Ruey-Bing Yang

A novel secreted, cell-surface glycoprotein containing multiple epidermal growth factor-like repeats and one CUB domain is highly expressed in primary osteoblasts and bones.

We have previously identified a novel family of secreted, cell-surface proteins expressed in human vascular endothelium. To date, two family members have been described, sharing a characteristic domain structure including an amino-terminal signal peptide followed by multiple copies of epidermal growth factor (EGF)-like repeats, a spacer region, and one CUB domain at the carboxyl terminus. Thus, this family was termed SCUBE for signal peptide-CUB-EGF-like domain containing proteins. Here we described the identification and characterization of one additional member of the SCUBE family named SCUBE3 in humans, sharing an overall 60% protein identity and a similar domain structure with other family members. Real-time quantitative reverse transcriptase-PCR and Northern blot analyses revealed that this gene is highly expressed in primary osteoblasts and the long bones (humerus and femur), followed by a low level of expression in human umbilical vein endothelial cells and in heart. When overexpressed in human embryonic kidney 293T cells, the recombinant hSCUBE3 protein is a secreted glycoprotein that can form oligomers tethered to the cell surface. Interestingly, the secreted hSCUBE3 protein can be further proteolytically processed by a serum-associated protease to release the EGF-like repeats from the CUB domain. The SCUBE3 gene is mapped to human chromosome 6p21.3, a region that has been linked with the locus for a rare form of metabolic bone disease, Pagets disease of bone 1. Together, this novel secreted, cell-surface osteoblast protein may act locally and/or distantly through a proteolytic mechanism, and may play an important role in bone cell biology.

ATF3-Mediated Epigenetic Regulation Protects against Acute Kidney Injury

A variety of stress stimuli, including ischemia-reperfusion (I/R) injury, induce the transcriptional repressor ATF3 in the kidney. The functional consequences of this upregulation in ATF3 after renal I/R injury are not well understood. Here, we found that ATF3-deficient mice had higher renal I/R-induced mortality, kidney dysfunction, inflammation (number of infiltrating neutrophils, myeloperoxidase activity, and induction of IL-6 and P-selectin), and apoptosis compared with wild-type mice. Furthermore, gene transfer of ATF3 to the kidney rescued the renal I/R-induced injuries in the ATF3-deficient mice. Molecular and biochemical analysis revealed that ATF3 interacted directly with histone deacetylase 1 (HDAC1) and recruited HDAC1 into the ATF/NF-kappaB sites in the IL-6 and IL-12b gene promoters. The ATF3-associated HDAC1 deacetylated histones, which resulted in the condensation of chromatin structure, interference of NF-kappaB binding, and inhibition of inflammatory gene transcription after I/R injury. Taken together, these data demonstrate epigenetic regulation mediated by the stress-inducible gene ATF3 after renal I/R injury and suggest potential targeted approaches for acute kidney injury.

Isolation and characterization of a secreted, cell-surface glycoprotein SCUBE2 from humans

SCUBE2 [signal peptide, CUB domain, EGF (epidermal growth factor)-like protein 2] belongs to an evolutionarily conserved SCUBE protein family, which possesses domain organization characteristic of an N-terminal signal peptide sequence followed by nine EGF-like repeats, a spacer region, three cysteine-rich repeat motifs, and one CUB domain at the C-terminus. Despite several genetic analyses suggesting that the zebrafish orthologue of the mammalian SCUBE2 gene participates in HH (Hedgehog) signalling, the complete full-length cDNA and biochemical function for mammalian SCUBE2 on HH signalling remains uninvestigated. In the present study, we isolated the full-length cDNA and studied the role of human SCUBE2 in the HH signalling cascade. When overexpressed, recombinant human SCUBE2 manifests as a secreted surface-anchored glycoprotein. Deletion mapping analysis defines the critical role of the spacer region and/or cysteine-rich repeats for membrane association. Further biochemical analyses and functional reporter assays demonstrated that human SCUBE2 can specifically interact with SHH (Sonic Hedgehog) and SHH receptor PTCH1 (Patched-1), and enhance the SHH signalling activity within the cholesterol-rich raft microdomains of the plasma membranes. Together, our results reveal that human SCUBE2 is a novel positive component of the HH signal, acting upstream of ligand binding at the plasma membrane. Thus human SCUBE2 could play important roles in HH-related biology and pathology, such as during organ development and tumour progression.

SCUBE2 Suppresses Breast Tumor Cell Proliferation and Confers a Favorable Prognosis in Invasive Breast Cancer

Signal peptide-CUB-epidermal growth factor-like domain-containing protein 2 (SCUBE2), originally identified from the endothelium and several nonendothelial primary cell types, was recently shown to be expressed in invasive breast carcinomas. However, the protein localization and biological significance of SCUBE2 in breast cancer are unknown. In this report, we show by anti-SCUBE2 immunostaining that SCUBE2 is mainly expressed in vascular endothelial and mammary ductal epithelial cells in normal breast tissue. In addition, we observed positive staining for SCUBE2 in 55% (86 of 156) of primary breast tumors. Patients with positive SCUBE2 protein-expressing tumors had better prognosis than those with negative SCUBE2 protein-expressing tumors in terms of disease-free survival. Multivariate analysis confirmed SCUBE2 protein expression as an independent prognostic factor for disease-free survival. Furthermore, overexpression of ectopic SCUBE2 protein resulted in suppression of MCF-7 breast cancer cell proliferation and reduced MCF-7 xenograft tumor growth in nude mice. Molecular and biochemical analyses revealed that the COOH terminal region of SCUBE2 directly bound to and antagonized bone morphogenetic protein activity. Together, our results show for the first time that altered SCUBE2 expression is important in breast cancer progression and SCUBE2 may serve as a useful prognostic marker.

Procalcitonin as a Biomarker for Bacterial Infections in Patients With Liver Cirrhosis in the Emergency Department

OBJECTIVES The objective was to determine the diagnostic accuracy of procalcitonin measurement for bacterial infections in patients with all causes of liver cirrhosis. METHODS The authors conducted a cross-sectional study of 98 patients with cirrhosis treated in the emergency department (ED) of Chang-Gung Memorial Hospital, Taiwan. Serum procalcitonin levels and other clinical information were obtained concurrently. Patients were assigned to a sepsis or nonsepsis group after the medical records were reviewed by two emergency physicians blinded to the study. Receiver operating characteristic (ROC) curve analysis was conducted to determine the sensitivity, specificity, likelihood ratio, and suggested cutoff values. The diagnostic accuracy of the C-reactive protein (CRP) level was also determined for comparison. RESULTS A total of 98 patients were enrolled for analysis in 1 year. Twenty-seven patients (27.6%) were assigned to the sepsis group. Eleven patients (11.2%) had positive blood cultures. The areas under the ROC curves for procalcitonin and CRP in predicting sepsis were 0.89 (95% confidence interval [CI] = 0.77 to 0.92) and 0.81 (95% CI = 0.72 to 0.89), respectively (p = 0.11). The cutoff that maximized Youdens index was 0.49 ng/mL for procalcitonin and 24.7 mg/L for CRP. At these cutoffs, the sensitivity and specificity were 81.5 and 87.3% for procalcitonin and 80.0 and 80.3% for CRP. These results suggest that procalcitonin measurement shows at least an equivalent diagnostic accuracy to CRP measurement. CONCLUSIONS Procalcitonin provided satisfactory diagnostic accuracy in differentiating bacterial infections in patients with all causes of liver cirrhosis in the ED. A cutoff value of 0.5 ng/mL is suggested for clinical use.

Disruption of Guanylyl Cyclase-G Protects against Acute Renal Injury

The membrane forms of guanylyl cyclase (GC) serve as cell-surface receptors that synthesize the second messenger cGMP, which mediates diverse cellular processes. Rat kidney contains mRNA for the GC-G isoform, but the role of this receptor in health and disease has not been characterized. It was found that mouse kidney also contains GC-G mRNA, and immunohistochemistry identified GC-G protein in the epithelial cells of the proximal tubule and collecting ducts. Six hours after ischemia-reperfusion (I/R) injury, GC-G mRNA and protein expression increased three-fold and remained upregulated at 24 h. For determination of whether GC-G mediates I/R injury, a mutant mouse with a targeted disruption of the GC-G gene (Gucy2g) was created. At baseline, no histologic abnormalities were observed in GC-G(-/-) mice. After I/R injury, elevations in serum creatinine and urea were attenuated in GC-G(-/-) mice compared with wild-type controls, and this correlated with less tubular disruption, less tubular cell apoptosis, and less caspase-3 activation. Measures of inflammation (number of infiltrating neutrophils, myeloperoxidase activity, and induction of IL-6 and P-selectin) and activation of NF-kappaB were lower in GC-G(-/-) mice compared with wild-type mice. Direct transfer of a GC-G expression plasmid to the kidneys of GC-G(-/-) mice resulted in a dramatically higher mortality after renal I/R injury, further supporting a role for GC-G in mediating injury. In summary, GC-G may act as an early signaling molecule that promotes apoptotic and inflammatory responses in I/R-induced acute renal injury.

Receptor guanylyl cyclases in Inka cells targeted by eclosion hormone

A signature of eclosion hormone (EH) action in insect ecdysis is elevation of cGMP in Inka cells, leading to massive release of ecdysis triggering hormone (ETH) and ecdysis initiation. Although this aspect of EH-induced signal transduction is well known, the receptor mediating this process has not been identified. Here, we describe a receptor guanylyl cyclase BdmGC-1 and its isoform BdmGC-1B in the Oriental fruit fly Bactrocera dorsalis that are activated by EH. The B form exhibits the conserved domains and putative N-glycosylation sites found in BdmGC-1, but possesses an additional 46-amino acid insertion in the extracellular domain and lacks the C-terminal tail of BdmGC-1. Combined immunolabeling and in situ hybridization reveal that BdmGC-1 is expressed in Inka cells. Heterologous expression of BdmGC-1 in HEK cells leads to robust increases in cGMP following exposure to low picomolar concentrations of EH. The B-isoform responds only to higher EH concentrations, suggesting different physiological roles of these cyclases. We propose that BdmGC-1 and BdmGC-1Β are high- and low-affinity EH receptors, respectively.

Guanylate cyclase-G, expressed in the Grueneberg ganglion olfactory subsystem, is activated by bicarbonate.

GC (guanylate cyclase)-G is the most recently identified member of the receptor GC family. However, the regulation of its activity and protein expression in the mammalian olfactory system remains unclear. In the present study, we used a GC-G-specific antibody to validate that the GC-G protein is expressed in Grueneberg ganglion neurons, a newly recognized olfactory subsystem co-expressing other cGMP signalling components such as the cGMP-regulated PDE2A (phosphodiesterase 2A) and the cGMP-gated ion channel CNGA3 (cyclic nucleotide-gated cation channel α-3). Further molecular and biochemical analyses showed that heterologously expressed GC-G protein, specifically the C-terminal cyclase domain, was directly stimulated by bicarbonate in both in vivo cellular cGMP accumulation assays in human embryonic kidney-293T cells and in vitro GC assays with a purified recombinant protein containing the GC domain. In addition, overexpression of GC-G in NG108 neuronal cells resulted in a CO2-dependent increase in cellular cGMP level that could be blocked by treatment with acetazolamide, an inhibitor of carbonic anhydrases, which implies that the stimulatory effect of CO2 requires its conversion to bicarbonate. Together, our data demonstrate a novel CO2/bicarbonate-dependent activation mechanism for GC-G and suggest that GC-G may be involved in a wide variety of CO2/bicarbonate-regulated biological processes such as the chemosensory function in Grueneberg ganglion neurons.

Receptor guanylyl cyclase-G is a novel thermosensory protein activated by cool temperatures

Transmembrane guanylyl cyclases (GCs), with activity regulated by peptide ligands and/or calcium‐binding proteins, are essential for various physiological and sensory processes. The mode of activation of the GC subtype GC‐G, which is expressed in neurons of the Grueneberg ganglion that respond to cool temperatures, has been elusive. In searching for appropriate stimuli to activate GC‐G, we found that its enzymatic activity is directly stimulated by cool temperatures. In this context, it was observed that dimerization/oligomerization of GC‐G, a process generally considered as critical for enzymatic activity of GCs, is strongly enhanced by coolness. Moreover, heterologous expression of GC‐G in cultured cells rendered these cells responsive to coolness; thus, the protein might be a sensor for cool temperatures. This concept is supported by the observation of substantially reduced coolness‐induced response of Grueneberg ganglion neurons and coolness‐evoked ultrasonic vocalization in GC‐G‐deficient mouse pups. GC‐G may be a novel thermosensory protein with functional implications for the Grueneberg ganglion, a sensory organ responding to cool temperatures.

Identification of an orphan guanylate cyclase receptor selectively expressed in mouse testis.

We have identified a novel membrane form of guanylate cyclase (GC) from a mouse testis cDNA library and termed it mGC-G (mouse GC-G) based on its high sequence homology to rat GC-G. It encodes a potential type I transmembrane receptor, with the characteristic domain structure common to all members of the family of membrane GCs, including an extracellular, putative ligand-binding domain, a single membrane-spanning segment and cytoplasmic protein kinase-like and cyclase catalytic domains. Real-time quantitative reverse transcriptase--PCR and Northern-blot analyses showed that mGC-G is highly and selectively expressed in mouse testis. Phylogenetic analysis based on the extracellular protein sequence revealed that mGC-G is closely related to members of the subfamily of natriuretic peptide receptor GCs. When overexpressed in HEK-293T cells (human embryonic kidney 293T cells) or COS-7 cells, mGC-G manifests as a membrane-bound glycoprotein, which can form either homomeric or heteromeric complexes with the natriuretic peptide receptor GC-A. It exhibits marked cGMP-generating GC activity; however, notably, all ligands known to activate other receptor GCs failed to stimulate enzymic activity. The unique testis-enriched expression of mGC-G, which is completely different from the broader tissue distribution of rat GC-G, suggests the existence of as-yet-unidentified ligands and unappreciated species-specific physiological functions mediated through mGC-G/cGMP signalling in the testis.