PI3 kinase-unrelated effects of LY294002 and LY303511 on serotonin-induced Ca2+and cAMP signaling

ABSTRACT The phosphoinositide 3-kinase (PI3K) is involved in regulation of multiple intracellular processes. Although the inhibitory analysis is generally employed for validating a physiological role of PI3K, increasing body of evidence suggests that PI3K inhibitors can exhibit PI3K-unrelated activity as well. Here we studied effects of PI3K inhibitor LY294002 and its inactive analogue LY303511 on Ca 2+ and cAMP signals initiated by serotonin. In the present study several monoclonal HEK293 cell lines were used, in particular, monitoring of Ca 2+ signals were carried out on Fura-2 loaded cells expressed recombinant serotonin 5-HT 2C receptors, cAMP signals were studied on cells expressed the genetically encoded cAMP sensor Pink Flamindo and recombinant 5-HT 4 receptors, for monitoring PI3K activity cells stably expressed the genetically encoded PIP 3 sensor PH(Akt)-Venus were used. It turned out that LY294002 suppressed Ca 2+ signals initiated by activation 5-HT 2C receptors irrespectively of PI3K inhibition, but did not affect cAMP responses initiated by 5-HT 4 receptors. In turn LY303511 suppressed cAMP signals initiated by 5-HT 4 receptors, and elicited Ca 2+ transients exclusively in cells expressed 5-HT 2C receptors. Based on these facts and the results of the inhibitory analysis, we hypothesize that the described effects may be due to the activity of LY294002 and LY303511 on the serotonin 5-HT 2C and 5-HT 4 receptors.