GRK2 and prostate carcinoma: Finally, expression of an inhibitory peptide derived from the c-terminus of the ADRBK1 protein strongly inhibited growth of prostate cancer cells in vitro and in vivo, suggesting that GPCR signaling is a central positive regulator of cell cycle progression in these cells [50], although it remains unclear if this effect is directly linked to a specific regulatory function of ADRBK1 or results from global inhibitory effects of the c-terminal fragment.