G protein-coupled Receptor Kinase 6 (GRK6) is one of 7 members of the GRK serine/threonine kinase subfamily, which are known primarily for their role in desensitizing activated G protein-coupled receptors (GPCRs) . GRKs function by phosphorylating serine/threonine residues in activated GPCRs. Upon phosphorylation these residues serve as binding sites for β-arrestin proteins, inhibiting re-activation of GPCRs by blocking their re-association with G proteins . There is evidence that GRKs can also modulate selected non-GPCR signaling pathways . For example, GRK6 has been shown to modulate the Wnt signaling pathway via phosphorylation of LRP6 , and the insulin-like growth factor signaling pathway. GRK6 may also play a role in immune system function. Investigators have found GRK6 expression is typically abundant in hematopoietic tumor cell lines, and a recent research study demonstrated that GRK6 suppression was selectively lethal for a number of myeloma tumor cell lines .