Inhibition of p42/p44 mitogen-activated protein kinase by oxysterols in rat astrocyte primary cultures and C6 glioma cell lines

We previously demonstrated that oxysterols inhibit the growth of experimental glioblastoma induced in the rat brain cortex, Mechanism of action of these compounds remains obscure. In this study, we investigated the effect of 7 beta-hydroxycholesterol (7 beta-OHCH) and 7ketocholesterol (7k-CH) on the growth and MAP kinase activity in three in vitro biological models: rat astrocyte primary cultures, primary cultures treated by dibutyryl-cAMP (reactive cells), and the C6 glioma cell line. The oxysterols are not lethal to primary astrocytes, even if MAP kinase activity is decreased, particularly when cells were treated with 7k-CH, Both oxysterols are toxic to reactive astrocytes, and as compared with untreated primary cultures, they amplified the MAP kinase activity decrease. However, the mechanism of action of oxysterols on reactive astrocytes seems not to be linked to the MAP kinase pathway, In highly proliferating C6 cell lines, only 7 beta-OHCH has an antiproliferative effect and is cytotoxic. The inhibition of MAP kinase activity is a function of 7 beta-OHCH concentration. PD098059, a MAP kinase pathway inhibitor, has only a time-limited antiproliferative effect on C6 cell growth. We conclude that in C6 cells, the MAP kinase activity decrease is correlated with the toxic effect of 7 beta-OHCH and occurs at first stages of 7 beta-OHCH action. J, Neurosci, Res. 53:38-50, 1998, (C) 1998 Wiley-Liss, Inc.