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.

The interleukin-8 (IL-8/CXCL8) receptors, CXCR1 and CXCR2, couple to Gαi to induce leukocyte recruitment and activation at sites of inflammation. We have recently shown that CXCR1 couples predominantly to the G protein-coupled receptor (GPCR) kinase-2 (GRK2) whereas CXCR2 interacts with GRK6 to regulate cellular responses. In addition to GPCRs, GRKs have displayed a more diverse protein/protein interaction in cells. In this study we sought to identify GRK6 binding partner(s) that may influence CXCL8 activities, using RBL-2H3 cells stably expressing CXCR1 (RBL-CXCR1) or CXCR2 (RBL-CXCR2), as well as human and murine neutrophils. The data herein demonstrated that upon CXCR2 activation, GRK6 interacts with activator of G protein signaling 3 (AGS3) and Gαi2 to form a GRK6/AGS3/Gαi2 complex. This complex is time-dependent and peaked at 2-3 min post-activation. GTPγS pretreatment blocked GRK6/AGS3/Gαi2 formation suggesting that this assembly depends on G protein activation. Surprisingly, CXCR2 activation induced AGS3 phosphorylation in a PKC-dependent but GRK6-independent fashion. Overexpression of AGS3 in RBL-CXCR2 significantly inhibited CXCL8-induced Ca2+ mobilization, phosphoinositide (PI) hydrolysis and chemotaxis. In contrast, shRNA inhibition of AGS3 enhanced CXCL8-induced Ca2+ mobilization, receptor resistance to desensitization and recycling to the cell surface with no effect in receptor internalization. Interestingly, RBL-CXCR2-AGS3−/− cells displayed a significant increase in CXCR2 expression in the cell surface, but decreased (extracellular signal-regulated kinases) ERK1/2 and P38 mitogen-activated protein kinase (MAPK) activation. Taken together, these results indicate that GRK6 complexes with AGS3-Gαi2 to regulate CXCR2-mediated leukocyte functions at different levels including downstream effector activation, receptor trafficking and expression at the cell membrane.

Abstract Prostate cancer (PCa) is a leading cause of cancer death among men, with greater prevalence of the disease among the African American population in the USA. Activator of G-protein signaling 3 (AGS3/G-protein signaling modulator 1) was shown to be overexpressed in prostate adenocarcinoma relative to the prostate gland. In this study, we investigated the correlation between AGS3 overexpression and PCa malignancy. Immunoblotting analysis and real-time quantitative-PCR showed increase in AGS3 expression in the metastatic cell lines LNCaP (~3-fold), MDA PCa 2b (~2-fold), DU 145 (~2-fold) and TRAMP-C1 (~20-fold) but not in PC3 (~1-fold), relative to control RWPE-1. Overexpression of AGS3 in PC3, LNCaP and MDA PCa 2b enhanced tumor growth. AGS3 contains seven tetratricopeptide repeats (TPR) and four G-protein regulatory (GPR) motifs. Overexpression of the TPR or the GPR motifs in PC3 cells had no effect in tumor growth. Depletion of AGS3 in the TRAMP-C1 cells (TRAMP-C1-AGS3-/-) decreased cell proliferation and delayed wound healing and tumor growth in both C57BL/6 (~3-fold) and nude mice xenografts, relative to control TRAMP-C1 cells. TRAMP-C1-AGS3-/- tumors also exhibited a marked increase (~5-fold) in both extracellular signal-regulated kinase (ERK) 1/2 and P38 mitogen-activated protein kinase (MAPK) activation, which correlated with a significant increase (~3-fold) in androgen receptor (AR) expression, relative to TRAMP-C1 xenografts. Interestingly, overexpression of AGS3 in TRAMP-C1-AGS3-/- cells inhibited ERK activation and AR overexpression as compared with control TRAMP-C1 cells. Taken together, the data indicate that the effect of AGS3 in prostate cancer development and progression is probably mediated via a MAPK/AR-dependent pathway.

Prostate cancer constitutes a serious health challenge and remains one of the main causes of cancer-related death among men. The more aggressive form of the disease has been attributed to androgen independence; resulting in lack of response to androgen deprivation therapy and sustained activation of other growth pathways. The scaffold proteins β-arrestin 1 and 2 (βarr1 and βarr2) which are known to mediate G protein-coupled receptor desensitization and internalization, were also shown to modulate prostate tumorigenesis. βarr1 is significantly overexpressed (>4 fold) in prostate cancer cells relative to βarr2. In this study, we investigated the effect of βarr1 overexpression in prostate cancer development and progression using the mouse and human PCa cell xenografts, and autochthonous transgenic adenocarcinoma mouse prostate (TRAMP) models deficient in β-arrestins Depletion of βarr1 in TRAMP mice (TRAMP/βarr1 -/-) increased PCa growth and decreased overall survival relative to control TRAMP or TRAMP/βarr2 -/- animals. Prostate tissues from TRAMP/βarr1 -/- tumors displayed an increase in androgen receptor expression whereas overexpression of βarr1 in TRAMP-C1 (TRAMP-C1-βarr1-GFP) which derived from TRAMP decreased AR expression, cell proliferation and tumor growth in nude mice xenografts, relative to control TRAMP-C1-GFP. Knockdown of βarr1 expression in human MDA PCa 2b cells (MDA PCa 2b-βarr1 -/-) also decreased AR expression cell proliferation and tumor growth relative to control (MDA PCa 2b-Sham) cells. Interestingly, both TRAMP-C1-βarr1-GFP and MDA PCa 2b-βarr1 -/- xenografts showed a decrease in AKT phosphorylation, but an increase MAPK activation. Altogether, the data indicate that the effect of βarr1 in modulating AR signaling to regulate prostate cancer aggressiveness is cell and host autonomous.

G protein coupled receptor kinases (GRKs) phosphorylate the activated form of G protein coupled receptors (GPCRs) followed by the association of β-arrestin (βarr) with the phosphorylated 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 sought to investigate the role of GRK6 in CXCR2-mediated tumorigenesis using a murine model 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 pro-angiogenic chemokine or vascular endothelial growth factor (VEGF), but up-regulated matrix metalloproteinase (MMP)-2 and MMP-9 release, tumor-infiltrating PMNs and microvessel density. Treatment of the mice with a CXCR2 inhibitor (SB225002) or a murine anti-CXCR2 antibody blocked the effect of GRK6 deletion. Surprisingly, a GRK6−/−/βarr2−/− double knockout animal model exhibited faster tumor growth relative to GRK6−/− or βarr2−/− animals. Exposure of GRK6−/−/βarr2−/− mice to the anti-CXCR2 antibody totally inhibited tumor growth. This suggest that the effects of βarr2 and GRK6 knockdown in CXCR2-mediated tumor development are additive. 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−/− mice showed greater tumor growth relative to GRK6−/− or βarr2−/− mice, the data also suggest that CXCR2 couples to a different mechanism to mediate tumor progression and metastasis. Citation Format: Natalie Sutton, Nikia Smith, Ariel J. Thomas, Sandeep K. Raghuwanshi, Ricardo M. Richardson. GRK6 deficiency promotes tumor aggressiveness and metastasis in a murine model of human lung cancer . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2821. doi:10.1158/1538-7445.AM2013-2821

Ginger active components are widely known for being a potent antioxidant and recently as a potential anticancer agent. [6]-Gingerol, the most abundant and pungent bioactive component of ginger, was shown to inhibit angiogenesis and tumorigenesis in xenograph models of both prostate cancer (PCa) and melanoma. To date, the precise mechanism(s) for the antitumor effect of ginger is not well understood. The adaptor proteins, β-arrestins, have been shown to modulate tumor development and metastasis in both PCa and melanoma. In this study, we sought to determine the role of [6]-gingerol in β-arrestin (βarr) 1 and 2-mediated PCa and melanoma development, progression, and metastasis. To that end, the PCa cells PC-3 and the melanoma B16-F10 cells were treated with different concentrations of [6]-gingerol for 48 hours. Cell lysates were assayed by Western blot analysis for βarr-1 and βarr-2, CXCR1, and CXCR2 expression, as well as MAP kinase and transcription factors activation. The data demonstrated that pretreatment with [6]-gingerol caused a dose-dependent inhibition of βarr-2, but not βarr-1, in both cell lines, which correlated with significant decrease in Akt and NF-κB activation. [6]-Gingerol pretreatment decreased CXCR1 and CXCR2 expression, CXCL-8-induced intracellular calcium mobilization; and delayed wound closure. [6]-Gingerol exposure also decreased PC-3 and B16 metastasis in zebrafish. Altogether the data indicated that the protective effect of [6]-gingerol in tumorigenesis is likely mediated via a βarr-2-dependent mechanism. Citation Format: Tonelia A. Mowart, Timothy Adekoya, Nikia Smith, Tonya S. Lane, Ricardo M. Richardson. Ginger consumption inhibits β-arrestin-2 expression and functions in melanoma and prostate cancer cells [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B005.

Prostate cancer (PCa) is a leading cause of cancer death among men, with greater prevalence of the disease among the African American population in the US. Activator of G-protein Signaling 3 (AGS3/GPSM1), a receptor-independent activator of G-protein signaling has been shown to affect different cellular processes and cell cycle activity as well as tumor growth and development. AGS3 contains seven tetratricopeptide (TPR) repeats in its N-terminal half and four G-protein regulatory (GPR) motifs in its C-terminal half. The aim of this study is to assess the role of AGS3 in prostate cancer development and metastasis as well as to understand the molecular dynamics involved. To that end, the metastatic PCa cell lines LNCaP, PC3, MDA PCa 2b and DU-145 were analysed for AGS3 expression relative to RWPE-1, a non-metastatic Pca cell line. Quantitative RT-PCR and western blot analysis have shown that AGS3 expression varies in the PCa cell lines relative to control RWPE-1. Overexpression of AGS3 in PC3 and LNCaP cells significantly enhanced tumor progression in nude mice xenografts. Interestingly, expression of the TPR, not the GPR, repeats in LNCaP promoted tumor growth as well as the full length AGS3. Preliminary studies with a Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) mice deficient in AGS3 expression (TRAMP+/AGS3-/-) displayed decrease prostate tumorigenesis. Taken together, these results indicate that AGS3 expression promotes prostate tumor growth. The data also suggest that the effect of AGS3 in prostate tumorigenesis is mediated via its TPR, not GPR motif. Citation Format: Timothy O. Adekoya, Nikia Smith, Tonelia Mowatt, Temilade Aladeniyi, Ricardo M. Richardson. Effect of activator of G-protein signaling 3 (AGS3) on prostate tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5745.

African American men are more likely to develop and die from prostate cancer than Caucasian American men. While a complex interaction of social, environmental, and biological factors is likely to blame, molecular mechanisms of prostate cancer disparity remain poorly understood. Elucidation of these mechanisms is critical if we are to achieve better treatment options and ultimately, patient survival for African American men. β-arrestin-2 was initially recognized for its role in G-protein coupled receptor desensitization. More recent studies have demonstrated that several pathways critical to prostate cancer progression converge at β-arrestin-2 including androgen metabolism, angiogenesis, and metastasis. Preliminary data in our lab shows that prostate cell lines derived from Caucasian American men express less -arrestin-2 than those from African American men. This study aims to test the hypothesis that loss of β-arrestin-2 expression in prostate tumors attenuates tumor progression. In order to study this, we have established a β-arrestin-2 deficient TRAMP mouse model. TRAMP+/β-arrestin-2 KO mice develop tumors that are smaller than those in TRAMP+/β-arrestin-2 WT mice at 6 months of age. Similar results were observed when orthotopic TRAMP-C1 tumors were established in C57BL/6 mice. β-arrestin-2 knockdown in these cells resulted in delayed tumor growth. Taken together these data support the idea that increased β-arrestin-2 expression correlates with enhanced tumor progression providing a possible biological mechanism of prostate cancer disparity. Citation Information: Cancer Epidemiol Biomarkers Prev 2011;20(10 Suppl):B46.