Criticality in transient behavior of coupled oscillator system toward chimera and synchronization.

Chimera states in spatiotemporal dynamical systems have been investigated in physical, chemical, and biological systems, while how the system is steering toward different final destinies upon spatially localized perturbation is still unknown. Through a systematic numerical analysis of the evolution of the spatiotemporal patterns of multi-chimera states, we uncover a critical behavior of the system in transient time toward either chimera or synchronization as the final stable state. We measure the critical values and the transient time of chimeras with different numbers of clusters. Then, based on an adequate verification, we fit and analyze the distribution of the transient time, which obeys power-law variation process with the increase in perturbation strengths. Moreover, the comparison between different clusters exhibits an interesting phenomenon, thus we find that the critical value of odd and even clusters will alternatively converge into a certain value from two sides, respectively, implying that this critical behavior can be modeled and enabling the articulation of a phenomenological model.

Microenvironmental interleukin-6 suppresses toll-like receptor signaling in human leukemia cells through miR-17/19A.

The regulation of toll-like receptor (TLR) signaling in a tumor microenvironment is poorly understood despite its importance in cancer biology. To address this problem, TLR7-responses of chronic lymphocytic leukemia (CLL) cells were studied in the presence and absence of a human stromal cell-line derived from a leukemic spleen. CLL cells alone produced high levels of tumor necrosis factor (TNF)-α and proliferated in response to TLR7-agonists. A signal transducer and activator of transcription 3 -activating stromal factor, identified as interleukin (IL)-6, was found to upregulate microRNA (miR)-17 and miR-19a, target TLR7 and TNFA messenger RNA, and induce a state of tolerance to TLR7-agonists in CLL cells. Overexpression of the miR-17-92 cluster tolerized CLL cells directly and miR-17 and miR-19a antagomiRs restored TLR7-signaling. Inhibition of IL-6 signaling with antibodies or small-molecule Janus kinase inhibitors reversed tolerization and increased TLR7-stimulated CLL cell numbers in vitro and in NOD-SCIDγc (null) mice. These results suggest IL-6 can act as tumor suppressor in CLL by inhibiting TLR-signaling.

The miR-17-92 cluster expands multipotent hematopoietic progenitors whereas imbalanced expression of its individual oncogenic miRNAs promotes leukemia in mice.

The miR-17-92 cluster and its 6 encoded miRNAs are frequently amplified and aberrantly expressed in various malignancies. This study demonstrates that retroviral-mediated miR-17-92 overexpression promotes expansion of multipotent hematopoietic progenitors in mice. Cell lines derived from these miR-17-92-overexpressing mice are capable of myeloid and lymphoid lineage differentiation, and recapitulate the normal lymphoid phenotype when transplanted to nonobese diabetic/severe combined immunodeficiency mice. However, overexpression of individual miRNAs from this locus, miR-19a or miR-92a, results in B-cell hyperplasia and erythroleukemia, respectively. Coexpression of another member of this cluster miR-17, with miR-92a, abrogates miR-92a-induced erythroleukemogenesis. Accordingly, we identified several novel miR-92a and miR-17 target genes regulating erythroid survival and proliferation, including p53. Expression of this critical target results in marked growth inhibition of miR-92a erythroleukemic cells. In both murine and human leukemias, p53 inactivation contributed to the selective overexpression of oncogenic miR-92a and miR-19a, and down-regulation of tumor-suppressive miR-17. This miR-17-92 expression signature was also detected in p53- B-cell chronic lymphocytic leukemia patients displaying an aggressive clinical phenotype. These results revealed that imbalanced miR-17-92 expression, also mediated by p53, directly transforms the hematopoietic compartment. Thus examination of such miRNA expression signatures should aid in the diagnosis and treatment of cancers displaying miR-17-92 gene amplification.

Influence of Mycorrhiza on C:N:P Stoichiometry in Senesced Leaves.

Senesced leaves play a vital role in nutrient cycles in the terrestrial ecosystem. The carbon (C), nitrogen (N) and phosphorus (P) stoichiometries in senesced leaves have been reported, which are influenced by biotic and abiotic factors, such as climate variables and plant functional groups. It is well known that mycorrhizal types are one of the most important functional characteristics of plants that affect leaf C:N:P stoichiometry. While green leaves' traits have been widely reported based on the different mycorrhiza types, the senesced leaves' C:N:P stoichiometries among mycorrhizal types are rarely investigated. Here, the patterns in senesced leaves' C:N:P stoichiometry among plants associated with arbuscular mycorrhizal (AM), ectomycorrhizal (ECM), or AM + ECM fungi were explored. Overall, the senesced leaves' C, with 446.8 mg/g in AM plants, was significantly lower than that in AM + ECM and ECM species, being 493.1 and 501.4 mg/g, respectively, which was mainly caused by boreal biomes. The 8.9 mg/g senesced leaves' N in ECM plants was significantly lower than in AM (10.4 mg/g) or AM + ECM taxa (10.9 mg/g). Meanwhile, the senesced leaves' P presented no difference in plant associations with AM, AM + ECM and ECM. The senesced leaves' C and N presented contrary trends with the changes in mean annual temperature (MAT) and mean annual precipitation (MAP) in ECM or AM + ECM plants. The differences in senesced leaves' C and N may be more easily influenced by the plant mycorrhizal types, but not P and stoichiometric ratios of C, N and P. Our results suggest that senesced leaves' C:N:P stoichiometries depend on mycorrhizal types, which supports the hypothesis that mycorrhizal type is linked to the evolution of carbon-nutrient cycle interactions in the ecosystem.

The inositol phosphatase SHIP-1 is negatively regulated by Fli-1 and its loss accelerates leukemogenesis.

The activation of Fli-1, an Ets transcription factor, is the critical genetic event in Friend murine leukemia virus (F-MuLV)-induced erythroleukemia. Fli-1 overexpression leads to erythropoietin-dependent erythroblast proliferation, enhanced survival, and inhibition of terminal differentiation, through activation of the Ras pathway. However, the mechanism by which Fli-1 activates this signal transduction pathway has yet to be identified. Down-regulation of the Src homology 2 (SH2) domain-containing inositol-5-phosphatase-1 (SHIP-1) is associated with erythropoietin-stimulated erythroleukemic cells and correlates with increased proliferation of transformed cells. In this study, we have shown that F-MuLV-infected SHIP-1 knockout mice display accelerated erythroleukemia progression. In addition, RNA interference (RNAi)-mediated suppression of SHIP-1 in erythroleukemia cells activates the phosphatidylinositol 3-kinase (PI 3-K) and extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathways, blocks erythroid differentiation, accelerates erythropoietin-induced proliferation, and leads to PI 3-K-dependent Fli-1 up-regulation. Chromatin immunoprecipitation and luciferase assays confirmed that Fli-1 binds directly to an Ets DNA binding site within the SHIP-1 promoter and suppresses SHIP-1 transcription. These data provide evidence to suggest that SHIP-1 is a direct Fli-1 target, SHIP-1 and Fli-1 regulate each other in a negative feedback loop, and the suppression of SHIP-1 by Fli-1 plays an important role in the transformation of erythroid progenitors by F-MuLV.

Enrichment of Sca1+ hematopoietic progenitors in polycythemic mice inhibits leukemogenesis.

Polycythemia vera (PV) is a myeloproliferative disorder characterized by a pronounced increase in the number of erythroid cells. However, despite this aberrant proliferation, the incidence of erythroleukemia is paradoxically rare in PV patients. In this study, we show that the progression of Friend virus-induced erythroleukemia is delayed in a mouse model of primary familial congenital polycythemia in which the wild-type Epo-receptor (EpoR) gene is replaced with a truncated human EPOR gene. Herein, we show that these mice exhibit enrichment of Sca1(+)/cKit(-) progenitors and several mature immune cells, such as dendritic cells and macrophages. In cotransplantation experiments, Sca1(+)/cKit(-) progenitors inhibit the tumorigenicity of Sca1(-)/cKit(+) erythroleukemic cells. A cell line established from Sca1(+)/cKit(-) progenitors is also capable of inhibiting leukemic proliferation in culture and in mice. This phenomenon of leukemic inhibition, also detected in the serum of PV patients, is partially attributed to increased nitric oxide secretion. In addition, the administration of erythropoietin into leukemic mice induces a polycythemia-like state associated with the expansion of Sca1(+)/cKit(-) progenitors and derivative immune cells, thereby inhibiting leukemia progression. This study indicates that a combination therapy incorporating the enrichment of Sca1(+)/cKit(-) progenitors may serve as a novel approach for the treatment of leukemia.

Phosphorylation of HOX11/TLX1 on Threonine-247 during mitosis modulates expression of cyclin B1.

BACKGROUND: The HOX11/TLX1 (hereafter referred to as HOX11) homeobox gene was originally identified at a t(10;14)(q24;q11) translocation breakpoint, a chromosomal abnormality observed in 5-7% of T cell acute lymphoblastic leukemias (T-ALLs). We previously reported a predisposition to aberrant spindle assembly checkpoint arrest and heightened incidences of chromosome missegregation in HOX11-overexpressing B lymphocytes following exposure to spindle poisons. The purpose of the current study was to evaluate cell cycle specific expression of HOX11. RESULTS: Cell cycle specific expression studies revealed a phosphorylated form of HOX11 detectable only in the mitotic fraction of cells after treatment with inhibitors to arrest cells at different stages of the cell cycle. Mutational analyses revealed phosphorylation on threonine-247 (Thr247), a conserved amino acid that defines the HOX11 gene family and is integral for the association with DNA binding elements. The effect of HOX11 phosphorylation on its ability to modulate expression of the downstream target, cyclin B1, was tested. A HOX11 mutant in which Thr247 was substituted with glutamic acid (HOX11 T247E), thereby mimicking a constitutively phosphorylated HOX11 isoform, was unable to bind the cyclin B1 promoter or enhance levels of the cyclin B1 protein. Expression of the wildtype HOX11 was associated with accelerated progression through the G2/M phase of the cell cycle, impaired synchronization in prometaphase and reduced apoptosis whereas expression of the HOX11 T247E mutant restored cell cycle kinetics, the spindle checkpoint and apoptosis. CONCLUSIONS: Our results demonstrate that the transcriptional activity of HOX11 is regulated by phosphorylation of Thr247 in a cell cycle-specific manner and that this phosphorylation modulates the expression of the target gene, cyclin B1. Since it is likely that Thr247 phosphorylation regulates DNA binding activity to multiple HOX11 target sequences, it is conceivable that phosphorylation functions to regulate the expression of HOX11 target genes involved in the control of the mitotic spindle checkpoint.

Interleukin-24 induces expression of beta4 integrin but suppresses anchorage-independent growth of rat mammary tumor cells by a mechanism that is independent of beta4.

Wistar-Furth rats develop multiple mammary adenocarcinomas following initiation with methylnitrosourea, whereas Copenhagen rats are resistant to the development of mammary tumors. We have previously isolated cell lines from tumors induced in resistant Copenhagen x Wistar-Furth F(1) rats by infusion of a retrovirus harboring v-Ha-ras directly into the main mammary ducts. Some of the cell lines were able to grow in soft agar, but a significant number did not display anchorage-independent growth. Here, we compared by microarray analysis genes that are differentially expressed in these cell lines. The expression of interleukin-24 (IL-24) and beta(4) integrin was highly correlated with the inability of cells to grow in soft agar. Ectopic expression of IL-24 in anchorage-independent cells inhibited their growth in monolayer culture, in soft agar, and in nude mice in vivo and inhibited their ability to migrate and invade in in vitro assays. Furthermore, growth suppression by IL-24 was associated with the transcriptional up-regulation of p27(Kip1) via the activation of Stat3. We showed, for the first time, that beta(4) integrin is a downstream target of IL-24. However, beta(4) does not play a direct role in regulating the proliferative capacity of rat mammary tumor cells. Our results show that IL-24 suppresses the growth of rat mammary carcinoma cells and may play a role in the resistance of Copenhagen rats to mammary carcinogenesis.

Identification of diterpenoid compounds that interfere with Fli-1 DNA binding to suppress leukemogenesis.

The ETS transcription factor Fli-1 controls the expression of genes involved in hematopoiesis including cell proliferation, survival, and differentiation. Dysregulation of Fli-1 induces hematopoietic and solid tumors, rendering it an important target for therapeutic intervention. Through high content screens of a library of chemicals isolated from medicinal plants in China for inhibitors of a Fli-1 transcriptional reporter cells, we hereby report the identification of diterpenoid-like compounds that strongly inhibit Fli-1 transcriptional activity. These agents suppressed the growth of erythroleukemic cells by inducing apoptosis and differentiation. They also inhibited survival and proliferation of B-cell leukemic cell lines as well as primary B-cell lymphocytic leukemia (B-CLL) isolated from 7 patients. Moreover, these inhibitors blocked leukemogenesis in a mouse model of erythroleukemia, in which Fli-1 is the driver of tumor initiation. Computational docking analysis revealed that the diterpenoid-like compounds bind with high affinity to nucleotide residues in a pocket near the major groove within the DNA-binding sites of Fli-1. Functional inhibition of Fli-1 by these compounds triggered its further downregulation through miR-145, whose promoter is normally repressed by Fli-1. These results uncover the importance of Fli-1 in leukemogenesis, a Fli-1-miR145 autoregulatory loop and new anti-Fli-1 diterpenoid agents for the treatment of diverse hematological malignancies overexpressing this transcription factor.

Regulation of RAB22A by mir-193b inhibits breast cancer growth and metastasis mediated by exosomes.

Breast cancer is one of the main types of cancer affecting the health of females worldwide. Despite improvements in therapeutic approaches, cancer patients succumb to the disease due to metastasis itself, rather than the primary tumor from which metastases arise, emphasizing the need for the better understanding of the biological bases that contribute to disease progression. RAB22A, a member of the proto-oncogene RAS family, plays an important role in the formation, trafficking and metabolism of exosomes, and is associated with the occurrence and development of multiple human cancers. In this study, we demonstrate that the upregulation of RAB22A is associated with breast cancer progression and lymph node metastasis. We identified a signature of RAB22A and miR-193b that exhibited a negative association in metastatic as opposed to the surrounding normal cells, and RAB22A was identified as the target gene of miR-193b. While RAB22A was found to regulate exosomes-mediated breast cancer cell proliferation, invasion and migration, these biological characteristics were diminished in the breast cancer cells in which the RAB22A gene was knocked down or in the cells in which the exosomes were dissolved by proteinase K/RNase treatment. On the whole, the findings of this study demonstrate the critical role that miR-193b plays in the regulation of RAB22A-mediated exosome function during cancer growth and metastasis, which may have significant implications on cancer therapy.

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In order to explore the cultivation techniques for high yield, quality and nitrogen use efficiency of wheat and guide the production practice of late sowing, a two-year experiment of different sowing times and plant densities in fixed plots was conducted from October 2012 to June 2014. Weak-spring cultivar of Yanzhan4110 (YZ4110) and semi-winter cultivar of Aikang58 (AK58) were sowed with two cropping patterns: Normal sowing (sowing in the middle of October, 2.4×106 plants·hm-2) and extremely-late sowing (sowing in the middle of November, 6.0×106 plants·hm-2). The nitrate-N content in 0-40 cm soil, the nitrogen (N) uptake and utilization, grain yield, grain protein content and N uptake efficiency in winter wheat were investigated. Compared with normal sowing, extremely-late sowing significantly increased the nitrate-N content in 0-40 cm soil at jointing and anthesis stages, which in turn promoted the N uptake and accumulation of plants after jointing stage and increased the N distribution ratio of spikes at maturity. As a result, the grains with extremely-late sowing had higher protein contentin both YZ4110 and AK58, and higher protein yield and N uptake efficiency in YZ4110 than that with normal sowing. However, the effects of extremely-late sowing on grain yield were different in the two cultivars. Compared with normal sowing, extremely-late sowing clearly raised the grain yield of YZ4110, but significantly decreased that of AK58. These results indicated that extremely-late sowing is an alternative cropping technique to increase grain yield and protein content for winter wheat in irrigation zones through maintaining the soil N supply after jointing stage and increasing N uptake efficiency.

Novel flavagline-like compounds with potent Fli-1 inhibitory activity suppress diverse types of leukemia.

E26 transformation-specific (ETS) gene family contains a common DNA-binding domain, the ETS domain, responsible for sequence-specific DNA recognition on target promoters. The Fli-1 oncogene, a member of ETS gene family, plays a critical role in hematopoiesis and is overexpressed in diverse hematological malignancies. This ETS transcription factor regulates genes controlling several hallmarks of cancer and thus represents an excellent target for cancer therapy. By screening compounds isolated from the medicinal plant Dysoxylum binectariferum in China, we identified two chemically related flavagline-like compounds including 4'-demethoxy-3',4'-methylenedioxyrocaglaol and rocaglaol that strongly inhibited Fli-1 transactivation ability. These compounds altered expression of Fli-1 target genes including GATA1, EKLF, SHIP1, and BCL2. Consequently, the flavagline-like compounds suppressed proliferation, induced apoptosis, and promoted erythroid differentiation of leukemic cells in culture. These compounds also suppressed erythroleukemogenesis in vivo in a Fli-1-driven mouse model. Mechanistically, the compounds blocked c-Raf-MEK-MAPK/ERK signaling, reduced phosphorylation of eukaryotic translation initiation factor 4E (eIF4E), and inhibited Fli-1 protein synthesis. Consistent with its high expression in myelomas, B-cell lymphoma, and B chronic lymphocytic leukemia (B-CLL), pharmacological inhibition of Fli-1 by the flavagline-like compounds or genetic knock-down via shRNA significantly hindered proliferation of corresponding cell lines and patients' samples. These results uncover a critical role of Fli-1 in growth and survival of various hematological malignancies and point to flavagline-like agents as lead compounds for the development of anti-Fli-1 drugs to treat leukemias/lymphomas overexpressing Fli-1.

Low Density Lipoproteins Amplify Cytokine-signaling in Chronic Lymphocytic Leukemia Cells.

Recent studies suggest there is a high incidence of elevated low-density lipoprotein (LDL) levels in Chronic Lymphocytic Leukemia (CLL) patients and a survival benefit from cholesterol-lowering statin drugs. The mechanisms of these observations and the kinds of patients they apply to are unclear. Using an in vitro model of the pseudofollicles where CLL cells originate, LDLs were found to increase plasma membrane cholesterol, signaling molecules such as tyrosine-phosphorylated STAT3, and activated CLL cell numbers. The signaling effects of LDLs were not seen in normal lymphocytes or glycolytic lymphoma cell-lines but were restored by transduction with the nuclear receptor PPARδ, which mediates metabolic activity in CLL cells. Breakdown of LDLs in lysosomes was required for the amplification effect, which correlated with down-regulation of HMGCR expression and long lymphocyte doubling times (LDTs) of 53.6±10.4months. Cholesterol content of circulating CLL cells correlated directly with blood LDL levels in a subgroup of patients. These observations suggest LDLs may enhance proliferative responses of CLL cells to inflammatory signals. Prospective clinical trials are needed to confirm the therapeutic potential of lowering LDL concentrations in CLL, particularly in patients with indolent disease in the "watch-and-wait" phase of management.

Fli-1 overexpression in erythroleukemic cells promotes erythroid de-differentiation while Spi-1/PU.1 exerts the opposite effect.

The ETS transcription factors play a critical role during hematopoiesis. In F-MuLV-induced erythroleukemia, Fli­1 insertional activation producing high expression of this transcription factor required to promote proliferation. How deregulated Fli­1 expression alters the balance between erythroid differentiation and proliferation is unknown. To address this issue, we exogenously overexpressed Fli­1 in an erythroleukemic cell harboring activation of spi­1/PU.1, another ETS gene involved in erythroleukemogenesis. While the proliferation in culture remains unaffected, Fli­1 overexpression imparts morphological and immunohistochemical characteristics of immature erythroid progenitors. Fli­1 overexpression in erythroleukemic cells increased the numbers of erythroid colonies on methylcellulose and reduced tumorigenicity as evidenced by increase latency of erythroleukemogenesis in mice inoculated with these cells. Although all transplanted mice developed enlargement of the spleen and liver due to leukemic infiltration, Fli­1 overexpression altered the hematopoietic phenotype, significantly increasing the expression of regulatory hematopoietic genes cKIT, SCA-1, CD41 and CD71. In contrast, expression of Spi­1/PU.1 in a Fli­1 producing erythroleukemia cell line in which fli­1 is activated, resulted in increased proliferation through activation of growth promoting proteins MAPK, AKT, cMYC and JAK2. Importantly, these progenitors express high levels of markers such as CD71 and TER119 associated with more mature erythroid cells. Thus, Fli­1 overexpression induces a de-differentiation program by reverting CFU-E to BFU-E erythroid progenitor activity, while Spi­1/PU.1 promoting maturation from BFU-E to CFU-E.

A screen for Fli-1 transcriptional modulators identifies PKC agonists that induce erythroid to megakaryocytic differentiation and suppress leukemogenesis.

The ETS-related transcription factor Fli-1 affects many developmental programs including erythroid and megakaryocytic differentiation, and is frequently de-regulated in cancer. Fli-1 was initially isolated following retrovirus insertional mutagenesis screens for leukemic initiator genes, and accordingly, inhibition of this transcription factor can suppress leukemia through induction of erythroid differentiation. To search for modulators of Fli-1, we hereby performed repurposing drug screens with compounds isolated from Chinese medicinal plants. We identified agents that can transcriptionally activate or inhibit a Fli-1 reporter. Remarkably, agents that increased Fli-1 transcriptional activity conferred a strong anti-cancer activity upon Fli-1-expressing leukemic cells in culture. As opposed to drugs that suppress Fli1 activity and lead to erythroid differentiation, growth suppression by these new Fli-1 transactivating compounds involved erythroid to megakaryocytic conversion (EMC). The identified compounds are structurally related to diterpene family of small molecules, which are known agonists of protein kinase C (PKC). In accordance, these PKC agonists (PKCAs) induced PKC phosphorylation leading to activation of the mitogen-activated protein kinase (MAPK) pathway, increased cell attachment and EMC, whereas pharmacological inhibition of PKC or MAPK diminished the effect of our PKCAs. Moreover, in a mouse model of leukemia initiated by Fli-1 activation, the PKCA compounds exhibited strong anti-cancer activity, which was accompanied by increased presence of CD41/CD61 positive megakaryocytic cells in leukemic spleens. Thus, PKC agonists offer a novel approach to combat Fli-1-induced leukemia, and possibly other cancers,by inducing EMC in part through over-activation of the PKC-MAPK-Fli-1 pathway.

Cyclin D1 is necessary but not sufficient for anchorage-independent growth of rat mammary tumor cells and is associated with resistance of the Copenhagen rat to mammary carcinogenesis.

To identify genes associated with the resistance of Copenhagen (Cop) rats to mammary carcinogenesis, we infused a retrovirus harboring v-Ha-ras directly into the main mammary ducts of resistant F1 rats from a cross between Cop and susceptible Wistar Furth (WF) rats. Adenocarcinomas formed in approximately 50% of infused glands. Cell lines derived from these tumors were clonal, but did not share a common viral integration site, suggesting that a high level of v-Ha-ras expression was able to overcome resistance in the F1 rats. Some of the cell lines were able to grow in soft agar, but a significant number did not display anchorage-independent growth. These growth characteristics were independent of v-Ha-ras expression levels. The ability to grow in soft agar was associated with the size of tumors induced by injecting the cells into nude mice, and showed a striking positive association with the expression of cyclin D1. Furthermore, while resistance to anchorage-independent growth was fully overcome by transfection of cyclin D1 in some clones, in the others the effect was partial. A similar pattern of cyclin D1 upregulation and growth in soft agar was also observed when the cells were transfected with an active form of beta-catenin. Hybrid cells from the somatic fusion of an anchorage-dependent to an anchorage-independent clone did not grow in soft agar. These results suggest that while a high expression level of cyclin D1 is necessary for anchorage-independent growth in all clones, it is not sufficient for full growth capacity in soft agar, raising the possibility that the loss of a tumor suppressor gene in the cell lines is required to fully confer anchorage-independent growth. Our anchorage-dependent and -independent rat mammary tumor-derived cell lines may recapitulate the resistance and susceptibility of Cop and WF rats, respectively, to mammary carcinogenesis that could facilitate the identification of breast cancer susceptibility genes.

Phosphorylation status of c-Kit and Epo receptors, and the presence of wild-type p53 confer in vitro resistance of murine erythroleukemic cells to Celecoxib.

It is well established that selective COX-2 inhibitors exhibit potent effects against progression of select solid tumours. However, their effects on liquid tumours have not been fully established. By taking advantage of murine Friend Disease we have shown a strong antileukemic effect of celecoxib by determining novel in vitro targets. Western blot analyses revealed the expression of COX-2 in a panel of Friend Virus-transformed, splenic-derived primary erythroleukemic blasts and established cell lines generated in our laboratory. We have shown that celecoxib at concentrations as low as 20 microM significantly suppresses proliferation of the selected murine erythroleukemia cell line HB60-5. The greatest proliferative inhibition was seen at 40 microM of celecoxib, resulting in apoptosis. Our results also demonstrate that treatment of the established murine erythroleukemia cell line HB60-5 with celecoxib results in suppression of c-Kit and erythropoietin receptor (Epo-R) phosphorylation resulting in apoptosis, likely through decreased levels of survival factors. However, upon overexpression of c-Kit alone in these cells a significant increase in survival and twofold increase in proliferation in the presence of celecoxib were observed (P < 0.05). Finally, since responsiveness of our murine erythroleukemia cell lines to celecoxib is above the reported physiologically achievable levels in vivo, we have provided in vitro evidence to suggest that reduced sensitivity of erythroleukemic cells to lower doses of celecoxib may be a consequence of the loss of wild-type p53. These findings are pivotal in addressing potential discrepancies associated with sensitivity of murine erythroleukemic cells to celecoxib in vitro versus in vivo.

Suppression of Her2/Neu mammary tumor development in mda-7/IL-24 transgenic mice.

Melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) encodes a tumor suppressor gene implicated in the growth of various tumor types including breast cancer. We previously demonstrated that recombinant adenovirus-mediated mda-7/IL-24 expression in the mammary glands of carcinogen-treated (methylnitrosourea, MNU) rats suppressed mammary tumor development. Since most MNU-induced tumors in rats contain activating mutations in Ha-ras, which arenot frequently detected in humans, we presently examined the effect of MDA-7/IL-24 on Her2/Neu-induced mammary tumors, in which the RAS pathway is induced. We generated tet-inducible MDA-7/IL-24 transgenic mice and crossed them with Her2/Neu transgenic mice. Triple compound transgenic mice treated with doxycycline exhibited a strong inhibition of tumor development, demonstrating tumor suppressor activity by MDA-7/IL-24 in immune-competent mice. MDA-7/IL-24 induction also inhibited growth of tumors generated following injection of Her2/Neu tumor cells isolated from triple compound transgenic mice that had not been treated with doxycycline, into the mammary fat pads of isogenic FVB mice. Despite initial growth suppression, tumors in triple compound transgenic mice lost mda-7/IL-24 expression and grew, albeit after longer latency, indicating that continuous presence of this cytokine within tumor microenvironment is crucial to sustain tumor inhibitory activity. Mechanistically, MDA-7/IL-24 exerted its tumor suppression effect on HER2+ breast cancer cells, at least in part, through PERP, a member of PMP-22 family with growth arrest and apoptosis-inducing capacity. Overall, our results establish mda-7/IL-24 as a suppressor of mammary tumor development and provide a rationale for using this cytokine in the prevention/treatment of human breast cancer.

MDA-7/IL-24 functions as a tumor suppressor gene in vivo in transgenic mouse models of breast cancer.

Melanoma differentiation associated gene-7/Interleukin-24 (MDA-7/IL-24) is a novel member of the IL-10 gene family that selectively induces apoptosis and toxic autophagy in a broad spectrum of human cancers, including breast cancer, without harming normal cells or tissues. The ability to investigate the critical events underlying cancer initiation and progression, as well as the capacity to test the efficacy of novel therapeutics, has been significantly advanced by the development of genetically engineered mice (GEMs) that accurately recapitulate specific human cancers. We utilized three transgenic mouse models to better comprehend the in vivo role of MDA-7/IL-24 in breast cancer. Using the MMTV-PyMT spontaneous mammary tumor model, we confirmed that exogenously introducing MDA-7/IL-24 using a Cancer Terminator Virus caused a reduction in tumor burden and also produced an antitumor "bystander" effect. Next we performed xenograft studies in a newly created MMTV-MDA-7 transgenic model that over-expresses MDA-7/IL-24 in the mammary glands during pregnancy and lactation, and found that MDA-7/IL-24 overexpression delayed tumor growth following orthotopic injection of a murine PDX tumor cell line (mPDX) derived from a tumor formed in an MMTV-PyMT mouse. We also crossed the MMTV-MDA-7 line to MMTV-Erbb2 transgenic mice and found that MDA-7/IL-24 overexpression delayed the onset of mammary tumor development in this model of spontaneous mammary tumorigenesis as well. Finally, we assessed the role of MDA-7/IL-24 in immune regulation, which can potentially contribute to tumor suppression in vivo. Our findings provide further direct in vivo evidence for the role of MDA-7/IL-24 in tumor suppression in breast cancer in immune-competent transgenic mice.