Ubiquitylation of the chemokine receptor CCR7 enables efficient receptor recycling and cell migration

Abstract

SummaryThe chemokine receptor CCR7 is essential for lymphocyte and dendritic cell homing to secondary lymphoid organs. Owing to the ability to induce directional migration, CCR7 and its ligands CCL19 and CCL21 are pivotal for the regulation of the immune system. Here, we identify a novel function for receptor ubiquitylation in the regulation of the trafficking process of this G-protein-coupled seven transmembrane receptor. We discovered that CCR7 is ubiquitylated in a constitutive, ligand-independent manner and that receptor ubiquitylation regulates the basal trafficking of CCR7 in the absence of chemokine. Upon CCL19 binding, we show that internalized CCR7 recycles back to the plasma membrane via the trans-Golgi network. An ubiquitylation-deficient CCR7 mutant internalized normally after ligand binding, but inefficiently recycled in immune cells and was transiently retarded in the trans-Golgi network compartment of HEK293 transfectants. Finally, we demonstrate that the lack of CCR7 ubiquitylation profoundly impairs immune cell migration. Our results provide evidence for a novel function of receptor ubiquitylation in the regulation of CCR7 recycling and immune cell migration.

Overview and potential unifying themes of the atypical chemokine receptor family

“…2B). However, of note, constitutive trafficking is not a unique feature of scavenger ACKRs, as increasing, emerging evidence indicates that several conventional chemokine receptors also undergo constitutive internalization and recycling in specific cell types and conditions (CXCR4 [141][142][143]; CXCR3 [144]; CCR7 [145]; CCR1 [146]). Interestingly, constitutive trafficking correlates with ACKR subcellular localization, as scavenger ACKRs are mainly located in recycling endosomes [138][139][140] [unpublished results], whereas transporter and presenter ACKRs are preferentially expressed on the cell membrane [42, 62,82,128,129] (Fig.…”

On the move: endocytic trafficking in cell migration

“…After internalization, CCR7 enters the recycling compartment and traffics back to the plasma membrane to actively participate in directed cell migration, whereas its ligand CCL19 is sorted to lysosomes for degradation [19]. Interestingly, ubiquitylation of CCR7 serves as control mechanism for receptor trafficking as an ubiquitylationdeficient mutant on one hand reduces the intracellular pool of CCR7 in the steady-state and, on the other hand, shows a significant retardation in receptor recycling after ligandmediated endocytosis, resulting in a reduced CCR7 surface pool and in inefficient cell migration [21].…”

Endocytic trafficking of chemokine receptors

“…CCR7 is also constitutively ubiquitinated, however, in contrast to CXCR7, agonist has no effect on its ubiquitination status [47]. Constitutive ubiquitination of CXCR7 and CCR7 may serve to regulate cell surface expression of the receptors from an intracellular pool.…”