Adaptor protein complex 1 facilitates ciliary localization of serotonin receptor type 6

Area of Science:

• Cell Biology
• Neuroscience
• Molecular Biology

Background:

• Primary cilia are crucial cellular organelles involved in sensing extracellular stimuli.
• Specific G protein-coupled receptors (GPCRs), like serotonin receptor type 6 (Htr6), are found in primary cilia and mediate ciliary chemical detection.
• The transport mechanism of GPCRs to primary cilia is not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanism of Htr6 transport to primary cilia.
• To identify the specific protein interactions facilitating Htr6 ciliary localization.

Main Methods:

• Yeast two-hybrid screening to identify interacting proteins.
• Immunoprecipitation assays in HEK293T cells to confirm protein interactions.
• Gene ablation and rescue experiments in RPE-1 cells and cultured hippocampal neurons to assess the role of γ1-Adaptin in Htr6 ciliary localization.

Main Results:

• A specific region in the fourth intracellular domain of Htr6 (Htr6 i4) is sufficient for ciliary localization.
• Htr6 i4 interacts with the C-terminal region of γ1-Adaptin, a subunit of adaptor protein complex 1 (AP-1).
• Ablation of γ1-Adaptin significantly reduces Htr6 and Htr6 i4 localization to primary cilia in both cell lines and neurons, which can be rescued by exogenous γ1-Adaptin expression.

Conclusions:

• Htr6 ciliary localization is dependent on γ1-Adaptin and AP-1-mediated membrane trafficking.
• This study reveals a novel mechanism for GPCR transport into primary cilia, essential for their function in cellular signaling and homeostasis.