The C-terminal Helix 9 motif regulates cannabinoid receptor type 1 trafficking and surface expression

Cannabinoid type 1 receptor (CB1R) is only stably surface expressed in axons, where it downregulates neurotransmitter release. How this tightly regulated axonal surface polarity is established and maintained is unclear. To address this question, we used time-resolved imaging to determine the trafficking of CB1R from biosynthesis to mature polarised localisation. We show that the secretory pathway delivery of CB1R is axonally biased and that surface expressed CB1R is more stable in axons than in dendrites. This dual mechanism is mediated by the CB1R C-terminal and involves the Helix 9 ( H9 ) domain. Removal of the H9 domain increases dendrite secretory pathway delivery and decreases in surface stability. Furthermore, CB1R ΔH9 is more sensitive to agonist-induced internalisation and less efficient at downstream signalling than CB1R WT . Together, these results shed new light on how polarity of CB1R is mediated and indicate that the C-terminal H9 domain plays key roles in this process.