Phosphoinositide 3-kinase mediated signaling in lobster olfactory receptor neurons

In vertebrates and some invertebrates, odorant molecules bind to G protein-coupled receptors on olfactory receptor neurons (ORNs) to initiate signal transduction. Phosphoinositide 3-kinase (PI3K) activity has been implicated physiologically in olfactory signal transduction, suggesting a potential role for a G protein-coupled receptor-activated class I PI3K. Using isoform-specific antibodies, we identified a protein in the olfactory signal transduction compartment of lobster ORNs that is antigenically similar to mammalian PI3K gamma and cloned a gene for a PI3K with amino acid homology with PI3K beta. The lobster olfactory PI3K co-immunoprecipitates with the G protein alpha and beta subunits, and an odorant-evoked increase in phosphatidylinositol (3,4,5)-trisphosphate can be detected in the signal transduction compartment of the ORNs. PI3K gamma and beta isoform-specific inhibitors reduce the odorant-evoked output of lobster ORNs in vivo. Collectively, these findings provide evidence that PI3K is indeed activated by odorant receptors in lobster ORNs and further support the potential involvement of G protein activated PI3K signaling in olfactory transduction.