EFFECTS OF IL-1-BETA ON RECEPTOR-MEDIATED POLY-PHOSPHOINOSITIDE SIGNALING PATHWAY IN IMMORTALIZED ASTROCYTES (DITNC)

Astrocytes are known to play multi-functional roles in support of many homeostatic mechanisms in the central nervous system including host d efense mechanisms. Despite the ability of cytokines to alter gene expr ession and cellular activity, their effect on receptor-mediated poly-p hosphoinositide (poly-PI) signaling pathway has not been examined in d etail. In this study, an immortalized astrocyte cell line (DITNC) was used to test the effect of IL-1 beta exposure on me poly-PI signaling pathway. Similar to primary astrocytes, DITNC cells exhibit P-2-purine rgic receptor response to ATP and UTP leading to transient increases i n inositol 1,4,5-trisphosphate [Ins(1,4,5)P-3] and intracellular calci um concentration, [Ca2+](i). Upon exposure of DITNC cells to IL-1 beta (100U/ml) for 24 hrs, an increased response to the poly-PI agonists w as observed. The increase in ATP-mediated Ins(1,4,5)P-3 release could not be attributed to a shift in the ATP dose or an alteration of the t ime profile for the release of Ins(1,4,5)P-3. Since the increase in re sponse required a lag time of 4 hr after IL-1 beta exposure, it is unl ikely that this effect was due to a direct interaction of IL-1 beta wi th the purinergic receptor. On the other hand, an increase in ATP resp onse could be observed in DITNC cells exposed to conditioned medium ob tained after IL-1 beta treatment. It can be concluded that exposure of astrocytes to cytokines may lead to an increase in receptor-mediated poly-PI signaling activity and this may involve compounds secreted int o the culture medium, e.g., the secretory phospholipase A(2).