S_ry Factors involved in the control of the biological properties of gliomas, the major form of brain tumour in man, are poorly documented. We investigated the role of transforming growth factor P, (TGF-P,) in the control of proliferation of human glioma cell lnes as well as normal human fetal brain cells. The data presented show that TGF-, exerts a growth-inhibitory action on both human fetal brain cells and three cell lines derived from human glioma of different grades of malignancy. In addition, this growth-inhibitory effect is dose dependent and serum independenL Since TGF-4 is known to be involved in the control of cell migration during ontogenesis and oncogenesis, we investigated the role of this factor in the motile and invasive behaviour that characterises human gliomas in vivo. was Transforming growth factor PI (TGF-i1) is a member of a large family of structurally related proteins which play a role in the control of proliferation, differentiation and morphogenesis in cultured cells and organisms from insects to mammals (reviewed in Massague, 1990). TGF-P, was initially defined by its ability to induce anchorage-independent growth of non-transformed rat kidney cells (Roberts et al., 1981 The IPNT-H cell line was derived from a pilocytic astrocytoma of the hypothalamus in a 6-month-old child. Despite the fact that the tumour from which this cell line was derived was histologically classified as a pilocytic astrocytoma, it showed a high proliferative rate in agreement with recent reports demonstrating that occasionally these tumours possess a high mitotic index (Ito et al., 1992). Histological analysis showed the presence of mitoses in one-tenth of high-power fields, but no necrosis or endothelial cell proliferation was noted. In some areas there was an increase in cellularity and very occasional entrapped neurons could be discerned within the tumour. IPNT-H cells were used at passage 7; IPSB-18 was derived from a human grade 3 tumour of the temporal lobe in a 48-year-old man (Knott et al., 1990) Cell proliferation assay Cells were plated at 5 x I04 cells per well in six-well culture plates in DMEM containing FCS in the absence or presence of 5 ng ml-' TGF-,B. The medium was changed once, after 3 days of incubation, and the cell number was determined, after 7 days, by trypinisation and counting in a haemocytometer. All experiments were performed in triplicate and repeated at least twice.

Glial precursor cells express NG2 and GD3 in the developing brain. These antigens are both over-expressed during neoplasia, which suggests they may have specific functions in the malignant progression of human brain tumours. This study describes the expression of NG2 and GD3 in 28 paediatric and adult brain tumours. Glioblastoma biopsy spheroids were also implanted into nude rats to assess the regional distribution of the molecules within the tumour. These xenografts showed extensive infiltration and growth that mimicked the growth patterns of human gliomas in situ. NG2 was identified in 20 out of 28 brain tumours, where the expression was confined to the main mass of the tumour, and was reduced towards the tumour periphery. NG2 was mainly associated with blood vessels on both the pericyte and basement membrane components of the tumour vasculature. Ki67 (MIB-1) labelling indicated that NG2 expression was associated with areas of high cellular proliferation. Conversely, all the tumours expressed GD3, which was present both in the tumour main mass and throughout the periphery. Thus, the expression of NG2 may be indicative of tumour progression and might be an amenable target for future therapeutic interventions.

The expression and function of NG2, a transmembrane chondroitin sulfate proteoglycan was studied in human gliomas of various histological types in culture using immunocytochemistry and flow cytometry. NG2 was differentially expressed in the neoplasms, with higher expression in high compared to low-grade gliomas. In acutely isolated cells from human biopsies, NG2 +ve and NG2 -ve populations were morphologically distinct from each other, and NG2 +ve cells were more proliferative than NG2 -ve cells. The mitogens platelet derived growth factor (PDGF-AA) and basic fibroblast growth factor (bFGF) added in combination to serum-free medium (SFM) upregulated NG2 expression on glioblastoma multiforme cells in culture but had little effect on NG2 expression on the anaplastic astrocytoma cells. Furthermore, NG2 was colocalised with the platelet derived growth factor alpha receptor (PDGFalphaR) and antibody blockade of the PDGF-alphaR ablated NG2 expression on the glioblastoma multiforme cells, suggesting that increased NG2 expression in the presence of PDGF-AA is mediated via the PDGF-alphaR. Assays of migration and invasion indicate that NG2 +ve glioma cells migrated more efficiently on collagen IV and that NG2 -ve cells were more invasive than their NG2 +ve counterparts. The results indicate that NG2 may be, respectively, positively and negatively related to the proliferative and invasive capacity of glioma cells. Thus, expression of the NG2 proteoglycan may have major implications for malignant progression in glial neoplasms and may prove a useful target for future therapeutic regimens.

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Despite renewed attempts by the WHO at updating the system of classification for brain tumours, most of the dynamic biological processes which underlie both the morphological appearances which form the basis for such systems and the malignant potential of gliomas remain an enigma to the neuropathologist. One feature recognized in human gliomas is their phenotypic and genotypic heterogeneity. Such cellular heterogeneity seen in the histological section is retained in vitro, at least during early passage. It is proposed that this heterogeneity is important in the growth and maintenance of the tumour and may be related to the activity of growth factors and gangliosides. Such molecules may not only influence the histoarchitecture of glial neoplasms but may also determine malignant progression and invasive potential. Moreover, there may be an intimate relationship between growth factors and gangliosides constituting an intricate feedback mechanism upon which the biological progression of gliomas depends.