Modification of the response of olfactory receptors to acetophenone by CYP1a2.

Olfaction is mediated by the binding of odorant molecules to olfactory receptors (ORs). There are numerous proteins in the nasal mucus, and they contribute to olfaction through various mechanisms. Cytochrome P450 (CYP) family members are known to be present in the olfactory epithelium and are thought to affect olfaction by enzymatic conversion of odorant molecules. In this study, we examined the effects of CYPs on the ligand responses of ORs in heterologous cells. Among the CYPs tested, co-expression of CYP1a2 significantly affected the responses of various ORs, including MOR161-2, to acetophenone. Conversion of acetophenone to methyl salicylate was observed in the medium of CYP1a2-expressing cells. MOR161-2-expressing cells exhibited significantly greater responses to methyl salicylate than to acetophenone. Finally, we analyzed the responses of olfactory neurons expressing MOR161-2 in vivo using the phosphorylated ribosomal protein S6 as a marker. MOR161-2 responded to both acetophenone and methyl salicylate in vivo. When the olfactory mucus was washed out by the injection of PBS to mouse nasal cavity, the response of MOR161-2 to acetophenone was reduced, while that to methyl salicylate did not change. Our data suggest that CYP1a2 affects OR activation by converting acetophenone to methyl salicylate.