The intracellular trafficking of opioid receptors directed by carboxyl tail and a di-leucine motif in Neuro2A cells

The μ- and δ-opioid receptors (MOR and DOR) differ significantly in their intracellular trafficking. MORs recycle back to the cell surface upon agonist treatment, whereas most internalized DORs are targeted to lysosomes for degradation. By exchanging the carboxyl tail domains of MOR and DOR and expressing the receptor chimeras in mouse neuroblastoma Neuro2A cells, it could be demonstrated that the carboxyl tail domain is not the sole determinant in directing the intracellular trafficking in these Neuro2A cells. Deletion of the dileucine motif (Leu²⁴⁵-Leu²⁴⁶) within the third intracellular loop of DOR or the mutation of Leu²⁴⁵ to Met slowed the lysosomal targeting of these δ-opioid receptors. Meanwhile the mutation of Met²⁶⁴ to Leu increased the rate of agonist-induced receptor internalization and the lysosomal targeting of the wild type and the δ-opioid receptor carboxyl tail chimera of the μ-opioid receptor. These studies suggest interplay between a di-leucine motif and the carboxyl tail in the lysosomal targeting of the receptor.