Aberrant signaling through G-protein coupled receptors promotes metastasis, the major cause of breast cancer death. We identified regulator of G-protein signaling 4 (RGS4) as a novel suppressor of breast cancer migration and invasion, important steps of metastatic cascades. By blocking signals initiated through G i -coupled receptors, such as proteaseactivated receptor 1 and CXC chemokine receptor 4, RGS4 disrupted Rac1-dependent lamellipodia formation, a key step involved in cancer migration and invasion. RGS4 has GTPaseactivating protein (GAP) activity, which inhibits G-protein coupled receptor signaling by deactivating G-proteins. An RGS4 GAP-deficient mutant failed to inhibit migration and invasion of breast cancer cells in both in vitro assays and a mouse xenograft model. Interestingly, both established breast cancer cell lines and human breast cancer specimens showed that the highest levels of RGS4 protein were expressed in normal breast epithelia and that RGS4 down-regulation by proteasome degradation is an index of breast cancer invasiveness. Proteasome blockade increased endogenous RGS4 protein to levels that markedly inhibit breast cancer cell migration and invasion, which was reversed by an RGS4-targeted short hairpin RNA. Our findings point to the existence of a mechanism for posttranslational regulation of RGS4 function, which may have important implications for the acquisition of a metastatic phenotype by breast cancer cells. Preventing degradation of RGS4 protein should attenuate aberrant signal inputs from multiple G i -coupled receptors, thereby retarding the spread of breast cancer cells and making them targets for surgery, radiation, and immune treatment.

Signaling through G protein-coupled receptors (GPCRs) promotes breast cancer metastasis. G proteins convey GPCR signals by dissociating into G␣ and G␤␥ subunits. The aim of the present study was to determine whether blockade of G␤␥ signaling suppresses breast cancer cell migration and invasion, which are critical components of metastasis. Conditioned media (CM) of NIH-3T3 fibroblasts are widely used as chemoattractants in in vitro cancer metastasis studies. Expression of a G␤␥ scavenger peptide attenuated NIH-3T3 CM-induced migration and invasion of both metastatic breast cancer MDA-MB-231 and MDA-MB-436 cells by 40 to 50% without effects on cell viability. Migration and invasion of cells in response to NIH-3T3 CM were also blocked by 8-(4,5,6-trihydroxy-3-oxo-3H-xanthen-9-yl)-1-naph-thalene-carboxylic acid) (M119K), a G␤␥ inhibitor, with maximum inhibition exceeding 80% and half-maximal inhibitory concentration (IC 50 ) values of 1 to 2 M.M119K also attenuated Rac-dependent formation of lamellipodia, a key structure required for metastasis. Constitutively active Rac1 rescued G␤␥ blockade-mediated inhibition of breast cancer cell migration, whereas dominant negative Rac1 inhibited cell migration similar to G␤␥ blockade. Furthermore, M119K suppressed G i protein-coupled CXC chemokine receptor 4 (CXCR4)-dependent MDA-MB-231 cell migration by 80% with an IC 50 value of 1 M, whereas tyrosine kinase receptor-dependent cell migration was significantly less inhibited. However, CXCR4-dependent inhibition of adenylyl cyclase, a G i ␣-mediated response in MDA-MB-231 cells, was not blocked by M119K but was blocked by pertussis toxin, which selectively inactivates G i ␣. This report is the first to directly demonstrate the role of G␤␥ in cancer cell migration and invasion and suggests that targeting G␤␥ signaling pathways may provide a novel strategy for suppressing breast cancer metastasis.Breast cancer is the second largest killer of women by cancer with approximately 40,000 deaths in the United States each year (Jemal et al., 2008). Patients who cannot be cured are primarily those in whom breast cancer has metastasized. Metastasis is a complex pathophysiological process, beginning with the migration and invasion of cancer cells into the surrounding tissues and lymphatics. From these sites, cancer cells can gain access to the circulation and proliferate to form new colonies at metastatic sites in vital organs such as the lung, bone, liver, and brain (StetlerStevenson and Kleiner, 2001). This directed cell migration and invasion is triggered by chemoattractants such as chemokines, growth factors, and matrix metalloproteases, which are sensed by cancer cell surface receptors including integrins, receptor tyrosine kinases, and G protein-coupled receptors (GPCRs). Evidence from preclinical and clinical studies shows excessive activation of GPCRs in breast cancer caused by overexpression of receptors, abnormally elevated ligands for GPCRs, and/or down-regulation of RGS proteins (Dorsam and Gutkind, 2007;Xie et al., 200...

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Metastasis is the major cause of breast cancer mortality. We recently reported that aberrant G-protein coupled receptor (GPCR) signaling promotes breast cancer metastasis by enhancing cancer cell migration and invasion. Phosphatidylinositol 3-kinase γ (PI3Kγ) is specifically activated by GPCRs. The goal of the present study was to determine the role of PI3Kγ in breast cancer cell migration and invasion. Immunohistochemical staining showed that the expression of PI3Kγ protein was significantly increased in invasive human breast carcinoma when compared to adjacent benign breast tissue or ductal carcinoma in situ. PI3Kγ was also detected in metastatic breast cancer cells, but not in normal breast epithelial cell line or in non-metastatic breast cancer cells. In contrast, PI3K isoforms α, β and δ were ubiquitously expressed in these cell lines. Overexpression of recombinant PI3Kγ enhanced the metastatic ability of non-metastatic breast cancer cells. Conversely, migration and invasion of metastatic breast cancer cells were inhibited by a PI3Kγ inhibitor or by siRNA knockdown of PI3Kγ but not by inhibitors or siRNAs of PI3Kα or PI3Kβ. Lamellipodia formation is a key step in cancer metastasis, and PI3Kγ blockade disrupted lamellipodia formation induced by the activation of GPCRs such as CXC chemokine receptor 4 and protease-activated receptor 1, but not by the epidermal growth factor tyrosine kinase receptor. Taken together, these results indicate that upregulated PI3Kγ conveys the metastatic signal initiated by GPCRs in breast cancer cells, and suggest that PI3Kγ may be a novel therapeutic target for development of chemotherapeutic agents to prevent breast cancer metastasis.

Titanium dioxide (TiO2) polymorphs have recently gained a lot of attention in dye-sensitized solar cells (DSSCs). The brookite polymorph, among other TiO2 polymorphs, is now becoming the focus of research in DSSC applications, despite the difficulties in obtaining it as a pure phase experimentally. The current theoretical study used different nonmetals (C, S and N) and (C-S, C-N and S-N) as dopants and co-dopants, respectively, to investigate the effects of mono-doping and co-doping on the electronic, structural, and optical structure properties of (210) TiO2 brookite surfaces, which is the most exposed surface of brookite. The results show that due to the narrowing of the band gap and the presence of impurity levels in the band gap, all mono-doped and co-doped TiO2 brookite (210) surfaces exhibit some redshift. In particular, the C-doped, and C-N co-doped TiO2 brookite (210) surfaces exhibit better absorption in the visible region of the electromagnetic spectrum in comparison to the pure, S-doped, N-doped, C-S co-doped and N-S co-doped TiO2 brookite (210) surfaces.