Lysophosphatidic acid reverts the beta-adrenergic agonist-induced morphological response in C6 rat glioma cells

Elevation of cAMP changes the morphology of C6 rat glioma cells from a fibroblast to an astrocyte type of appearance. This change is prevented by the presence of serum from different species (chicken, mouse, rat, horse, adult bovine, fetal bovine, and human) in the cell culture medium. In this communication the component in serum responsible for this effect is identified as lysophosphatidic acid for the following reasons: First, lysophosphatidic acid alone at concentrations which are present in serum reverts the morphological response. Second, both lysophosphatidic acid and the component in serum no longer revert the morphological response after treatment with phospholipase B (E.C.3.1.1.5). Third, lysophosphatidic acid and serum produce an analogous intracellular Cai2+ signal in rat glioma C6 cells as measured by fluorescence spectrophotometry with the Ca2+ ion indicator Fura 2. Fourth, both the morphological response and the Cai2+ increase are prevented by pretreatment of the cells with 100 ng/ml phorbol 12-myristate 13-acetate. Finally, a maximal Cai2+ increase induced by FCS prevents the subsequent Cai2+ signal by lysophosphatidic acid. Interestingly, the morphological response is also reverted by Al3+ together with F- ions and also by lower n-alkanols such as ethanol and n-propanol suggesting that a regulatory GTP-binding protein is involved in the reversion. It is further shown that activation of the phosphatidylinositol 4,5-bisphosphate cleavage signal system is not responsible for the reversion of the morphological response.