Altered phospholipid metabolism in sodium butyrate-induced differentiation of C6 glioma cells.

We examined the changes in phospholipid metabolisms in sodium butyrate-treated C6 glioma cells. Treatment of 2.5 mM sodium butyrate for 24 h induced an increase in the activity of glutamine synthetase, suggesting that these cells were under differentiation. Similar treatment was associated with (i) increased arachidonic acid incorporation into phosphatidylcholine, and (ii) decreased arachidonic acid incorporation into phosphatidylinositol and (iii) phosphatidylethanolamine. These effects were subsequently investigated by examining the acylation process, de novo biosynthesis, and the agonist-stimulated phosphoinositides hydrolysis in these cells. Our results indicated that sodium butyrate stimulated the acylation of arachidonic acid into lysophosphatidylcholine, lysophosphatidylethanolamine, and lysophosphatidylinositol. The glycerol incorporation into these lipids was not affected, but the inositol incorporation into total chloroform extracts and Pl and phosphatidylinositol 4-phosphate was decreased in the sodium butyrate-treated cells. Moreover, the accumulation of the rapid histamine-stimulated phosphoinositide metabolites, i.e., inositol monophosphate, inositol diphosphate, and inositol triphosphate (IP3) was decreased in these cells. To elucidate whether the decreased inositol phosphates were due to a decrease in the phosphoinositides hydrolysis, we measured the transient IP3 production directly by a receptor-binding assay. Our results indicated that histamine-stimulated transient IP3 formations were decreased. Taken together, these results indicated that multiple changes by multiple mechanisms of phospholipid metabolisms were found in sodium butyrate-treated C6 glioma cells. The decreased IP3 formation and its subsequent action, i.e., Ca2+ mobilization, may play an early but pivotal role by which sodium butyrate induces C6 glioma cell differentiation.