Transformation in vitro of glial hamster cells by Rous sarcoma virus

Physiological relevance and functional potential of central nervous system-derived cell lines

Central nervous system (CNS)-derived neural cell lines have proven to be extremely useful for delineating mechanisms controlling such diverse phenomena as cell lineage choice and differentiation, synaptic maturation, neurotransmitter synthesis and release, and growth factor signalling. In addition, there has been hope that such lines might play pivotal roles in CNS gene therapy and repair. The ability of some neural cell lines to integrate normally into the CNS following transplantation and to express foreign, often corrective gene products in situ might offer potential therapeutic approaches to certain neurodegenerative diseases. Five general strategies have evolved to develop neural cell lines: isolation and cloning of spontaneous or mutagenically induced malignancies, targeted oncogenesis in transgenic mice, somatic cell fusion, growth factor mediated expansion of CNS progenitor or stem cells, and retroviral transduction of neuroepithelial precursors. in this article, we detail recent progress in these areas, focusing on those cell lines that have enabled novel insight into the mechanisms controlling neuronal cell lineage choice and differentiation, both in vitro and in vivo.

Isolation and characterization of conditionally immortalized astrocyte cell lines derived from adult human spinal cord

As an approach to develop both oligodendrocytic and astrocytic cell lines from adult human spinal cord, a cellular preparation of highly enriched oligodendrocytes and their precursors was infected with a replication-deficient retrovirus containing DNA sequences encoding the temperature-sensitive mutant of SV40 large T antigen. Six immortal cell lines were obtained. At both permissive (33 degrees C) and non-permissive (38.5 degrees C) temperatures, all cell lines were positive for vimentin, two demonstrated glial fibrillary acidic protein (GFAP) immunoreactivity, and none expressed oligodendrocyte or microglial markers. The 2 GFAP-positive cell lines [human spinal cord (HSC)2 and HSC6] were further characterized. Karyotype analysis revealed that both HSC2 and HSC6 cells showed gain of chromosomal material and structural chromosomal abnormalities. However, at non-permissive temperature both cell lines were indistinguishable from primary human astrocytes by a number of criteria. These properties included glutamine synthetase activity, Na(+)-dependent glutamate uptake, K+ flux, purine-evoked Ca2+ mobilization and entry, and the ability to support neurite outgrowth from embryonic rat retinal explants. The HSC2 and HSC6 cell lines may prove to be valuable models for studying the physiological properties of adult human astrocytes.

Transformation of rat cerebral endothelial cells by Rous sarcoma virus

Rat cerebral microvascular endothelial cells were infected with Schmidt-Ruppin Rous sarcoma virus-strain D (SR-RSV-D), an avian retrovirus. A single focus of transformed cells was isolated and the resultant cell line designated RCE-T1. The specificity for SR-RSV-D transformation was determined by virus rescue assay and demonstration of virus-specific antigens. RCE-T1 cells are virogenic when fused with chicken embryo fibroblasts (CEF) and do not produce infectious virus as demonstrated by the absence of detectable virus in culture fluid from these cells alone. Studies using an enzyme-linked immunosorbent assay (ELISA) for avian retrovirus-coded internal proteins show that RSV-transformed endothelial cells contain mainly p27 and react to some extent to p19 and p15 viral antigens. These data demonstrate conclusively that the transformation event was indeed due to SR-RSV-D. In addition, chromosome analysis confirmed these cells to be of rat origin. RSV-transformed endothelial cells express the typical array of transformation-related properties such as anchorage-independent cell growth in soft agar, decreased cell adhesiveness, ability to grow in low serum, and capability of producing tumors in newborn rats. Demonstration of differentiated endothelial characteristics included positive immunofluorescent staining for factor VIII antigen and angiotensin-converting enzyme and histochemical localization of gamma-glutamyl transpeptidase activity. This cell line should provide a useful model to study not only specialized biochemical and other functional characteristics of cerebrovascular endothelium but also the cellular mechanisms that involve the transition from normal to neoplastic expression.

Properties of two temperature-sensitive Rous sarcoma virus transformed cerebellar cell lines

Cells from the cerebellum of 3-day-old BD-IX rats were obtained as permanent lines by transforming them with temperature-sensitive Rous sarcoma virus. The presence or absence of veratridine-stimulated Na+-uptake (voltage-dependent channels) was used to operationally classify them as neuronal or glial. When incubated at 34 degrees C, the permissive temperature for transformation, the cerebellar cells exhibit a transformed phenotype determined by anchorage independence, rounded morphology, high growth rate and absence of density-dependent inhibition of growth. In contrast, when the transformed cerebellar cell lines are kept at a temperature (38 degrees C) non-permissive for transformation, they exhibit a normal cellular phenotype with respect to the above properties. Moreover, changes toward neuronal morphology, increase in veratridine-stimulated Na+-uptake, decreased growth rate and the expression of the astrocyte specific protein, glial fibrillary acidic protein, suggest that a degree of differentiation is expressed at the non-permissive temperature.

Tumorigenic clones of hamster brain cells transformed in vitro by polyoma virus. Ultrastructural and immunohistochemical study

The morphological characteristics of three clones of hamster brain cells transformed in vitro by polyoma virus and of the tumors obtained after subcutaneous grafting of these cells in syngenic animals are reported. These clones appeared to be glial in nature by light and electron microscopy. The initial tumors induced by the three clones presented astrocytic features both by electron microscopy and immunohistochemistry. Analysis of the subsequent in vivo passages showed a decrease in cell differentiation, which was accompanied by a decrease in the latency period; after 2 years of serial transplantation, the tumors seemed poorly differentiated gliomas. A control cell line of hamster cerebellar cells evolved similarly.

Normal and benzo(a)pyrene-transformed fetal mouse brain cells. II. Ultrastructural study

An ultrastructural study was performed on normal and Benzo(a)-pyrene(B(a)P)-transformed fetal mouse brain cells. Early subcultures of a strain initiated from whole brain presented three cell types in vitro: astroglial, poorly differentiated glial, and spongioblastic types. After B(a)P-treatment, there was an exclusive transformation and the growth of neuroglia sometimes without gliofibrillary maturation, but with the presence of glial fibrillary acidic protein (GFAP) in the cytoplasm. Early subcultures of another strain initiated from cortex only presented poorly differentiated neuroglial cells. After transformation, cell maturation as evidenced by gliofibrillogenesis and GFAP production by these cells was observed. In both cases, the potentiality of glial differentiation after in vitro malignant transformation by a chemical carcinogen seemed preserved.

Normal and benzo(a)pyrene-transformed fetal mouse brain cell. I. Tumorigenicity and immunochemical detection of glial fibrillary acidic protein

Primary cultures of whole brain and cortex cells origination from 14-day-old A/Jax or C3H mouse fetuses were treated with benzo(a)pyrene (B(a)P) for 24 h. After 7 to 8 passages a malignant transformation was observed in the chemically treated whole brain and cortex cultures. Control cultures of cortex remained non-transplantable during the whole experiment (up to 14 passages) whereas in the control cultures originating from whole brain a spontaneous transformation appeared after 11 passages. With horseradish peroxidase-labelled antibody, the specific glial fibrillary acidic protein (GFAP) was detected in both control and transformed total brain and cortex cultures, and in the tumors initiated by the in vitro transformed cells. This finding shows that glialike cells persisted after a long in vitro maintanance and transformation.