Impaired flow-dependent control of vascular tone and remodeling in P2X4-deficient mice

The structure and function of blood vessels adapt to environmental changes such as physical development and exercise. This phenomenon is based on the ability of the endothelial cells to sense and respond to blood flow; however, the underlying mechanisms remain unclear. Here we show that the ATP-gated P2X4 ion channel, expressed on endothelial cells and encoded by P2rx4 in mice, has a key role in the response of endothelial cells to changes in blood flow. P2rx4(-/-) mice do not have normal endothelial cell responses to flow, such as influx of Ca(2+) and subsequent production of the potent vasodilator nitric oxide (NO). Additionally, vessel dilation induced by acute increases in blood flow is markedly suppressed in P2rx4(-/-) mice. Furthermore, P2rx4(-/-) mice have higher blood pressure and excrete smaller amounts of NO products in their urine than do wild-type mice. Moreover, no adaptive vascular remodeling, that is, a decrease in vessel size in response to a chronic decrease in blood flow, was observed in P2rx4(-/-) mice. Thus, endothelial P2X4 channels are crucial to flow-sensitive mechanisms that regulate blood pressure and vascular remodeling.     

Detection of allogeneic Qa/TL and Ly specificities on murine tumor cells with IgD in tumor-regressor serum

Summary Serum from C3H/He mice, which show regression of MM2 tumor cells after transplantation and removal (regressor serum, RS) contains non-gammaglobulin components that cross-react with various tumor cells of mice [22, 23]. In addition to tumor cells, various allogeneic lymphocytes are also susceptible to an RS-dependent lymphocyte-mediated cytotoxic reaction. To identify tumor cell surface antigens that cause the cross-reactive host response, the serum components were analyzed by absorption of RS with allogeneic lymphocytes. RS components were found to recognize allogeneic lymphocyte antigens including Qa-2 and Ly6.2. Specificity for the Qa-2 antigen was further tested using Qa-2-congenic mice. The expression of Qa-2 antigen was detected on the surfaces of MM2 and other tumor cells derived from H-2^k mice (seven among nine cell lines tested) by a membrane immunofluorescence method using a Qa-2-specific mAb. Physical characteristics of the Qa-2-specific component in RS were determined and found to differ from those of regular IgGs but to be similar to those of IgDs. Using an enzyme-linked immunosorbent assay with an IgD-specific mAb and Qa-2-lacZ fusion protein, the existence of IgD in RS with specificity for Qa-2 was confirmed. These results suggest that the RS component with Qa-2 specificity is an IgD, the specificity and physiological role of which are unknown.     

Maturation ameloblasts of the porcine tooth germ do not express amelogenin

 Amelogenins are the most abundant constituent in the enamel matrix of developing teeth. Recent investigations of rodent incisors and molar tooth germs revealed that amelogenins are expressed not only in secretory ameloblasts but also in maturation ameloblasts, although in relatively low levels. In this study, we investigated expression of amelogenin in the maturation stage of porcine tooth germs by in situ hybridization and immunocytochemistry. Amelogenin mRNA was intensely expressed in ameloblasts from the differentiation to the transition stages, but was not detected in maturation stage ameloblasts. C-terminal specific anti-amelogenin antiserum, which only reacts with nascent amelogenin molecules, stained ameloblasts from the differentiation to the transition stages. This antiserum also stained the surface layer of immature enamel at the same stages. At the maturation stage, no immunoreactivity was found within the ameloblasts or the immature enamel. These results indicate that, in porcine tooth germs, maturation ameloblasts do not express amelogenins, suggesting that newly secreted enamel matrix proteins from the maturation ameloblast are not essential to enamel maturation occurring at the maturation stage. Accepted: 14 January 1999     

Absence of mechanical allodynia and Abeta-fiber sprouting after sciatic nerve injury in mice lacking membrane-type 5 matrix metalloproteinase

Matrix metalloproteinases (MMPs) are a family of endopeptidases that degrade extracellular matrix components. Membrane-type 5 MMP (MT5-MMP/MMP-24) was identified as neuron-specific, and is believed to contribute to neuronal circuit formation and plasticity. To elucidate its function in vivo, we have generated mice lacking MT5-MMP by gene targeting. MT5-MMP-deficient mice were born without obvious morphological abnormalities. No apparent histological defects were observed in the nervous system either. However, MT5-MMP-deficient mice did not develop neuropathic pain with mechanical allodynia after sciatic nerve injury, though responses to acute noxious stimuli were normal. Neuropathic pain induced by peripheral nerve lesions is known to accompany structural reorganization of the nervous system. Intraneural injection of cholera toxin B subunit, a transganglionic tracer, into the injured sciatic nerve of wild-type mice revealed that the myelinated Abeta-fiber primary afferents sprouted from laminae III-VI of the dorsal horn of the spinal cord and invaded lamina II. However, no such sprouting and invasion of Abeta-fibers were observed in MT5-MMP-deficient mice. These findings suggest that MT5-MMP is essential for the development of mechanical allodynia and plays an important role in neuronal plasticity in this mouse model.     

Solution structure of the SEA domain from the murine homologue of ovarian cancer antigen CA125 (MUC16)

Human CA125, encoded by the MUC16 gene, is an ovarian cancer antigen widely used for a serum assay. Its extracellular region consists of tandem repeats of SEA domains. In this study we determined the three-dimensional structure of the SEA domain from the murine MUC16 homologue using multidimensional NMR spectroscopy. The domain forms a unique alpha/beta sandwich fold composed of two alpha helices and four antiparallel beta strands and has a characteristic turn named the TY-turn between alpha1 and alpha2. The internal mobility of the main chain is low throughout the domain. The residues that form the hydrophobic core and the TY-turn are fully conserved in all SEA domain sequences, indicating that the fold is common in the family. Interestingly, no other residues are conserved throughout the family. Thus, the sequence alignment of the SEA domain family was refined on the basis of the three-dimensional structure, which allowed us to classify the SEA domains into several subfamilies. The residues on the surface differ between these subfamilies, suggesting that each subfamily has a different function. In the MUC16 SEA domains, the conserved surface residues, Asn-10, Thr-12, Arg-63, Asp-75, Asp-112, Ser-115, and Phe-117, are clustered on the beta sheet surface, which may be functionally important. The putative epitope (residues 58-77) for anti-MUC16 antibodies is located around the beta2 and beta3 strands. On the other hand the tissue tumor marker MUC1 has a SEA domain belonging to another subfamily, and its GSVVV motif for proteolytic cleavage is located in the short loop connecting beta2 and beta3.     

Munc13-4 is a GTP-Rab27-binding protein regulating dense core granule secretion in platelets

Platelets store self-agonists such as ADP and serotonin in dense core granules. Although exocytosis of these granules is crucial for hemostasis and thrombosis, the underlying mechanism is not fully understood. Here, we show that incubation of permeabilized platelets with unprenylated active mutant Rab27A-Q78L, wild type Rab27A, and Rab27B inhibited the secretion, whereas inactive mutant Rab27A-T23N and other GTPases had no effects. Furthermore, we affinity-purified a GTP-Rab27A-binding protein in platelets and identified it as Munc13-4, a homologue of Munc13-1 known as a priming factor for neurotransmitter release. Recombinant Munc13-4 directly bound to GTP-Rab27A and -Rab27B in vitro, but not other GTPases, and enhanced secretion in an in vitro assay. The inhibition of secretion by unprenylated Rab27A was rescued by the addition of Munc13-4, suggesting that Munc13-4 mediates the function of GTP-Rab27. Thus, Rab27 regulates the dense core granule secretion in platelets by employing its binding protein, Munc13-4.     

Rapid inhibition of leptin signaling by glucocorticoids in vitro and in vivo

Elevated secretion of glucocorticoids (GCs) or hypersensitivity to GCs has a permissive effect on the development of obesity and leads to abnormalities of body fat distribution. Recent studies demonstrated GCs act as antagonists of leptin in rodents. However, little is known about the interaction between GCs and leptin signaling. In the present study, we investigated the effects of GCs on leptin action in vitro and in vivo. GCs rapidly inhibited the leptin-induced STAT3 phosphorylation in a dose- and time-dependent manner, as assayed by Western blotting using anti-phosphospecific-STAT3 in human hepatoma cell lines (Huh7) transiently expressing long form leptin receptor. GCs also inhibited the leptin-induced JAK2 tyrosine phosphorylation but unaltered the specific binding of (125)I-leptin to the cells. Parallel experiments, however, demonstrated that the inhibitory effects of GCs were not observed in either IL-6- or LIF-induced STAT3 phosphorylation. Furthermore, we examined the feeding behavior and hypothalamic leptin signaling following intracerebroventricular (icv) infusion of GCs prior to icv leptin infusion in Sprague-Dawley rats. The food intake after 24 h of icv leptin injection increased 3-fold in GCs-treated animals. In addition, central infusion of GCs resulted in a marked reduction of hypothalamic STAT3 phosphorylation in response to icv infusion of leptin. To clarify the molecular mechanism by which GCs rapidly reduce leptin-induced JAK/STAT signaling, we examined the intracellular signal transduction pathway potentially mediated by GCs. PD98059, a specific MEK inhibitor, blocked the inhibitory effects of GCs on leptin-induced JAK/STAT activation in Huh7 cells. These results suggest GCs antagonize leptin action by a rapid inhibition of the leptin-induced JAK/STAT pathway partly via MAPK cascade.