Novel TCF4:TCF12 heterodimer inhibits glioblastoma growth

TWIST1 (TW) is a pro-oncogenic basic helix-loop-helix (bHLH) transcription factor and promotes the hallmark features of malignancy (e.g., cell invasion, cancer cell stemness, and treatment resistance), which contribute to poor prognoses of glioblastoma (GBM). We previously reported that specific TW dimerization motifs regulate unique cellular phenotypes in GBM. For example, the TW:E12 heterodimer increases periostin (POSTN) expression and promotes cell invasion. TW dimer-specific transcriptional regulation requires binding to the regulatory E-box consensus sequences, but alternative bHLH dimers that balance TW dimer activity in regulating pro-oncogenic TW target genes are unknown. We leveraged the ENCODE DNase I hypersensitivity data to identify E-box sites and tethered TW:E12 and TW:TW proteins to validate dimer binding to E-boxes in vitro. Subsequently, TW knockdown revealed a novel TCF4:TCF12 bHLH dimer occupying the same TW E-box site that, when expressed as a tethered TCF4:TCF12 dimer, markedly repressed POSTN expression and extended animal survival. These observations support TCF4:TCF12 as a novel dimer with tumor-suppressor activity in GBM that functions in part through displacement of and/or competitive inhibition of pro-oncogenic TW dimers at E-box sites.

Intratumoral injection of hydrogel-embedded nanoparticles enhances retention in glioblastoma

Intratumoral drug delivery is a promising approach for the treatment of glioblastoma multiforme (GBM). However, drug washout remains a major challenge in GBM therapy. Our strategy, aimed at reducing drug clearance and enhancing site-specific residence time, involves the local administration of a multi-component system comprised of nanoparticles (NPs) embedded within a thermosensitive hydrogel (HG). Herein, our objective was to examine the distribution of NPs and their cargo following intratumoral administration of this system in GBM. We hypothesized that the HG matrix, which undergoes rapid gelation upon increases in temperature, would contribute towards heightened site-specific retention and permanence of NPs in tumors. BODIPY-containing, infrared dye-labeled polymeric NPs embedded in a thermosensitive HG (HG-NPs) were fabricated and characterized. Retention and distribution dynamics were subsequently examined over time in orthotopic GBM-bearing mice. Results demonstrate that the HG-NPs system significantly improved site-specific, long-term retention of both NPs and BODIPY, with co-localization analyses showing that HG-NPs covered larger areas of the tumor and the peri-tumor region at later time points. Moreover, NPs released from the HG were shown to undergo uptake by surrounding GBM cells. Findings suggest that intratumoral delivery with HG-NPs has immense potential for GBM treatment, as well as other strategies where site-specific, long-term retention of therapeutic agents is warranted.

Targeting TWIST1 through loss of function inhibits tumorigenicity of human glioblastoma

TWIST1 (TW) is a bHLH transcription factor (TF) and master regulator of the epithelial-to-mesenchymal transition (EMT). In vitro, TW promotes mesenchymal change, invasion, and self-renewal in glioblastoma (GBM) cells. However, the potential therapeutic relevance of TW has not been established through loss-of-function studies in human GBM cell xenograft models. The effects of TW loss of function (gene editing and knockdown) on inhibition of tumorigenicity of U87MG and GBM4 glioma stem cells were tested in orthotopic xenograft models and conditional knockdown in established flank xenograft tumors. RNAseq and the analysis of tumors investigated putative TW-associated mechanisms. Multiple bioinformatic tools revealed significant alteration of ECM, membrane receptors, signaling transduction kinases, and cytoskeleton dynamics leading to identification of PI3K/AKT signaling. We experimentally show alteration of AKT activity and periostin (POSTN) expression in vivo and/or in vitro. For the first time, we show that effect of TW knockout inhibits AKT activity in U87MG cells in vivo independent of PTEN mutation. The clinical relevance of TW and candidate mechanisms was established by analysis of the TCGA and ENCODE databases. TW expression was associated with decreased patient survival and LASSO regression analysis identified POSTN as one of top targets of TW in human GBM. While we previously demonstrated the role of TW in promoting EMT and invasion of glioma cells, these studies provide direct experimental evidence supporting protumorigenic role of TW independent of invasion in vivo and the therapeutic relevance of targeting TW in human GBM. Further, the role of TW driving POSTN expression and AKT signaling suggests actionable targets, which could be leveraged to mitigate the oncogenic effects of TW in GBM.

Twist1 mediated regulation of glioma tumorigenicity is dependent on mode of mouse neural progenitor transformation

Twist1 is a master regulator of epithelial mesenchymal transition and carcinoma metastasis. Twist1 has also been associated with increased malignancy of human glioma. However, the impact of inhibiting Twist1 on tumorigenicity has not been characterized in glioma models in the context of different oncogenic transformation paradigms. Here we used an orthotopic mouse glioma model of transplanted transformed neural progenitor cells (NPCs) to demonstrate the effects of Twist1 loss of function on tumorigenicity. Decreased tumorigenicity was observed after shRNA mediated Twist knockdown in HPV E6/7 Ha-RasV12 transformed NPCs and Cre mediated Twist1 deletion in Twist1 fl/fl NPCs transformed by p53 knockdown and Ha-RasV12 expression. By contrast, Twist1 deletion had no effect on tumorigenicity of NPCs transformed by co-expression of Akt and Ha-RasV12. We demonstrated a dramatic off-target effect of Twist1 deletion with constitutive Cre expression, which was completely reversed when Twist1 deletion was achieved by transient administration of recombinant Cre protein. Together these findings demonstrate that the function of Twist1 in these models is highly dependent on specific oncogenic contexts of NPC transformation. Therefore, the driver mutational context in which Twist1 functions may need to be taken into account when evaluating mechanisms of action and developing therapeutic approaches to target Twist1 in human gliomas.

Placental ABC Transporters: Biological Impact and Pharmaceutical Significance

The human placenta fulfills a variety of essential functions during prenatal life. Several ABC transporters are expressed in the human placenta, where they play a role in the transport of endogenous compounds and may protect the fetus from exogenous compounds such as therapeutic agents, drugs of abuse, and other xenobiotics. To date, considerable progress has been made toward understanding ABC transporters in the placenta. Recent studies on the expression and functional activities are discussed. This review discusses the placental expression and functional roles of several members of ABC transporter subfamilies B, C, and G including MDR1/P-glycoprotein, the MRPs, and BCRP, respectively. Since placental ABC transporters modulate fetal exposure to various compounds, an understanding of their functional and regulatory mechanisms will lead to more optimal medication use when necessary in pregnancy.

Parallel microfluidic chemosensitivity testing on individual slice cultures

There is a critical unmet need to tailor chemotherapies to individual patients. Personalized approaches could lower treatment toxicity, improve the patient's quality of life, and ultimately reduce mortality. However, existing models of drug activity (based on tumor cells in culture or animal models) cannot accurately predict how drugs act in patients in time to inform the best possible treatment. Here we demonstrate a microfluidic device that integrates live slice cultures with an intuitive multiwell platform that allows for exposing the slices to multiple compounds at once or in sequence. We demonstrate the response of live mouse brain slices to a range of drug doses in parallel. Drug response is measured by imaging of markers for cell apoptosis and for cell death. The platform has the potential to allow for identifying the subset of therapies of greatest potential value to individual patients, on a timescale rapid enough to guide therapeutic decision-making.

Deep sequencing of multiple regions of glial tumors reveals spatial heterogeneity for mutations in clinically relevant genes

Background

The extent of intratumoral mutational heterogeneity remains unclear in gliomas, the most common primary brain tumors, especially with respect to point mutation. To address this, we applied single molecule molecular inversion probes targeting 33 cancer genes to assay both point mutations and gene amplifications within spatially distinct regions of 14 glial tumors.

Results

We find evidence of regional mutational heterogeneity in multiple tumors, including mutations in TP53 and RB1 in an anaplastic oligodendroglioma and amplifications in PDGFRA and KIT in two glioblastomas (GBMs). Immunohistochemistry confirms heterogeneity of TP53 mutation and PDGFRA amplification. In all, 3 out of 14 glial tumors surveyed have evidence for heterogeneity for clinically relevant mutations.

Conclusions

Our results underscore the need to sample multiple regions in GBM and other glial tumors when devising personalized treatments based on genomic information, and furthermore demonstrate the importance of measuring both point mutation and copy number alteration while investigating genetic heterogeneity within cancer samples.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0530-z) contains supplementary material, which is available to authorized users.

Periostin is a novel therapeutic target that predicts and regulates glioma malignancy

BACKGROUND

Periostin is a secreted matricellular protein critical for epithelial-mesenchymal transition and carcinoma metastasis. In glioblastoma, it is highly upregulated compared with normal brain, and existing reports indicate potential prognostic and functional importance in glioma. However, the clinical implications of periostin expression and function related to its therapeutic potential have not been fully explored.

METHODS

Periostin expression levels and patterns were examined in human glioma cells and tissues by quantitative real-time PCR and immunohistochemistry and correlated with glioma grade, type, recurrence, and survival. Functional assays determined the impact of altering periostin expression and function on cell invasion, migration, adhesion, and glioma stem cell activity and tumorigenicity. The prognostic and functional relevance of periostin and its associated genes were analyzed using the TCGA and REMBRANDT databases and paired recurrent glioma samples.

RESULTS

Periostin expression levels correlated directly with tumor grade and recurrence, and inversely with survival, in all grades of adult human glioma. Stromal deposition of periostin was detected only in grade IV gliomas. Secreted periostin promoted glioma cell invasion and adhesion, and periostin knockdown markedly impaired survival of xenografted glioma stem cells. Interactions with αvβ3 and αvβ5 integrins promoted adhesion and migration, and periostin abrogated cytotoxicity of the αvβ3/β5 specific inhibitor cilengitide. Periostin-associated gene signatures, predominated by matrix and secreted proteins, corresponded to patient prognosis and functional motifs related to increased malignancy.

CONCLUSION

Periostin is a robust marker of glioma malignancy and potential tumor recurrence. Abrogation of glioma stem cell tumorigenicity after periostin inhibition provides support for exploring the therapeutic impact of targeting periostin.

Mapping of Mcs30, a new mammary carcinoma susceptibility quantitative trait locus (QTL30) on rat chromosome 12: identification of fry as a candidate Mcs gene

Rat strains differ dramatically in their susceptibility to mammary carcinogenesis. On the assumption that susceptibility genes are conserved across mammalian species and hence inform human carcinogenesis, numerous investigators have used genetic linkage studies in rats to identify genes responsible for differential susceptibility to carcinogenesis. Using a genetic backcross between the resistant Copenhagen (Cop) and susceptible Fischer 344 (F344) strains, we mapped a novel mammary carcinoma susceptibility (Mcs30) locus to the centromeric region on chromosome 12 (LOD score of ∼8.6 at the D12Rat59 marker). The Mcs30 locus comprises approximately 12 Mbp on the long arm of rat RNO12 whose synteny is conserved on human chromosome 13q12 to 13q13. After analyzing numerous genes comprising this locus, we identified Fry, the rat ortholog of the furry gene of Drosophila melanogaster, as a candidate Mcs gene. We cloned and determined the complete nucleotide sequence of the 13 kbp Fry mRNA. Sequence analysis indicated that the Fry gene was highly conserved across evolution, with 90% similarity of the predicted amino acid sequence among eutherian mammals. Comparison of the Fry sequence in the Cop and F344 strains identified two non-synonymous single nucleotide polymorphisms (SNPs), one of which creates a putative, de novo phosphorylation site. Further analysis showed that the expression of the Fry gene is reduced in a majority of rat mammary tumors. Our results also suggested that FRY activity was reduced in human breast carcinoma cell lines as a result of reduced levels or mutation. This study is the first to identify the Fry gene as a candidate Mcs gene. Our data suggest that the SNPs within the Fry gene contribute to the genetic susceptibility of the F344 rat strain to mammary carcinogenesis. These results provide the foundation for analyzing the role of the human FRY gene in cancer susceptibility and progression.

Abstract 1210: Periostin expression in glioma correlates with genes related to mesenchymal transition and survival

Background: Gliomas are the most common primary brain tumors and their prognosis is related to WHO histopathological grade. Glioblastoma (grade IV astrocytoma or GBM) is characterized by microscopic invasion into surrounding brain and universally poor prognosis despite treatment with surgery, radiation and chemotherapy . Recently, the matricellular protein periostin (POSTN) has been shown to be associated with increased parenchymal invasion (measured by edema on MRI) and poor prognosis in GBM. The specific aim of the present analysis was to determine the mechanistic impact of POSTN on glioma outcome.

Methods: We used the gene expression of POSTN from 559 GBM patients (pts) included in the Cancer Genome Atlas (TCGA) to build a gene expression model of the expression of 12184 genes to predict POSTN expression using elastic net. This model was used to predict the POSTN expression in a testing set of 419 pts with gliomas included in Repository for Brain Neoplasia Data (REMBRANDT) (99 grade II, 71 grade III and 125 grade IV and 124 with no grade). Receiver-operating characteristic (ROC) and survival analysis were performed to measure the performance of the model, and gene-set enrichment analysis (GSEA) was used to reveal network topology perturbations.

Results: The gene expression model discovered 721 genes highly correlated to POSTN expression that predict POSTN in the testing set with an area under the curve (AUC) of 0.96 on ROC curve. GSEA reveals genes involved in “mesenchymal transition,” transition of invasive ductal carcinoma (IDC) from ductal carcinoma in situ (DCIS) in breast cancer and stem cell signatures. Survival analysis of the TCGA GBM pts showed that the cohort with “high POSTN” had worse survival (median 12 months versus 15 months, log-rank p=0.0002). When applied to all pts in REMBRANDT, the model predicted classes also had significantly different survival (median 13.4 versus 38 months, log-rank p<0.0001). Interestingly, this classification of survival persists in the subset of pts with grade III (n=71, median survival 17.7 versus 42.4 months, p=0.0125) and grade II (n=99, median survival 17.9 versus 50.8, p=0.02) gliomas.

Conclusions: We have developed a gene expression model related to POSTN, a gene linked to poor prognosis in GBM, to investigate the role correlated genes may play in the aggressive phenotype. Some of the genes found to be highly correlated to POSTN are related to mesenchymal transition, invasive behavior in breast cancer and stemness. We verify that high POSTN expression is a strong prognostic indicator for poor outcome in GBM, and reveal for the first time that pts with grade II and III glioma with a “high” POSTN signature have significantly worse survival. Given that low grade glioma pts often have less aggressive treatment at time of diagnosis, we propose studying the role of early chemoradiation in the subset of pts with poor POSTN signature to potentially improve their outcome.

Citation Format: Andrew D. Trister, Andrei M. Mikheev, Jason K. Rockhill, Stephen H. Friend, Robert C. Rostomily. Periostin expression in glioma correlates with genes related to mesenchymal transition and survival. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1210. doi:10.1158/1538-7445.AM2013-1210

Increased age of transformed mouse neural progenitor/stem cells recapitulates age-dependent clinical features of human glioma malignancy

Increasing age is the most robust predictor of greater malignancy and treatment resistance in human gliomas. However, the adverse association of clinical course with aging is rarely considered in animal glioma models, impeding delineation of the relative importance of organismal versus progenitor cell aging in the genesis of glioma malignancy. To address this limitation, we implanted transformed neural stem/progenitor cells (NSPCs), the presumed cells of glioma origin, from 3- and 18-month-old mice into 3- and 20-month host animals. Transplantation with progenitors from older animals resulted in significantly shorter (P ≤ 0.0001) median survival in both 3-month (37.5 vs. 83 days) and 20-month (38 vs. 67 days) hosts, indicating that age-dependent changes intrinsic to NSPCs rather than host animal age accounted for greater malignancy. Subsequent analyses revealed that increased invasiveness, genomic instability, resistance to therapeutic agents, and tolerance to hypoxic stress accompanied aging in transformed NSPCs. Greater tolerance to hypoxia in older progenitor cells, as evidenced by elevated HIF-1 promoter reporter activity and hypoxia response gene (HRG) expression, mirrors the upregulation of HRGs in cohorts of older vs. younger glioma patients revealed by analysis of gene expression databases, suggesting that differential response to hypoxic stress may underlie age-dependent differences in invasion, genomic instability, and treatment resistance. Our study provides strong evidence that progenitor cell aging is responsible for promoting the hallmarks of age-dependent glioma malignancy and that consideration of progenitor aging will facilitate development of physiologically and clinically relevant animal models of human gliomas.

Increased re-entry into cell cycle mitigates age-related neurogenic decline in the murine subventricular zone

Although new neurons are produced in the subventricular zone (SVZ) of the adult mammalian brain, fewer functional neurons are produced with increasing age. The age-related decline in neurogenesis has been attributed to a decreased pool of neural progenitor cells (NPCs), an increased rate of cell death, and an inability to undergo neuronal differentiation and develop functional synapses. The time between mitotic events has also been hypothesized to increase with age, but this has not been directly investigated. Studying primary-cultured NPCs from the young adult and aged mouse forebrain, we observe that fewer aged cells are dividing at a given time; however, the mitotic cells in aged cultures divide more frequently than mitotic cells in young cultures during a 48-hour period of live-cell time-lapse imaging. Double-thymidine-analog labeling also demonstrates that fewer aged cells are dividing at a given time, but those that do divide are significantly more likely to re-enter the cell cycle within a day, both in vitro and in vivo. Meanwhile, we observed that cellular survival is impaired in aged cultures. Using our live-cell imaging data, we developed a mathematical model describing cell cycle kinetics to predict the growth curves of cells over time in vitro and the labeling index over time in vivo. Together, these data surprisingly suggest that progenitor cells remaining in the aged SVZ are highly proliferative.

Aging neural progenitor cells have decreased mitochondrial content and lower oxidative metabolism

Although neurogenesis occurs in discrete areas of the adult mammalian brain, neural progenitor cells (NPCs) produce fewer new neurons with age. To characterize the molecular changes that occur during aging, we performed a proteomic comparison between primary-cultured NPCs from the young adult and aged mouse forebrain. This analysis yielded changes in proteins necessary for cellular metabolism. Mitochondrial quantity and oxygen consumption rates decrease with aging, although mitochondrial DNA in aged NPCs does not have increased mutation rates. In addition, aged cells are resistant to the mitochondrial inhibitor rotenone and proliferate in response to lowered oxygen conditions. These results demonstrate that aging NPCs display an altered metabolic phenotype, characterized by a coordinated shift in protein expression, subcellular structure, and metabolic physiology.

Abstract LB-131: Decreased nuclear localization and expression of the FRY tumor suppressor gene, a repressor of epithelial mesenchymal transition, are highly correlated with breast cancer phenotype, grade, and progression

Using Quantitative Trait Locus (QTL) mapping in a backcross between susceptible Fischer 344 and resistant Copenhagen rat strains, we identified Fry, the rat ortholog of the Drosophila melanoganster furry gene, as a mammary carcinoma susceptibility (Mcs) gene. The Fischer 344 Fry allele harbors two single nucleotide polymorphisms that alter amino acid residues that are highly conserved from yeast to humans. One of these SNPs replaces an Alanine with a Serine residue, creating a de novo concensus sequence for several cancer-associated protein kinases. In the lower eucaryoyes, the furry orthologs are implicated in diverse cell processes including epithelial cell polarization, morphogenesis, proliferation, cytokinesis, and regulation of the NDR family of kinases, some of which are putative human tumor suppressor genes. Consistent with its function as a tumor suppressor gene, ectopic expression of the FRY gene was reduced in 3 of 4 human breast cancer cell lines. Ectopic expression of the wildtype allele significantly reduced the tumorigenicity of the human MDA-MB-231 mammary carcinoma cell line. In contrast to the parental MDA-MB-231 cells, which grew randomly in Matrigel® matrix, those expressing Fry (231CFry) formed spherical colonies of differentiated cells, closely resembling those formed by MCF-10A normal mammary epithelial cell line. When xenographed into nude mice, the 231CFry cells demonstrated a dramatic reduction in tumorigenicity (8x reduction in tumor volume at 15 days) and diminished invasiveness into surrounding tissues. Gene expression profiling suggested that in MDA-MB-231 cells, ectopic Fry induced the expression of gene networks involved in cell differentiation, proliferation, and polarization, consistent with a role for FRY in suppressing epithelial-mesenchymal transition (EMT). To investigate the role of human FRY in breast cancer, we examined FRY mRNA expression in >1,500 human breast cancers, representing distinct eight cohorts entered into the Oncomine 3.0 Cancer Profiling Database. Our analysis revealed that decreased FRY mRNA was highly correlated with poorly differentiated breast cancer phenotypes (p<0.0001), increasing Elston tumor grade (p<0.0001) and clinically aggressive cancer phenotypes (p<0.05). Using an anti-FRY peptide antiserum, we examined FRY protein expression in cores comprising the BR208 breast cancer and tissue microarrays from US Biomax, Inc. Immunohistochemical staining patterns were analyzed by quantitative image analysis software and independently by a board certified pathologist. The analyses indicated that decreased nuclear localization and expression of FRY were highly correlated with histopathology, clinical grade and progression, indicating that the FRY tumor suppressor is an important new biomarkers of breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-131. doi:10.1158/1538-7445.AM2011-LB-131

Fast bound pool fraction imaging of the in vivo rat brain: association with myelin content and validation in the C6 glioma model

Cross-relaxation imaging (CRI) is a quantitative magnetic resonance technique that measures the kinetic parameters of magnetization transfer between protons bound to water and protons bound to macromolecules. In this study, in vivo, four-parameter CRI of normal rat brains (N=5) at 3.0 T was first directly compared to histology. The bound pool fraction, f, was strongly associated with myelin density (Pearson's r=0.99, p<0.001). The correlation persisted in separate analyses of gray matter (GM; r=0.89, p=0.046) and white matter (WM; r=0.97, p=0.029). Subsequently, a new time-efficient approach for solely capturing the whole-brain parametric map of f was proposed, validated with histology, and used to estimate myelin density. Since the described approach for the rapid acquisition of f applied constraints to other CRI parameters, a theoretical analysis of error was performed. Estimates of f in normal and pathologic tissue were expected to have <10% error. A comparison of values for f obtained from the traditional four-parameter fit of CRI data versus the proposed rapid acquisition of f was within this expected margin for in vivo rat brain gliomas (N=4; mean±SE; 3.9±0.2% vs. 4.0±0.2%, respectively). In both whole-brain f maps and myelin density maps, replacement of normal GM and WM by proliferating and invading tumor cells could be readily identified. The rapid, whole-brain acquisition of the bound pool fraction may provide a reliable method for detection of glioma invasion in both GM and WM during animal and human imaging.

Quantitative proteomic analysis of oligodendrogliomas with and without 1p/19q deletion

Approximately 50-80% of oligodendrogliomas demonstrate a combined loss of chromosome 1p and 19q. Chromosome 1p/19q deletion, appearing early in tumorigenesis, is associated with improved clinical outcomes, including response to chemotherapy and radiation. Although many hypotheses have been proposed, the molecular mechanisms underlying improved clinical outcomes with 1p/19q deletion in oligodendrogliomas have not been characterized fully. To investigate the molecular differences between oligodendrogliomas, we employed an unbiased proteomic approach using microcapillary liquid chromatography mass spectrometry, along with a quantitative technique called isotope-coded affinity tags, on patient samples of grade II oligodendrogliomas. Following conventional biochemical separation of pooled tumor tissue from five samples of undeleted and 1p/19q deleted grade II oligodendrogliomas into nuclei-, mitochondria-, and cytosol-enriched fractions, relative changes in protein abundance were quantified. Among the 442 total proteins identified, 163 nonredundant proteins displayed significant changes in relative abundance in at least one of the three fractions between oligodendroglioma with and without 1p/19q deletion. Bioinformatic analyses of differentially regulated proteins supported the potential importance of metabolism and invasion/migration to the codeleted phenotype. A subset of altered proteins, including the pro-invasive extracellular matrix protein BCAN, was further validated by Western blotting as candidate markers for the more aggressive undeleted phenotype. These studies demonstrate the utility of proteomic analysis to identify candidate biological motifs and molecular mechanisms that drive differential malignancy related to 1p19q phenotypes. Future analysis of larger patient samples are warranted to further refine biomarker panels to predict biological behavior and assist in the identification of deleted gene products that define the 1p/19q phenotype.

TWIST1 promotes invasion through mesenchymal change in human glioblastoma

Background

Tumor cell invasion into adjacent normal brain is a mesenchymal feature of GBM and a major factor contributing to their dismal outcomes. Therefore, better understandings of mechanisms that promote mesenchymal change in GBM are of great clinical importance to address invasion. We previously showed that the bHLH transcription factor TWIST1 which orchestrates carcinoma metastasis through an epithelial mesenchymal transition (EMT) is upregulated in GBM and promotes invasion of the SF767 GBM cell line in vitro.

Results

To further define TWIST1 functions in GBM we tested the impact of TWIST1 over-expression on invasion in vivo and its impact on gene expression. We found that TWIST1 significantly increased SNB19 and T98G cell line invasion in orthotopic xenotransplants and increased expression of genes in functional categories associated with adhesion, extracellular matrix proteins, cell motility and locomotion, cell migration and actin cytoskeleton organization. Consistent with this TWIST1 reduced cell aggregation, promoted actin cytoskeletal re-organization and enhanced migration and adhesion to fibronectin substrates. Individual genes upregulated by TWIST1 known to promote EMT and/or GBM invasion included SNAI2, MMP2, HGF, FAP and FN1. Distinct from carcinoma EMT, TWIST1 did not generate an E- to N-cadherin "switch" in GBM cell lines. The clinical relevance of putative TWIST target genes SNAI2 and fibroblast activation protein alpha (FAP) identified in vitro was confirmed by their highly correlated expression with TWIST1 in 39 human tumors. The potential therapeutic importance of inhibiting TWIST1 was also shown through a decrease in cell invasion in vitro and growth of GBM stem cells.

Conclusions

Together these studies demonstrated that TWIST1 enhances GBM invasion in concert with mesenchymal change not involving the canonical cadherin switch of carcinoma EMT. Given the recent recognition that mesenchymal change in GBMs is associated with increased malignancy, these findings support the potential therapeutic importance of strategies to subvert TWIST1-mediated mesenchymal change.

A syngeneic glioma model to assess the impact of neural progenitor target cell age on tumor malignancy

Human glioma incidence, malignancy, and treatment resistance are directly proportional to patient age. Cell intrinsic factors are reported to contribute to human age-dependent glioma malignancy, but suitable animal models to examine the role of aging are lacking. Here, we developed an orthotopic syngeneic glioma model to test the hypothesis that the age of neural progenitor cells (NPCs), presumed cells of glioma origin, influences glioma malignancy. Gliomas generated from transformed donor 3-, 12-, and 18-month-old NPCs in same-aged adult hosts formed highly invasive glial tumors that phenocopied the human disease. Survival analysis indicated increased malignancy of gliomas generated from older 12- and 18-month-old transformed NPCs compared with their 3-month counterparts (median survival of 38.5 and 42.5 vs. 77 days, respectively). This study showed for the first time that age of target cells at the time of transformation can affect malignancy and demonstrated the feasibility of a syngeneic model using transformed NPCs for future examination of the relative impacts of age-related cell intrinsic and cell-extrinsic factors in glioma malignancy.

Quantitative analysis of mitotic Olig2 cells in adult human brain and gliomas: implications for glioma histogenesis and biology

The capacity of adult human glial progenitor cells (AGPs), to proliferate and undergo multipotent differentiation, positions them as ideal candidate cells of origin for human gliomas. To investigate this potential role we identified AGPs as mitotically active Olig2 cells in nonneoplastic adult human brain and gliomas. We conservatively estimated that one in 5,000 human temporal lobe neocortical gray or subcortical white matter cells is mitotic. Extrapolating from a mean Olig2/Mib-1 labeling index (LI) of 52% and total cell number of 100 billion, we estimated the overall prevalence of mitotic Olig2 AGPs in nonneoplastic human brain parenchyma at 10 million. These data identify a large reservoir of Olig2 AGPs which could be potential targets for human gliomagenesis. The vast majority of mitotic cells in Grade II and Grade III gliomas of all histologic subtypes expressed Olig2 (mean LI 75%) but rarely S100B (LI 0.6%), identifying the Olig2 cell as a distinct contributor to the proliferating cell population of human gliomas of both oligodendroglial and astrocytic lineages. In the most malignant Grade IV glioma, or glioblastoma multiforme (GBM), the prevalence of Olig2/Mib-1 cells was significantly decreased (24.5%). The significantly lower Olig2/Mib-1 LI in GBMs suggests that a decrease in the prevalence of Olig2 cells to the total mitotic cell pool accompanies increasing malignancy. The novel framework provided by this quantitative and comparative analysis supports future studies to examine the histogenetic role of Olig2 AGPs in adult gliomas, their potential contribution to the tumor stroma and the molecular role of Olig2 in glioma pathogenesis.

Profiling gene expression in human placentae of different gestational ages: an OPRU Network and UW SCOR Study

We used the whole-genome approach to identify major functional categories of genes whose expression depends on gestational age. Using microarray analysis, we compared gene expression profiles in the villous tissues of first (45-59 days) and second trimester (109-115 days) placentae with C-section term placentae. We found that in first trimester placentae, genes related to cell cycle, DNA, amino acids, and carbohydrate metabolism were significantly overrepresented, while genes related to signal transduction were underrepresented. Among genes involved in organism defense, we identified genes involved in chemical response, metabolism, and transport. Analysis of signal transduction pathways suggested, and subsequently confirmed independently, that the Wnt pathway was changed with gestational age leading to inhibition of beta-catenin protein expression. Our study will serve as a reference database to gain insight into the regulation of gene expression in the developing placentae and to compare with gene expression in placentae from complicated pregnancies.

Effect of pregnancy on cytochrome P450 3a and P-glycoprotein expression and activity in the mouse: mechanisms, tissue specificity, and time course

The plasma concentrations of orally administered anti-human immunodeficiency virus protease inhibitors are significantly reduced during human and mouse pregnancy. We have shown that in the mouse, at gestational day 19, this reduction is due to increased hepatic cytochrome P450 3a (Cyp3a) protein expression and activity. In the current study, we investigated the mechanisms by which Cyp3a activity is increased by pregnancy and the time course of change in expression of Cyp3a and P-glycoprotein (P-gp) in various tissues. We found that hepatic transcripts of Cyp3a16, Cyp3a41, and Cyp3a44 were significantly increased during pregnancy, whereas those of Cyp3a11 and Cyp3a25 were significantly decreased. This resulted in a net increase in Cyp3a protein expression and activity in the liver during pregnancy. The increase in Cyp3a41 and Cyp3a44 transcripts was positively correlated (p < 0.05) with hepatocyte nuclear factor 6 and estrogen receptor-alpha transcripts. The pregnancy-related factors that transcriptionally activated mouse Cyp3a isoforms also activated the human CYP3A4 promoter in pregnant CYP3A4-promoter-luciferase transgenic (CYP3A4-tg) mice. In contrast, intestinal Cyp3a protein expression was not significantly affected by pregnancy. No change in P-gp protein expression was observed in the liver or kidney during pregnancy, although a significant decrease was observed in the placenta. Because hepatic CYP3A activity also seems to be induced during human pregnancy, the mouse (including CYP3A4-tg mouse) seems to be an excellent animal model to determine the molecular mechanisms for such an induction.

Dickkopf-1 mediated tumor suppression in human breast carcinoma cells

Dickkopf-1 (DKK-1) is a secreted inhibitor of the Wnt signaling pathway. We previously identified DKK-1 as a candidate tumor suppressor and demonstrated that ectopic expression of the DKK-1 suppressed the tumorigenicity of HeLa cells in vitro and in vivo. Since suppression of tumorigenicity of HeLa cells by DKK-1 overexpression was not mediated by effects on beta-catenin dependent transcription, we hypothesized that DKK-1 might also inhibit tumorigenicity of breast carcinoma cell lines lacking an activated canonical Wnt pathway. In the present study we show that ectopic expression of DKK-1 in various breast cancer cell lines resulted in a change in the cell phenotype, increased sensitivity to apoptosis, inhibition of anchorage independent growth in vitro, and suppression of tumorigenicity in vivo. Consistent with known effects of DKK-1 on the canonical Wnt signaling pathway, ectopic expression of DKK-1 in breast carcinoma cells was associated with increased phosphorylation and degradation of beta-catenin. However, none of the breast tumor cells used in this study showed detectable levels of beta-catenin dependent activation of TCF/Lef promoter activity measured by reporter constructs. Consistent with the results of these transient transfection assays, we were unable to demonstrate the expected beta-catenin dependent, TCF/Lef mediated inhibition of cyclin D1 and c-myc gene transcription in breast cells overexpressing DKK-1. However, we found that cells with DKK-1 overexpression have increased activity of CamKII pathway. Overexpression of the constitutively active form of CamKII (T286D) resulted in inhibition of breast cancer cell tumorigenicity. Thus, our study supports the hypothesis that DKK-1 mediated tumor suppressor effect is independent of beta-catenin dependent transcription and identified the CamKII pathway that contributes into DKK-1 signaling.

Comparative genomics of susceptibility to mammary carcinogenesis among inbred rat strains: role of reduced prolactin signaling in resistance of the Copenhagen strain

To elucidate the molecular basis for differential susceptibilities to mammary carcinogenesis, we compared the transcriptomes of normal mammary glands from pubescent female rats of the resistant Copenhagen (Cop) strain with those of the susceptible Fischer 344 (F344), August x Copenhagen Irish (ACI), Buffalo/N (Buf/N), Wistar-Furth (WF) strains and F1 (Cop x F344) progeny (F1). Gene expression profiles in mammary tissue within each rat strain were remarkably similar, indicating that gene expression was determined by genetic background. We next identified the subset of genes that were differentially expressed in all susceptible strains relative to the resistant Cop strain. Among these, the messenger RNAs encoding prolactin (Prl) and its cell surface receptor were significantly elevated in all susceptible strains. The expression levels of several Prl-regulated genes were also significantly elevated, indicating the presence of increased Prl signaling in mammary glands of all susceptible strains. Pathway analysis of gene expression profiles further identified the Prl-activated Jak/STAT-signaling pathway among the pathways that most distinguished sensitive rat strains from the resistant Cop rat. To test the hypothesis that reduced levels of the Prl signaling in mammary tissue partially contributed to the genetic resistance to mammary carcinogenesis, we used the neuroleptic drug, perphenazine, to transiently elevate serum Prl levels in the Cop strain. Whereas Cop rats are resistant to N-nitroso-N-methylurea (NMU)-induced mammary carcinogenesis, approximately 5% of pubescent Cop females treated with perphenazine and NMU exposure developed mammary adenocarcinomas with latencies comparable with those of sensitive strains. Together, these finding indicated that in the rat, the molecular mechanisms underlying genetic susceptibility to mammary carcinogenesis include de-regulation of Prl signaling.

Dickkopf-1 activates cell death in MDA-MB435 melanoma cells

Dickkopf-1 (DKK-1) is known inhibitor of the canonical Wnt pathway. Recent studies strongly suggested that activation of DKK-1 expression results in inhibition of cell tumorigenicity. Reduced levels of DKK-1 in melanomas were recently shown. However, it is not known if DKK-1 activation in melanoma cells will inhibit cell tumorigenicity. In the present study, we overexpressed DKK-1 in melanoma cell line MDA-MB435. We show that while DKK-1 did not affect cell growth in soft agar, weak but significant inhibition of tumorigenicity in nude mice in vivo was observed. Analysis of resulting tumors revealed activation of cell death. In tumors originating from cells transduced with DKK-1, tumor mass was permeated with areas of necrosis. In tumors, originated from control cells, areas of necrosis were limited to the central region, a common feature of large tumors growing in nude mice. TUNEL assay revealed that in tumors originating from cells transduced with DKK-1 apoptotic cells were detected along the border of necrotic and viable areas of the tumors indicating significant increase in apoptotic process. Thus, our results indicate that activation of DKK-1 in melanoma cells leads to activation of apoptosis in vivo and, thus, is incompatible with tumor growth in nude mice.

Frequent activation of CArG binding factor-A expression and binding in N-methyl-N-nitrosourea-induced rat mammary carcinomas

We previously identified a positive transcriptional element identical to human Ha-ras response element (HRE) within the promoter of the rat Ha-ras gene. We further identified CArG binding factor A (CBF-A), a member of heterogeneous nuclear ribonuclear protein (hnRNP) gene family, as a trans-acting factor that binds the HRE sequence with high affinity in rat mammary carcinoma cells. To determine if activation of CBF-A plays a role in tumor development in vivo , we investigated CBF-A expression and binding activity in rat mammary tumors induced by N-methyl-N-nitrosourea. We found that approximately 82% of tumors expressed CBF-A at levels that were 3-20 fold higher than detected in normal mammary gland. Moreover, elevated CBF-A protein levels were invariably associated with increased binding activity to the HRE. CBF-A mRNA levels in tumors were on average elevated only two fold as compared to normal mammary gland, indicating that increased CBF-A protein levels in tumors resulted from both translational and/or post-translational regulation. The level of CBF-A expression in mammary tumors was independent of Ha-ras mutational status. Together, these findings indicated that deregulation of CBF-A contributes to mammary carcinogenesis via a mechanism that is distinct from its hnRNP functions in binding and post-transcriptional regulation of RNA.

Alterations in gene expression induced in day-9 mouse embryos exposed to hyperthermia (HS) or 4-hydroperoxycyclophosphamide (4CP): analysis using cDNA microarrays

Teratogen-induced alterations in gene expression play an important role in the genesis of malformations in animals. The recent development of DNA microarrays now offers the opportunity to monitor global changes in gene expression and therefore the potential to obtain significant new information concerning both normal and abnormal development. RNA was isolated from day-9 mouse embryos at 1 and 5 h after exposure to hyperthermia (HS) or 4-hydroperoxycyclophosphamide (4CP) and compared to RNA isolated from concurrent controls using mouse cDNA microarrays. Cy5/Cy3 intensity data were extracted using Spot-on Image software and then normalized using the statistical software program R/maanova. Differentially expressed genes were identified using a linear mixed-effects model and p values derived from t-test statistics. Approximately 9000 genes show statistically significant alterations in expression in day-9 mouse embryos exposed to HS or 4CP. HS and 4CP also induce alterations in the expression of distinct sets of genes, e.g., DNA replication/repair, cell cycle, signal transduction, and transcription-related genes. As expected, a variety of heat shock genes are upregulated by HS but not 4CP. Among genes whose expression is altered by both HS and 4CP, cluster analysis identified three p53 target genes (Cyclin G1, Gtse1, and Mdm2), and follow up studies confirmed that p53 is activated in embryos exposed to these two teratogens. In addition, cluster analyses also revealed that HS but not 4CP induces the downregulation of genes encoding key enzymes in the cholesterol biosynthesis pathway. Thus, our microarray data have identified one potentially important pathway (p53) common to both HS- and 4CP-induced teratogenesis and another pathway (cholesterol biosynthesis) potentially important, but specific to HS-induced teratogenesis.

A functional genomics approach for the identification of putative tumor suppressor genes: Dickkopf-1 as suppressor of HeLa cell transformation

We described previously the isolation and characterization of two non-tumorigenic revertants from the HeLa cervical carcinoma cell line, and demonstrated that loss of the transformed phenotype in these cells was the result of dominant somatic mutations. The goal of the present study was to use cDNA microarrays to identify candidate tumor suppressors among the set of genes whose increased expression correlated with loss of tumorigenicity in both revertants. Among the genes with significantly increased expression levels in both HA and HF revertants we identified Insulin Growth Factor Binding Protein-3 (IGFBP-3) and the Dickkopf-1 (DKK-1) genes. Both of these genes encode secreted proteins implicated in the modulation cell growth and differentiation, and IGFBP-3 was shown previously to have tumor suppressing activity. To test the hypothesis that increased expression of IGFBP-3 or the DKK-1 genes could have contributed to the suppression of tumorigenicity in the revertants, we expressed IGFBP-3 or DKK-1 in HeLa cells, and assessed their effects on anchorage dependent and independent growth, and tumor formation in athymic nude mice. Ectopic expression of IGFBP-3 or DKK-1 resulted in significantly decreased growth in soft agar. HeLa cells expressing ectopic IGFBP-3 or DKK-1 showed statistically significant differences in the kinetics of tumor formation. In any tumors that arose in animals injected with the IGFBP-3 expressing cells, there was a complete loss of IGFBP-3 activity, as measured by binding to IGF-1 and IGF-2 proteins. All tumors that arose after injection of cells expressing DKK-1, invariably showed almost a complete loss of ectopic DKK-1 expression. The observations that loss of DKK-1 expression or IGFBP-3 activity was required for tumorigenicity suggested that both proteins encode putative tumor suppressor genes. We also show that while DKK-1 expression does not affect cell growth in vitro, the protein does sensitize cells to apoptosis. We also demonstrated that effect of DKK-1 was not due to inhibition of beta-catenin/TCF4-regulated transcription. Taken together, our results indicate that somatic cell genetics combining with gene expression profiling may be a useful approach for the identification of functional suppressors of malignant cell growth.

CArG binding factor A (CBF-A) is involved in transcriptional regulation of the rat Ha-ras promoter

In the present study we identified a positive transcriptional element within the rat Ha-ras promoter previously known as Ha-ras response element (HRE) and identified a trans-acting factor that binds HRE sequences in rat mammary cells. To identify the binding protein we employed sequence specific DNA affinity chromatography. Amino acid sequence analysis of the affinity-purified proteins was performed by tandem mass spectroscopy. The results unexpectedly demonstrated that in rat mammary cells CArG box-binding factor A (CBF-A) is the major protein species that bind specifically to the rat and human HRE sequences with high affinity. The affinity of CBF-A binding to HRE was significantly higher than to the CArG box described as a recognition sequence for CBF-A protein. Transient transfection assays using reporter plasmids verified that mutations within the HRE that disrupt binding of CBF-A also reduced the activity of the rat Ha-ras promoter. Despite the fact that the HRE within the Ha-ras promoter resembles a binding site for Ets transcription factors, we did not detect the binding of Ets-related proteins to the rat HRE in BICR-M1Rk cells. We further demonstrated a correlation between the presence of HRE binding activity and induction of Ha-ras mRNA expression following serum stimulation in the mammary carcinoma cell line. Taken together, our results suggest that CBF-A may play an important role in transcriptional regulation of Ha-ras promoter activity during normal mammary cell growth and carcinogenesis.

Stabilization and reactivation of the p53 tumor suppressor protein in nontumorigenic revertants of HeLa cervical cancer cells

We demonstrated previously that loss of in vitro transformation and in vivo tumorigenicity in two independent revertant clones of HeLa cells (designated HA and HF) resulted from dominant-acting genetic changes. Analysis of the p53 tumor suppressor gene revealed stabilization and at least partial restoration of wild-type p53 transactivation properties pathways in both revertants of HPV-induced cell transformation. The half-lives of the p53 protein and both of the HA and HF clones were increased approximately 4 fold compared with the parental HeLa cells (16, 17, and 4 min, respectively). The levels of E6 viral protein expression were similar in the three cell lines, whereas the levels of the ubiquitin ligase protein, E6 associated protein (E6-AP), were elevated in the revertants. Western blot analysis of immunoaffinity-purified p53 demonstrated that stabilization of p53 in the revertants was correlated with a reduction in the in vivo formation of complexes involving the E6 oncoprotein and p53. Stabilization of p53 function in the revertants did not result from mutations in either the p53 or E6-AP genes. Despite the observed stabilization and restoration of p53 transactivation function in the revertants, exposure of the revertants to DNA-damaging agents did not result in elevated levels of p21(waf-1) protein and failed to induce growth arrest in the G1 phase of the cell cycle. However, p53-independent induction of p21(waf-1) protein also failed to induce the G1 phase of the cell cycle. Thus, restoration of wild-type p53 transactivation activity in the HA and HF revertants is insufficient to induce G1 arrest and reversion from HPV-induced cell transformation in our model system.

[The geterogenity of 137Cs and 90Sr distribution and dose loading on critical tissues of main seedling root]

It is shown, that the roots of plants concentrate 137Cs and 90Sr from water solutions in different zones: 137Cs--mainly in a meristem zone, 90Sr--in a stretching zone. The similar character of radionuclide distribution was established regarding water and soil cultures. The real dose loading on critical tissues of main root have appeared to be much higher than it was expected from the assumption of uniform distribution of radionuclides in tissues.

Alterations in H-ras1 promoter conformation during N-nitroso-N-methylurea-induced mammary carcinogenesis and pregnancy

We previously demonstrated that H-ras1 oncogene mutations detected in N-nitroso-N-methylurea (NMU)-induced mammary tumors arose as background mutations within rat mammary cells (RMCs) and that NMU promoted the outgrowth of these preexisting mutants. We have now detected a putative DNA structure in the H-ras1 promoter of RMCs in vivo that was absent in NMU-induced mammary tumor cells. Analysis of the promoter in RMCs as a function of time after exposure to carcinogens indicated that NMU, but not 7,12-dimethylbenz(a)anthracene, initiated the loss of this structure with a half-life of 7 days. Although loss of the structure was irreversible in cells that gave rise to tumors, it was restored in normal RMCs by 120 days after exposure and was present in normal RMCs of animals bearing tumors, even 1 year after NMU exposure. The structure was also abrogated in RMCs during pregnancy and restored after lactation was terminated, suggesting that reversible regulation of the structure by hormones contributed to normal RMC growth. Thus, NMU may promote abnormal RMC growth by mimicking the effects of hormones on DNA conformation. We hypothesize that the NMU-induced alterations in promoter conformation irreversibly deregulates H-ras1 expression in initiated cells, thereby increasing the phenotypic penetrance of the conditional H-ras1 mutations.

Expression of neurotrophin genes in human fibroblasts: differential regulation of the brain-derived neurotrophic factor gene

Brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF) and neurotrophin-3 (NT-3) are structurally related survival and differentiation factors for distinct sets of peripheral and central neurons. We previously reported that BDNF and NGF gene expression are differentially regulated in mouse L929 fibroblasts. Here we examine expression of these three neurotrophins in human fibroblasts. Northern blots detected BDNF and NT-3 mRNAs in fibroblasts derived from lung (WI-38), calvarium and foreskin. WI-38 cells and foreskin fibroblasts expressed 1.6 kb as well as 4 kb BDNF mRNAs whereas only the smaller BDNF mRNA was detected in calvarium fibroblasts. NGF mRNA was present in foreskin and calvarium but not lung fibroblasts. In WI-38 cells serum treatment increased levels of BDNF mRNA within 2 hr. Cycloheximide did not inhibit the increase. Treatment with 12-O-tetradecanoyl phorbol-13-acetate (TPA) transiently suppressed BDNF mRNA. Treatment with both serum and TPA first stimulated and then transiently suppressed BDNF mRNA. TPA and/or serum did not significantly affect BDNF mRNA in calvarium fibroblasts. These results show that human fibroblasts derived from different tissues express and regulate neurotrophin genes differentially.

Immunohistochemical detection of DNA alkylation adducts in rat and hamster liver after treatment with dimethylnitrosamine

Monoclonal and polyclonal antibodies specific for methylation adducts have been applied in an immunohistochemical study of DNA damage in rat and hamster liver following exposure to dimethylnitrosamine. The approach was validated, for frozen and paraffin-embedded sections, by comparison with biochemical data on adduct levels in whole tissues or specific cell populations in the same experimental systems. The potential application of this method to human exposure assessment is discussed.

[An analysis of blood serum proteins in chronic alcoholism patients by a cross immunoelectrophoresis method]

Prealbumin, albumin, alpha 1-antitrypsin, alpha 1-antichymotrypsin, ceruloplasmin, haptoglobin, transferrin, IgG, IgM and IgA were studied in blood serum of healthy donors and of patients with chronic alcoholism by means of cross immuno-electrophoresis and immunodiffusion. Only content of alpha 1-antitrypsin was distinctly altered in blood serum of the patients with alcoholism as compared with normal state, while individual variations in content of the proteins studied were considerably higher in blood serum of the patients. At the same time, distinct dissimilarity of the patterns studied was found between healthy donors and patients with chronic alcoholism when concentration ratios of some positively and negatively charged acute phase proteins were calculated (alpha 1-antitrypsin/albumin, haptoglobin/albumin, haptoglobin/transferrin).