.