Role of β-Adrenergic Receptor Kinases in the Internalization of C-C Chemokine Receptor Seven (CCR7) in Mammalian T Cells

Abstract

Abstract Ligand mediated GPCR internalization/signaling is regulated by G protein-coupled receptor kinase (GRK) induced receptor phosphorylation and recruitment of β arrestins. The GPCR chemokine receptor, CCR7, has two ligands, CCL19 and CCL21 that mediate chemotactic migration of CCR7 expressing immune cells, including naïve T cells. Distinct internalization/signaling pathways are activated in T cells depending upon which ligand is bound to the receptor. It remains unclear to what extent the β-Adrenergic Receptor Kinase family, GRK2 and GRK3 regulate CCR7 internalization. Incubation of primary mouse T cells or human T cell lines, Hut 78 and CEM with 200 nM CCL19, but not CCL21 led to rapid CCR7 internalization. To determine the roles of GRK2 and GRK3 in CCR7 internalization, we co-transfected HEK cells with plasmids expressing either GRK2 or GRK3 along with arrestin-3, which we have previously shown is required for CCR7 internalization. Immunofluorescence microscopy showed that CCR7 co-localized with arrestin-3 in cells co-transfected with GRK2 after 30 minutes incubation with CCL19, but not CCL21. Limited co-localization of CCR7/arrestin-3 was observed in cells co-transfected with GRK3. Further CCL19/CCR7 incubation studies showed that GRK2-dependent CCR7 internalization was dependent upon the expression level of GRK2 with high protein levels being inhibitory. To further assess the role of GRK2, we used a GRK2 kinase dead mutant (GRK2-K220R) that does not facilitate the internalization of CCR7, GRK2-K220R did, however, result in some clustering of CCR7/arrestin-3. Overall, these data suggest that GRK2 plays an important role in CCR7 internalization in mammalian T cells; however, other GRKs are likely involved in this process.