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

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 Ca2+ and cAMP signals initiated by serotonin. In the present study several monoclonal HEK293 cell lines were used, in particular, monitoring of Ca2+ signals were carried out on Fura-2 loaded cells expressed recombinant serotonin 5-HT2C receptors, cAMP signals were studied on cells expressed the genetically encoded cAMP sensor Pink Flamindo and recombinant 5-HT4 receptors, for monitoring PI3K activity cells stably expressed the genetically encoded PIP3 sensor PH(Akt)-Venus were used. It turned out that LY294002 suppressed Ca2+ signals initiated by activation 5-HT2C receptors irrespectively of PI3K inhibition, but did not affect cAMP responses initiated by 5-HT4 receptors. In turn LY303511 suppressed cAMP signals initiated by 5-HT4 receptors, and elicited Ca2+ transients exclusively in cells expressed 5-HT2C 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-HT2C and 5-HT4 receptors.