Transformation of rat cerebral endothelial cells by Rous sarcoma virus

Heparan sulfate proteoglycans mediate Aβ-induced oxidative stress and hypercontractility in cultured vascular smooth muscle cells

BACKGROUND

Substantial evidence suggests that amyloid-β (Aβ) species induce oxidative stress and cerebrovascular (CV) dysfunction in Alzheimer's disease (AD), potentially contributing to the progressive dementia of this disease. The upstream molecular pathways governing this process, however, are poorly understood. In this report, we examine the role of heparan sulfate proteoglycans (HSPG) in Aβ-induced vascular smooth muscle cell (VSMC) dysfunction in vitro.

RESULTS

Our results demonstrate that pharmacological depletion of HSPG (by enzymatic degradation with active, but not heat-inactivated, heparinase) in primary human cerebral and transformed rat VSMC mitigates Aβ(1-40⁻) and Aβ(1-42⁻)induced oxidative stress. This inhibitory effect is specific for HSPG depletion and does not occur with pharmacological depletion of other glycosaminoglycan (GAG) family members. We also found that Aβ(1-40) (but not Aβ(1-42)) causes a hypercontractile phenotype in transformed rat cerebral VSMC that likely results from a HSPG-mediated augmentation in intracellular Ca(2+) activity, as both Aβ(1-40⁻)induced VSMC hypercontractility and increased Ca(2+) influx are inhibited by pharmacological HSPG depletion. Moreover, chelation of extracellular Ca(2+) with ethylene glycol tetraacetic acid (EGTA) does not prevent the production of Aβ(1-40⁻) or Aβ(1-42⁻)mediated reactive oxygen species (ROS), suggesting that Aβ-induced ROS and VSMC hypercontractility occur through different molecular pathways.

CONCLUSIONS

Taken together, our data indicate that HSPG are critical mediators of Aβ-induced oxidative stress and Aβ(1-40⁻)induced VSMC dysfunction.

Dynamic regulation of platelet-derived growth factor D (PDGF-D) activity and extracellular spatial distribution by matriptase-mediated proteolysis

The oncogenic roles of PDGF-D and its proteolytic activator, matriptase, have been strongly implicated in human prostate cancer. Latent full-length PDGF-D (FL-D) consists of a CUB domain, a growth factor domain (GFD), and the hinge region in between. Matriptase processes the FL-D dimer into a GFD dimer (GFD-D) in a stepwise manner, involving generation of a hemidimer (HD), an intermediate product containing one FL-D subunit and one GFD subunit. Although the HD is a pro-growth factor that can be processed into the GFD-D by matriptase, the HD can also act as a dominant-negative ligand that prevents PDGF-B-mediated β-PDGF receptor activation in fibroblasts. The active GFD-D can be further cleaved into a smaller and yet inactive form if matriptase-mediated proteolysis persists. Through mutagenesis and functional analyses, we found that the R(340)R(341)GR(343)A (P4-P1/P1') motif within the GFD is the matriptase cleavage site through which matriptase can deactivate PDGF-D. Comparative sequence analysis based on the published crystal structure of PDGF-B predicted that the matriptase cleavage site R(340)R(341)GR(343)A is within loop III of the GFD, a critical structural element for its binding with the β-PDGF receptor. Interestingly, we also found that matriptase processing regulates the deposition of PDGF-D dimer species into the extracellular matrix (ECM) with increased binding from the FL-D dimer, to the HD, and to the GFD-D. Furthermore, we provide evidence that R(340)R(341)GR(343)A within the GFD is critical for PDGF-D deposition and binding to the ECM. In this study, we report a structural element crucial for the biological function and ECM deposition of PDGF-D and provide molecular insight into the dynamic functional interplay between the serine protease matriptase and PDGF-D.

Spontaneously immortalised bovine mammary epithelial cells exhibit a distinct gene expression pattern from the breast cancer cells

BACKGROUND

Spontaneous immortalisation of cultured mammary epithelial cells (MECs) is an extremely rare event, and the molecular mechanism behind spontaneous immortalisation of MECs is unclear. Here, we report the establishment of a spontaneously immortalised bovine mammary epithelial cell line (BME65Cs) and the changes in gene expression associated with BME65Cs cells.

RESULTS

BME65Cs cells maintain the general characteristics of normal mammary epithelial cells in morphology, karyotype and immunohistochemistry, and are accompanied by the activation of endogenous bTERT (bovine Telomerase Reverse Transcriptase) and stabilisation of the telomere. Currently, BME65Cs cells have been passed for more than 220 generations, and these cells exhibit non-malignant transformation. The expression of multiple genes was investigated in BME65Cs cells, senescent BMECs (bovine MECs) cells, early passage BMECs cells and MCF-7 cells (a human breast cancer cell line). In comparison with early passage BMECs cells, the expression of senescence-relevant apoptosis-related gene were significantly changed in BME65Cs cells. P16INK4a was downregulated, p53 was low expressed and Bax/Bcl-2 ratio was reversed. Moreover, a slight upregulation of the oncogene c-Myc, along with an undetectable level of breast tumor-related gene Bag-1 and TRPS-1, was observed in BME65Cs cells while these genes are all highly expressed in MCF-7. In addition, DNMT1 is upregulated in BME65Cs. These results suggest that the inhibition of both senescence and mitochondrial apoptosis signalling pathways contribute to the immortality of BME65Cs cells. The expression of p53 and p16INK4a in BME65Cs was altered in the pattern of down-regulation but not "loss", suggesting that this spontaneous immortalization is possibly initiated by other mechanism rather than gene mutation of p53 or p16INK4a.

CONCLUSIONS

Spontaneously immortalised BME65Cs cells maintain many characteristics of normal BMEC cells and exhibit non-malignant transformation. Although this cell line displays altered patterns of gene expression, it is clearly distinct from malignant breast cancer cell line. It showed that co-inhibition of cellular senescence and mitochondrial apoptosis pathways coordinates BME65Cs cells immortalisation. Additionally, mechanisms other than gene mutation are likely to be involved in regulation of cellular functions. This study provides an insight into the relationship between cell senescence and immortalisation. BME65Cs cells will be useful in future studies of cellular senescence and tumorigenesis.

Immortalization of bovine mammary epithelial cells alone by human telomerase reverse transcriptase

Immortal bovine mammary epithelial cell lines are useful for providing an efficient indicator for transgene expression and for the technological improvement of genetic modification. The preparation of hTERT (human telomerase reverse transcriptase)-mediated immortalized MECs (mammary epithelial cells) requires a down-regulation of p16(INK4a). Here, we report the establishment of two immortal bovine MEC lines by expression of hTERT gene alone under serum-containing culture conditions. This two cell lines maintain the general characteristics of MECs and have been stably passed more than 200 generations accompanying telomere extension, and were identified as non-malignant transformation. Investigation on transcriptional profile showed a similar down-regulation in both p16(INK4a) and p53. By comparing with non-immortal hTERT-positive MECs, we speculated that there are some spontaneous p16(INK4a)-reduced cells under normal culture conditions and the immortalization required for a co-ordinate repression of p53 and p16(INK4a) signalling pathways. Interestingly, two immortal cell lines showed a significant distinction in proliferation rate, implying that other mechanisms might be involved in proliferation control.

Soluble amyloid-beta, effect on cerebral arteriolar regulation and vascular cells

Background

Evidence indicates that soluble forms of amyloid-β (Aβ) are vasoactive, which may contribute to cerebrovascular dysfunction noted in patients with Alzheimer's Disease and cerebral amyloid angiopathy. The effects of soluble Aβ on penetrating cerebral arterioles - the vessels most responsible for controlling cerebrovascular resistance - have not been studied.

Results

Freshly dissolved Aβ_1-40 and Aβ_1-42, but not the reverse peptide Aβ_40-1 constricted isolated rat penetrating arterioles and diminished dilation to adenosine tri-phosphate (ATP). Aβ_1-42 also enhanced ATP-induced vessel constriction. Aβ_1-40 diminished arteriolar myogenic response, and an anti-Aβ antibody reduced Aβ_1-40 induced arteriolar constriction. Prolonged Aβ exposure in vessels of Tg2576 mice resulted in a marked age-dependent effect on ATP-induced vascular responses. Vessels from 6 month old Tg2576 mice had reduced vascular responses whereas these were absent from 12 month old animals. Aβ_1-40 and Aβ_1-42 acutely increased production of reactive oxygen species (ROS) in cultured rat cerebro-microvascular cells. The radical scavenger MnTBAP attenuated this Aβ-induced oxidative stress and Aβ_1-40-induced constriction in rat arterioles.

Conclusions

Our results suggest that soluble Aβ_1-40 and Aβ_1-42 directly affect the vasomotor regulation of isolated rodent penetrating arterioles, and that ROS partially mediate these effects. Once insoluble Aβ deposits are present, arteriolar reactivity is greatly diminished.

[Cerebral transfer and neuroprotection]

In contrast to other vascular beds, the endothelial cells in brain capillaries, which constitute the blood-brain barrier, are sealed together by continuous tight junctions and have little transcellular vesicular transport. In addition to these morphological properties, the presence of specific enzymes and proteins highly restricts the passage of molecules from the blood to the brain. To provide an in vitro system for studying brain capillary functions, we have developed a process of coculture that closely mimics the in vivo situation by culturing brain capillary endothelial cells on one side of a filter and glial cells on the other. In these culture conditions, endothelial cells retain all the endothelial cell markers and the characteristics of the blood-brain barrier, including gamma-glutamyl transpeptidase and P-glycoprotein activities. Moreover, the close correlation between the results obtained in vitro with our model and in vivo allows us to conclude that our in vitro blood-brain barrier model is a relevant model for the screening of new molecules to the brain.

New approaches to in vitro models of blood-brain barrier drug transport

The pharmaceutical industry has been searching for an in vitro blood-brain barrier (BBB) model that preserves in vivo transporter functions in CNS drug discovery and development. The application of conditionally immortalized cell lines derived from transgenic animals harboring temperature-sensitive SV40 large T-antigen gene, is a rational and promising approach to such a workable in vitro BBB model. The established brain capillary endothelial cell lines retain the in vivo transport rate of several compounds and various forms of gene expression. Furthermore, this new approach has enabled the development of stable and reproducible co-culture models with a pericyte cell line and/or an astrocyte cell line.

Bacterial invasion and transcytosis in transfected human brain microvascular endothelial cells

Most cases of neonatal bacterial meningitis develop as a result of a hematogenous spread, but it is not clear how circulating bacteria cross the blood-brain barrier. Attempts to answer these questions have been hampered by the lack of a reliable model of the human blood-brain barrier. Human brain microvascular endothelial cells (HBMEC) were isolated and transfected with a pBR322 based plasmid containing simian virus 40 large T antigen (SV40-LT). The transfected HBMEC exhibited similar brain endothelial cell characteristics as the primary HBMEC, i.e. gamma glutamyl transpeptidase and a high transendothelial electrical resistance. Escherischia coli and Citrobacter spp, two important Gram-negative bacilli causing neonatal meningitis, were found to transcytose across primary and transfected HBMEC, without affecting the integrity of the monolayer. In addition, E. coli and C. freundii invaded transfected HBMEC as shown previously with primary HBMEC. We conclude that E. coli and C. freundii are able to invade and transcytose HBMEC and these bacterial-HBMEC interactions are similar between primary and transfected HBMEC. Therefore, our transfected HBMEC should be useful for studying pathogenesis of CNS infections.

gamma-Glutamyl transpeptidase. What does the organization and expression of a multipromoter gene tell us about its functions?

gamma-Glutamyl transpeptidase is a key enzyme in glutathione (GSH) salvage, metabolism of endogenous mediators such as leukotrienes and prostaglandins, detoxification of xenobiotics including environmentally important compounds and carcinogens, and cellular processes dependent on the oxidation/reduction of glutathione. The enzyme is widely distributed, and these functions often occur in separate tissues and in response to different stimuli. Evidence indicates that gamma-glutamyl transpeptidase plays a direct role in some hepatic and renal responses to injury. In the mouse gamma-glutamyl transpeptidase is a single copy gene expressed from at least seven promoters, and many of the transcribed gamma-glutamyl transpeptidase RNAs are restricted in their expression. Studies that combine analyses of cellular processes with a knowledge of gene structure and expression hold promise for unravelling how these two different levels of function are integrated.

Satellite I DNA in transformed rat cells

P93-50, a 93-basepair (bp) repetitive DNA sequence from rats, was hybridized to transformed sublines of rat endothelial origin. The sequence hybridized at or near the centromeres of most but not all chromosomes in two transformed cell lines and three single-cell derived cultures. The hybridization signal was also frequently present at the telomeres. These cell lines have a highly aberrant karyotype including dicentric and multicentric chromosomes; however, even though this sequence labeled the centromere regions of some chromosomes, it did not hybridize with the telomere regions of the cell line XC, which rarely shows any dicentrics. Apparently, the telomere signals represent prematurely separating, inactive, terminal centromeres. The p93-50 sequence does not influence the timing of centromere separation, nor it is necessary for formation of heterochromatin.

Regulation of gamma-glutamyl transpeptidase and alkaline phosphatase activities in immortalized rat brain microvessel endothelial cells

Rat brain microvessel endothelial cells were immortalized by transfection with a plasmid containing the E1A adenovirus gene. One clone, called RBE4, was further characterized. These cells display a nontransformed phenotype and express typical endothelial markers, Factor VIII-related antigen and Bandeiraea simplicifolia binding sites. When RBE4 cells were grown in the presence of bFGF and on collagen-coated dishes, confluent cultures developed sprouts that extend above the monolayer and organized into three-dimensional structures. The activity of the blood-brain barrier-associated enzyme, gamma-glutamyl transpeptidase (gamma GTP), was expressed in these structures, not in the surrounding monolayer. Similar results were obtained with the microvessel-related enzyme alkaline phosphatase (ALP). Addition of agents that elevate intracellular cAMP reduced the formation of three-dimensional structures, but every cell inside the aggregates still expressed gamma GTP and ALP activities. Such structures, associated with high levels of gamma GTP and ALP activities, were also induced by astroglial factors, including (1) plasma membranes from newborn rat primary astrocytes or rat glioma C6 cells, (2) C6 conditioned media, or (3) diffusible factors produced by primary astrocytes grown in the presence of, but not in contact with RBE4 cells. RBE4 cells thus remain sensitive to angiogenic and astroglial factors for the expression of the blood-brain barrier-related gamma GTP activity, as well as for ALP activity, and could constitute the basis of a valuable in vitro model of the blood-brain barrier.

The cerebral microvessels in culture, an update

Recent advances in our knowledge of the blood-brain barrier (BBB) have in part been made by studying the properties and function of cerebral endothelial cells in vitro. After an era of working with a fraction, enriched in cerebral microvessels by centrifugation, the next generation of in vitro BBB model systems was introduced, when the conditions for routinely culturing the endothelial cells were established. This review summarizes the results obtained from this rapidly growing field. It can be stated with certainty that, in addition to providing a better insight into the chemical composition of cerebral endothelial cells, much has been learned from these studies about the characteristics of transport processes and cell-to-cell interactions during the last 12 years. With the application of new technologies, the approach offers a new means of investigation, applicable not only to biochemistry and physiology but also to the drug research, and may improve the transport of substances through the BBB. The in vitro approach has been and should remain an excellent model of the BBB to help unravel the complex molecular interactions underlying and regulating the permeability of the cerebral endothelium.

Cytogenetic variability and kinetochore proteins. Comparison among populations derived from single-cell cultures

This study reports comparative changes in five sub-lines obtained from a transformed culture of rat cerebral origin. Two of the lines were obtained from the original cell population while three others were raised from single-cell cultures. The comparative study was carried out on the DNA content and several cytogenetic parameters including variability in chromosome number, anaphase bridges, acentric fragments, chromosomes without detectable kinetochore proteins, and the frequency of micronuclei in these five lines. All cell lines, including the single-cell-derived clones expressed considerable variability in all aspects. One interesting aspect is the evolution of a chromosome with compound centromere, which is present only in two cell lines. The data indicate that the clone derived from a single cell does not maintain uniformity and even single cells have some sort of inherent potential to generate extreme variability. Some numerical variability may be attributed to a new phenomenon of a lack of kinetochore proteins seen on some chromosomes.

Generation of recombinant murine retroviral genomes containing the v-src oncogene: isolation of a virus inducing hemangiosarcomas in the brain

A series of recombinant retroviral genomes was generated by cotransformation of NIH 3T3 cells with a mixture of cloned DNAs: a proviral copy of the wild-type Moloney murine leukemia virus, and Moloney-based vectors containing defective copies of the chicken v-src and the murine v-abl oncogenes. Morphologically transformed foci, appearing at low frequencies in these cultures, released high titers of transforming viruses. Analysis of one group of these viruses showed that the genomes were recombinants containing portions of the viral gag gene juxtaposed to the v-src oncogene. Biologically active cloned DNAs of two of these viruses were obtained and mapped in detail. One of these viruses did not cause disease after inoculation into newborn mice, but the other induced rapidly fatal hemangiosarcomas located exclusively in the brain.

Centromere structure and function in neoplasia

The mammalian centromere plays an essential role in maintenance of diploidy in the cell. It is therefore imperative that we understand the structure and function of the mammalian centromere in order to plan strategy to control the incidence of aneuploidy and resultant malformations of the nonneoplastic as well as neoplastic tissues. Even though considerable information is available about the structure and some functional aspects of centromeres of lower eukaryotes such as yeast, the structure of the mammalian centromere is still a matter of conjecture limited to an understanding of the base composition of the alphoid sequences putatively located in the centromeric DNA of higher apes. We do, however, have a better understanding of the structure and role of the kinetochore. In all eukaryotes analyzed so far, the centromeres in a given genome separate in a sequential manner dependent upon the time of replication of pericentric and centromeric DNA. Some chromosomes, generally found in neoplastic cells, that carry more than one centromere show premature separation of the accessory centromeres. These centromeres and the associated pericentric regions replicate their DNA in an earlier part of the S phase than those that show kinetochore activity; both, however, carry DNA of the same composition. The active centromeres in these chromosomes show kinetochore protein binding as detected by antikinetochore antibody; the inactive centromeres are usually devoid of these proteins. The double minutes in neoplastic cells also lack kinetochore proteins, perhaps due to a lack of any centromere. Some dicentric and multicentric chromosomes in cancer cells and transformed cell lines do not display premature centromere separation. In these chromosomes, all centromeric sites show kinetochore proteins and all centromeric regions replicate their DNA simultaneously. These chromosomes also exhibited meiotic-like behavior of some centromeres and show postanaphase separation of some centromeres, resulting in bridges. These bridges, upon breakage and rejoining of sister chromatids, generate new multicentric chromosomes. The resulting chromosomes also exhibit formation of compound kinetochores. Some of these phenomena are novel descriptions of the centromere behavior in cancer cells. This review also discusses the role of aberrant centromere separation in human biology, providing correlates between errors of centromere separation and neoplasia.

Bovine brain endothelial cells express tight junctions and monoamine oxidase activity in long-term culture

The passage of substances across the blood-brain barrier is regulated by cerebral capillaries which possess certain distinctly different morphological and enzymatic properties compared to capillaries of other organs. Investigations of the functional characteristics of brain capillaries have been facilitated by the use of cultured brain endothelial cells, but in most studies a number of characteristics of the in vivo system are lost. To provide an in vitro system for studies of brain capillary functions, we developed a method of isolating and producing a large number of bovine brain capillary endothelial cells. These cells, absolutely free of pericyte contamination, are subcultured, at the split ratio of 1:20 (20-fold increase of the cultured surface), with no apparent changes in cell morphology up to the fiftieth generation (10 passages). Retention of endothelial-specific characteristics (factor VIII-related antigen, angiotensin-converting enzyme, and nonthrombogenic surface) is shown for brain capillary-derived endothelial cells up to passage 10, even after frozen storage at passage 3. Furthermore, we showed that bovine brain capillary endothelial cells retain, up to the fiftieth generation, some of the characteristics of the blood-brain barrier: occurrence of tight junctions, paucity of pinocytotic vesicles, and monoamine oxidase activity.

Evolution of compound centromeres. A new phenomenon

A new type of centromere aberration in a transformed cell line of rat cerebral endothelial origin is described. These cells exhibit normal monocentric, dicentric, and multicentric chromosomes. The centromeres in dicentrics and multicentrics express variable locations along the chromosome. The centromeres in some of the multicentrics are located next to each other, with small intervening noncentromeric chromatin. In others, the centromeres appear to be in the immediate vicinity of each other with no evidence of intervening chromatin. This organization of the centromeres results in what appears to be a compound centromere composed of some multiples of single centromeres. All centromeres deposit kinetochore proteins that respond to kinetochore antibody. This evidence and that obtained from electron microscopy permits the conclusion that various centromeres/kinetochores in the compound structure are functional. The study presented here points to the existence of compound large centromeres--a novel phenomenon in cytogenetics--that may be prevalent in cancer cells. In the present cell line these regions appear as long, neck-like structures in some chromosomes and may be similar to some in vivo situations such as the X in Indian muntjac.

Sequence of centromere separation: characterization of multicentric chromosomes in a rat cell line

The B1 cell line of rat cerebral endothelium origin exhibits several dicentric and multicentric chromosomes. These chromosomes, unlike multicentrics in mouse (Vig and Zinkowski 1986) do not show premature centromere separation. All centromeres deposit kinetochore proteins and appear to be functional. Even the centromeres which fail to migrate to the poles during anaphase and make side arm bridges bind to spindle microtubules. Some multicentric chromosomes show kinetochores spaced apart with intervening stretches of euchromatin while others are located adjacent to each other thus exhibiting tandem repeats and forming a "compound" kinetochore (Brinkeley et al. 1984). Also, unlike mouse multicentric chromosomes in which different pericentric regions and the centromeres replicate at different times, the rat chromosomes appear to replicate all pericentric and centric regions in a given multicentric simultaneously. The present studies indicate that centromeres in rat and mouse replicate during the last part of the S-phase and in continuation with the pericentric heterochromatin.

Sequence of centromere separation: kinetochore formation and DNA replication in dicentric chromosomes showing premature centromere separation in rat cerebral cells

A subpopulation of rat cerebral endothelial cells, designated B1, exhibits an array of multicentric chromosomes. Because of the formation of bridges at anaphase, this cell population produced new types of multicentrics at every cell division. These chromosomes showed kinetochore proteins at every centromeric site and all centromeric regions replicated their DNA at the end of the S phase, more or less simultaneously. A new subpopulation of cells, designated B2, obtained from the original sample frozen at Wayne State University displayed several dicentrics. In contrast to B1 these chromosomes exhibit premature centromere separation as reported for mouse and human cell lines. These B2 dicentrics show only one site of kinetochore protein deposition. The timing of DNA replication around the centric region of prematurely separating centromere is also changed similar to the earlier reported premature DNA synthesis for mouse dicentrics. These observations suggest a universality of relationship between premature centromere separation, a lack of kinetochore formation, and early replication of the centric/pericentric DNA associated with these centromeres. The cause of sudden change from activity to inactivity of these chromosomes, though interesting, is not clear.

Sequence of centromere separation: generation of unstable multicentric chromosomes in a rat cell line

A transformed cell line, B1, of cerebral endothelial origin from the Wistar-Kyoto male rat has chromatid and chromosome type bridges in virtually every cell. It exhibits various dicentric and polycentric chromosomes. Most dicentrics are symmetric isochromosomes. Certain isodicentrics are present in a fair segment of the cell population; however, almost all cells have some newly arising isodicentrics. The live cells show a lengthened prometaphase. Anaphase is also retarded possibly due to the occurrence of bridges. At anaphase some multicentrics split at only one centromere. When pulled to the two poles the unsplit centromeres and the distal chromosome segment form a side arm bridge. Another mechanism appears to be a total lack of separation of daughter centromeres at meta-anaphase ('meiotic-like' behavior of mitotic chromosomes). This is realized by the pulling of each of the two unsplit centromeres to opposite poles and results in bridges with both sister chromatids running parallel to each other. A break at corresponding weak points in the two sister chromatids followed by rejoining can form a dicentric isochromosome. A third mechanism, the breakage-fusion-bridge cycle, is also operative but would not produce isodicentrics. In the case of the first two mechanisms some or all centromeres apparently split between telophase and onset of the following DNA synthesis rather than at the usual time at late metaphase. These observations may suggest some previously unknown behavior of multicentric chromosomes during mitosis.

Rat heart-derived endothelial and smooth muscle cell cultures: isolation, cloning and characterization

This report describes the initiation, cloning and establishment of long-term serial cultures of rat heart-derived vascular endothelial (EC) and smooth muscle cells (SMC). Populations of these cells derived from both the macro-and microcirculation were obtained utilizing isolated heart perfusion technique. Elimination of potential mesothelial cell contamination was achieved by ethanol fixation of the pericardial surface prior to perfusion. Initial outgrowths from perfusate yielded both endothelial (rapid adhering) and smooth muscle (slow adhering) appearing cell populations. Subsequent pooling of individual EC colonies resulted in maintaining, with gradual subcultivation, a stable homogeneous population which was designated RHE-parent. Upon continual subculture late passage (greater than P10) RHE-parent cell cultures expressed a marked heterogeneity in endothelial phenotypes. Cloning experiments resulted in establishing two distinct EC populations designated RHE-clone 1A and RHE-clone 2A. All RHE cell cultures exhibited the typical cobblestone growth pattern and positive immunofluorescent staining for factor VIII related antigen. In contrast, rat heart-derived smooth muscle cell (RH-SMC) cultures displayed the typical multilayered 'hill and valley' pattern and positive fluorescence for SMC-specific actin and myosin antibodies. Additional EC preparations, obtained without prior fixation of the pericardial surface, revealed cell clusters which stained positive for cytokeratin. On the other hand, RHE parent and cloned populations stained exclusively for vimentin, further confirming the absence of mesothelial cell contamination in these cultures. Cell growth studies on early (less than P10) and late (greater than P10) passage RHE-parent population revealed markedly different cell growth responses and cell morphology. Both EC cloned populations and more notably RHE-parent (less than P10) cultures were capable of significant growth when maintained in limiting serum concentration. Growth studies using serum-free RHE-parent conditioned medium demonstrated mitogenic activity when tested on RHE-parent cultures indicating the presence of an endothelial cell-derived growth factor. These studies indicate that long-term RHE and RH-SMC derived cell cultures can serve as a useful model to study the biology of vascular cells derived from different sites. In addition the demonstration of mitogenic activity in these cultures will enable us to explore further the nature of this response and compare this phenomenon with growth factors identified in large vessel cell systems.

Inhibition of tumor cell-platelet interactions and tumor metastasis by the calcium channel blocker, nimodipine

Nimodipine, a dihydropyridine calcium channel blocker, was evaluated in vitro for its ability to inhibit platelet aggregation induced by B16 amelanotic melanoma (B16a) and Walker 256 carcinosarcoma (W256) cells, and for its ability to inhibit platelet-enhanced B16a and W256 adhesion to rat microvascular endothelial cells. Nimodipine produced a dose-dependent inhibition of tumor-cell-induced platelet aggregation (TCIPA). Platelets enhanced tumor cell adhesion to endothelium both in the presence and absence of overt platelet aggregation. However, the greatest enhancement of adhesion occurred under aggregatory conditions. Nimodipine at a dose of 40 micrograms/ml inhibited platelet-enhanced adhesion to endothelium under aggregatory and nonaggregatory conditions. Nimodipine was tested in vivo for its ability to inhibit both "experimental' and spontaneous metastasis. Nimodipine produced a 46 per cent inhibition of lung colony formation at a dose of 5 mg/kg body-weight. Over a dose range of 0.1-80 mg/kg, nimodipine produced a significant dose-dependent inhibition in the formation of lung metastases from a subcutaneous tumor. The in vitro results demonstrate that a dihydropyridine calcium channel blocker can inhibit tumor cell-platelet-endothelial cell interactions. The in vivo results suggest that these compounds may be a new class of antimetastatic agent.

Inhibition by dihydropyridine class calcium channel blockers of tumor cell-platelet-endothelial cell interactions in vitro and metastasis in vivo

Three calcium channel blockers of the dihydropyridine class were tested in vitro for their effects on tumor cell-platelet-endothelial cell interactions and in vivo for antimetastatic properties. Felodipine, nimodipine and nifedipine inhibited tumor cell-induced platelet aggregation in vitro in a dose-dependent manner. These compounds also inhibited platelet-enhanced tumor cell adhesion to endothelial cells in vitro. Lung colony formation ("experimental" metastasis) and spontaneous pulmonary metastasis were inhibited by felodipine, nimodipine and nifedipine. From the present studies on three calcium channel blockers of the dihydropyridine class we hypothesize that calcium channel blockers may represent a new generic class of antimetastatic agents.

Expression of gamma-glutamyltranspeptidase in a transformed rat cerebral endothelial cell line

Brain capillary endothelium in vivo contains high levels of gamma-glutamyltranspeptidase activity. In addition, the presence of this enzyme has been used as a marker of neoplastic cells. Normal rat cerebral endothelial cells in culture exhibit a specific activity for gamma-glutamyltranspeptidase of 2 units/10(6) cells. In vitro transformation of these cells is achieved by the use of an avian retrovirus, Schmidt-Ruppin RSV-strain D. The resultant cell line, designated RCE-T1, demonstrates a significant increase in gamma-glutamyltranspeptidase activity up to 20 units/10(6) cells in early passage levels (9-26) after which enzyme activity declines and returns to normal levels by passage 80. This variation in enzyme activity correlates with histochemical staining for this enzyme. Furthermore, the enzyme activity increases linearly over a 1000-fold range of cell concentrations. Various culture modifications do not influence this pattern of enzyme expression. These parameters include trypsin dissociation, cell freezing, degree of confluency and culture maintenance with serum or with conditioned medium obtained from passage levels exhibiting high or low enzyme activity. RCE-T1 cells will provide a unique model system to study the distribution and regulation of this enzyme during differentiation and viral carcinogenesis.

Karyotype evolution in a transformed rat cerebral endothelial cell line

Primary cultures of rat microvascular endothelial cells were transformed, in vitro, by exposure to Rous sarcoma virus. Transformed cells were followed and evaluated cytogenetically through numerous passages. Highly specific karyotypic changes in karyotype (both structural and numerical) were documented. These changes became established and intimately involved in further "karyotypic evolution". The findings were reproducible, and when considered in the light of the literature suggest regular patterns of karyotypic change in rat tumors. The in vitro methodology utilized promises to be of practical value in the study of the early stages of malignancy.