CDKN2A/B deletions are strongly associated with meningioma progression: a meta-analysis of individual patient data

Homozygous CDKN2A/B deletion has been associated with an increased risk of recurrence in meningiomas. However, the evidence is confined to a limited number of studies, and the importance of heterozygous CDKN2A/B deletions remains insufficiently investigated. Hence, the present meta-analysis reconstructs individual patient data (IPD) and reconstructs the probabilities of progression-free survival (PFS) stratified by CDKN2A/B status. IPD of PFS rates were extracted from published Kaplan-Meier plots using the R package IPDfromKM in R studio (RStudio, Boston, MA, USA). Reconstructed Kaplan-Meier Plots of the pooled IPD data were created. One-stage and two-stage meta-analyses were performed. Hazard ratios (HR) were used as effective measures. Of 181 records screened, four articles with 2521 participants were included. The prevalence of homozygous CDKN2A/B deletions in the included studies was 0.049 (95% CI 0.040-0.057), with higher tumor grades associated with a significantly greater proportion of CDKN2A/B deletions. The reconstructed PFS curves for the pooled cohort showed that the median PFS time of patients with a CDKN2A/B wild-type status, heterozygous or homozygous CDKN2A/B deletion was 180.0 (95% CI 145.7-214.3), 26.1 (95% CI 23.3-29.0), and 11.00 (95% CI 8.6-13.3) months, respectively (p < 0.0001). Both hetero- or homozygous CDKN2A/B deletions were significantly associated with shortened time to meningioma progression. One-stage meta-analysis showed that hetero- (HR: 5.5, 95% CI 4.0-7.6, p < 0.00001) and homozygous CDKN2A/B deletions (HR: 8.4, 95% CI 6.4-11.0, p < 0.00001) are significantly associated with shortened time to meningioma progression. Multivariable Cox regression analysis of progression in a subgroup with available covariates (age, sex, WHO grade, and TERT status) and also two-stage meta-analysis confirmed and validated the results of the one-stage analysis that both heterozygous and homozygous CDKN2A/B deletions are of prognostic importance. Further large-scale studies of WHO grade 2 and 3 meningiomas are needed to validate the importance of heterozygous CDKN2A/B deletions with consideration of established factors.

De novo variants in ATP2B1 lead to neurodevelopmental delay

Calcium (Ca²⁺) is a universal second messenger involved in synaptogenesis and cell survival; consequently, its regulation is important for neurons. ATPase plasma membrane Ca²⁺ transporting 1 (ATP2B1) belongs to the family of ATP-driven calmodulin-dependent Ca²⁺ pumps that participate in the regulation of intracellular free Ca²⁺. Here, we clinically describe a cohort of 12 unrelated individuals with variants in ATP2B1 and an overlapping phenotype of mild to moderate global development delay. Additional common symptoms include autism, seizures, and distal limb abnormalities. Nine probands harbor missense variants, seven of which were in specific functional domains, and three individuals have nonsense variants. 3D structural protein modeling suggested that the variants have a destabilizing effect on the protein. We performed Ca²⁺ imaging after introducing all nine missense variants in transfected HEK293 cells and showed that all variants lead to a significant decrease in Ca²⁺ export capacity compared with the wild-type construct, thus proving their pathogenicity. Furthermore, we observed for the same variant set an incorrect intracellular localization of ATP2B1. The genetic findings and the overlapping phenotype of the probands as well as the functional analyses imply that de novo variants in ATP2B1 lead to a monogenic form of neurodevelopmental disorder.

RNA sequencing of glioblastoma tissue slice cultures reveals the effects of treatment at the transcriptional level

One of the major challenges in cancer research is finding models that closely resemble tumors within patients. Human tissue slice cultures are a promising approach to provide a model of the patient's tumor biology ex vivo. Recently, it was shown that these slices can be successfully analyzed by whole transcriptome sequencing as well as automated histochemistry, increasing their usability as preclinical model. Glioblastoma multiforme (GBM) is a highly malignant brain tumor with poor prognosis and little is known about its genetic background and heterogeneity regarding therapy success. In this study, tissue from the tumors of 25 patients with primary GBM was processed into slice cultures and treated with standard therapy (irradiation and temozolomide). Total RNA sequencing and automated histochemistry were performed to enable analysis of treatment effects at a transcriptional and histological level. Slice cultures from long‐term survivors (overall survival [OS] > 24 months) exhibited more apoptosis than cultures from patients with shorter OS. Proliferation within these slices was slightly increased in contrast to other groups, but not significantly. Among all samples, 58 protein‐coding genes were upregulated and 32 downregulated in treated vs. untreated slice cultures. In general, an upregulation of DNA damage‐related and cell cycle checkpoint genes as well as enrichment of genotoxicity pathways and p53‐dependent signaling was found after treatment. Overall, the current study reproduces knowledge from former studies regarding the feasibility of transcriptomic analyses and automated histology in tissue slice cultures. We further demonstrate that the experimental data merge with the clinical follow‐up of the patients, which improves the applicability of our model system.

Surfactant protein C is associated with perineuronal nets and shows age-dependent changes of brain content and hippocampal deposits in wildtype and 3xTg mice

Surfactant protein C (SP-C) modulates cerebrospinal fluid (CSF) rheology. During ageing, its declining levels are accompanied by an increased burden of white matter lesions. Pulmonary SP-C intermediates harbouring the BRICHOS-domain prevent protein misfolding in the lungs. Thus, cerebral SP-C intermediates may counteract cerebral β-amyloidosis, a hallmark of Alzheimer's disease (AD). However, data on the molecular neuroanatomy of SP-C and its alterations in wildtype and triple transgenic (3xTg) mice, featuring essential elements of AD-neuropathology, are lacking. Therefore, this study investigated SP-C-containing structures in murine forebrains and their spatial relationships with vascular, glial and neuronal components of the neurovascular unit. Fluorescence labelling demonstrated neuronal SP-C in the medial habenula, the indusium griseum and the hippocampus. Glial counterstaining elucidated astrocytes in the corpus callosum co-expressing SP-C and S100β. Notably, perineuronal nets were associated with SP-C in the nucleus reticularis thalami, the lateral hypothalamus and the retrosplenial cortex. In the hippocampus of aged 3xTg mice, an increased number of dot-like depositions containing SP-C and Reelin, but devoid of BRICHOS-immunoreactivity were observed apart from AD-like lesions. Wildtype and 3xTg mice revealed an age-dependent increase of such deposits markedly pronounced in about 24-month-old 3xTg mice. SP-C levels of the intracellular and extracellular compartments in each group revealed an inverse correlation of SP-C and Reelin, with reduced SP-C and increased Reelin in an age-dependent fashion especially in 3xTg mice. Taken together, extracellular SP-C, as modulator of glymphatic clearance and potential ligand of PNs, declines in 3xTg mice, which show an accumulation of extracellular Reelin depositions during ageing.

Antifibrotic Effects of Amyloid-Beta and Its Loss in Cirrhotic Liver

The function and regulation of amyloid-beta (Aβ) in healthy and diseased liver remains unexplored. Because Aβ reduces the integrity of the blood-brain barrier we have examined its potential role in regulating the sinusoidal permeability of normal and cirrhotic liver. Aβ and key proteins that generate (beta-secretase 1 and presenilin-1) and degrade it (neprilysin and myelin basic protein) were decreased in human cirrhotic liver. In culture, activated hepatic stellate cells (HSC) internalized Aβ more efficiently than astrocytes and HSC degraded Aβ leading to suppressed expression of α-smooth muscle actin (α-SMA), collagen 1 and transforming growth factor β (TGFβ). Aβ also upregulated sinusoidal permeability marker endothelial NO synthase (eNOS) and decreased TGFβ in cultured human liver sinusoidal endothelial cells (hLSEC). Liver Aβ levels also correlate with the expression of eNOS in transgenic Alzheimer’s disease mice and in human and rodent cirrhosis/fibrosis. These findings suggest a previously unexplored role of Aβ in the maintenance of liver sinusoidal permeability and in protection against cirrhosis/fibrosis via attenuation of HSC activation.

Non-enzymatic reaction of carnosine and glyceraldehyde-3-phosphate accompanies metabolic changes of the pentose phosphate pathway

OBJECTIVES

Carnosine (β-alanyl-l-histidine) is a naturally occurring dipeptide that selectively inhibits cancer cell growth, possibly by influencing glucose metabolism. As its precise mode of action and its primary targets are unknown, we analysed carnosine's effect on metabolites and pathways in glioblastoma cells.

MATERIALS AND METHODS

Glioblastoma cells, U87, T98G and LN229, were treated with carnosine, and metabolites were analysed by gas chromatography coupled with mass spectrometry. Furthermore, mitochondrial ATP production was determined by extracellular flux analysis and reaction products of carnosine were investigated using mass spectrometry.

RESULTS

Carnosine decreased the intracellular abundance of several metabolites indicating a reduced activity of the pentose phosphate pathway, the malate-aspartate shuttle and the glycerol phosphate shuttle. Mitochondrial respiration was reduced in U87 and T98G but not in LN229 cells, independent of whether glucose or pyruvate was used as substrate. Finally, we demonstrate non-enzymatic reaction of carnosine with dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. However, glycolytic flux from glucose to l-lactate appeared not to be affected by the reaction of carnosine with the metabolites.

CONCLUSIONS

Carnosine reacts non-enzymatically with glycolytic intermediates reducing the activity of the pentose phosphate pathway which is required for cell proliferation. Although the activity of the malate-aspartate and the glycerol phosphate shuttle appear to be affected, reduced mitochondrial ATP production under the influence of the dipeptide is cell-specific and appears to be independent of the effect on the shuttles.

Carnosine increases efficiency of temozolomide and irradiation treatment of isocitrate dehydrogenase-wildtype glioblastoma cells in culture

Aim: The naturally occurring dipeptide carnosine (CAR) has been considered for glioblastoma therapy. As CAR also protects against ionizing irradiation (IR), we investigated whether it may counteract standard therapy consisting of postsurgery IR and treatment with temozolomide (TMZ). Materials & methods: Four isocitrate dehydrogenase-wildtype primary cell cultures were exposed to different doses of IR and different concentrations of TMZ and CAR. After exposure, viability under the different conditions and combinations of them was determined. Results: All cultures responded to treatment with TMZ and IR with reduced viability. CAR further decreased viability when TMZ and IR were combined. Conclusion: Treatment with CAR does not counteract glioblastoma standard therapy. As the dipeptide also protects nontumor cells from IR, it may reduce deleterious side effects of treatment.

The Chk1 inhibitor SAR-020106 sensitizes human glioblastoma cells to irradiation, to temozolomide, and to decitabine treatment

Background

Glioblastoma is the most common and aggressive brain tumour in adults with a median overall survival of only 14 months after standard therapy with radiation therapy (IR) and temozolomide (TMZ). In a novel multimodal treatment approach we combined the checkpoint kinase 1 (Chk1) inhibitor SAR-020106 (SAR), disrupting homologue recombination, with standard DNA damage inducers (IR, TMZ) and the epigenetic/cytotoxic drug decitabine (5-aza-2′-deoxycitidine, 5-aza-dC). Different in vitro glioblastoma models are monitored to evaluate if the impaired DNA damage repair may chemo/radiosensitize the tumour cells.

Methods

Human p53-mutated (p53-mut) and -wildtype (p53-wt) glioblastoma cell lines (p53-mut: LN405, T98G; p53-wt: A172, DBTRG) and primary glioblastoma cells (p53-mut: P0297; p53-wt: P0306) were treated with SAR combined with TMZ, 5-aza-dC, and/or IR and analysed for induction of apoptosis (AnnexinV and sub-G1 assay), cell cycle distribution (nuclear PI staining), DNA damage (alkaline comet or gH2A.X assay), proliferation inhibition (BrdU assay), reproductive survival (clonogenic assay), and potential tumour stem cells (nestin^pos/GFAP^neg fluorescence staining). Potential treatment-induced neurotoxicity was evaluated on nestin-positive neural progenitor cells in a murine entorhinal-hippocampal slice culture model.

Results

SAR showed radiosensitizing effects on the induction of apoptosis and on the reduction of long-term survival in p53-mut and p53-wt glioblastoma cell lines and primary cells. In p53-mut cells, this effect was accompanied by an abrogation of the IR-induced G2/M arrest and an enhancement of IR-induced DNA damage by SAR treatment. Also TMZ and 5-aza-dC acted radioadditively albeit to a lesser extent. The multimodal treatment achieved the most effective reduction of clonogenicity in all tested cell lines and did not affect the ratio of nestin^pos/GFAP^neg cells. No neurotoxic effects were detected when the number of nestin-positive neural progenitor cells remained unchanged after multimodal treatment.

Conclusion

The Chk1 inhibitor SAR-020106 is a potent sensitizer for DNA damage-induced cell death in glioblastoma therapy strongly reducing clonogenicity of tumour cells. Selectively enhanced p53-mut cell death may provide stronger responses in tumours defective of non-homologous end joining (NHEJ). Our results suggest that a multimodal therapy involving DNA damage inducers and DNA repair inhibitors might be an effective anti-tumour strategy with a low risk of neurotoxicity.

Carnosine inhibits glioblastoma growth independent from PI3K/Akt/mTOR signaling

Glioblastoma is a high-grade glioma with poor prognosis even after surgery and standard therapy. Here, we asked whether carnosine (β-alanyl-L-histidine), a naturally occurring dipeptide, exert its anti-neoplastic effect on glioblastoma cells via PI3K/Akt/mTOR signaling. Therefore, glioblastoma cells from the lines U87 and T98G were exposed to carnosine, to the mTOR inhibitor rapamycin and to the PI3K inhibitor Ly-294,002. Pyruvate dehydrogenase kinase (PDK4) expression, known to be a target of PI3K/Akt/mTOR, and which is also affected by carnosine, was analyzed by RT-qPCR, and reporter gene assays with the human PDK4 promoter were performed. Cell viability was assessed by cell-based assays and mTOR and Akt phosphorylation by Western blotting. Rapamycin and Ly-294,002 increased PDK4 mRNA expression in both cell lines but significance was only reached in U87. Carnosine significantly increased expression in both lines. A significant combinatorial effect of carnosine was only detected in U87 when the dipeptide was combined with Ly-294,002. Reporter gene assays revealed no specific effect of carnosine on the human PDK4 promoter, whereas both inhibitors increased reporter gene expression. Rapamycin reduced phosphorylation of mTOR, and Ly-294,002 that of Akt. A significant reduction of Akt phosphorylation was observed in the presence of carnosine in U87 but not in T98G, and carnosine had no effect on mTOR phosphorylation. Cell viability as determined by ATP in cell lysates was reduced only in the presence of carnosine. We conclude that carnosine’s anti-neoplastic effect is independent from PI3K/Akt/mTOR signaling. As the dipeptide reduced viability in tumor cells that do not respond to PI3K or mTOR inhibitors, it appears to be worth to further investigate the mechanisms by which carnosine exerts its anti-tumor effect and to consider it for therapy, especially as it is a naturally occurring compound that has already been used for the treatment of other diseases without indication of side-effects.

The proton-coupled oligopeptide transporters PEPT2, PHT1 and PHT2 mediate the uptake of carnosine in glioblastoma cells

The previous studies demonstrated that carnosine (β-alanyl-L-histidine) inhibits the growth of tumor cells in vitro and in vivo. Considering carnosine for the treatment of glioblastoma, we investigated which proton-coupled oligopeptide transporters (POTs) are present in glioblastoma cells and how they contribute to the uptake of carnosine. Therefore, mRNA expression of the four known POTs (PEPT1, PEPT2, PHT1, and PHT2) was examined in three glioblastoma cell lines, ten primary tumor cell cultures, in freshly isolated tumor tissue and in healthy brain. Using high-performance liquid chromatography coupled to mass spectrometry, the uptake of carnosine was investigated in the presence of competitive inhibitors and after siRNA-mediated knockdown of POTs. Whereas PEPT1 mRNA was not detected in any sample, expression of the three other transporters was significantly increased in tumor tissue compared to healthy brain. In cell culture, PHT1 expression was comparable to expression in tumor tissue, PHT2 exhibited a slightly reduced expression, and PEPT2 expression was reduced to normal brain tissue levels. In the cell line LN405, the competitive inhibitors β-alanyl-L-alanine (inhibits all transporters) and L-histidine (inhibitor of PHT1/2) both inhibited the uptake of carnosine. SiRNA-mediated knockdown of PHT1 and PHT2 revealed a significantly reduced uptake of carnosine. Interestingly, despite its low expression at the level of mRNA, knockdown of PEPT2 also resulted in decreased uptake. In conclusion, our results demonstrate that the transporters PEPT2, PHT1, and PHT2 are responsible for the uptake of carnosine into glioblastoma cells and full function of all three transporters is required for maximum uptake.

Assessment of ApoC1, LuzP6, C12orf75 and OCC-1 in cystic glioblastoma using MALDI-TOF mass spectrometry, immunohistochemistry and qRT-PCR

Mass spectrometric analysis of glioblastoma cyst fluids has disclosed a protein peak with m/z 6424–6433. Among the proteins, potentially generating this peak are ApoC1 and LuzP6. To further elucidate protein expression of glioblastoma cells, we analyzed MALDI–TOF results of cyst fluid, performed immunohistochemistry and mRNA analysis. MALDI–TOF protein extraction from 24 glioblastoma cyst fluids was performed with a weak cation exchange. 50 glioblastoma samples were stained with two custom-made antibodies against LuzP6 and commercial antibodies against ApoC1, C12orf75 and OCC-1 and analyzed. For mRNA detection, 16 tissue samples were stored in RNAlater, extracted using the miRNeasy kit and reversely transcribed. For 12 patients, synopsis of results from all three examinations was possible. MALDI–TOF confirmed the peak at 6433 Da in 75% of samples. Immunohistochemically, LuzP6 was detected in 92% (LuzP6_1–29) and 96% (LuzP6_30–58) of samples and ApoC1 in 66%. Mean mRNA levels were highest for ApoC1, followed by LuzP6. No correlation between mRNA expression, immunohistochemical staining and intensity of the MALDI–TOF peaks was found. An unequivocal identification of one protein as the source for the 6433 peak is not possible, but our results point to ApoC1 and LuzP6 as the underlying proteins.

β-Catenin and Yes-Associated Protein 1 Cooperate in Hepatoblastoma Pathogenesis

Hepatoblastoma (HB), the most common pediatric primary liver neoplasm, shows nuclear localization of β-catenin and yes-associated protein 1 (YAP1) in almost 80% of the cases. Co-expression of constitutively active S127A-YAP1 and ΔN90 deletion-mutant β-catenin (YAP1-ΔN90-β-catenin) causes HB in mice. Because heterogeneity in downstream signaling is being identified owing to mutational differences even in the β-catenin gene alone, we investigated if co-expression of point mutants of β-catenin (S33Y or S45Y) with S127A-YAP1 led to similar tumors as YAP1-ΔN90-β-catenin. Co-expression of S33Y/S45Y-β-catenin and S127A-YAP1 led to activation of Yap and Wnt signaling and development of HB, with 100% mortality by 13 to 14 weeks. Co-expression with YAP1-S45Y/S33Y-β-catenin of the dominant-negative T-cell factor 4 or dominant-negative transcriptional enhanced associate domain 2, the respective surrogate transcription factors, prevented HB development. Although histologically similar, HB in YAP1-S45Y/S33Y-β-catenin, unlike YAP1-ΔN90-β-catenin HB, was glutamine synthetase (GS) positive. However, both ΔN90-β-catenin and point-mutant β-catenin comparably induced GS-luciferase reporter in vitro. Finally, using a previously reported 16-gene signature, it was shown that YAP1-ΔN90-β-catenin HB tumors exhibited genetic similarities with more proliferative, less differentiated, GS-negative HB patient tumors, whereas YAP1-S33Y/S45Y-β-catenin HB exhibited heterogeneity and clustered with both well-differentiated GS-positive and proliferative GS-negative patient tumors. Thus, we demonstrate that β-catenin point mutants can also collaborate with YAP1 in HB development, albeit with a distinct molecular profile from the deletion mutant, which may have implications in both biology and therapy.

The Wnt/β-catenin pathway determines the predisposition and efficiency of liver-to-pancreas reprogramming

Transdifferentiation (TD) is the direct reprogramming of adult cells into cells of alternate fate and function. We have previously shown that liver cells can be transdifferentiated into beta-like, insulin-producing cells through ectopic expression of pancreatic transcription factors (pTFs). However, the efficiency of the process was consistently limited to <15% of the human liver cells treated in culture. The data in the current study suggest that liver-to-pancreas TD is restricted to a specific population of liver cells that is predisposed to undergo reprogramming. We isolated TD-predisposed subpopulation of liver cells from >15 human donors using a lineage tracing system based on the Wnt response element, part of the pericentral-specific promoter of glutamine synthetase. The cells, that were propagated separately, consistently exhibited efficient fate switch and insulin production and secretion in >60% of the cells upon pTF expression. The rest of the cells, which originated from 85% of the culture, resisted TD. Both populations expressed the ectopic pTFs with similar efficiencies, followed by similar repression of hepatic genes. Our data suggest that the TD-predisposed cells originate from a distinct population of liver cells that are enriched for Wnt signaling, which is obligatory for efficient TD. In TD-resistant populations, Wnt induction is insufficient to induce TD. An additional step of chromatin opening enables TD of these cells.

CONCLUSION

Liver-to-pancreas TD occurs in defined predisposed cells. These cells' predisposition is maintained by Wnt signaling that endows the cells with the plasticity needed to alter their transcriptional program and developmental fate when triggered by ectopic pTFs. These results may have clinical implications by drastically increasing the efficacy of TD in future clinical uses. (Hepatology 2018).

Carnosine selectively inhibits migration of IDH-wildtype glioblastoma cells in a co-culture model with fibroblasts

Background

Glioblastoma (GBM) is a tumor of the central nervous system. After surgical removal and standard therapy, recurrence of tumors is observed within 6–9 months because of the high migratory behavior and the infiltrative growth of cells. Here, we investigated whether carnosine (β-alanine-l-histidine), which has an inhibitory effect on glioblastoma proliferation, may on the opposite promote invasion as proposed by the so-called “go-or-grow concept”.

Methods

Cell viability of nine patient derived primary (isocitrate dehydrogenase wildtype; IDH1R132H non mutant) glioblastoma cell cultures and of eleven patient derived fibroblast cultures was determined by measuring ATP in cell lysates and dehydrogenase activity after incubation with 0, 50 or 75 mM carnosine for 48 h. Using the glioblastoma cell line T98G, patient derived glioblastoma cells and fibroblasts, a co-culture model was developed using 12 well plates and cloning rings, placing glioblastoma cells inside and fibroblasts outside the ring. After cultivation in the presence of carnosine, the number of colonies and the size of the tumor cell occupied area were determined.

Results

In 48 h single cultures of fibroblasts and tumor cells, 50 and 75 mM carnosine reduced ATP in cell lysates and dehydrogenase activity when compared to the corresponding untreated control cells. Co-culture experiments revealed that after 4 week exposure to carnosine the number of T98G tumor cell colonies within the fibroblast layer and the area occupied by tumor cells was reduced with increasing concentrations of carnosine. Although primary cultured tumor cells did not form colonies in the absence of carnosine, they were eliminated from the co-culture by cell death and did not build colonies under the influence of carnosine, whereas fibroblasts survived and were healthy.

Conclusions

Our results demonstrate that the anti-proliferative effect of carnosine is not accompanied by an induction of cell migration. Instead, the dipeptide is able to prevent colony formation and selectively eliminates tumor cells in a co-culture with fibroblasts.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0611-2) contains supplementary material, which is available to authorized users.

Pyruvate attenuates the anti-neoplastic effect of carnosine independently from oxidative phosphorylation

Here we analyzed whether the anti-neoplastic effect of carnosine, which inhibits glycolytic ATP production, can be antagonized by ATP production via oxidative phosphorylation fueled by pyruvate. Therefore, glioblastoma cells were cultivated in medium supplemented with glucose, galactose or pyruvate and in the presence or absence of carnosine. CPI-613 was employed to inhibit the entry of pyruvate into the tricarboxylic acid cycle and 2,4-dinitrophenol to inhibit oxidative phosphorylation. Energy metabolism and viability were assessed by cell based assays and histochemistry.ATP in cell lysates and dehydrogenase activity in living cells revealed a strong reduction of viability under the influence of carnosine when cells received glucose or galactose but not in the presence of pyruvate. CPI-613 and 2,4-dinitrophenol reduced viability of cells cultivated in pyruvate, but no effect was seen in the presence of glucose. No effect of carnosine on viability was observed in the presence of glucose and pyruvate even in the presence of 2,4-dinitrophenol or CPI-613.In conclusion, glioblastoma cells produce ATP from pyruvate via the tricarboxylic acid cycle and oxidative phosphorylation in the absence of a glycolytic substrate. In addition, pyruvate attenuates the anti-neoplastic effect of carnosine, even when ATP production via tricarboxylic acid cycle and oxidative phosphorylation is blocked. We also observed an inhibitory effect of carnosine on the tricarboxylic acid cycle and a stimulating effect of 2,4-dinitrophenol on glycolytic ATP production.

Phenotypic Screen Identifies a Small Molecule Modulating ERK2 and Promoting Stem Cell Proliferation

Stem cells display a fundamentally different mechanism of proliferation control when compared to somatic cells. Uncovering these mechanisms would maximize the impact in drug discovery with a higher translational applicability. The unbiased approach used in phenotype-based drug discovery (PDD) programs can offer a unique opportunity to identify such novel biological phenomenon. Here, we describe an integrated phenotypic screening approach, employing a combination of in vitro and in vivo PDD models to identify a small molecule increasing stem cell proliferation. We demonstrate that a combination of both in vitro and in vivo screening models improves hit identification and reproducibility of effects across various PDD models. Using cell viability and colony size phenotype measurement we characterize the structure activity relationship of the lead molecule, and identify that the small molecule inhibits phosphorylation of ERK2 and promotes stem cell proliferation. This study demonstrates a PDD approach that employs combinatorial models to identify compounds promoting stem cell proliferation.

Metabolic response of glioblastoma cells associated with glucose withdrawal and pyruvate substitution as revealed by GC-MS

BACKGROUND

Tumor cells are highly dependent on glucose even in the presence of oxygen. This concept called the Warburg effect is a hallmark of cancer and strategies are considered to therapeutically exploit the phenomenon such as ketogenic diets. The success of such strategies is dependent on a profound understanding of tumor cell metabolism. With new techniques it is now possible to thoroughly analyze the metabolic responses to the withdrawal of substrates and their substitution by others. In the present study we used gas chromatography coupled to mass spectrometry (GC-MS) to analyze how glioblastoma brain tumor cells respond metabolically when glucose is withdrawn and substituted by pyruvate.

METHODS

Glioblastoma brain tumor cells were cultivated in medium with high (25 mM), medium (11 mM) or low (5.5 mM) glucose concentration or with pyruvate (5 mM). After 24 h GC-MS metabolite profiling was performed.

RESULTS

The abundances of most metabolites were dependent on the supply of glucose in tendency but not in a linear manner indicating saturation at high glucose. Noteworthy, a high level of sorbitol production and release was observed at high concentrations of glucose and high release of alanine, aspartate and citrate were observed when glucose was substituted by pyruvate. Intermediates of the TCA cycle were present under all nutritional conditions and evidence was found that cells may perform gluconeogenesis from pyruvate.

CONCLUSIONS

Our experiments reveal a high plasticity of glioblastoma cells to changes in nutritional supply which has to be taken into account in clinical trials in which specific diets are considered for therapy.

Specific inhibition by synthetic analogs of pyruvate reveals that the pyruvate dehydrogenase reaction is essential for metabolism and viability of glioblastoma cells

The pyruvate dehydrogenase complex (PDHC) and its phosphorylation are considered essential for oncotransformation, but it is unclear whether cancer cells require PDHC to be functional or silenced. We used specific inhibition of PDHC by synthetic structural analogs of pyruvate to resolve this question. With isolated and intramitochondrial PDHC, acetyl phosphinate (AcPH, K_i^AcPH = 0.1 μM) was a much more potent competitive inhibitor than the methyl ester of acetyl phosphonate (AcPMe, K_i^AcPMe = 40 μM). When preincubated with the complex, AcPH also irreversibly inactivated PDHC. Pyruvate prevented, but did not reverse the inactivation. The pyruvate analogs did not significantly inhibit other 2-oxo acid dehydrogenases. Different cell lines were exposed to the inhibitors and a membrane-permeable precursor of AcPMe, dimethyl acetyl phosphonate, which did not inhibit isolated PDHC. Using an ATP-based assay, dependence of cellular viability on the concentration of the pyruvate analogs was followed. The highest toxicity of the membrane-permeable precursor suggested that the cellular action of charged AcPH and AcPMe requires monocarboxylate transporters. The relevant cell-specific transcripts extracted from Gene Expression Omnibus database indicated that cell lines with higher expression of monocarboxylate transporters and PDHC components were more sensitive to the PDHC inhibitors. Prior to a detectable antiproliferative action, AcPH significantly changed metabolic profiles of the investigated glioblastoma cell lines. We conclude that catalytic transformation of pyruvate by pyruvate dehydrogenase is essential for the metabolism and viability of glioblastoma cell lines, although metabolic heterogeneity causes different cellular sensitivities and/or abilities to cope with PDHC inhibition.

Understanding cytoskeleton regulators in glioblastoma multiforme for therapy design

The cellular cytoskeleton forms the primary basis through which a cell governs the changes in size, shape, migration, proliferation, and forms the primary means through which the cells respond to their environment. Indeed, cell and tissue morphologies are used routinely not only to grade tumors but also in various high-content screening methods with an aim to identify new small molecules with therapeutic potential. This study examines the expression of various cytoskeleton regulators in glioblastoma multiforme (GBM). GBM is a very aggressive disease with a low life expectancy even after chemo- and radiotherapy. Cancer cells of GBM are notorious for their invasiveness, ability to develop resistance to chemo- and radiotherapy, and to form secondary site tumors. This study aims to gain insight into cytoskeleton regulators in GBM cells and to understand the effect of various oncology drugs, including temozolomide, on cytoskeleton regulators. We compare the expression of various cytoskeleton regulators in GBM-derived tumor and normal tissue, CD133-postive and -negative cells from GBM and neural cells, and GBM stem-like and differentiated cells. In addition, the correlation between the expression of cytoskeleton regulators with the clinical outcome was examined to identify genes associated with longer patient survival. This was followed by a small molecule screening with US Food and Drug Administration (FDA)-approved oncology drugs, and its effect on cellular cytoskeleton was compared to treatment with temozolomide. This study identifies various groups of cytoskeletal regulators that have an important effect on patient survival and tumor development. Importantly, this work highlights the advantage of using cytoskeleton regulators as biomarkers for assessing prognosis and treatment design for GBM.

Global increase of p16INK4a in APC-deficient mouse liver drives clonal growth of p16INK4a-negative tumors

Reduction of β-catenin (CTNNB1) destroying complex components, for example, adenomatous polyposis coli (APC), induces β-catenin signaling and subsequently triggers activation of genes involved in proliferation and tumorigenesis. Though diminished expression of APC has organ-specific and threshold-dependent influence on the development of liver tumors in mice, the molecular basis is poorly understood. Therefore, a detailed investigation was conducted to determine the underlying mechanism in the development of liver tumors under reduced APC levels. Mouse liver at different developmental stages was analyzed in terms of β-catenin target genes including Cyp2e1, Glul, and Ihh using real-time RT-PCR, reporter gene assays, and immunohistologic methods with consideration of liver zonation. Data from human livers with mutations in APC derived from patients with familial adenomatous polyposis (FAP) were also included. Hepatocyte senescence was investigated by determining p16(INK4a) expression level, presence of senescence-associated β-galactosidase activity, and assessing ploidy. A β-catenin activation of hepatocytes does not always result in β-catenin positive but unexpectedly also in mixed and β-catenin-negative tumors. In summary, a senescence-inducing program was found in hepatocytes with increased β-catenin levels and a positive selection of hepatocytes lacking p16(INK4a), by epigenetic silencing, drives the development of liver tumors in mice with reduced APC expression (Apc(580S) mice). The lack of p16(INK4a) was also detected in liver tumors of mice with triggers other than APC reduction.

IMPLICATIONS

Epigenetic silencing of p16(Ink4a) in selected liver cells bypassing senescence is a general principle for development of liver tumors with β-catenin involvement in mice independent of the initial stimulus.

The antineoplastic effect of carnosine is accompanied by induction of PDK4 and can be mimicked by L-histidine

Carnosine (β-alanyl-L-histidine) is a naturally occurring dipeptide that shows antineoplastic effects in cell culture as well as in animal experiments. Since its mode of action and the targets at the molecular level have not yet been elucidated, we performed qRT-PCR experiments with RNA isolated from glioblastoma cell lines treated with carnosine, β-alanine, L-alanine, L-histidine and the dipeptide L-alanine-L-histidine. The experiments identified a strong induction of expression of the gene encoding pyruvate dehydrogenase 4 (PDK4) under the influence of carnosine and L-histidine, but not by the other substances employed. In addition, inhibition of cell viability was only detected in cells treated with carnosine and L-histidine, with the latter showing a significantly stronger effect than carnosine. Since the tumor cells expressed the tissue form of carnosinase (CN2) but almost no serum carnosinase (CN1), we conclude that cleavage by CN2 is a prerequisite for the antineoplastic effect of carnosine. In addition, enhanced expression of PDK4 under the influence of carnosine/L-histidine opens a new perspective for the interpretation of the ergogenic potential of dietary β-alanine supplementation and adds a new contribution to a growing body of evidence that single amino acids can regulate key metabolic pathways important in health and disease.

Organotypic slice cultures of human glioblastoma reveal different susceptibilities to treatments

BACKGROUND

Glioblastoma multiforme is the most common lethal brain tumor in human adults, with no major therapeutic breakthroughs in recent decades. Research is based mostly on human tumor cell lines deprived of their organotypic environment or inserted into immune-deficient animals required for graft survival. Here, we describe how glioblastoma specimens obtained from surgical biopsy material can be sectioned and transferred into cultures within minutes.

METHODS

Slices were kept in 6-well plates, allowing direct observation, application of temozolomide, and irradiation. At the end of experiments, slice cultures were processed for histological analysis including hematoxylin-eosin staining, detection of proliferation (Ki67), apoptosis/cell death (cleaved caspase 3, propidium iodide), DNA double-strand breaks (γH2AX), and neural subpopulations. First clinical trials employed irradiation with the heavy ion carbon for the treatment of glioblastoma patients, but the biological effects and most effective dose regimens remain to be established. Therefore, we developed an approach to expose glioblastoma slice cultures to (12)C and X-rays.

RESULTS

We found preservation of the individual histopathology over at least 16 days. Treatments resulted in activation of caspase 3, inhibition of proliferation, and cell loss. Irradiation induced γH2AX. In line with clinical observations, individual tumors differed significantly in their susceptibility to temozolomide (0.4%-2.5% apoptosis and 1%-15% cell loss).

CONCLUSION

Glioblastoma multiforme slice cultures provide a unique tool to explore susceptibility of individual tumors for specific therapies including heavy ions, thus potentially allowing more personalized treatments plus exploration of mechanisms of (and strategies to overcome) tumor resistance.

Transfection of normal human epidermal keratinocytes with lipid/dna complexes in vitro

Highly proliferative normal human epidermal keratinocytes (NHK) were isolated from human foreskin biopsies, cultivated in serum-free medium and characterized by flow cytometry. The expression of cytokeratin 19, cytokeratin 14 and vimentin indicated that the suspension contained a high percentage of undifferentiated cells of the basal epidermal layer. The NHK were transfected in vitro with lipid/DNA complexes made of Effectene or Lipofectamine and different reporter genes. The transfection efficiency of Effectene/DNA complexes was 20fold higher compared to Lipofectamine. Transfected keratinocytes continued to grow and developed within 2 weeks a cellular multilayer (3-D culture). Areas of transfected cells were detected within this layer.

Hedgehog signaling in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most malignant brain tumor in adults with a median survival of 14.6 mo under the best available treatment. New treatment strategies are therefore urgently required, for which a profound understanding of tumor biology is necessary. Much effort has been devoted to tumor-specific aberrant signaling processes. Recently it was discovered that the transcription factor Gli1, which is activated by hedgehog signaling, is a highly predictive marker in GBM, as determined by immunohistochemistry. To determine whether GBM cells have transcriptionally active Gli1, we performed experiments with reporter genes with cells isolated from surgically removed human tumors and cell lines. We also determined whether the hedgehog signaling inhibitor cyclopamine influences reporter gene expression and cell viability, and we determined the expression of Gli1, SHH and Patched1 by quantitative real-time RT-PCR. Reporter gene analysis of nine cultures and four cell lines demonstrated a significantly enhanced transcriptional activity in six tumor cell cultures and all cell lines. Analysis of cell viability in the presence of cyclopamine revealed a response of all cell cultures with the exception of one primary culture and one cell line, but only one cell line responded to cyclopamine with reduced hedgehog signaling activity. This indicates that the toxicity of cyclopamine toward GBM cells is independent from hedgehog signaling. Since no correlation between hedgehog activity and SHH, Gli1 and Patched1 mRNA levels was observed we conclude that other mechanisms aside from transcriptional regulation of these factors are responsible for hedgehog activity in tumor cells derived from GBM.

Differential and stereoselective in vitro cytotoxicity of eremophilane sesquiterpenes of Petasites hybridus rhizomes in rat hepatocytes

We tested two CO (2) extracts of Petasites hybridus L. rhizomes, A (rich in furanoeremophilanes) and B (rich in petasins), for IN VITRO cytotoxicity in rat hepatocytes by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay (EC (50) values of 0.64 mg/mL for A and 0.32 mg/mL for B). Eight eremophilane sesquiterpene lactones (SL) (1- 8) and one petasin (9) isolated from A were nontoxic or showed moderate cytotoxicity. The presence and type of the ester side chain most probably control the extent of cytotoxicity of the eremophilanolides. (8 R)-2-[(angeloyl)oxy]eremophil-7(11)-en-12,8-olide (1) damaged the hepatocytes most. The 8 α-stereoisomers of both 8-H epimeric couples of the 2-angeloyloxy- and 2-methacroyloxy-esters seem to be more cytotoxic (up to approx. 10-fold) than the corresponding 8 β-H stereoisomers. Moreover, the results of the MTT assay depended on the cell density being more pronounced with both 8 α-stereoisomers. Further investigations were conducted to study the influence of the stereochemistry on cell respiration, energy metabolism, and membrane integrity [release of lactate dehydrogenase (LDH)] with both couples of the 2-angeloyloxy- and 2-methacroyloxy-esters. In the LDH-leakage assay, (8 R)-2-[(methacroyl)oxy]eremophil-7(11)-en-12,8-olide (2) was the most toxic eremophilane. The stereoselectivity of cell damage of some SL points to a specific, yet unidentified molecular cytotoxicity target.

Alpha2-macroglobulin inhibits the malignant properties of astrocytoma cells by impeding beta-catenin signaling

Targets that could improve the treatment of brain tumors remain important to define. This study of a transformation-associated isoform of alpha2-macroglobulin (A2M*) and its interaction with the low-density lipoprotein receptor-related protein-1 (LRP1) suggests a new mechanism for abrogating the malignant potential of astrocytoma cells. LRP1 bound A2M* found to be associated with an inhibition of tumor cell proliferation, migration, invasion, spheroid formation, and anchorage-independent growth. Transcriptional studies implicated effects on the Wnt/beta-catenin signaling pathway. Notably, LRP1 antibodies could phenocopy the effects of A2M*. Our findings suggest a pathway of tumor suppression in astrocytoma that might be tractable to therapeutic exploitation.

Carnosine retards tumor growth in vivo in an NIH3T3-HER2/neu mouse model

Background

It was previously demonstrated that the dipeptide carnosine inhibits growth of cultured cells isolated from patients with malignant glioma. In the present work we investigated whether carnosine also affects tumor growth in vivo and may therefore be considered for human cancer therapy.

Results

A mouse model was used to investigate whether tumor growth in vivo can be inhibited by carnosine. Therefore, NIH3T3 fibroblasts, conditionally expressing the human epidermal growth factor receptor 2 (HER2/neu), were implanted into the dorsal skin of nude mice, and tumor growth in treated animals was compared to control mice. In two independent experiments nude mice that received tumor cells received a daily intra peritoneal injection of 500 μl of 1 M carnosine solution. Measurable tumors were detected 12 days after injection. Aggressive tumor growth in control animals, that received a daily intra peritoneal injection of NaCl solution started at day 16 whereas aggressive growth in mice treated with carnosine was delayed, starting around day 19. A significant effect of carnosine on tumor growth was observed up to day 24. Although carnosine was not able to completely prevent tumor growth, a microscopic examination of tumors revealed that those from carnosine treated animals had a significant lower number of mitosis (p < 0.0003) than untreated animals, confirming that carnosine affects proliferation in vivo.

Conclusion

As a naturally occurring substance with a high potential to inhibit growth of malignant cells in vivo, carnosine should be considered as a potential anti-cancer drug. Further experiments should be performed in order to understand how carnosine acts at the molecular level.

Carnosine inhibits ATP production in cells from malignant glioma

OBJECTIVES

Recently, it was revealed that carnosine inhibits growth of cells isolated from human malignant glioma. In order to understand how this effect is mediated, experiments were performed that addressed a possible influence of carnosine on energy metabolism.

METHODS

Cells from the glioma line T98G and primary cultured cells from human malignant glioma were cultivated in the presence of carnosine and inhibitors of cellular energy metabolism. As a specific inhibitor for anaerobic glycolysis, oxamate, and as an inhibitor for mitochondrial oxidative phosphorylation, potassium cyanide, were used, and the influence on ATP production was determined using cell-based assays.

RESULTS

The experiments identified glycolysis as crucial for ATP production in gliomas. In addition, ATP production by mitochondrial activity did not significantly contribute to ATP production and carnosine was identified to be an inhibitor of the vital anaerobic glycolysis.

DISCUSSION

Carnosine might be considered as a potential drug for the treatment of malignant glioma or other tumors since it inhibits the glycolytic energy metabolism that is crucial for cancer cells and malignant gliomas as shown in the current study. This is especially interesting since the dipeptide is a naturally occurring substance that should be well tolerated.

4-Aminoethylamino-emodin--a novel potent inhibitor of GSK-3beta--acts as an insulin-sensitizer avoiding downstream effects of activated beta-catenin

Glycogen synthase kinase-3β (GSK-3β) is a key target and effector of downstream insulin signalling. Using comparative protein kinase assays and molecular docking studies we characterize the emodin-derivative 4-[N-2-(aminoethyl)-amino]-emodin (L4) as a sensitive and potent inhibitor of GSK-3β with peculiar features. Compound L4 shows a low cytotoxic potential compared to other GSK-3β inhibitors determined by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay and cellular ATP levels. Physiologically, L4 acts as an insulin-sensitizing agent that is able to enhance hepatocellular glycogen and fatty acid biosynthesis. These functions are particularly stimulated in the presence of elevated concentrations of glucose and in synergy with the hormone action at moderate but not high insulin levels. In contrast to other low molecular weight GSK-3β inhibitors (SB216763 and LiCl) or Wnt-3α-conditioned medium, however, L4 does not induce reporter and target genes of activated β-catenin such as TOPflash, Axin2 and glutamine synthetase. Moreover, when present together with SB216763 or LiCl, L4 counteracts expression of TOPflash or induction of glutamine synthetase by these inhibitors. Because L4 slightly activates β-catenin on its own, these results suggest that a downstream molecular step essential for activation of gene transcription by β-catenin is also inhibited by L4. It is concluded that L4 represents a potent insulin-sensitizing agent favouring physiological effects of insulin mediated by GSK-3β inhibition but avoiding hazardous effects such as activation of β-catenin-dependent gene expression which may lead to aberrant induction of cell proliferation and cancer.

Real-time RT-PCR discriminating mRNA encoding osteocalcin from unspecific targets

Osteocalcin is a noncollagenous protein produced by osteoblasts and odontoblasts. It is used as a marker for bone formation in regenerative medical approaches. In addition, serum levels in humans are used to indicate bone turnover. Expression is usually determined by real-time reverse transcription PCR. Analysis of sequence data revealed that the frequently used primers for the determination of osteocalcin expression also detect the expression of messenger RNA (mRNA) encoding polyamine-modulated factor 1 (PMF1). In the present study we developed a method to determine the real amount of mRNA encoding osteocalcin. Bone-derived cells were treated with osteogenic differentiation medium and expression of osteocalcin was determined to test the method. It was found that the classic method that does not correct for PMF1 expression leads to overestimations as high as 70%.

Cytotoxicity of advanced glycation endproducts in human micro- and astroglial cell lines depends on the degree of protein glycation

Advanced glycation endproducts (AGEs) arise from the reaction of sugars with side chains and the N-terminus of proteins and are thought to be involved in the pathogenesis of several diseases by inducing oxidative stress, inflammation and cell death presumably mediated through activation of the receptor of AGE (RAGE). To address the question whether the cell damaging effect of AGE depends on the degree of its protein glycation, differential modified AGEs derived from incubating human serum albumin with increasing concentrations of methyl glyoxal were tested on cell viability, reactive oxygen species (ROS) formation, intracellular ATP levels, and activation of caspases 3/7 in two human glial cell lines, which were used as a model for human glia cells. All AGEs tested, regardless of their degree of modification, were found to induce ROS formation in both microglial (CHME-5) and astroglial cells (U373 MG), while only highly modified AGEs were able to decrease the cell viability and to induce apoptosis. This indicates that apoptotic events may be involved in the change of physiological parameters.

Correlation between beta-catenin mutations and expression of Wnt-signaling target genes in hepatocellular carcinoma

Aberrant Wnt-signaling caused by mutants of β-catenin, a key regulator of the canonical Wnt-signaling pathway, is frequently detected in cancer. Only recently, it was suggested that in hepatocellular carcinoma (HCC) the expression of the target gene glutamine synthetase (GS) is a highly reliable marker for the identification of β-catenin mutations. In order to prove this hypothesis, 52 samples from human hepatocellular carcinomas were analysed for the activation of β-catenin and the expression of GS. In total, 45 samples stained positive for cytoplasmic/nuclear β-catenin. A strong correlation between expression of GS and activated β-catenin (100% of nuclear and 84% of cytosolic) was found. However, among 35 GS positive tumors that were analysed for β-catenin mutations no mutations were detected in 25 GS-positive carcinomas although 24 out of the 25 carcinomas exhibited at least abnormal expression of β-catenin. Since the mutational analysis identified 9 different point mutations of the β-catenin gene including the rare mutation H36P and the yet unknown mutation P44A it was asked whether these mutations may differently effect β-catenin target genes. Therefore, expression plasmids for different mutations were constructed and cotransfected with the TOP-flash luciferase reporter and a reporter carrying the GS-5'-enhancer. The experiments confirmed that there are differences between different β-catenin target sequences and different β-catenin mutations. In addition, the failure that the endogenous expression of GS in GS-negative cells was not induced by the transient transfection experiment indicated that the effect of β-catenin on the GS-5'-enhancer is only one aspect of gene activation induced by β-catenin.

The expression of prolactin and its cathepsin D-mediated cleavage in the bovine corpus luteum vary with the estrous cycle

In the corpus luteum (CL), blood vessels develop, stabilize, and regress. This process depends on the ratio of pro- and antiangiogenic factors, which change during the ovarian cycle. The present study focuses on the possible roles of 23,000 (23K) prolactin (PRL) in the bovine CL and its antiangiogenic NH(2)-terminal fragments after extracellular cleavage by cathepsin D (Cath D). PRL RNA and protein were demonstrated in the CL tissue, in luteal endothelial cells, and in steroidogenic cells. Cath D was detected in CL tissue, cell extracts, and corresponding cell supernatants. In the intact CL, 23K PRL levels decreased gradually, whereas Cath D levels concomitantly increased between early and late luteal stages. In vitro, PRL cleavage occurred in the presence of acidified homogenates of CL tissue, cells, and corresponding cell supernatants. Similar fragments were obtained with purified Cath D, and their appearance was inhibited by pepstatin A. The aspartic protease specific substrate MOCAc-GKPILF~FRLK(Dnp)-D-R-NH(2) was cleaved by CL cell supernatants, providing further evidence for Cath D activity. The 16,000 PRL inhibited proliferation of luteal endothelial cells accompanied by an increase in cleaved caspase-3. In conclusion, 1) the bovine CL is able to produce PRL and to process it into antiangiogenic fragments by Cath D activity and 2) PRL cleavage might mediate angioregression during luteolysis.

Heme oxygenase-1 protein localizes to the nucleus and activates transcription factors important in oxidative stress

Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme degradation, is an integral membrane protein of the smooth endoplasmic reticulum. However, we detected an HO-1 immunoreactive signal in the nucleus of cultured cells after exposure to hypoxia and heme or heme/hemopexin. Under these conditions, a faster migrating HO-1 immunoreactive band was enriched in nuclear extracts, suggesting that HO-1 was cleaved to allow nuclear entry. This was confirmed by the absence of immunoreactive signal with an antibody against the C terminus and the lack of a C-terminal sequence by gas chromatographymass spectrometry. Incubation with leptomycin B prior to hypoxia abolished nuclear HO-1 and the faster migrating band on Western analysis, suggesting that this process was facilitated by CRM1. Furthermore, preincubation with a cysteine protease inhibitor prevented nuclear entry of green fluorescent protein-labeled HO-1, demonstrating that protease-mediated C-terminal cleavage was also necessary for nuclear transport of HO-1. Nuclear localization was also associated with reduction of HO activity. HO-1 protein, whether it was enzymatically active or not, mediated activation of oxidant-responsive transcription factors, including activator protein-1. Nevertheless, nuclear HO-1 protected cells against hydrogen peroxide-mediated injury equally as well as cytoplasmic HO-1. We speculate that nuclear localization of HO-1 protein may serve to up-regulate genes that promote cytoprotection against oxidative stress.

Hepatocellular expression of glutamine synthetase: an indicator of morphogen actions as master regulators of zonation in adult liver

Glutamine synthetase (GS) has long been known to be expressed exclusively in pericentral hepatocytes most proximal to the central veins of liver lobuli. This enzyme as well as its peculiar distribution complementary to the periportal compartment for ureogenesis plays an important role in nitrogen metabolism, particularly in homeostasis of blood levels of ammonium ions and glutamine. Despite this fact and intensive studies in vivo and in vitro, many aspects of the regulation of its activity on the protein and on the genetic level remained enigmatic. Recent experimental advances using transgenic mice and new analytic tools have revealed the fundamental role of morphogens such as wingless-type MMTV integration site family member signals (Wnt), beta-catenin, and adenomatous polyposis coli in the regulation of this particular enzyme. In addition, novel information concerning the structure of transcription factor binding sites within regulatory regions of the GS gene and their interactions with signalling pathways could be collected. In this review we focus on all aspects of the regulation of GS in the liver and demonstrate how the new findings have changed our view of the determinants of liver zonation. What appeared as a simple response of hepatocytes to blood-derived factors and local cellular interactions must now be perceived as a fundamental mechanism of adult tissue patterning by morphogens that were considered mainly as regulators of developmental processes. Though GS may be the most obvious indicator of morphogen action among many other targets, elucidation of the complex regulation of the expression of the GS gene could pave the road for a better understanding of the mechanisms involved in patterning of liver parenchyma. Based on current knowledge we propose a new concept of how morphogens, hormones and other factors may act in concert, in order to restrict gene expression to small subpopulations of one differentiated cell type, the hepatocyte, in different anatomical locations. Although many details of this regulatory network are still missing, and an era of exciting new discoveries is still about to come, it can already be envisioned that similar mechanisms may well be active in other organs contributing to the fine-tuning of organ-specific functions.

Hepatic expression of glutamine synthetase in rats is controlled by STAT5 and TCF transcription factors

In mammalian liver, high glutamine synthetase (GS) expression is restricted to hepatocytes surrounding the terminal venules. The most important enhancer of the GS gene is located approximately 2520 base pairs (bp) upstream from the transcriptional start point. The nature of the transcription factors that bind to the enhancers has remained enigmatic. In this study, we purified nuclear proteins binding to the element. Supershift assays and footprint experiments with purified protein identified activated STAT5 as a transcription factor binding to a site within the enhancer. In addition, a second binding site close to the STAT5 site was observed that also binds a protein present in nuclear extracts. Sequence analysis indicated that the second site may bind a member of the LEF/TCF transcription factor family. Reporter gene assays demonstrate that the STAT5 binding site mediates enhancement of expression whereas the LEF/TCF site functions as a silencer of growth hormone-mediated enhancement in normal hepatocytes. LEF/TCF-sites are known to function as silencers in the absence and as enhancers in the presence of activated beta-catenin. In conclusion, the GS 5' enhancer contains elements important for GS expression in cells carrying an activated form of beta-catenin as previously shown in experimentally induced hepatocellular carcinomas.

Dynamic Network Reconstruction from Gene Expression Data Describing the Effect of LiCl Stimulation on Hepatocytes

Wnt/β-catenin signalling plays an important role in zonation of liver parenchyma and in patterning of hepatocyte heterogeneity. A characteristic marker of this heterogeneity is glutamine synthetase, which is expressed only in a subset of pericentrally located hepatocytes. To investigate, whether and how the Wnt/β-catenin signalling pathway is involved a culture of hepatocytes was stimulated by LiCl. This resulted in an increase in the specific GS activity, indicating that the Wnt/β-catenin pathway may participate in regulating GS levels. Affymetrix GeneChip oligonucleotide arrays were used to monitor the gene expression changes during a period from 2 to 24 hours after stimulation by LiCl. Samples from a cultivation without stimulation were used as controls. Based on the gene expression profiles a hypothetic signal transduction network was constructed by a reverse engineering algorithm. The network robustness was tested and the most stable structure was identified.

An intronic silencer element is responsible for specific zonal expression of glutamine synthetase in the rat liver

The most striking phenomenon of glutamine synthetase (GS) expression in the liver is its unique restriction to cells surrounding the terminal hepatic venules. Expression is positively regulated by elements located in the 5'-upstream region and in the first intron of the gene. It was long believed that transcription factors present in GS-positive cells and absent in GS-negative cells are responsible for the phenomenon of zonal expression. However, strong enhancers are equally active in both types of cells. Therefore, the existence of a silencer mechanism in GS-negative hepatocytes was postulated. In the present study, a GS silencer element was investigated that was previously identified within the first intron and was shown to be able to prevent glucocorticoid-induced expression in cells negative for a transacting factor designated GS silencer element-binding protein. Reporter gene assays with the silencer element in combination with the most potent 5'-enhancer of the GS gene demonstrate that the silencer element is able to prevent enhancement mediated by the 5'-enhancer in combination with a heterologous as well as with the homologous promoter. More importantly, the effect of the silencer is shown to be restricted to GS-negative hepatocytes. In conclusion, the phenomenon of zonal expression of GS in the liver is caused by a protein present in GS-negative cells and absent in GS-positive cells that interacts with the silencer element in the first intron and not by a differential expression of enhancer-binding proteins.

Characterization of the human P-type 6-phosphofructo-1-kinase gene promoter in neural cell lines

In humans three isoforms of 6-phosphofructo-1-kinase (PFK) exist. Among them platelet-type PFK (PFKP) is highly abundant in the brain. With its distinct allosteric properties PFKP is regarded to be the key enzyme for the regulation of glycolysis in this organ. We cloned 1.7 kb of the 5' upstream promoter of the human PFKP gene and analyzed the promoter activity by deletion and mutation analysis using a luciferase reporter. The transcription start point was determined at 48 bp upstream of the start codon. In deletion studies the region -65 to +48 turned out to be sufficient for promoter activity while fragment -153 to +48 showed the highest promoter activity. Sequence analysis of the region from -153 to +48 revealed a stretch of eight adjacent putative transcription factor binding sites, seven of which are Sp-family specific sites. Sp1 and Sp3 were shown to bind to most if not all of them. Additionally, an NF-Y binding site was identified. Results of deletion and mutation analysis suggest that all of these transcription factors contribute positively to promoter activity. The methylation status of the promoter region was analyzed in different neural tumor cell lines and compared with that in human leukocytes and muscle.

A silencer element in the first intron of the glutamine synthetase gene represses induction by glucocorticoids

The enzyme glutamine synthetase (GS) ranks as one of the most remarkable glucocorticoid-inducible mammalian genes. In many tissues and cell lines, the synthetic glucocorticoid dexamethasone alone increases GS expression several fold. The direct response is mainly mediated by a cellular glucocorticoid receptor that, upon binding of the hormone, interacts with glucocorticoid responsive elements (GREs) of the gene. In cells of hepatocellular origin the response is mediated by a GRE located in the first intron of the gene. Surprisingly, hepatocytes do not respond to glucocorticoids with enhanced GS expression, despite the presence of an intact glucocorticoid receptor, which, in the same cells, stimulates expression of other genes such as tyrosine amino transferase. Reporter gene assays identified a sequence element downstream from the intronic GRE that inhibits the enhancement of expression by glucocorticoids. This silencer was designated GS silencer element of the rat. Gel mobility shift assays demonstrate the binding of a factor in hepatocyte nuclear extract. This yet unknown factor was designated GS silencer-binding protein. It is absent in FAO cells that respond to glucocorticoids with enhanced expression of GS and present in HepG2 cells that do not respond.

Cloning and expression of the rat BACE1 promoter

The pathogenic processing of the amyloid precursor protein (APP) into beta-amyloid peptides, which give rise to beta-amyloid plaques in the brains of Alzheimer's disease patients, requires the enzymatic activity of the beta-site APP-cleaving enzyme 1 (BACE1). We report the cloning and sequence of a 1.5-kb DNA fragment upstream of the coding sequence of the rat BACE1 gene and the construction of a BACE1 promoter/luciferase reporter construct. The basal activity of this promoter construct was highest in neuronal cell lines such as BE(2)-C and PC12 and in the pancreatic cell line AR42J, somewhat lower in rat primary neurons, and astrocytic and microglial cultures, very low in hepatocytes, and almost absent in fibroblasts and in the monocyte-macrophage cell line RAW264.7. The first 600 bp of this promoter are highly conserved among rat, mouse, and human, suggesting that this region contains regulatory elements that modulate BACE1 transcription. Indeed, this fragment contains several putative transcription factor binding sites such as MZF1, Sp1, four GATA-1 sites, and one YY1 site. Directed mutagenesis of GATA-1 elements led to altered luciferase expression, indicating that these sites are involved in the regulation of BACE1 transcription. Additionally, the analysis of promoter activities of deletion mutants suggests the presence of activators of BACE1 transcription between bases -514 to -753 and of suppressor elements between bases -754 and -1541. The BACE1 promoter sequence data and the constructs described here will be useful to identify factors that influence the expression of BACE1 in experimental paradigms in vitro.

HTS Compatible Assay for Antioxidative Agents Using Primary Cultured Hepatocytes

We have used primary cultured rat hepatocytes to establish a system that is compatible with HTS for screening substance libraries for biologically active compounds. The hepatocytes were treated with t-BHP to induce oxidative stress, leading to the formation ROS. The involvement of ROS in oxidative stress and pathological alterations has been of major interest in recent years, and there is great demand to identify new compounds with antioxidant potential. In most HTS programs each compound is tested in duplicate, and may only be tested once. Because of this it is important to develop assays that can identify candidate compounds accurately and with high confidence. Using newly available cell-based assay systems, we have developed a system that can detect active compounds (hits) with a high degree of confidence. As an example of an agent that can be detected from a substance library, we analyzed the effect of fisetin as an antioxidative compound using this system. All measurements were performed using the newly developed and highly versatile Multilabel-Reader Mithras LB 940 (Berthold Technologies, Bad Wildbad, Germany). The data presented show that all Z' factors determined were highly reliable. Although the protocol is primarily designed to screen for substances with antioxidative potential, it can easily be adapted to screen for other biologically active substances.