Adhesion g protein-coupled receptors: signaling, pharmacology, and mechanisms of activation.
ABSTRACT The adhesion G protein-coupled receptors (GPCRs) are a distinct family of more than 30 receptors in vertebrate genomes. These receptors have been shown to play pivotal roles in a diverse range of biological functions and are characterized by extremely large N termini featuring various adhesion domains capable of mediating cell-cell and cell-matrix interactions. The adhesion GPCR N termini also contain GPCR proteolytic site motifs that undergo autocatalytic cleavage during receptor processing to create mature GPCRs existing as noncovalently attached complexes between the N terminus and transmembrane regions. There is mounting evidence that adhesion GPCRs can couple to G proteins to activate a variety of different downstream signaling pathways. Furthermore, recent studies have demonstrated that adhesion GPCR N termini can bind to multiple ligands, which may differentially activate receptor signaling and/or mediate cell adhesion. In addition, studies on several distinct adhesion GPCRs have revealed that truncations of the N termini result in constitutively active receptors, suggesting a model of receptor activation in which removal of the N terminus may be a key event in stimulating receptor signaling. Because mutations to certain adhesion GPCRs cause human disease and because many members of this receptor family exhibit highly discrete distribution patterns in different tissues, the adhesion GPCRs represent a class of potentially important drug targets that have not yet been exploited. For this reason, understanding the mechanisms of activation for these receptors and elucidating their downstream signaling pathways can provide insights with the potential to lead to novel therapeutic agents.
- SourceAvailable from: Erwin G Van Meir[show abstract] [hide abstract]
ABSTRACT: Angiogenesis is a critical physiologic process that is appropriated during tumorigenesis. Little is known about how this process is specifically regulated in the brain. Brain angiogenesis inhibitor-1 (BAI1) is a brain-predominant seven-transmembrane protein that contains five antiangiogenic thrombospondin type-1 repeats (TSR). We recently showed that BAI1 is cleaved at a conserved proteolytic cleavage site releasing a soluble, 120 kDa antiangiogenic factor called vasculostatin (Vstat120). Vstat120 has been shown to inhibit in vitro angiogenesis and suppress subcutaneous tumor growth. Here, we examine its effect on the intracranial growth of malignant gliomas and further study its antitumor mechanism. First, we show that expression of Vstat120 strongly suppresses the intracranial growth of malignant gliomas, even in the presence of the strong proangiogenic stimulus mediated by the oncoprotein epidermal growth factor receptor variant III (EGFRvIII). This tumor-suppressive effect is accompanied by a decrease in tumor vascular density, suggesting a potent antiangiogenic effect in the brain. Second, and consistent with this interpretation, we find that treatment with Vstat120 reduces the migration of cultured microvascular endothelial cells in vitro and inhibits corneal angiogenesis in vivo. Third, we show that these antivascular effects critically depend on the presence of the cell surface receptor CD36 on endothelial cells in vitro and in vivo, supporting the role of Vstat120 TSRs in mediating these effects. These results advance the understanding of brain-specific angiogenic regulation, and suggest that Vstat120 has therapeutic potential in the treatment of brain tumors and other intracerebral vasculopathies.Cancer Research 02/2009; 69(3):1212-20. · 8.65 Impact Factor
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ABSTRACT: The heterodimeric CD97 protein is a member of the EGF-TM7 family of class II seven-transmembrane (7TM) receptors of 75-90 kDa and structurally related to the secretin receptor family. CD97 is expressed on leucocytes, lymphocytes and in cells of the hematopoietic system. The precise role for CD97 is still unknown. The ubiquitously expressed CD55 (also known as decay accelerating factor, DAF) protects host cells from complement attack. In addition, CD55 is a bacterial/viral receptor and was identified as a ligand for CD97. Employing computer aided UV-laser microdissection CD97 and CD55 were investigated in C-cells of non-neoplastic thyroid specimens (n=3) and in medullary thyroid carcinomas (n=54) by multiplex RT-PCR. Frozen sections of all tissues were investigated by immunohistochemistry. All non-malignant thyroid specimens expressed CD97 mRNA weakly and were devoid of immunoreactive CD97 protein. Transcripts for CD97 were detected in all 54 MTC tissue specimens and CD97 gene activity directly correlated with the histopathological stage of the MTC. CD97 transcriptional activity was high in advanced stages of MTC such as pT3/4. pT1/2 tumors with exclusive intrathyroidal growth revealed weak CD97 expression. CD55 gene expression was significantly lower in normal C-cells than in tumor tissues and all MTC displayed strong and specific CD55 immunostaining. We did not observe a correlation between the expression of CD55 mRNA or protein, respectively, and pTNM classification. In summary, in the present study we have identified CD97 as a novel marker expressed in dedifferentiated neoplastic human thyroid C-cells. CD97 and CD55 may facilitate adhesion of C-cell carcinoma to surrounding surfaces which would result in rapid tumor cell spread.International Journal of Oncology 03/2004; 24(2):285-94. · 2.66 Impact Factor
Article: Proteinase-activated receptors.[show abstract] [hide abstract]
ABSTRACT: Proteinase-activated receptors are a recently described, novel family of seven-transmembrane G-protein-coupled receptors. Rather then being stimulated through ligand receptor occupancy, activation is initiated by cleavage of the N terminus of the receptor by a serine protease resulting in the generation of a new tethered ligand that interacts with the receptor within extracellular loop-2. To date, four proteinase-activated receptors (PARs) have been identified, with distinct N-terminal cleavage sites and tethered ligand pharmacology. In addition to the progress in the generation of PAR-1 antagonists, we describe the role of thrombin in such processes as wound healing and the evidence implicating PAR-1 in vascular disorders and cancer. We also identify advances in the understanding of PAR-1-mediated intracellular signaling and receptor desensitization. The cellular functions, signaling events, and desensitization processes involved in PAR-2 activation are also assessed. However, other major aspects of PAR-2 are highlighted, in particular the ability of several serine protease enzymes, in addition to trypsin, to function as activators of PAR-2. The likely physiological and pathophysiological roles for PAR-2 in skin, intestine, blood vessels, and the peripheral nervous system are considered in the context of PAR-2 activation by multiple serine proteases. The recent discovery of PAR-3 and PAR-4 as additional thrombin-sensitive PARs further highlights the complexity in assessing the effects of thrombin in several different systems, an issue that remains to be fully addressed. These discoveries have also highlighted possible PAR-PAR interactions at both functional and molecular levels. The future identification of other PARs and their modes of activation are an important future direction for this expanding field of study.Pharmacological Reviews 07/2001; 53(2):245-82. · 22.35 Impact Factor