RAB35 is required for murine hippocampal development and functions by regulating neuronal cell distribution.

RAB35 is a multifunctional small GTPase that regulates endocytic recycling, cytoskeletal rearrangement, and cytokinesis. However, its physiological functions in mammalian development remain unclear. Here, we generated Rab35-knockout mice and found that RAB35 is essential for early embryogenesis. Interestingly, brain-specific Rab35-knockout mice displayed severe defects in hippocampal lamination owing to impaired distribution of pyramidal neurons, although defects in cerebral cortex formation were not evident. In addition, Rab35-knockout mice exhibited defects in spatial memory and anxiety-related behaviors. Quantitative proteomics indicated that the loss of RAB35 significantly affected the levels of other RAB proteins associated with endocytic trafficking, as well as some neural cell adhesion molecules, such as contactin-2. Collectively, our findings revealed that RAB35 is required for precise neuronal distribution in the developing hippocampus by regulating the expression of cell adhesion molecules, thereby influencing spatial memory.

Clathrin-mediated endocytosis is essential for the selective degradation of maternal membrane proteins and preimplantation development.

Fertilization triggers significant cellular remodeling through the oocyte-to-embryo transition. In this transition, the ubiquitin-proteasome system and autophagy are essential for the degradation of maternal components; however, the significance of degradation of cell surface components remains unknown. In this study, we show that multiple maternal plasma membrane proteins, such as the glycine transporter GlyT1a, are selectively internalized from the plasma membrane to endosomes in mouse embryos by the late two-cell stage and then transported to lysosomes for degradation at the later stages. During this process, large amounts of ubiquitylated proteins accumulated on endosomes. Furthermore, the degradation of GlyT1a with mutations in potential ubiquitylation sites was delayed, suggesting that ubiquitylation may be involved in GlyT1a degradation. The clathrin inhibitor blocked GlyT1a internalization. Strikingly, the protein kinase C (PKC) activator triggered the heterochronic internalization of GlyT1a; the PKC inhibitor markedly blocked GlyT1a endocytosis. Lastly, clathrin inhibition completely blocked embryogenesis at the two-cell stage and inhibited cell division after the four-cell stage. These findings demonstrate that PKC-dependent clathrin-mediated endocytosis is essential for the selective degradation of maternal membrane proteins during oocyte-to-embryo transition and early embryogenesis.

Rer1-mediated quality control system is required for neural stem cell maintenance during cerebral cortex development.

Rer1 is a retrieval receptor for endoplasmic reticulum (ER) retention of various ER membrane proteins and unassembled or immature components of membrane protein complexes. However, its physiological functions during mammalian development remain unclear. This study aimed to investigate the role of Rer1-mediated quality control system in mammalian development. We show that Rer1 is required for the sufficient cell surface expression and activity of γ-secretase complex, which modulates Notch signaling during mouse cerebral cortex development. When Rer1 was depleted in the mouse cerebral cortex, the number of neural stem cells decreased significantly, and malformation of the cerebral cortex was observed. Rer1 loss reduced γ-secretase activity and downregulated Notch signaling in the developing cerebral cortex. In Rer1-deficient cells, a subpopulation of γ-secretase complexes and components was transported to and degraded in lysosomes, thereby significantly reducing the amount of γ-secretase complex on the cell surface. These results suggest that Rer1 maintains Notch signaling by maintaining sufficient expression of the γ-secretase complex on the cell surface and regulating neural stem cell maintenance during cerebral cortex development.

Rer1 and calnexin regulate endoplasmic reticulum retention of a peripheral myelin protein 22 mutant that causes type 1A Charcot-Marie-Tooth disease.

Peripheral myelin protein 22 (PMP22) resides in the plasma membrane and is required for myelin formation in the peripheral nervous system. Many PMP22 mutants accumulate in excess in the endoplasmic reticulum (ER) and lead to the inherited neuropathies of Charcot-Marie-Tooth (CMT) disease. However, the mechanism through which PMP22 mutants accumulate in the ER is unknown. Here, we studied the quality control mechanisms for the PMP22 mutants L16P and G150D, which were originally identified in mice and patients with CMT. We found that the ER-localised ubiquitin ligase Hrd1/SYVN1 mediates ER-associated degradation (ERAD) of PMP22(L16P) and PMP22(G150D), and another ubiquitin ligase, gp78/AMFR, mediates ERAD of PMP22(G150D) as well. We also found that PMP22(L16P), but not PMP22(G150D), is partly released from the ER by loss of Rer1, which is a Golgi-localised sorting receptor for ER retrieval. Rer1 interacts with the wild-type and mutant forms of PMP22. Interestingly, release of PMP22(L16P) from the ER was more prominent with simultaneous knockdown of Rer1 and the ER-localised chaperone calnexin than with the knockdown of each gene. These results suggest that CMT disease-related PMP22(L16P) is trapped in the ER by calnexin-dependent ER retention and Rer1-mediated early Golgi retrieval systems and partly degraded by the Hrd1-mediated ERAD system.

Regulation by SIRPα of dendritic cell homeostasis in lymphoid tissues.

The molecular basis for regulation of dendritic cell (DC) development and homeostasis remains unclear. Signal regulatory protein α (SIRPα), an immunoglobulin superfamily protein that is predominantly expressed in DCs, mediates cell-cell signaling by interacting with CD47, another immunoglobulin superfamily protein. We now show that the number of CD11c(high) DCs (conventional DCs, or cDCs), in particular, that of CD8-CD4+ (CD4+) cDCs, is selectively reduced in secondary lymphoid tissues of mice expressing a mutant form of SIRPα that lacks the cytoplasmic region. We also found that SIRPα is required intrinsically within cDCs or DC precursors for the homeostasis of splenic CD4+ cDCs. Differentiation of bone marrow cells from SIRPα mutant mice into DCs induced by either macrophage-granulocyte colony-stimulating factor or Flt3 ligand in vitro was not impaired. Although the accumulation of the immediate precursors of cDCs in the spleen was also not impaired, the half-life of newly generated splenic CD4+ cDCs was markedly reduced in SIRPα mutant mice. Both hematopoietic and nonhematopoietic CD47 was found to be required for the homeostasis of CD4+ cDCs and CD8-CD4- (double negative) cDCs in the spleen. SIRPα as well as its ligand, CD47, are thus important for the homeostasis of CD4+ cDCs or double negative cDCs in lymphoid tissues.

Association of the manganese superoxide dismutase polymorphism with vasospastic angina pectoris.

BACKGROUND: Vasospastic angina (VSA) is closely related to endothelial dysfunction caused by oxidative damage. Manganese superoxide dismutase (MnSOD) is an antioxidant enzyme that functions in mitochondria. There are two genetic variants of MnSOD arising from a substitution of an alanine for a valine in the signal peptide. We previously reported that the valine allele of MnSOD decreases the mitochondrial MnSOD (mtMnSOD) activity. Here, we investigated the association of the MnSOD polymorphism (Ala16Val) with VSA. METHODS AND RESULTS: Blood samples were collected from 618 healthy subjects who did not have any symptoms or other evidence suggesting angina pectoris, and 228 patients who underwent coronary angiography on suspicion of angina, and were diagnosed to have VSA by acetylcholine test. MnSOD genotype of each subject was determined by real-time polymerase chain reaction. The valine allele frequency was higher in the VSA patients (0.890) than in the healthy subjects (0.839) [odds ratio (OR)=1.55, p=0.0085]. In healthy subjects the MnSOD genotype distribution was as follows: alanine/alanine 1.9%, alanine/valine 28.3%, and valine/valine 69.8%, and in VSA patients the prevalence was: alanine/alanine 1.3%, alanine/valine 19.3%, and valine/valine 79.4%. Thus, the valine allele was closely associated with VSA (p=0.019). Multivariate logistic regression analysis showed valine/valine homozygosity to be an independent risk factor for VSA (OR=2.02, 95% CI 1.43, 2.85; p=0.0012). CONCLUSION: The valine variant of MnSOD signal peptide increases the risk of VSA.

Age-induced reduction in mitochondrial manganese superoxide dismutase activity and tolerance of macrophages against apoptosis induced by oxidized low density lipoprotein.

BACKGROUND: Oxidative stress is thought to play an important role in age-induced atherogenesis. Manganese superoxide dismutase (MnSOD) is an antioxidant enzyme that is localized in mitochondria and protects macrophages against apoptosis induced by oxidized low density lipoprotein (oxLDL). We previously reported that genetic polymorphism of MnSOD modifies mitochondrial MnSOD (mtMnSOD) activity and increases the risk of coronary artery disease. In this study, we investigated the association of mtMnSOD activity with aging. METHODS AND RESULTS: Blood samples were taken from 69 healthy participants aged 20-52. The MnSOD genotype was analyzed using real-time polymerase chain reaction. Leukocyte mtMnSOD activity was measured by inhibition of WST-1. Macrophages were treated with oxLDL and the apoptotic cells were counted. mtMnSOD activity was inversely correlated with the age of the participant regardless of the MnSOD genotype. The percentage of apoptotic macrophages after incubation with oxLDL correlated with age. Thus, the percentage of apoptotic macrophages after incubation with oxLDL was inversely related to mtMnSOD activity. Lecithinized SOD, which can easily transfer into cells, improved the tolerance of macrophages against oxLDL. CONCLUSIONS: mtMnSOD activity decreases with age, thereby reducing the tolerance of macrophages against oxLDL-induced apoptosis. Our data may provide an important clue to clarify the mechanisms of age-induced atherosclerosis.

Essential roles of SHPS-1 in induction of contact hypersensitivity of skin.

SHPS-1 is a transmembrane protein that binds the protein tyrosine phosphatases SHP-1 and SHP-2 and is abundant on the surface of CD11c(+) dendritic cells (DCs). We recently showed that SHPS-1 is essential for priming by DCs of CD4(+) T cells and for development of Th17 cell-mediated experimental autoimmunity. We have now further evaluated the importance of SHPS-1 and that of its ligand CD47 in contact hypersensitivity (CHS) to 2,4-dinitro-1-fluorobenzene (DNFB). Whereas the DNFB-induced CHS response was impaired in mice that express a mutant form of SHPS-1 lacking most of the cytoplasmic region, it was unaffected in CD47-deficient mice. Moreover, treatment of wild-type mice with mAbs to SHPS-1 that either block or do not block the binding of SHPS-1 to CD47 inhibited the CHS response. A mAb to CD47 had no such effect. The 2,4-dinitro-benzenesulfonic acid-induced proliferation of, and production of IFN-gamma or IL-17 by, T cells from DNFB-sensitized wild-type mice were inhibited by either mAb to SHPS-1 but not by that to CD47. In contrast, the blocking mAbs to SHPS-1, but not that to CD47, inhibited an allogeneic mixed leukocyte reaction. Both mAbs to SHPS-1, but not that to CD47, also inhibited the lipopolysaccharide- or polyinosinic-polycytidylic acid-induced production of TNF-alpha by DCs. These results suggest that SHPS-1 is essential for development of CHS, likely as a result of its positive regulation of the priming by DCs of CD4(+) T cells. However, such regulation by SHPS-1 does not appear to require its interaction with CD47.

Expression of Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 in pancreatic beta-Cells and its role in promotion of insulin secretion and protection against diabetes.

Insulin secretion by beta-cells of pancreatic islets is regulated by various soluble factors including glucose and hormones. The importance of direct cell-cell communication among beta-cells or between beta-cells and other cell types for such regulation has remained unclear, however. Transmembrane proteins Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 (SHPS-1) and its ligand CD47 interact through their extracellular regions and contribute to intercellular communication. We now show that both SHPS-1 and CD47 are prominently expressed in beta-cells of the pancreas. The plasma insulin level in the randomly fed state was markedly reduced in mice that express a mutant form of SHPS-1 lacking most of the cytoplasmic region compared with that in wild-type (WT) mice, although the blood glucose concentrations of the two types of mice were similar. This reduction in the plasma insulin level of SHPS-1 mutant mice was even more pronounced in animals maintained on a high-fat diet. Glucose tolerance was also markedly impaired in SHPS-1 mutant mice on a high-fat diet, whereas both peripheral insulin sensitivity and the insulin content of the pancreas in the mutant animals were similar to those of WT mice. Glucose-stimulated insulin secretion was similar for islets isolated from WT or SHPS-1 mutant mice. The impaired glucose tolerance of SHPS-1 mutant mice was ameliorated by treatment with the alpha2-adrenergic antagonist yohimbine. These results suggest that SHPS-1 promotes insulin secretion from beta-cells and thereby protects against diabetes. Preventing of alpha2-adrenergic receptor-mediated inhibition of insulin secretion may partly participate in such a function of SHPS-1.

Manganese superoxide dismutase polymorphism affects the oxidized low-density lipoprotein-induced apoptosis of macrophages and coronary artery disease.

AIMS: Oxidative damage promotes atherosclerosis. Manganese superoxide dismutase (MnSOD) is an antioxidant enzyme localized in mitochondria. We investigated the associations of the MnSOD polymorphism (valine-to-alanine in the mitochondrial-targeting domain) with its activity in leukocytes, with macrophage apoptosis by oxidized low-density lipoprotein (oxLDL), and with coronary artery disease (CAD). METHODS AND RESULTS: Blood samples were taken from 50 healthy subjects. The mitochondrial MnSOD activities in leukocytes were 542.4 +/- 71.6 U/mg protein (alanine/alanine, n = 2), 302.0 +/- 94.9 U/mg protein (alanine/valine, n = 12), and 134.0 +/- 67.1 U/mg protein (valine/valine, n = 36; P < 0.0001 for non-valine/valine vs. valine/valine). Macrophages were treated with oxLDL. After incubation, the percentages of apoptotic macrophages were 48.6 +/- 3.6% (alanine/alanine), 78.6 +/- 9.8% (alanine/valine), and 87.5 +/- 7.0% (valine/valine) (P < 0.0001, non-valine/valine vs. valine/valine). The association of the MnSOD polymorphism with CAD was investigated using blood samples collected from 498 CAD patients and 627 healthy subjects; the alanine allele was found to reduce the risk of CAD and acute myocardial infarction (AMI). CONCLUSION: Our data indicate that the alanine variant of signal peptide increases the mitochondrial MnSOD activity, protects macrophages against the oxLDL-induced apoptosis, and reduces the risk of CAD and AMI.

Carbon monoxide protects against cardiac ischemia--reperfusion injury in vivo via MAPK and Akt--eNOS pathways.

BACKGROUND: Carbon monoxide (CO) is postulated to protect tissues against several types of injuries. We investigated the role of CO in amelioration of cardiac ischemia-reperfusion injury in vivo and the mechanisms involved in it. METHODS AND RESULTS: Rats inhaled CO (250 ppm, 500 ppm, or 1000 ppm) for 24 hours in a chamber after myocardial ischemia-reperfusion induced by occluding the left anterior descending coronary artery for 30 minutes. Pre-exposure to 1000 ppm of CO significantly reduced the ratio of infarct areas to risk areas and suppressed the migration of macrophages and monocytes into infarct areas, and the expression of tumor necrosis factor (TNF)-alpha in the heart; however, 250 ppm, 500 ppm of CO, or low barometric pressure hypoxia (0.5 atm) did not affect them. Exposure to 1000 ppm CO resulted in the activation of p38 mitogen-activated protein kinase (p38MAPK), protein kinase Balpha(Akt), endothelial nitric oxide synthase (eNOS), and cyclic guanosine monophosphate (cGMP) in the myocardium. Inhibition of p38MAPK, PI3kinase, NO, and soluble guanylate cyclase with SB203580, wortmannin, N(G)-nitro-L-arginine methyl ester (L-NAME), and methylene blue, respectively, attenuated the cytoprotection by CO. CONCLUSIONS: CO has beneficial effects on cardiac ischemia-reperfusion injury; this effect is mediated by p38MAPK pathway and Akt-eNOS pathway, including production of cGMP.

Ectodomain shedding of SHPS-1 and its role in regulation of cell migration.

SHPS-1 is a transmembrane protein whose cytoplasmic region undergoes tyrosine phosphorylation and then binds the protein-tyrosine phosphatase SHP-2. Formation of the SHPS-1-SHP-2 complex is implicated in regulation of cell migration. In addition, SHPS-1 and its ligand CD47 constitute an intercellular recognition system that contributes to inhibition of cell migration by cell-cell contact. The ectodomain of SHPS-1 has now been shown to be shed from cells in a reaction likely mediated by a metalloproteinase. This process was promoted by activation of protein kinase C or of Ras, and the released ectodomain exhibited minimal CD47-binding activity. Metalloproteinases catalyzed the cleavage of a recombinant SHPS-1-Fc fusion protein in vitro, and the primary cleavage site was localized to the juxtamembrane region of SHPS-1. Forced expression of an SHPS-1 mutant resistant to ectodomain shedding impaired cell migration, cell spreading, and reorganization of the actin cytoskeleton. It also increased the tyrosine phosphorylation of paxillin and FAK triggered by cell adhesion. These results suggest that shedding of the ectodomain of SHPS-1 plays an important role in regulation of cell migration and spreading by this protein.

Regulation of multiple functions of SHPS-1, a transmembrane glycoprotein, by its cytoplasmic region.

SHPS-1 is a receptor-type transmembrane glycoprotein, which contains four tyrosine residues in its cytoplasmic region, and the phosphorylation of these tyrosine residues serves the binding sites for SHP-2 protein-tyrosine phosphatase. Its extracellular region interacts with another membrane protein, CD47, thereby constituting a cell-cell communication system. We analyzed this ligand-receptor interaction using Chinese hamster ovary (CHO) cells expressing wild-type (WT) or mutant SHPS-1. The binding affinity of an SHPS-1 mutant such as deltaCyto, that lacked most of cytoplasmic region, or 4F, in which all four tyrosine residues in cytoplasmic region were substituted with phenylalanine, for a recombinant CD47-Fc was greater than that of WT. In addition, oligomerization of deltaCyto or 4F mutant by binding of CD47-Fc was greater than WT. Chemical cross-linking of SHPS-1 indicated that SHPS-1 formed a cis-dimer. Furthermore, WT cells exhibited a less polarized cell shape with decreased formation of actin stress fibers, compared with parental CHO cells and mutant SHPS-1 expressing cells. Prominent lamellipodium formation and membrane ruffling were also observed at leading edges of migrating WT cells but not at those of other mutant SHPS-1 expressing cells. These results suggest that the binding affinity of SHPS-1 to CD47, clustering ability of SHPS-1, and cytoskeletal reorganization are regulated by the cytoplasmic region of SHPS-1.

Characterization of nucleotide pyrophosphatase-5 as an oligomannosidic glycoprotein in rat brain.

Membrane glycoproteins of neural cells play crucial roles in axon guidance, synaptogenesis, and neuronal transmission. We have here characterized membrane glycoproteins containing terminal alpha-mannose residues in rat brain membranes. Affinity purification using Galanthus nivalis agglutinin, that is highly specific for terminal alpha-mannose residues, revealed a 50-kDa protein as well as 80-kDa SHPS-1 and 45-kDa beta2 subunit of Na,K-ATPase in rat brain membranes. Combination of N-terminal peptide sequencing and mass spectrometry indicated that the 50-kDa protein was rat nucleotide pyrophosphatase-5 (NPP-5). In contrast to other NPPs, NPP-5 was a type-I transmembrane protein. Northern blot analysis showed that NPP-5 was highly expressed in brain, but also expressed in other peripheral tissues. However, we could not detect either the NPP activity or the lysophospholipase D activity in the immunoprecipitates with antibodies to NPP-5 from rat brain membranes. These data, therefore, suggest that NPP-5 is a neural oligomannosidic glycoprotein that may participate in neural cell communications.

Role of the CD47-SHPS-1 system in regulation of cell migration.

SHPS-1 is a transmembrane protein whose extracellular region interacts with CD47 and whose cytoplasmic region undergoes tyrosine phosphorylation and there by binds the protein tyrosine phosphatase SHP-2. Formation of this complex is implicated in regulation of cell migration by an unknown mechanism. A CD47-Fc fusion protein or antibodies to SHPS-1 inhibited migration of human melanoma cells or of CHO cells overexpressing SHPS-1. Overexpression of wild-type SHPS-1 promoted CHO cell migration, whereas expression of the SHPS-1-4F mutant, which lacks the phosphorylation sites required for SHP-2 binding, had no effect. Antibodies to SHPS-1 failed to inhibit migration of CHO cells expressing SHPS-1-4F. SHPS-1 ligands induced the dephosphorylation of SHPS-1 and dissociation of SHP-2. Antibodies to SHPS-1 also enhanced Rho activity and induced both formation of stress fibers and adoption of a less polarized morphology in melanoma cells. Our results suggest that engagement of SHPS-1 by CD47 prevents the positive regulation of cell migration by this protein. The CD47- SHPS-1 system and SHP-2 might thus contribute to the inhibition of cell migration by cell-cell contact.

DIF-1, an anti-tumor substance found in Dictyostelium discoideum, inhibits progesterone-induced oocyte maturation in Xenopus laevis.

Differentiation-inducing factor-1 (DIF-1; 1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one) is a putative morphogen that induces stalk-cell formation in the cellular slime mold Dictyostelium discoideum. DIF-1 has previously been shown to suppress cell growth in mammalian cells. In this study, we examined the effects of DIF-1 on the progesterone-induced germinal vesicle breakdown in Xenopus laevis, which is thought to be mediated by a decrease in intracellular cAMP and the subsequent activation of mitogen-activated protein kinase (MAPK) and maturation-promoting factor, a complex of cdc2 and cyclin B, which regulates germinal vesicle breakdown. DIF-1 at 10-40 microM inhibited progesterone-induced germinal vesicle breakdown in de-folliculated oocytes in a dose-dependent manner. Progesterone-induced cdc2 activation, MAPK activation, and c-Mos accumulation were inhibited by DIF-1. Furthermore, DIF-1 was found to inhibit the progesterone-induced cAMP decrease in the oocytes. These results indicate that DIF-1 inhibits progesterone-induced germinal vesicle breakdown possibly by blocking the progesterone-induced decrease in [cAMP](i) and the subsequent events in Xenopus oocytes.

3',5'-cyclic adenosine monophosphate augments intracellular Ca2+ concentration and gonadotropin-releasing hormone (GnRH) release in immortalized GnRH neurons in an Na+ -dependent manner.

In GT1-7 cells, cAMP increases the intracellular Ca2+ concentration ([Ca2+](i)) through activation of the voltage-gated Ca2+ channels, thereby facilitating GnRH release. To activate these channels, the membrane potential must be depolarized. In the present study we hypothesize that cAMP depolarizes the cells by increasing the membrane Na+ permeability, as in the case of somatotrophs and pancreatic beta-cells. To examine this, we analyzed [Ca2+](i) and [Na+](i) in GT1-7 cells by an intracellular ion-imaging technique along with cAMP assay by RIA. Forskolin, a direct activator of adenylyl cyclase, increased [Ca2+](i) and [Na+](i) via cAMP formation. The forskolin-induced increase in [Ca2+](i) depended on the presence of Ca2+ and Na+ in the extracellular solution. This response was blocked by the voltage-gated Ca2+ channel blocker, nifedipine; the nonselective cation channel blocker, gadolinium (Gd3+); and the cyclic nucleotide-gated channel blocker, l-cis-diltiazem. In contrast, the forskolin-induced increase in [Na+](i) depended only on extracellular Na+, not on Ca2+. Gd3+ and l-cis-diltiazem also blocked the increase in [Na+](i). Furthermore, the forskolin-induced increase in GnRH release was blunted in both low Ca2+ and low Na+ media. The results indicate that cAMP increases the membrane Na+ permeability, probably through nonselective cation channels on GT1-7 cells, thereby promoting GnRH release.