Potent inhibition of angiotensin AT1 receptor signaling by RGS8: importance of the C-terminal third exon part of its RGS domain.

R4/B subfamily RGS (regulator of G protein signaling) proteins play roles in regulation of many GPCR-mediated responses. Multiple RGS proteins are usually expressed in a cell, and it is difficult to point out which RGS protein species are functionally important in the cell. To evaluate intrinsic potency of these RGS proteins, we compared inhibitory effects of RGS1, RGS2, RGS3, RGS4, RGS5, RGS8 and RGS16 on AT1 receptor signaling. Intracellular Ca(2+) responses to angiotensin II were markedly attenuated by transiently expressed RGS2, RGS3 and RGS8, compared to weak inhibition by RGS1, RGS4, RGS5 and RGS16. N-terminally deleted RGS2 (RGS2 domain) lost this potent inhibitory effect, whereas RGS domains of RGS3 and RGS8 showed strong inhibition similar to those of the full-length proteins. To investigate key determinants that specify the differences in potency, we constructed chimeric domains by replacing one or two of three exon parts of RGS8 domain with the corresponding part of RGS5. The chimeric RGS8 domains containing the first or the second exon part of RGS5 showed strong inhibitory effects similar to that of wild type RGS8, but the chimeric domain with the third exon part of RGS5 lost its activity. On the contrary, replacement of the third exon part of RGS5 with the corresponding residues of RGS8 increased the inhibitory effect. The role of the third exon part of RGS8 domain was further confirmed with the chimeric RGS8/RGS4 domains. These results indicate the potent inhibitory activity of RGS8 among R4/B subfamily proteins and importance of the third exon.

Potent and selective inhibition of angiotensin AT1 receptor signaling by RGS2: roles of its N-terminal domain.

Emerging evidence indicates that R4/B subfamily RGS (regulator of G protein signaling) proteins play roles in functional regulation in the cardiovascular system. In this study, we compared effects of three R4/B subfamily proteins, RGS2, RGS4 and RGS5 on angiotensin AT1 receptor signaling, and investigated roles of the N-terminus of RGS2. In HEK293T cells expressing AT1 receptor stably, intracellular Ca(2+) responses induced by angiotensin II were much more strongly attenuated by RGS2 than by RGS4 and RGS5. N-terminally deleted RGS2 proteins lost this potent inhibitory effect. Replacement of the N-terminal residues 1-71 of RGS2 with the corresponding residues (1-51) of RGS5 decreased significantly the inhibitory effect. On the other hand, replacement of the residues 1-51 of RGS5 with the residues 1-71 of RGS2 increased the inhibitory effect dramatically. Furthermore, we investigated functional contribution of N-terminal subdomains of RGS2, namely, an N-terminal region (residues 16-55) with an amphipathic α helix domain (the subdomain N1), a probable non-specific membrane-targeting subdomain, and another region (residues 56-71) between the α helix and the RGS box (the subdomain N2), a probable GPCR-recognizing subdomain. RGS2 chimera proteins with the residues 1-33 or 34-52 of RGS5 showed weak inhibitory activity, and either of RGS5 chimera proteins with residues 1-55 or 56-71 of RGS2 showed strong inhibitory effects on AT1 receptor signaling. The present study indicates the essential roles of both N-terminal subdomains for the potent inhibitory activity of RGS2 on AT1 receptor signaling.

Up-regulation of CXC chemokines and their receptors: implications for proinflammatory microenvironments of ovarian carcinomas and endometriosis.

Molecular abnormalities in the epithelial cells of endometriosis and their relevance to carcinogenesis of the ovary have been well studied. On the other hand, the differences of proinflammatory microenvironments between endometriosis and ovarian carcinomas have not been well documented yet. In this study, the expression patterns of CXC chemokines (IL-8, ENA-78, GRO-alpha, I-TAC, Mig, and SDF-1) and their receptors (CXCR2, CXCR3, and CXCR4) were compared among 12 ovarian carcinomas, 8 endometriosis, and 6 normal ovaries using quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry. The CXCR3-mediated signaling in ovarian carcinoma cells in vitro was also investigated. In quantitative reverse transcriptase polymerase chain reaction, ENA-78 was up-regulated both in endometriosis and carcinomas, whereas I-TAC was detected exclusively in carcinomas. CXCR3 was up-regulated both in carcinomas and endometriosis. However, immunohistochemical studies revealed that the localization of CXCR3 in carcinomas was distinctively different from that in endometriosis. In carcinoma-endometriosis coexisting cases, CXCR3-positive lymphocytes in benign lesions decreased in proportion as CXCR3-positive tumor cells replaced the tissues. CXCR3 was also detected in ovarian carcinoma cell lines in vitro. Administration of interferon gamma (IFN-gamma)-inducible chemokines induced extracellular signal-regulated kinase phosphorylation in these carcinoma cells. The results indicated that CXC chemokines might contribute to the progression of ovarian carcinomas and endometriosis in different manners. Aberrant expression of IFN-gamma-inducible chemokines and CXCR3 in carcinoma cells in association with reduced CXCR3-positive immune cells raised the possibility that IFN-gamma-inducible chemokines might not exert effective antitumor immune responses but that they might work in favor of tumor progression.

CD151 dynamics in carcinoma-stroma interaction: integrin expression, adhesion strength and proteolytic activity.

A member of tetraspanin CD151 is a scaffold protein of laminin-binding integrins and it plays an important role in stable interaction between cells and basement membrane. Although the upregulation of CD151 in tumor cells is thought to accelerate tumor invasion and metastasis, detailed pathological investigation on CD151 and its association with integrins has not been well documented, yet. In the present study, we showed that the expression levels of CD151 and its associated integrin subunits in epidermal carcinoma cell HSC5 were higher than those in immortalized epidermal cell HaCaT. By the stimulation of epidermal growth factor, CD151 was dissociated from cell surface and dispersed in the cytoplasm, and alpha3beta1 integrin was concomitantly internalized. To understand the significance of CD151 in tumor cell dynamics, CD151 in HSC5 was knocked down (HSC5(CD151-)), and the expression of integrin subunits and matrix metalloproteinases (MMPs) were investigated. In HSC5(CD151-), striking morphological alteration on Matrigel and laminin, and cytoskeletal rearrangements were demonstrated. alpha3beta1 integrin was internalized in part, and alpha6beta4 integrin was re-distributed from basal site to cell periphery. Quantitative RT-PCR, Western blot and zymography revealed that the expression levels of MMP2, MMP7 and MMP9 were markedly downregulated in HSC5(CD151-). Immunoprecipitation assay demonstrated that MMP7 was co-immunoprecipitated with CD151. In double stainings, MMP7 was colocalized with CD151 at the leading edge of lamellipodia under migratory status. These results elucidated the importance of CD151 as one of the key molecules for integrin-dependent carcinoma-stroma interaction. It is indicated that CD151 might contribute not only to cell stabilization by associating with adhesion complexes but also to cell migration by inducing integrins re-localization and MMPs production.

Phosphorylation of Ser166 in RGS5 by protein kinase C causes loss of RGS function.

RGS5 is a member of regulators of G protein signaling (RGS) proteins that attenuate heterotrimeric G protein signaling by functioning as GTPase-activating proteins (GAPs). We investigated phosphorylation of RGS5 and the resulting change of its function. In 293T cells, transiently expressed RGS5 was phosphorylated by endogenous protein kinases in the basal state. The phosphorylation was enhanced by phorbol 12-myristate 13-acetate (PMA) and endothelin-1 (ET-1), and suppressed by protein kinase C (PKC) inhibitors, H7, calphostin C and staurosporine. These results suggest involvement of PKC in phosphorylation of RGS5. In in vitro experiments, PKC phosphorylated recombinant RGS5 protein at serine residues. RGS5 protein phosphorylated by PKC showed much lower binding capacity for and GAP activity toward Galpha subunits than did the unphosphorylated RGS5. In cells expressing RGS5, the inhibitory effect of RGS5 on ET-1-induced Ca(2+) responses was enhanced by staurosporine. Mass spectrometric analysis of the phosphorylated RGS5 revealed that Ser166 was one of the predominant phosphorylation sites. Substitution of Ser166 by aspartic acid abolished the binding capacity to Galpha subunits and the GAP activity, and markedly reduced the inhibitory effect on ET-1-induced Ca(2+) responses. These results indicate that phosphorylation at Ser166 of RGS5 by PKC causes loss of the function of RGS5 in G protein signaling. Since this serine residue is conserved in RGS domains of many RGS proteins, the phosphorylation at Ser166 by PKC might act as a molecular switch and have functional significance.

Involvement of p38alpha mitogen-activated protein kinase in lung metastasis of tumor cells.

To study the role of p38 mitogen-activated protein kinase (p38) activity during the process of metastasis, p38alpha(+/-) mice were subjected to an in vivo metastasis assay. The number of lung colonies of tumor cells intravenously injected in p38alpha(+/-) mice was markedly decreased compared with that in wild-type (WT) mice. On the other hand, the time-dependent increase in tumor volume after subcutaneous tumor cells transplantation was comparable between WT and p38alpha(+/-) mice. Platelets of p38alpha(+/-) mice were poorly bound to tumor cells in vitro and in vivo compared with those of WT mice. E- and P-selectin mRNAs were markedly induced in the lung after intravenous injection of tumor cells. However, the induction of these selectin mRNAs in p38alpha(+/-) mice was weaker than that in WT mice. Furthermore, the resting expression levels of E-selectin in lung endothelial cells and P-selectin in platelets of p38alpha(+/-) mice were suppressed compared with those of WT mice. The number of tumor cells attached on lung endothelial cells of p38alpha(+/-) mice was significantly reduced compared with that of WT mice. The transmigrating activity of tumor cells through lung endothelial cells of p38alpha(+/-) mice was similar to that of WT mice. These results suggest that p38alpha plays an important role in extravasation of tumor cells, possibly through regulating the formation of tumor-platelet aggregates and their interaction with the endothelium involved in a step of hematogenous metastasis.

Pathophysiology of tumor neovascularization.

Neovascularization is essential to the process of development and differentiation of tissues in the vertebrate embryo, and is also involved in a wide variety of physiological and pathological conditions in adults, including wound repair, metabolic diseases, inflammation, cardiovascular disorders, and tumor progression. Thanks to cumulative studies on vasculature, new therapeutic approaches have been opened for us to some life-threatening diseases by controlling angiogenesis in the affected organs. In cancer therapy, for example, modulation of factors responsible for tumor angiogenesis may be beneficial in inhibiting of tumor progression. Several antiangiogenic approaches are currently under preclinical trial. However, the mechanisms of neovascularization in tumors are complicated and each tumor shows unique features in its vasculature, depending on tissue specificity, angiogenic micromilieu, grades and stages, host immunity, and so on. For better understanding and effective therapeutic approaches, it is important to clarify both the general mechanism of angiogenic events and the disease-specific mechanism of neovascularization. This review discusses the general features of angiogenesis under physiological and pathological conditions, mainly in tumor progression. In addition, recent topics such as contribution of the endothelial progenitor cells, tumor vasculogenic mimicry, markers for tumor-derived endothelial cells and pericytes, and angiogenic/angiostatic chemokines are summarized.

Up-regulation of the interferon gamma (IFN-gamma)-inducible chemokines IFN-inducible T-cell alpha chemoattractant and monokine induced by IFN-gamma and of their receptor CXC receptor 3 in human renal cell carcinoma.

BACKGROUND: The antiangiogenic CXC chemokines interferon gamma (IFN-gamma)-inducible T-cell alpha chemoattractant (I-TAC) and monokine induced by IFN-gamma (Mig) are known as members of IFN-gamma-inducible antiangiogenic CXC chemokines. However, the expression of these chemokines in highly angiogenic tumors remains poorly understood. The authors examined expression of I-TAC, Mig, and their receptor, CXCR3, in tissue samples from patients with renal cell carcinoma (RCC). METHODS: Twenty-one samples of untreated RCC and corresponding normal renal tissues were obtained from surgical specimens. The expression levels of I-TAC, Mig, and CXCR3 were investigated using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, real-time RT-PCR analysis, and Western blot analysis. Immunohistochemistry was carried out to clarify the localization of both chemokines and of CXCR3. RESULTS: RT-PCR analysis showed strong expression levels of I-TAC, Mig, and CXCR3 in RCC tissues and very weak or undetectable expression in normal kidney tissues. Real-time RT-PCR analysis showed that expression levels of I-TAC, Mig, and CXCR3 in RCC tissues were 14.9 times greater, 30.3 times greater, and 9.9 times greater compared with the levels in the corresponding normal kidney tissues, respectively (P < 0.01). Western blot analysis showed up-regulation of I-TAC, Mig, and CXCR3 at the protein level. Immunofluorescence double stainings revealed that I-TAC coincided with pericytes and vascular smooth muscle cells (VSMCs) in tumor angiogenic vessels. Mig was detected in tumor endothelial cells (TECs) and in infiltrating leukocytes. In the corresponding normal kidney tissues, neither VSMCs nor endothelial cells showed positive stainings for these chemokines. CXCR3 was expressed in both tumor cells and infiltrating leukocytes. CONCLUSIONS: The results revealed special feature of vascular mural cells and TECs in RCC. The up-regulated I-TAC and Mig, produced by tumor vessels, may interact with CXCR3 expressed in tumor cells, with possible pathophysiologic significance in RCC progression.

Expression of regulator of G protein signalling protein 5 (RGS5) in the tumour vasculature of human renal cell carcinoma.

The gene expression profiles of tumour and normal vasculature are distinctively different. The altered expression of various angiogenesis-related genes in tumour-derived endothelial cells has been investigated intensively, but there may be as yet unidentified molecules that regulate tumour angiogenesis. In the present study, the distinctive expression of regulator of G protein signalling protein 5 (RGS5) in tumour vessels in human renal cell carcinoma (RCC) has been clarified. RGS5 is a member of the RGS superfamily and acts as a negative regulator of heterotrimeric G protein-mediated signalling through G protein-coupled receptors (GPCRs). RT-PCR showed strong expression of RGS5 in all RCCs examined, but expression was very weak or undetectable in normal kidneys. By real-time RT-PCR, the ratio of RGS5 mRNA in RCC to that in normal kidney was 6.6 : 1 (p = 0.0012). In situ hybridization showed strong expression of RGS5 in vessels within tumour cell nests. It was expressed neither in tumour cells nor in normal renal capillaries. Immunohistochemical staining using serial sections for endothelial cell markers (CD31 and CD34) and smooth muscle cell markers (alpha-SMA and desmin), as well as fluorescence double staining, strongly suggested that tumour endothelial cells were the main location of RGS5 in RCC. These findings suggest that RGS5 may be involved in G protein-mediated signalling in tumour vessels in human RCC.

Characterization of a novel C. elegans RGS protein with a C2 domain: evidence for direct association between C2 domain and Galphaq subunit.

RGS (regulator of G protein signaling) proteins are GTPase-activating proteins (GAPs) for heterotrimeric G protein alpha subunits and negatively regulate G protein-mediated signal transduction. In this study, we determined the cDNA sequence of a novel Caenorhabditis elegans (C. elegans) RGS protein. The predicted protein, termed C2-RGS, consists of 782 amino acids, and contains a C2 domain and an RGS domain. C2 domains are typically known to be Ca(2+) and phospholipid binding sites, found in many proteins involved in membrane traffic or signal transduction, and most of their biological roles are not identified. To study the function of C2-RGS protein, a series of six truncated versions of C2-RGS were constructed. When the full-length protein of C2-RGS was expressed transiently in AT1a-293T cells, ET-1-induced Ca(2+) responses were strongly suppressed. When each of the mutants with either RGS domain or C2 domain was expressed, the Ca(2+) responses were suppressed moderately. Furthermore, we found that C2 domain of PLC-beta1 also had a similar moderate inhibitory effect. RGS domain of C2-RGS bound to mammalian and C. elegans Galphai/o and Galphaq subunits only in the presence of GDP/AlF(4)(-), and had GAP activity to Galphai3. On the other hand, C2 domains of C2-RGS and PLC-beta1 also bound strongly to Galphaq subunit, in the presence of GDP, GDP/AlF(4)(-), and GTPgammaS, suggesting the stable persistent association between these C2 domains and Galphaq subunit at any stage during GTPase cycle. These results indicate that both the RGS domain and the C2 domain are responsible for the inhibitory effect of the full-length C2-RGS protein on Galphaq-mediated signaling, and suggest that C2 domains of C2-RGS and PLC-beta1 may act as a scaffold module to organize Galphaq and the respective whole protein molecule in a stable signaling complex, both in the absence and presence of stimulus.