Epididymal G protein-coupled receptor (GPCR): two hats and a two-piece suit tailored at the GPS motif

Gene expression analysis of soft tissue sarcomas: characterization and reclassification of malignant fibrous histiocytoma

In soft tissue sarcomas, the diagnosis of malignant fibrous histiocytoma (MFH) has been a very controversial issue, and MFH is now considered to be reclassified into pleomorphic subtypes of other sarcomas. To characterize MFH genetically, we used an oligonucleotide microarray to analyze gene expression in 105 samples from 10 types of soft tissue tumors. Spindle cell and pleomorphic sarcomas, such as dedifferentiated liposarcoma, myxofibrosarcoma, leiomyosarcoma, malignant peripheral nerve sheath tumor (MPNST), fibrosarcoma and MFH, showed similar gene expression patterns compared to other tumors. Samples from those five sarcoma types could be classified into respective clusters based on gene expression by excluding MFH samples. We calculated distances between MFH samples and other five sarcoma types (dedifferentiated liposarcoma, myxofibrosarcoma, leiomyosarcoma, MPNST and fibrosarcoma) based on differentially expressed genes and evaluated similarities. Three of the 21 MFH samples showed marked similarities to one of the five sarcoma types, which were supported by histological findings. Although most of the remaining 18 MFH samples showed little or no histological resemblance to one of the five sarcoma types, 12 of them showed moderate similarities in terms of gene expression. These results explain the heterogeneity of MFH and show that the majority of MFHs could be reclassified into pleomorphic subtypes of other sarcomas. Taken together, gene expression profiling could be a useful tool to unveil the difference in the underlying molecular backgrounds, which leads to a rational taxonomy and diagnosis of a diverse group of soft tissue sarcomas.

Role of epididymal receptor HE6 in the regulation of sperm microenvironment

HE6 (GPR64) is a highly conserved, tissue-specific heptahelical receptor of the human epididymis. The seven transmembrane (TM7) domains are a hallmark of G-protein-coupled receptors (GPCRs) which have a proven history of being excellent therapeutic targets. Of all currently marketed drugs, >30% are modulators of specific heptahelical receptors, emphasizing the potential of HE6 as a target for pharmaceutical intervention. Targeted mutation of the mouse HE6 counterpart resulted in male infertility, further emphasizing its role as a candidate target for male contraception. However, the precise function of HE6, together with its potential ligand(s), and signal transduction pathways have remained largely unknown. On the basis of shared sequence motifs within the TM7 region, HE6 has been grouped into the B class of GPCRs. Within this class, HE6 belongs to the 'large N-termini' family-B seven-transmembrane (LNB-TM7) receptors, also termed the adhesion-GPCRs. Members of this subgroup are 'orphan' receptors, and they all seem to be cleaved within a conserved GPCR proteolytic site (GPS) domain. The biological significance of the two-subunit architecture is still unknown. Clues to the function of HE6 within the epithelium of male excurrent ducts may come from its co-localisation with the apical actin cytoskeleton and from the down-regulation in "knockout" male mice of various proteins specific to the initial segment.

Brain-specific angiogenesis inhibitor 2 regulates VEGF through GABP that acts as a transcriptional repressor

Previously, we reported that decreased brain-specific angiogenesis inhibitor 2 (BAI2) induced increased VEGF expression. The regulatory mechanisms for this process are not understood. Here we show that GA-binding protein gamma (GABPgamma) associates with the cytoplasmic domain of BAI2, and GABPalpha/gamma or GABPalpha/beta works as a transcriptional repressor of VEGF in SHSY5Y cells. Transcriptional activity of wild-type VEGF promoter was significantly increased in anti-sense BAI2-transfected cells, but not that of VEGF promoter harboring mutated GABP sites. In in vivo focal cerebral ischemia model, the decrease in BAI2 accompanied by decreased GABPalpha and GABPgamma elicited increased VEGF expression before the onset of HIF-1alpha. Our results point out that BAI2 controls VEGF transcription through GABP under normal conditions and cerebral ischemia.

GPR56 is a GPCR that is overexpressed in gliomas and functions in tumor cell adhesion

GPR56 (also known as TM7XN1) is a newly discovered orphan G-protein-coupled receptor (GPCR) of the secretin family that has a role in the development of neural progenitor cells and has been linked to developmental malformations of the human brain. GPR56 diverges from other secretin-like family members in that it has an extremely large N-terminal extracellular region (381 amino acids) and contains a novel feature among this new subclass, consisting of four cysteine residues that define a GPCR proteolytic site (GPS motif) located just before the first transmembrane spanning domain. The rest of the amino-terminal domain contains a large number of possible N- and O-linked glycosylation sites similar to mucin-like proteins. These features suggest a role in cell-cell, or cell-matrix interactions. Here, we demonstrate upregulation of GPR56 in glioblastoma multiforme tumors using functional genomics. Immunohistochemistry studies confirmed the expression of GPR56 protein in a majority of glioblastoma/astrocytoma tumor samples with undetectable levels of expression in normal adult brain tissue. Immunofluorescence analysis of human glioma cells using anti-GPR56 antibodies demonstrate that GPR56 is expressed on the leading edge of membrane filopodia and colocalizes with alpha-actinin. Purified recombinant GPR56 extracellular domain protein inhibits glioma cell adhesion and causes abnormal cytoskeletal morphology and cell rounding. These results indicate that the extracellular domain may compete for unidentified ligand(s), and block the normal function of GPR56 in cell attachment. In reporter assays, overexpression of GPR56 activates the NF-kappaB, PAI-1 and TCF transcriptional response elements. These pathways have been implicated in cytoskeletal signaling, adhesion and tumor biology. The above results indicate that GPR56 serves as an adhesion GPCR and is involved in adhesion signaling.

Expression of brain-specific angiogenesis inhibitor 3 (BAI3) in normal brain and implications for BAI3 in ischemia-induced brain angiogenesis and malignant glioma

Murine brain-specific angiogenesis inhibitor 1 and 2 (mBAI1, mBAI2) are involved in angiogenesis after cerebral ischemia. In this study, mBAI3 was cloned and characterized. Northern and Western blot analyses demonstrated a unique developmental expression pattern in the brain. The level of mBAI3 in brain peaked 1 day after birth, unlike mBAI1 and mBAI2, which peaked 10 days after birth. In situ hybridization analyses of the brain showed the same localization of BAI3 as BAI1 and BAI2, which includes most neurons of cerebral cortex and hippocampus. In the in vivo focal cerebral ischemia model, BAI3 expression decreased from 0.5 h after hypoxia until 8 h, but returned to control level after 24 h. The expression of vascular endothelial growth factor following ischemia showed an inverse pattern. The decreased expressions of BAIs in high-grade gliomas were observed, but BAI3 expression was generally lower in malignant gliomas than in normal brain. Our results indicate that the expression and distribution of BAI3 in normal brain, but not its developmental expression, are very similar to those of BAI1 and BAI2, and that BAI3 may participate in the early phases of ischemia-induced brain angiogenesis and in brain tumor progression.

Transmembrane domain analysis of polycystin-1, the product of the polycystic kidney disease-1 (PKD1) gene: evidence for 11 membrane-spanning domains

Polycystin-1, the protein product of the polycystic kidney disease-1 (PKD1) gene, was originally predicted to be an integral membrane glycoprotein with 11 transmembrane (TM) domains (TM 1-11). Subsequent comparative sequence analyses led to a revision of the original model, which retained the overall topology and 11 TM segments (TM I-XI) but dropped 3 of the original domains and introduced 3 new TM domains. The membrane-spanning potential and the orientation of each of the proposed TM domains following the extracellular REJ domain (TM I-XI and TM 11) have now been tested. Using a series of N-terminal polycystin TM-glycosylation reporter gene fusions expressed in vivo, we assayed N-linked glycosylation of the C-terminal glycosylation reporter as an indicator of TM domain presence and orientation. This approach has clearly demonstrated that 7 of the 12 TM domains tested function as membrane-spanning domains. In vitro analysis of the topogenic potential of the five remaining TM domains revealed that four of these also function as membrane-spanning domains, thus supporting an 11 TM structure for polycystin-1 comprised of TM domains I-XI. In addition, these studies suggest that the membrane insertion of TM domains I-IX occurs in a cotranslational and sequential manner, while multiple topogenic determinants appear to be required for the integration of the C-terminal-most TM segments of polycystin-1.