Endosomal Chemokine Receptor Signaling as Basis for Metastasis in Malignant Melanoma

Melanoma is the deadliest form of skin cancer with few treatment options to patients with advanced metastatic disease.

Melanoma metastasis to lymph nodes is associated with expression of the chemokine receptor CCR7, a member of the G protein-coupled receptors (GPCRs) superfamily that promote cell migration of immune cells. Classically, upon agonist stimulation, GPCRs at the cell membrane activate heterotrimeric G proteins, causing downstream signaling throughout the cell. In order to terminate G protein signaling, cells have devised a specialized desensitization mechanism that includes receptor phosphorylation by GPCR kinases and subsequent recruitment of β-arrestins (βarrs) to the phosphorylated receptors. The GPCR–βarrs interaction both blocks the G proteinbinding site and promotes receptor endocytosis.

However, we recently discovered that some GPCRs interact with G proteins and βarrs simultaneously to form GPCR–G protein–βarr ‘megaplexes’, which allows the receptor to continue to stimulate G protein signaling while being internalized into endosomes by βarrs. Our preliminary results suggest that CCR7 forms megaplexes and promotes G protein signaling from internalized compartments. Interestingly, endosomal signaling, in general, is highly involved in cell migration, and different proteins are trafficked between plasma membrane and endosomes during this process. Thus, the proposed project aims to investigate the involvement of endosomal CCR7 signaling in melanoma cell migration. Furthermore, using a combination of highly advanced cryo-electron tomography and APEX2 proteomics, we will visualize the mechanism of CCR7-mediated melanoma cell migration protein-by-protein. Such detailed mechanistic knowledge will assist in designing innovative therapeutics to treat metastatic malignant melanoma.