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A case of meningioma coexisting with both lipomatous and secretory components, the latter characterized by hyaline inclusion bodies, is reported. The neuroradiological features of lipomeningioma are reevaluated, and the possible pathogenetic mechanisms of this unique combination in the present case are discussed.
Porcine secretory immunoglobulin A (SIgA) was isolated in a single step from porcine milk whey by affinity chromatography, using antiporcine alpha-chain specific antibody linked to CNBr-activated agarose. The isolated SIgA contained no other proteins detectable by immunodiffusion of immunoelectrophoresis. After reduction and alkylation with dithiothreitol and iodoacetamide, the SIgA was chromatographed on gel equilibrated with 6.0 M urea and 1.0 M propionic acid. Polyacrylamide gel electrohoresis of the fractions eluted revealed the presence of light chain, alpha-chain secretory component, and J-chain.
An acid phosphatase (acPAse) activity was released during germination and tube growth of pollen of Lilium longiflorum Thunb. By inhibiting components of the secretory pathway, the export of the acPase activity was affected and tube growth stopped. Brefeldin A (1 microM) and cytochalasin D (1 microM), which block the production and transport of secretory vesicles, respectively, inhibited the acPase secretion. The Ca2+ channel blocker gadolinium (100 microM Gd3+) also inhibited acPase secretion and tube growth, whereas 3 mM caffeine, another Ca2+ uptake inhibitor, stimulated the acPase release, while tube growth was inhibited. The Yariv reagent (beta-D-glucosyl)3 Yariv phenylglycoside stopped tube growth by binding to arabinogalactan proteins of the tube tip cell wall but did not affect acPase secretion. A strong correlation between tube growth and acPase release was detected. The secreted acPase activity had a pH optimum at pH 5.5, a KM of 0.4 mM for p-nitrophenyl phosphate, and was inhibited by zinc, molybdate, phosphate, and fluoride ions, but not by tartrate. In electrophoresis gels the main acPase activity was detected at 32 kDa. The conspicuous correlation between activity of the secretory pathway and acPase secretion during tube elongation strongly indicates an important role of the acPase during pollen tube growth and the secreted acPase activity may serve as a useful marker enzyme assay for secretory activity in pollen tubes.
Size exclusion chromatography of the cytosolic fraction of SecA-overproducing cells of Escherichia coli suggested that SecA, an essential component of the secretory machinery, exists as an oligomer. The subunit structure of SecA was then studied using a purified specimen. Estimation of the molecular mass by means of ultracentrifugation and chemical crosslinking analysis revealed that SecA exists as a homodimer. The purified SecA was denatured in 6 M guanidine-HCl and renatured to a dimer, which was fully active in terms of translocation, even in the presence of 1 mM dithiothreitol. It is suggested that the dimeric structure is not critically maintained by disulfide bonding between the two subunits, each of which contains four cysteine residues.
Secretory IgA is a major protein component of rabbit lung surfactant purified by NaBr density gradient centrifugation from endobronchial lavage and minced lung tissue. Secretory IgA was found in both surfactant and non-surfactant fractions obtained from endobronchial lung washings. By contrast in minced-lung washings, which are not contaminated with proteins from the upper respiratory tree, secretory IgA is prominent only in the surfactant fraction. These findings indicate that in rabbit lung secretory IgA is present in the alveoli and is intimately associated with the surfactant system.
The mouse corticotrope tumor cell line AtT-20/D16v was used to investigate the effects of chronic treatment with various secretagogues on individual components of the secretory pathway. Secretagogues acting in part through receptors linked to guanine nucleotide-binding regulatory proteins [CRF and somatostatin (SS)] and agents by-passing membrane receptors (phorbol myristate acetate and dexamethasone) were examined. Effects on the secretory product were evaluated by measuring levels of pro-ACTH/endorphin mRNA and hormone secretion. Effects on posttranslational processing enzymes were evaluated by measuring levels of the mRNAs encoding carboxypeptidase-E and peptidyl-glycine-alpha-amidating monooxygenase (PAM); cellular levels of PAM activity were also measured. The mRNAs encoding the G-proteins in AtT-20 cells were identified, and secretagogue effects on the G-protein signal transduction system were evaluated by measuring levels of the mRNAs encoding (alpha s, alpha)i2, and beta 2. No single parameter adequately characterizes the regulatory state of the complex secretory apparatus. Although levels of pro-ACTH/endorphin (PAE) mRNA accurately reflected hormone secretion after chronic CRF or dexamethasone treatment, chronic SS treatment elevated PAE mRNA levels in the face of reduced hormone secretion. Levels of PAM mRNA generally changed in parallel with levels of PAE mRNA; in contrast, levels of carboxypeptidase-E mRNA were unaffected by any of the secretagogues tested. Secretagogues acting through distinct G-proteins (CRF and SS) as well as dexamethasone brought about a coordinate increase in the level of the mRNAs encoding the three G-protein subunits examined. Treatment with phorbol myristate acetate caused a slight decrease in the levels of the G-protein subunit mRNAs.
An increasing number of human disorders have been linked to mutations in genes of the secretory pathway. The chemically induced zebrafish crusher variant results in malformed craniofacial skeleton, kinked pectoral fins and a short body length. By positional cloning, we identified a nonsense mutation converting leucine to a stop codon (L402X) in the sec23a gene, an integral component of the COPII complex, which is critical for anterograde protein trafficking between endoplasmic reticulum and Golgi apparatus. Zebrafish crusher mutants develop normally until the onset of craniofacial chondrogenesis. crusher chondrocytes accumulate proteins in a distended endoplasmic reticulum, resulting in severe reduction of cartilage extracellular matrix (ECM) deposits, including type II collagen. We demonstrate that the paralogous gene sec23b is also an essential component of the ECM secretory pathway in chondrocytes. In contrast, knockdown of the COPI complex does not hinder craniofacial morphogenesis. As SEC23A lesions cause the cranio-lenticulo-sutural dysplasia syndrome, crusher provides the first vertebrate model system that links the biology of endoplasmic reticulum to Golgi trafficking with a clinically relevant dysmorphology.
Meningiomas exhibit a broad spectrum of differentiation potency corresponding to different histological subtypes. The separate secretory or lipomatous transformation of meningothelial cells is uncommonly encountered in meningiomas classified into distinct secretory or lipomatous variants. The coexistence of these two different histological subtypes is extremely rare. We report an exceptional case of secretory meningioma associated with extensive lipomatous component in a 58-year-old woman. CT scan and MRI of the brain showed a well-defined tumor mass in the right temporal lobe with areas of adipose tissue and extensive surrounding brain edema. Microscopically, the tumor was composed of two components: whorls of meningothelial cells with numerous PAS-positive hyaline inclusions (pseudopsammoma bodies) and numerous mature adipocyte-like cells. The presence of neutral fat was confirmed by oil-red-O staining. The hyaline inclusions and tumor cells surrounding them showed strong immunoreactivity for EMA and CEA. Ultrastructural findings confirmed both secretory and lipomatous differentiation of tumor cells. The majority of lipidized neoplastic cells shared the features of meningothelial cells and adipocytes. Our result supports the opinion that lipomatous component ought to be considered as an advanced lipidization of neoplastic meningothelial cells rather than true metaplastic transformation of meningothelial cells into mature fat tissue. The present case of meningioma demonstrates a unique coexistence of secretory and lipomatous meningothelial components, reflecting the multipotency of phenotypic transformation of primary meningothelial cells.
Translocation of eucaryotic secretory proteins across the phospholipid membrane containing, no protein components has been studied on the model system. The level of translocation was found to depend critically on physical and chemical properties of membranes. It was found that the cell-free system components can exhibit membrane activity.
Secretory breast carcinoma is a rare entity. It was first reported in pediatric patients in 1966, and was named juvenile breast carcinoma. Incidences of pediatric and adult patients are similar. Prognosis is favorable in both groups, but distant metastases have been reported. The authors describe a case of secretory breast carcinoma with extensive intraductal component.
Secretory vesicle exocytosis is the mechanism of release of neurotransmitters and neuropeptides. Secretory vesicles are localized in at least two morphologically and functionally distinct compartments: the reserve pool and the release-ready pool. Filamentous actin networks play an important role in this compartmentalization and in the trafficking of vesicles between these compartments. The cortical F-actin network constitutes a barrier (negative clamp) to the movement of secretory vesicles to release sites, and it must be locally disassembled to allow translocation of secretory vesicles in preparation for exocytosis. The disassembly of the cortical F-actin network is controlled by scinderin (a Ca(2+)-dependent F-actin severing protein) upon activation by Ca2+ entering the cells during stimulation. There are several factors that regulate scinderin activation (i.e., Ca2+ levels, phosphatidylinositol 4,5-bisphosphate (PIP2), etc.). The results suggest that scinderin and the cortical F-actin network are components of the secretory machinery.
The Fischer rat shows an age-related loss of both hepatic blood to bile transport and secretory component-specific binding sites for polymeric immunoglobulin (Ig) A. This age-related loss of hepatic IgA receptor function is also shown by cultured hepatocytes. It is reported here that compared with young cells, binding and uptake of 125I-polymeric IgA by cultured hepatocytes was markedly reduced in cells from senescent animals. In addition, cells from old animals showed markedly diminished secretion of secretory component determined by enzyme-linked immunosorbent assay and expression of polymeric immunoglobulin receptor determined by incorporation of 35S-labeled amino acid and fluorography. It is suggested that the age-related decrease in IgA receptor-mediated transport from serum to bile results, at least in part, from decreased expression and secretion of total hepatic secretory component.
Secretory conglutinin-like factor (SKF) reacts directly with an unknown surface component of some, but not all, oral gram-positive organisms. The absorption of SKF by bacteria is EDTA-sensitive and cannot be blocked with immunoglobulins. High levels of SKF in EDTA extracts of washed salivary sediment reveal the direct in vivo reaction of SKF with oral bacteria. Mixed aggregation with alexinated erythrocytes showed the SKF corresponds to the secretory bacterial aggregating factor (SBAF) for Streptococcus mutans serotype c and also that for Streptococcus mitis. These reactions represent a cross-reaction between bacteria and complement component C3. SKF/SBAF non-mucin glycoproteins and immunoglobulins possess receptors for bacterial components while mucins are passive carriers of blood group determinants.
The content of alkaline phosphatase (ALP) was determined in neutrophils isolated from patients with acute bacterial infections by a standard enzyme assay. Compared with control cells, patient cells exhibited about a fivefold increase in ALP activity. There was no difference between the ALP Km values of control and patient cells, which indicates that the elevated activity in patient cells was due to the presence of increased amounts of the enzyme. The ALP isozyme in both cell types was determined to be the tissue-unspecific ALP. The fact that much of the ALP activity was measurable only in the presence of detergent suggested that the enzyme was localized in the secretory vesicles, a putative reservoir of plasma membrane components. The amount and subcellular distribution of two other secretory vesicle membrane proteins, i.e., cytochrome b and complement receptor 3, were not altered; hence, we conclude that there was no general increase in amounts of secretory vesicle membrane constituents in the patient cells.
Sec20p is an essential endoplasmic reticulum (ER) membrane protein in yeasts, functioning as a tSNARE component in retrograde vesicle traffic. We show that Sec20p in the human fungal pathogen Candida albicans is extensively O mannosylated by protein mannosyltransferases (Pmt proteins). Surprisingly, Sec20p occurs at wild-type levels in a pmt6 mutant but at very low levels in pmt1 and pmt4 mutants and also after replacement of specific Ser/Thr residues in the lumenal domain of Sec20p. Pulse-chase experiments revealed rapid degradation of unmodified Sec20p (38.6 kDa) following its biosynthesis, while the stable O-glycosylated form (50 kDa) was not formed in a pmt1 mutant. These results suggest a novel function of O mannosylation in eukaryotes, in that modification by specific Pmt proteins will prevent degradation of ER-resident membrane proteins via ER-associated degradation or a proteasome-independent pathway.
Mutations in SHR3 block amino acid uptake into yeast by reducing the levels of multiple amino acid permeases within the plasma membrane. SHR3 is a novel integral membrane protein component of the endoplasmic reticulum (ER). shr3 null mutants specifically accumulate amino acid permeases in the ER; other plasma membrane proteins, secretory proteins, and vacuolar proteins are processed and targeted correctly. Our findings suggest that SHR3 interacts with a structural domain shared by amino acid permeases, an interaction required for permease-specific processing and transport from the ER. Even in the presence of excess amino acids, shr3 mutants exhibit starvation responses. shr3 mutants constitutively express elevated levels of GCN4, and mutant shr3/shr3 diploids undergo dimorphic transitions that result in filamentous growth at enhanced frequencies.
Glycoprotein II (GpII) is a heterogenous glycoprotein isolated from the membranes of bovine chromaffin granules in the adrenal medulla. When viewed by two-dimensional electrophoresis this glycoprotein consists of two components, upper (GpIIa) and lower (GpIIb), with a molecular mass of 80,000-100,000 daltons and a pI of 4.2-4.7. NH2-terminal sequence analysis of GpIIa and GpIIb revealed sequence similarity with lysosomal membrane glycoproteins (lamp-1 and lamp-2), which was supported by sequence data of peptides from trypsin and cyanogen bromide digestions. An oligonucleotide probe was used to isolate a cDNA clone encoding the nucleotide sequence of GpIIa. The predicted amino acid sequence of GpIIa shares a 72% identity with the human lamp-1 type protein, which belongs to a highly conserved group of lysosomal-associated membrane glycoproteins (lamp proteins), whose function is still unknown. The COOH-terminal region of GpIIa was identical to the COOH-terminal region of lamp proteins. This COOH-terminal determinant has been demonstrated to be essential for the intracellular targeting of lamp proteins to lysosomes. A synthetic peptide antisera to the COOH-terminal region of GpIIa was used to show that this region is present on purified chromaffin granules and not proteolytically processed. The sequence analysis of GpIIa and immunological data confirm GpII as the secretory granule counterpart of lamp proteins and raise some questions regarding intracellular targeting between lysosomes and secretory granules within the chromaffin cell.
The isolation and characterization of a Drosophila melanogaster gene (Dtrp1) that encodes a protein displaying the properties of both a structural and functional homolog of the yeast endoplasmic reticulum membrane-bound translocation protein Sec62p is reported. We show that Dtrp1 can not only rescue the lethality associated with a SEC62 gene knockout in yeast, but also complement the sec62-associated defective transport of a precursor polypeptide from the cytoplasm into the lumen of the endoplasmic reticulum. Expression of the Dtrp1 gene throughout Drosophila development is characterized by peaks in mid-embryo-genesis and mid-pupation, followed by a sustained period of mRNA accumulation in adults. The examination of male reproductive tissues showed a very high level of preferential expression of a 1.6 kb message, while a 2.2 kb message was confined almost exclusively to the non-reproductive tissues. Within the reproductive tract itself the 1.6 kb message was expressed in testes, ejaculatory duct and particularly strongly in the paragonial glands. Since these latter organs are specialized secretory tissues we suggest that the 1.6 kb message may encode a protein isoform that performs a unique, tissue-specific role in the protein translocation pathway. Such observations may indicate a hitherto unexpected diversity in components of the protein translocation pathway in respect to stage, tissue and, potentially, substrate specificity.