Interaction of fas and fas Ligand
Object. An experimental model of the fas and fas ligand (fasL) interaction in malignant glioma was developed. Methods. Using plasmid-based delivery, 36B10 rat glioma cells were modified to express fas (36B10-fas), and a delivery fibroblast cell line was modified to produce fasL, resulting in the FR-fasL cell line. Evaluation of fas expression was performed with flow cytometry and expression of fasL confirmed by Western blot analysis. Once the cell lines were created and partially characterized, fas-induced cytotoxicity was evaluated using an antibody-mediated assay for 36B10-fas that demonstrated significant toxicity at 24 and 48 hours. To evaluate the potential for activating the fas molecule by using cell-mediated delivery, coculture cytotoxicity studies were performed with a target cell line (36B10-fas) and effector cell line (FR-fasL). Using a series of culture ratios, increasing cytotoxicity was noted, suggesting that activation of the transfected fas receptor by fasL expression on the carrier cell was occurring.
Conclusion. Based on their experiments, the authors describe a model for evaluating the interaction of fas and fasL in a cellular model of malignant glioma.

Fas is a type I membrane protein that mediates the induction of apoptosis in selected cells when ligated either by an anti-fas antibody or by interaction with fasL. Fas is a member of the TNF/nerve growth factor receptor superfamily. Fas ligand is a membrane-type cytokine belonging to the TNF family and is expressed in T cells activated by various factors including interleukin 2, phorbol myrisate acetate, and anti-CD3. The fas/fasL pathway has been shown to play a role in T cell-mediated cytotoxicity.

The role of apoptosis, or programmed cell death, in the development of CNS neoplasia has received increasing interest as techniques for studying the signaling pathways and genetics of this process have been developed. The mechanism of apoptotic cell death is complex. It involves receptor-mediated protease activation, cytolytic plasma protein interactions, and ultimately distinct morphological alterations. These alterations can be observed microscopically and include DNA degradation and margination, condensation of chromatin, cell membrane alterations and the formation of apoptotic cascade. Research specifically focused on apoptosis and CNS neoplasia has included interaction of p53 with the retinoblastoma gene and TNF-alpha, the identification of apoptosis-protective genes in glioma, and upregulation of protease enzymes important to the apoptotic cascade. A recent description of the interaction of fas-induced apoptosis with transforming growth factor-beta₁ suggests the central role of these interactions in the modulation of the cell cycle. In a series of studies, Weller, et al., have examined fas-induced cytotoxicity in a series of human glioma explants. They have shown, under selective conditions, that apoptosis can be induced when ligated by an anti-fas antibody.

Given the increasing evidence that apoptosis may play a role either in the induction or propagation of neoplastic transformation, we undertook to develop a model in which to examine fas/fasL interaction in glioma cells. In this report we describe the development of a plasmid-based delivery system for fas and fasL that allows the interaction of these molecules to be examined in malignant glial tissue. Because antibodies to these molecules are available, they can be assayed in a semiquantitative fashion to determine expression, and assays for cytotoxicity allow the effect of their interaction to be determined. Because of the complexity of the apoptotic cascade and the multifactorial events involved in neoplastic transformation, it is unlikely that any single system will allow these cells to be eliminated. However, additional examination of the fas and fasL system and other interactions in the apoptotic cascade will provide insight into the steps involved in the maintenance and control of cellular proliferation.