An extracellular proteasome-like structure from C6 astrocytoma cells with serine collagenase IV activity and metallo-dependent activity on alpha-casein and beta-insulin

Neurotrophic molecules in the treatment of neurodegenerative disease with focus on the retina: status and perspectives

Neurotrophic factors are operationally defined as molecules that promote the survival and differentiation of neurons. Chemically, they belong to divergent classes of molecules but most of the classic neurotrophic factors are proteins. Together with stem cells, viral vectors and genetically engineered cells, they constitute important tools in neuroprotective and regenerative neurobiology. Protein neurotrophic molecules signal through receptors located on the cell membrane. Their downstream signaling exploits pathways that are often common to chemically different factors and frequently target a relatively restricted set of transcription factors, RNA interference and diverse molecular machinery involved in the life vs. death decisions of neurons. Application of neurotrophic factors with the aim of curing or, at least, improving the outcome of neurodegenerative diseases requires (1) profound knowledge of the complex molecular pathology of the disease, (2) the development of animal models as closely as possible resembling the human disease, (3) the identification of target cells to be addressed, (4) intense efforts in chemical engineering to ensure the stability of molecules or to design carriers and small analogs with the ability to cross the blood-brain barrier and (5) scrutinity with regard to possible side effects. Last, but not least, engineering efforts to optimize administration, e.g., by designing the right canulae and infusion devices, are important for the successful translation of preclinical advances into clinical benefit. This article presents selected examples of neurotrophic factors that are currently being tested in animal models or developed for transfer to the clinic, with a major focus on factors with the potential of becoming applicable in various forms of retinal degeneration.

Alveolar extracellular 20S proteasome in patients with acute respiratory distress syndrome

RATIONALE

Repair mechanisms resulting in alveolar protein degradation in acute respiratory distress syndrome (ARDS) are largely unknown.

OBJECTIVES

To test whether the 20S proteasome is present and functional in the alveolar space in patients with ARDS.

METHODS

Proteasome antigenic concentration in bronchoalveolar lavage (BAL) supernatants was measured by ELISA in patients with ARDS (n = 64), acute lung injury (ALI) (n = 8), sarcoidosis (n = 13), and in healthy subjects (n = 8). Cleavage of specific fluorogenic substrates (+/-epoxomicin), I(125) albumin degradation rate, and gel filtration were used to quantify and characterize proteasomal activity. The presence of proteasomes was confirmed independently by electron microscopic techniques.

MEASUREMENTS AND MAIN RESULTS

Proteasome concentrations in patients with ARDS were markedly increased (1,069 +/- 1,194 ng/ml) in comparison to healthy subjects (60.8 +/- 49.8; P < 0.001), ALI (154 +/- 43; P = 0.006), and sarcoidosis (97.6 +/- 42.2; P = 0.037). All fluorogenic substrates were hydrolyzed (Suc-LLVY-AMC, 3.6 +/- 8.8 pkat/mg; BZ-VGR-AMC, 1.8 +/- 3.1; Suc-LLE-AMC, 1 +/- 1.7) by BAL supernatants of patients with ARDS, with inhibition by epoxomicin (P = 0.0001), and the majority of proteolytic activity was detected in BAL supernatant. Maximum hydrolyzing activity occurred at 660 kD and 20S proteasome was seen microscopically after purification and being released by pneumocytes type II. Proteasomal activity and albumin degradation rate in patients with ARDS were approximately 17-fold lower than in healthy subjects. Proteasomal activity in normal BAL was inhibited by BAL aliquots from patients with ARDS but not by denatured BAL, and returned to normal by purification.

CONCLUSIONS

For the first time, we identified extracellular, biologically active 20S proteasome in the alveolar space of patients with ARDS in concentrations much higher than in normal subjects or in those with ALI.

Signal integration in the galactose network of Escherichia coli

The gal regulon of Escherichia coli contains genes involved in galactose transport and metabolism. Transcription of the gal regulon genes is regulated in different ways by two iso-regulatory proteins, Gal repressor (GalR) and Gal isorepressor (GalS), which recognize the same binding sites in the absence of d-galactose. DNA binding by both GalR and GalS is inhibited in the presence of d-galactose. Many of the gal regulon genes are activated in the presence of the adenosine cyclic-3',5'-monophosphate (cAMP)-cAMP receptor protein (CRP) complex. We studied transcriptional regulation of the gal regulon promoters simultaneously in a purified system and attempted to integrate the two small molecule signals, d-galactose and cAMP, that modulate the isoregulators and CRP respectively, at each promoter, using Boolean logic. Results show that similarly organized promoters can have different input functions. We also found that in some cases the activity of the promoter and the cognate gene can be described by different logic gates. We combined the transcriptional network of the galactose regulon, obtained from our experiments, with literature data to construct an integrated map of the galactose network. Structural analysis of the network shows that at the interface of the genetic and metabolic network, feedback loops are by far the most common motif.

Extracellular proteasome in the human alveolar space: a new housekeeping enzyme?

We hypothesized that 20S proteasome is present and functional in the extracellular alveolar space in humans. Proteasomal activity was measured in bronchoalveolar lavage (BAL) supernatant from eight humans using specific proteasomal fluorogenic substrates and I(125)-albumin with and without specific proteasome inhibitors. Furthermore, gelfiltration, Western blot technique, and mass spectrometry were applied for proteasome characterization. All proteasomal fluorogenic substrates were hydrolyzed by BAL supernatant, with hydrolysis inhibited by epoxomicin (P = 0.024) and other proteasome inhibitors as well. E64, a lysosomal inhibitor, did not inhibit enzyme activity. The majority of proteolytic activity was detected in BAL supernatant rather than in the cell pellet. No correlation was found between proteasomal hydrolysis in BAL supernatant and lactate dehydrogenase activity, the total cell count in the cell pellet, and the fraction of avital cells in the cell pellet, ruling out cell lysis as a major source of proteasomal activity. Gelfiltration revealed hydrolyzing activity in the supernatant at 660 kDa and proteasome core proteins after analysis by ESI-QqTOF mass spectrometry. Furthermore, Western blots using a polyclonal antibody against proteasomal alpha-/beta-subunits detected proteasomal proteins in the typical 20- to 30-kDa range in BAL supernatant. Incubation of BAL supernatant with I(125)-albumin showed a high mean cleavage rate (101.8 microg/ml x h lavage +/- 46 SD) that was inhibited by epoxomicin (P = 0.013) and was ATP and ubiquitin independent. We identified for the first time extracellular, biologically active, ATP- and ubiquitin-independent 20S proteasome in the human alveolar space, with a high albumin cleavage rate. Possibly, the proteasome assists in maintenance of a low intra-alveolar oncotic pressure and/or alveolar protein degradation.

Neurotrophins

Nerve growth factor was the first identified protein with anti-apoptotic activity on neurons. This prototypic neurotrophic factor, together with the three structurally and functionally related growth factors brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT3) and neurotrophin-4/5 (NT4/5), forms the neurotrophin protein family. Target T cells for neurotrophins include many neurons affected by neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and peripheral polyneuropathies. In addition, the neurotrophins act on neurons affected by other neurological and psychiatric pathologies including ischemia, epilepsy, depression and eating disorders. Work with cell cultures and animal models provided solid support for the hypothesis that neurotrophins prevent neuronal death. While no evidence exists that a lack of neurotrophins underlies the etiology of any neurodegenerative disease, these studies have spurred on hopes that neurotrophins might be useful symptomatic-therapeutic agents. However first clinical trials led to variable results and severe side effects were observed. For future therapeutic use of the neurotrophins it is therefore crucial to expand our knowledge about their physiological functions as well as their pharmacokinetic properties. A major challenge is to develop methods for their application in effective doses and in a precisely timed and localized fashion.

Dynamics of C6 astrocytoma invasion into three-dimensional collagen gels

OBJECTIVE

The dynamic mechanisms underlying the three-dimensional invasive paradigm of C6 astrocytoma cells has been assessed.

METHODS

Spheroids of C6 astrocytoma cells were implanted into three-dimensional collagen type I gels (vitrogen 100) and individual C6 astrocytoma cell invasion monitored. Time-lapsed videomicroscopy was used to assess the dynamic components of cell invasion in three dimensions while scanning and transmission electron microscopy were used to assess matrix architecture and the static aspects of cell invasion.

RESULTS

Videomicroscopy outlined an invasion paradigm continuum with repeating phases. A cell surface ruffling phase was followed by invadopodia extension and pull up phases. For some cells the collagen type I matrix extracellular matrix appeared to modify the ability of C6 cells to carry out their invasion paradigm.

CONCLUSIONS

C6 astrocytoma cells invading a three-dimensional collagen type I matrix utilize a invasion paradigm made up of a number of phases. A better understanding of the dynamic invasion paradigms of malignant glial cells may be useful in the development of effective treatment strategies to prevent or modify malignant glioma invasion.

The expression and activation of matrix metalloproteinase-2 in rat brain after implantation of C6 rat glioma cells

It has been reported that matrix metalloproteinases (MMPs) are highly expressed in malignant glioma cells and that this increased expression may facilitate the invasiveness of tumor cells. The authors investigated the expression and enzymatic activity of MMPs in rat brain during the growth of malignant gliomas at different time intervals. C6 rat glioma cells were unilaterally implanted into rat cerebral hemispheres. After 7 or 14 days, these brain tissues were prepared for SDS-PAGE zymography, Western blotting, immunohistochemistry, and in situ zymography. SDS-PAGE zymography and Western blotting revealed that the expression of proMMP-2 in rat brains with C6 glioma cells was significantly higher than that in normal or the sham-operated rat brains, and that the activated form of MMP-2 was detected only in the former but not in the latter. On immunohistochemistry, C6 glioma cells presenting invasive growth into the rat brain parenchyma and vessels demonstrated MMP-2 immunoreactivity. On in situ zymography, foci of invasive C6 glioma cells in rat brain tissue showed gelatinolytic activity. These results suggest that expression and activation of MMP-2 may be one of the crucial steps for glioma cell invasion into the brain parenchyma in vivo.

Validation of a rat pheochromocytoma (PC12)-based cell survival assay for determining biological potency of recombinant human nerve growth factor

A method has been validated, according to the Guidelines of the International Conference on Harmonization (ICH), for precise quantitation of the biological activity of recombinant human nerve growth factor (rhNGF) for lot release testing. The assay is based on the survival of a subclone of rat pheochromocytoma PC12 cells (PC12-CF) in response to rhNGF. Cell survival is measured by monitoring the reduction, by living cells, of the alamarBlue dye into a red form which is highly fluorescent. The assay is simple, has high throughput (performed in 96-well microtiter plates) and shows reproducible dose-response curves in the concentration range of 0.2-50 ng/ml. The method was validated for its linearity, accuracy, precision, robustness, and to meet current regulatory requirements. The assay demonstrated good linearity, yielding a coefficient of determination of 0.9902. Sample recovery studies demonstrated an accuracy ranging from 96 to 98%. The repeatability of the assay and intermediate precision had coefficients of variation (CV) of <9%. The assay was stability-indicating since it was able to detect changes in rhNGF samples degraded by protease treatment and in a number of isolated rhNGF variants. Robustness was demonstrated by the relative insensitivity of the assay to small deliberate changes in key method parameters. The validation data, provided in this manuscript, indicate that the newly described bioassay for rhNGF is robust, accurate, precise, and suitable for lot release potency testing of rhNGF.

Sugar transporters from bacteria, parasites and mammals: structure-activity relationships

Sugar transport across the plasma membrane is one of the most important transport processes. The cloning and expression of cDNAs from a superfamily of related sugar transporters that all adopt a 12-membrane-spanning-domain structure has opened new avenues of investigation, including presteady-state kinetic analysis. Structure-function analyses of mammalian and bacterial sugar transporters, and comparisons of these transporters with those of parasitic trypanosomatids, indicate that different environmental pressures have tailored the evolution of the various members of the sugar-transporter superfamily. Subtle distinctions in the function of these proteins can be related to particular amino acid residue substitutions.

The importance of cell density in the interpretation of growth factor effects on collagenase IV activity release and extracellular matrix production from C6 astrocytoma cells

We have examined the influence of basic fibroblast growth factor (FGF-2) and vascular endothelial growth factor (VEGF) on the release of collagenase type IV activity and the production of extracellular matrix (ECM) molecules using C6 astrocytoma cells in monolayer culture. Collagenase type IV activity was significantly increased in a dose dependent manner in the low cell density group by treatment with FGF-2 and VEGF but significantly decreased in a dose dependent fashion in the high cell density group. These results were corroborated using Western blot technique with an antibody to gelatinase A. Addition of exogenous laminin and fibronectin to the media decreased collagenase type IV activity in a dose dependent fashion with the minimum concentration of 0.1 microgram/ml. Laminin and fibronectin reached a concentration of 0.1 microgram/ml in only the high cell density group after treatment with the growth factors tested. These findings indicate that C6 astrocytoma cells appear to have two regulatory mechanisms for collagenase type IV activity which are dependent on cell density. In a low cell density, C6 astrocytoma cells respond to the dominant effect of FGF-2 and VEGF by increasing the release of collagenase IV activity. In a high cell density collagenase type IV activity is decreased due to it's down regulation by released ECM molecules in response to FGF-2 and VEGF. These regulatory mechanisms may be crucial to the understanding of the coordination of tumor-associated angiogenesis by malignant glial cells.

In vitro expression of MMP-2 and MMP-9 in glioma cells following exposure to inflammatory mediators

Progression of glioma is associated with local degenerative processes which are attributed to the activity of gelatinases. As glioma cells are candidate for secretion of these enzymes, we have studied in vitro the potential of cytokines (interleukin-1alpha (IL-1), tumor necrosis factor-alpha (TNFalpha) and transforming growth factor-beta (TGFbeta2)) to regulate the expression of gelatinase A and B (Gels A and B, respectively) in two glioma cells of human (A172) and rat origin (C6). We showed that IL-1 and TNFalpha both induced gene expression and protein secretion of Gel B in both cell lines, as revealed by RT-PCR and gelatin zymography, respectively. In C6 cells, TNFalpha had no effect on Gel A constitutive expression while IL-1 increased its production, but only at high doses. We have also demonstrated that TGFbeta2 inhibited both IL-1- or TNFalpha-induced gene expression and Gel B production in a dose-dependent manner but had no effect on Gel A secretion. The effect of TGFbeta2 on Gel B secretion was reversed by phorbol myristate acetate (PMA). Taken together, these data suggest that IL-1, TNFalpha and TGFbeta2 tightly regulate Gel B secretion in glioma cells, an enzyme which is believed to play an important role in the local invasion of brain tissue by tumor cells.

Implantation of C6 astrocytoma spheroid into collagen type I gels: invasive, proliferative, and enzymatic characterizations

A three-dimensional model has been developed in which C6 astrocytoma spheroids of defined sizes are embedded into collagen type I gels. The authors have monitored cell invasive behavior; obtained quantitative data on cell invasion, proliferation, and enzymatic activity; assessed cell-cell interactions by altering the spheroid size used; and studied cell-matrix interactions by modifying the matrix components. Their results show that C6 astrocytoma cells detach from the spheroid surface and invade the gel as single cells by means of a system that appears to be dependent on metalloprotease function. These invasive cells have a low proliferative index. Larger spheroids with central hypoxic microregions possess cells that invade the gel at faster rates; this could be correlated with the release of increased collagen type I degrading activity. Extracellular matrix proteins, such as laminin, fibronectin, and collagen type IV have no significant influence on invasive activity, whereas hyaluronic acid decreases and human central nervous system myelin increases invasion. New strategies directed at the treatment of malignant gliomas must take into account the subpopulation of malignant cells located long distances from the major tumor mass. The spheroid invasion model may provide specific insights into the behavior of these invasive cells.

Mechanisms of glioma invasion: role of matrix-metalloproteinases

One of the most lethal properties of high grade gliomas is their ability to invade the surrounding normal brain tissue, as infiltrated cells often escape surgical resection and inevitably lead to tumour recurrence. The consequent poor prognosis and survival rate underscore the need to further understand and target the cellular mechanisms that underly tumour invasiveness. Proteases which degrade the surrounding stromal cells and extracellular matrix proteins have been demonstrated to be critical effectors of invasion for tumours of both central and peripheral origin. Within the nervous system, the role of metalloproteinases as well as other classes of proteases in mediating the invasive phenotype of high grade gliomas has been an intense area of research. We present in this article a review of this literature and address the possibility that these proteases and the biochemical pathways that regulate their expression, such as protein kinase C, may represent potential targets in the therapy of high grade gliomas.

Release of collagen type IV degrading activity from C6 astrocytoma cells and cell density

Type IV collagen is a major protein component of the vascular basement membrane and its degradation is crucial to the initiation of tumor-associated angiogenesis. The authors have investigated the influence of cell density on the release of collagen type IV degrading activity by C6 astrocytoma cells in monolayer culture. The release of collagen type IV degrading activity was assessed biochemically, immunocytochemically, and by Western blot analysis. The results demonstrate that increasing plating density and increasing cell density are associated with decreased collagen type IV degrading activity released per tumor cell. These findings indicate the existence of regulatory mechanisms dependent on cell-cell communication, which modulate release of collagen type IV degrading activity. The extrapolation of these results to the in vivo tumor microenvironment would suggest that individual and/or small groups of invading tumor cells, distant from the main tumor mass, would release substantial collagen type IV degrading activity, which may be crucial to their continued invasion and to angiogenesis.

Cytomegalovirus-caused release of collagenase IV from human cerebral microvascular endothelial cells

BACKGROUND

Human cytomegalovirus (HCMV) in most normal individuals results in an asymptomatic infection, but under some circumstances, such as in the transplant setting, AIDS and intrauterine infection of the fetus, HCMV infection can lead to more serious consequences, including central nervous system infection. Recently it has been demonstrated that HCMV-infected endothelial cells can be detected in the circulation; however, no mechanism has been suggested.

OBJECTIVE

To determine whether HCMV infection of confluent human microvascular endothelial cells (HMEC) in culture results in the induction of type IV collagenase. This would provide a mechanism by which HCMV-infected HMECs could be released into the circulation.

STUDY DESIGN

Confluent cultures of brain-derived HMECs were infected with HCMV and culture supernatants were sampled for collagenase IV, general protease and viral titers.

RESULTS

HCMV infection of HMECs stimulated a significant release of collagenase type IV activity which peaked early in the assay within 3-5 days and fell off rapidly thereafter. This stimulation of protease activity differed only slightly between non-infected and infected cultures. By day 6, viral cytopathic effects became evident and HCMV titers reached approximately 5 x 10(5) PFU/ml by day 9.

CONCLUSIONS

These results demonstrate that HCMV infection of HMEC induces the release of collagenase type IV. This may lead to the degradation of the basement membrane and subsequently to the release of fully infected endothelial cells into the circulation resulting in further dissemination of the infection.

Degradation of collagen type IV by C6 astrocytoma cells

The key event associated with the initiation of angiogenesis is the localized degradation of the vascular basement membrane. Because of its complex structure, any remodelling and/or modification of the basement membrane must involve the co-ordinated function of a number of different enzyme systems. Type IV collagen is a major protein component (60-90%) of the basement membrane and its degradation is crucial to the initiation of angiogenesis. This study has focused on the mechanisms by which C6 astrocytoma cells degrade human type IV collagen. C6 astrocytoma cells use components of two major degradative pathways to degrade collagen type IV. The major matrix metalloproteinase identified is the activated form (68-KDa) of gelatinase A (72-KDa matrix metalloproteinase) and a serine sensitive 1000-KDa collagenase type IV degrading activity which appears to have the characteristics of a novel extracellular proteasome.