GRK6 deficiency promotes angiogenesis, tumor progression and metastasis

G protein coupled receptor kinases (GRKs) phosphorylate the activated form of G protein coupled receptors (GPCRs) leading to receptor desensitization and down-regulation. We have recently shown that the chemokine receptor, CXCR2, couples to GRK6 to regulate cellular responses including chemotaxis, angiogenesis and wound healing. In this study, we investigate the role of GRK6 in tumorigenesis using murine models of human lung cancer. Mice deficient in GRK6 (GRK6 −/− ) exhibited a significant increase in Lewis lung cancer (LLC) growth and metastasis relative to control littermates (GRK6 +/+ ). GRK6 deletion had no effect on the expression of proangiogenic chemokine or vascular endothelial growth factor (VEGF), but up-regulated matrix metalloproteinase (MMP)-2 and MMP-9 release, tumor-infiltrating PMNs and microvessel density. Since βarr2 −/− mice exhibited increase LLC growth and metastasis similar to that of GRK6 −/− we developed a double GRK6 −/− /βarr2 −/− mouse model. Surprisingly, GRK6 −/− /βarr2 −/− mice exhibited faster tumor growth relative to GRK6 −/− or βarr2 −/− mice. Treatment of the mice with anti-CXCR2 antibody inhibited tumor growth in both GRK6 −/− and GRK6 −/− /βarr2 −/− animals. Altogether, the results indicate that CXCR2 couples to GRK6 to regulate angiogenesis, tumor progression and metastasis. Deletion of GRK6 increases the activity of the host CXCR2, resulting in greater PMN infiltration and MMP release in the tumor microenvironment thereby promoting angiogenesis and metastasis. Since GRK6 −/− /βarr2 −/− showed greater tumor growth relative to GRK6 −/− or βarr2 −/− mice, the data further suggest that CXCR2 couples to different mechanisms to mediate tumor progression and metastasis.