Laminin and other basal lamina proteins with neurite promoting activity in medium conditioned by C6 glioma cells

Circadian properties of cancer stem cells in glioma cell cultures and tumorspheres

Increased cancer risk is linked to disruption of circadian rhythms. Cancer stem cells (CSCs) are a known cause of cancer aggressiveness, but their circadian properties have not been described. We discovered circadian rhythms in gene expression within C6 glioma tumorspheres enriched in CSCs and found that the circadian clock is particularly robust in medium lacking any growth factors. A method is introduced for identifying individual CSCs in culture for single-cell analysis. CSCs in monolayer cell culture failed to show a circadian rhythm in nuclear localization of mPER2 protein, suggesting that cell interactions or the tumor-like microenvironment within tumorspheres enable circadian timing.

GDNF mRNA levels are induced by FGF-2 in rat C6 glioblastoma cells

Glia cell line-derived neurotrophic factor (GDNF), a recently cloned member of the transforming growth factor-beta (TGF-beta) superfamily, has been implicated in the survival, morphological and functional differentiation of midbrain dopaminergic neurons and motoneurons in vitro and in vivo. The factor may thus have utility in the treatment of various human neurodegenerative disorders. Mechanisms regulating expression of GDNF in normal and diseased brain as a possible means to increase the local availability of GDNF are only beginning to be explored. We have established and employed a competitive reverse transcriptase-polymerase chain reaction (RT-PCR) to study and compare levels of expression of GDNF mRNA in several cell types and to investigate its regulation. GDNF expression was clearly evident in primary cultured astrocytes, the glioma B49 and C6 cell, but less pronounced in the Schwannoma RN22 cell lines. Little or no signal could be observed in neuroblastoma cell lines (IMR32, LAN-1) or the pheochromocytoma cell line PC12, emphasizing the glial character of this factor. Using the C6 cell line we found that fibroblast growth factor-2 (FGF-2; bFGF) can increase GDNF mRNA levels, whereas FGF-1, platelet-derived growth factor (PDGF), and vasoactive intestinal polypeptide (VIP) are apparently ineffective. Several other factors (forskolin, kainic acid, triiodothyronine dexamethasone, GDNF, TGF-beta 1, and interleukin-6) appear to have slightly negative effects on GDNF mRNA levels at the concentrations tested. To further explore the relationship between FGF-2 and GDNF, we also addressed the question whether GDNF, like FGF-2, may have an effect on C6 cell proliferation. We conclude that (1) glial and glial tumor cells, rather than neuronal cell lines, express GDNF, (2) that FGF-2 has a prominent inductive effect on GDNF expression and (3) that GDNF stimulates C6 cell proliferation. Finally, these data suggest that neurotrophic actions of FGF-2 in mixed glial-neuronal cell cultures might be mediated in part by GDNF.

Identification of a collagen potentiated neurite promoting factor isolated from C6 glioma cells

The C6 glial cell line has been used as a model cell system for the investigation of new glial produced neurotrophic and neurotropic molecules. By using the C6 cell line grown in a defined medium on collagen, this laboratory has isolated a distinct neurite promoting factor (NPF) that is potentiated by the presence of collagen (CPNPF). We have observed that C6 cells cultured in a defined medium on collagen (rat type-I) slowed their growth rate and expressed an astrocytic- or oligodendrocytic-like morphology. CPNPF, at this state of purity, appears to be a distinct NPF which induces neurite outgrowth (neurites of 1 or more somal diameters) in PC12 cells. These neurite promotion effects, however, appear to support the neuron morphology for only a short period (4 days) of time without the presence of neurotrophic factor (NTF). The neurite promoting activity is ineffective in inducing neurite outgrowth using mouse neuroblastoma cells (neuro-2a). CPNPF appears to be a heat stable protein whose activity does not depend on the presence of intact collagen, heparin sulfate proteoglycan (HSPG), or chondroitin sulfate proteoglycan (CSPG). Exposure to dissociative conditions results in a loss of neurite promoting activity. CPNPF is not a glycoprotein that contains an accessible alpha-D-mannopyranosyl, alpha-D-glucopyranosyl, or a sterically related residue (hydroxyl groups in the C-3,4, and 5 positions). Although these residues are not present on all glycoproteins, it does indicate that CPNPF is most likely not a glycoprotein. CPNPF activity is not blocked by neutralizing antibodies directed toward NGF, beta-FGF, IL-1 beta, IL-6, TGF-beta 2, TGF-beta 1.2, TGF-beta 3, TGF-beta 5, or EGF. CPNPF appears to either be oligomeric protein or a complex of proteins. On the basis of indirect evidence, it does not appear to be glial derived protease nexin-I. The alteration in morphology of the C6 glial cell line by serum-free conditions in the presence of collagen may have induced the production of a potentially new NPF not seen by previous investigators.

Expression of multiple integrins and extracellular matrix components by C6 glioma cells

We have investigated the expression of integrins in C6 glioma, a chemically-induced glial tumor cell line from rat brain. Immunochemical analysis revealed that C6 cells express sets of integrin receptor complexes which immunologically and electrophoretically are indistinguishable from those expressed by normal rat skin fibroblasts. These include the well-characterized fibronectin (alpha 5 beta 1) and the multi-specific laminin, collagen and fibronectin (alpha 3 beta 1) receptors. Assay of cell adhesion indicated that C6 cells adhere to fibronectin-coated surfaces or matrix deposited by the C6 glioma cells (CGM) in an RGD- and divalent cation-dependent fashion. However, anti-fibronectin antibodies, which are able to inhibit fibroblast adhesion to fibronectin, did not inhibit adhesion of the C6 cells to fibronectin or CGM. This may reflect differences in functional properties and/or distribution patterns of integrins in C6 cells and normal fibroblasts.

Basic fibroblast growth factor (bFGF) and rat C6 glioma cells: regulation of expression, absence of release, and response to exogenous bFGF

Basic fibroblast growth factor (bFGF) is a potent mitogen for several types of cells, including glial cells, which also seem to express bFGF. We have used rat C6 glioma cells as a model system to study the expression and release of bFGF by glioma cells, as well as the effects of exogenous bFGF on these cells. We have shown that C6 cells express 18 kD bFGF and several higher molecular weight immunoreactive forms. The expression of bFGF could be induced by a factor present in fetal calf serum. Subsequent to its initial appearance, bFGF is regulated in a cell density-dependent manner. Neither bFGF-like immunoreactive material, nor bFGF-like neurotrophic activity were found to be released by C6 cells. Exogenously applied bFGF changed C6 cell morphology similar to cyclic AMP induced alterations but had no significant influence on C6 cell proliferation and biochemical differentiation. From these results we conclude that bFGF in C6 cells might act as an endogenous (not autocrine) mitogen. Possible roles for bFGF in glial cells are discussed.

Survival of purified embryonic chick retinal ganglion cells in the presence of neurotrophic factors

In a search for neurotrophic factors (NTFs) regulating retinal ganglion cell (RGC) death in the chick embryo we have used purified and cultured RGCs. Purification of RGCs from embryonic day 10 was achieved by employing the "panning" method (Silverstein and Chun: Soc Neurosci Abstr 13:1054, 1987). The obtained neuron population consisted of 97% RGCs as demonstrated by retrograde labeling with a fluorescence dye. RGCs were cultured at low density in a chemically defined medium and short-term survival (24 hr) was determined. In the absence of NTFs, less than 3% of the RGCs survived. In the presence of various crude or purified NTFs (eye, brain, and tectum extracts; glial-conditioned medium; ciliary neurotrophic factor [CNTF]; nerve growth factor [NGF]) 31% to 52% of the RGCs were maintained. The effects of NGF and CNTF were not additive. Neither acidic nor basic fibroblast growth factor was able to maintain RGCs in culture. Our results, obtained with a culture system which allowed the analysis of direct trophic actions, suggest that NGF and CNTF may be NTFs for overlapping subpopulations of chick RGCs.