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A 45-kDa serpin secreted by a murine colon adenocarcinoma cell line, colon26, was isolated, purified, and characterized. It was found to bind specifically to type I collagen with high affinity and to type III collagen with lower affinity. Immunohistochemical studies of murine embryonic tissues showed a specific distribution of this collagen-associated serpin, named caspin, in relation to the formation of bone, cartilage, teeth, and basement membrane. The expression of caspin in high and low lung metastatic subclones of colon26 cell lines was inversely correlated with their metastatic capacity: low lung metastatic cells secreted higher amounts of caspin than their high lung metastatic counterparts. Caspin also demonstrated high homology with human pigment epithelium-derived factor/early population doubling level cDNA-1, which reportedly induces neuronal differentiation of human retinoblastoma cells and is expressed in association with G0 growth arrest. These findings suggest that caspin/pigment epithelium-derived factor/early population doubling level cDNA-1 is a novel factor that might play a crucial role in embryogenesis and tumor metastasis through binding to the extracellular matrix.

The susceptibility of mouse embryonic cells to murine cytomegalovirus (MCMV) infection was studied by injecting the virus in the early and mid-gestation stages. For the early stage, blastocysts from BDF1 mice were injected with MCMV or minimal essential medium (MEM) by micromanipulator and returned to the uteri of pseudopregnant ICR mice. On day 11 of gestation, the embryos were examined immunohistochemically, using antibody specific to the early antigen of MCMV, and the placentae were examined by plaque assay. No infection was detected by either method. Furthermore, no infection was detected in MCMV-infected blastocysts that were cultured and examined for infection by immunofluorescence. For mid-gestation embryos, the conceptus was injected with MCMV on day 8.5 of gestation and was subjected to immunohistochemical analysis from day 10.5 to 12.5 of gestation. Viral antigen-positive cells were first observed in the placentae, then antigen-positive cells appeared among the blood cells, endothelial and mesodermal cells of the embryos. On day 12.5 of gestation, clusters of viral antigen-positive cells were sometimes observed in the hearts and livers. Although the incidence was lower, viral antigen-positive cells were also observed in the neuroectoderm and the eyes. These results suggest that MCMV does not infect early embryos and that infection first occurs in the placenta of postimplantation embryos, whence it extends through the blood cells to the endothelial and mesodermal cells of different embryonic regions, eventually extending to the neuroectoderm.

To investigate the pathogenesis of brain abnormalities caused by congenital cytomegalovirus (CMV) infection, we previously reported experimental murine models of brain damage induced by intraventricular injection of murine CMV (MCMV) at the late stage of gestation. In the present study, viral DNA-positive cells in the damaged brain at different postnatal stages detected by in situ hybridization were compared with viral antigen-positive cells detected by an immunoperoxidase method using a monoclonal antibody against the immediate early antigen. At birth, the number of viral DNA-positive cells almost equalled that of viral antigen-positive cells. Seven to ten days after birth, the number of viral DNA-positive cells in the brain of MCMV-injected mice was one-fifth that of viral antigen-positive cells. Viral DNA-positive cells were more numerous in the hippocampus than in the cortex, and their density was dependent on the presence of viral antigen-positive cells. Dotted reaction products were observed in the nuclei of viral DNA-positive cells. These cells were rarely detected in lesions of later stages such as atrophy of the cortex and hippocampus, or the wall of the cystic lesions. These results suggest that viral DNA-positive cells detected by in situ hybridization are infected cells in which viral DNA replication is occurring actively. Acta Pathol Jpn 41: 661–667, 1991.

Neuroglycan C (NGC) is a transmembrane chondroitin sulfate proteoglycan with an EGF module. We studied the expression of NGC in the human brain, mainly in the hippocampus, and confirmed some observations by conducting experiments using rat brain. In humans, NGC mRNA was expressed exclusively in the brain, especially in the immature brain. The telencephalon, including the hippocampus and neocortex, showed strong mRNA expression. NGC was immunolocalized to neuropils in the hippocampus and neocortex of the adult rat. RT-PCR experiments showed that four splice variants (NGC-I, -II, -III, and -IV) were expressed in the adult human hippocampus. By Western blotting, the expression as proteins of all splice variants except NGC-II was confirmed in the adult rat hippocampus. NGC-IV, which was first found in the present study, had the shortest cytoplasmic domain among the four variants. NGC-IV mRNA was expressed by neurons, but not by astrocytes, in culture prepared from the fetal rat hippocampus, suggesting that NGC-IV plays a role specific to neurons. In addition, the human NGC gene, which is registered as CSPG5, comprised six exons and was approximately 19 kb in size. In exon 2, a single nucleotide polymorphism resulting in Val188Gly in the NGC ectodomain was observed.

The susceptibility of mice at different developmental stages to a relatively low titer of cell culture-passaged murine cytomegalovirus (MCMV) infection was compared in terms of the urinary excretion of MCMV examined by plaque assay and in terms of the distribution of viral infection, determined by immunohistochemistry, using antibodies specific to the early nuclear antigen of MCMV. Viral infection on day 8.5 of gestation (E8.5) into the conceptus and intraperitoneal infection on day 15.5 of gestation (E15.5), postnatal day 2 (P2), postnatal day 11 (P11), and 30 days after birth (P30), respectively, were performed. Embryonal and perinatal mice were more susceptible to MCMV in terms of urinary excretion of the virus and the presence of viral antigen-positive cells in the brain, lungs, and kidneys. In the embryonal and perinatal infection, the viral antigen-positive cells in the neurons of the cerebral cortex and hippocampus were retained late after birth, even though the positive cells in the lungs and kidneys had disappeared. In the mice infected on E8.5, small clusters of viral antigen-positive cells were detected only in the cortex and hippocampus late after birth, without the urinary excretion of virus. These results suggest that when mice are infected with MCMV at the embryonal and perinatal stages, elimination of the infected neurons is delayed compared with that of the other cells in the lungs and kidneys. These findings provide a model for the analysis of pathogenesis of the subclinical congenital CMV infection that manifested clinically late after birth in humans as brain disorders.

Endoplasmic reticulum (ER)p61, ERp72, and protein disulfide isomerase (PDI), which are members of the PDI family protein, are ubiquitously present in mammalian cells and are thought to participate in disulfide bond formation and isomerization. However, why the 3 different members need to be colocalized in the ER remains an enigma. We hypothesized that each PDI family protein might have different modes of enzymatic activity in disulfide bond formation and isomerization. We purified PDI, ERp61, and ERp72 proteins from rat liver microsomes and compared the effects of each protein on the folding of bovine pancreatic trypsin inhibitor (BPTI). ERp61 and ERp72 accelerated the initial steps more efficiently than did PDI. ERp61 and ERp72, however, accelerated the rate-limiting step less efficiently than did PDI. PDI or ERp72 did not impede the folding of BPTI by each other but rather catalyzed the folding reaction cooperatively with each other. These data suggest that differential enzymatic activities of ERp proteins and PDI represent a complementary contribution of these enzymes to protein folding in the ER.

Folding of secretory proteins is associated with the formation and isomerization of disulfide bonds. ERp72, a protein disulfide isomerase (PDI) family member, possesses 3 thioredoxin homology domains, but the participation of each domain in disulfide-bond formation and isomerization remains to be determined. We analyzed the function of individual domains in the insulin reduction assay system by site-directed mutagenesis with cysteine-to-serine replacement. All domains contributed to apparent steady-state binding (Km) and catalysis at saturating substrate concentrations (kcat) but in different manners. A mutant ERp72 with mutations in domains 1 and 2 (ERp72-mut-1+2) exhibited reductions in kcat of 73.9% when compared with wild type, whereas ERp72-mut-1+3 (mutations in domains 1 and 3) and ERp72-mut-2+3 (mutations in domains 2 and 3) exhibited less substantial reductions in kcat. ERp72-mut-1+3 and ERp72-mut-2+3 showed elevations in Km of 89.9% and 96.2%, respectively, when compared with wild type, whereas ERp72-mut-1+2 exhibited smaller elevations in Km. These results suggest that domains 1 and 2 make greater contributions to catalyzing efficacy and domain 3 to binding affinity. Domain 2 is involved in binding affinity, in combination with domain 3, in addition to its own contribution to catalyzing efficacy. This assignment of functions to individual domains is similar to that observed in other PDI domains, which is consistent with the high sequence homology between ERp and PDI domains.

Human teratocarcinoma NT2/D1 cells undergo differentiation into a variety of cell types, including neurons, treated with retinoic acid. In the present study, the concentrations of alpha S-100 and beta S-100 proteins (alpha and beta subunits of S-100 proteins), and three subunits (alpha, beta and gamma) of enolase in NT2/D1 cells were measured using the sensitive enzyme immunoassay method. The concentration of beta S-100 was markedly increased in the cells after treatment with retinoic acid, whereas the concentration of alpha S-100 was undetectably low, indicating that the S-100b (beta beta) protein was induced by retinoic acid. On the other hand, the concentrations of the three forms of enolase isozymes did not change in the same culture. The induction of S-100b protein was not observed in the NT2/D1 cells after treatment with forskolin, dibutyryl cyclic AMP or cholera toxin. The indirect double-labeled immunofluorescence, using antibodies specific to beta S-100 and monoclonal antibodies specific to neurofilaments, revealed that both the S-100b protein and the neurofilaments were induced in the same subpopulation of cells which underwent neuronal differentiation.

Summary Three groups of monoclonal antibodies which reacted with cells infected by guinea-pig cytomegalovirus (GPCMV) were prepared. The first group of antibodies immunoprecipitated a 50000 mol. wt. (50K) polypeptide of GPCMV-infected cells. This polypeptide was identified as part of the nuclear inclusion by immunofluorescence. This nuclear fluorescence was markedly diminished when the infected cells were incubated in the presence of phosphonoacetic acid. By immunoelectron microscopy the antibodies reacted mainly with filamentous structures (26 to 28 nm in diameter) in nuclear inclusions and occasionally stained nucleocapsids. Neither intracytoplasmic nor extracellular virions reacted with the antibodies. Therefore, the 50K protein with which the monoclonal antibodies reacted was nuclear inclusion-specific and a non-structural protein. The second group of antibodies reacted with a 76K polypeptide of the infected cells which was a matrix protein found in both cytoplasmic inclusions and extracellular dense virions. The third group of antibodies mainly reacted with a virion core protein by immunoelectron microscopy.