Mechanisms of Ciliary Targeting of the Olfactory Cyclic Nucleotide-Gated Channel.

Abstract

The olfactory system gives us an awareness of our environment by allowing us to detect volatile airborne stimuli. The components necessary for this odorant detection are compartmentalized in the cilia of olfactory sensory neurons (OSNs). Mislocalization of ciliary proteins and/or the loss of cilia can cause impaired olfactory function, which is now recognized as a clinical manifestation of a broad class of human diseases termed ciliopathies. Despite the critical importance of the ciliary localization of these signaling proteins, very little is known about the mechanisms regulating cargo entry into this subcellular compartment. Through the work of this thesis, we have established that heteromeric assembly with the CNGB1b subunit of the olfactory cyclic nucleotide-gated (CNG) channel is necessary for delivery of the channel to cilia of OSNs, where it functions as a major target of the olfactory signaling cascade. In addition, we determined that a carboxyl-terminal RVxP motif is necessary, but not sufficient, for this ciliary targeting. We defined the mechanism for this subunit-dependent trafficking by demonstrating that CNGB1b associates with the intracellular trafficking protein phosphofurin acidic cluster-sorting protein 1 (PACS-1), and that PACS-1 function is necessary for CNG channel ciliary localization. Finally, we demonstrated a role for the kinesin motor, KIF17, in the ciliary localization of the CNG channel. The significance of these findings is that they represent the first demonstration of a role for KIF17 in mammalian ciliary transport. Additionally, they show a CNGB1b-dependent trafficking of the olfactory CNG channel, which suggests a delegation of functional responsibilities among CNG channel subunits. These reports also define the mechanism for this subunit-dependent trafficking and give us insight into the stability of membrane proteins once inserted in the ciliary compartment. Finally, this work elucidates some of the processes controlling entry of cargo into the ciliary compartment, which may give us some understanding of the mechanisms of human disease.