Amyloid beta protein precursor is possibly a heparan sulfate proteoglycan core protein

The amyloid beta protein peptide is a major constituent of amyloid plaque cores in Alzheimer's disease and is apparently derived from a higher molecular weight precursor. It is now shown that the core protein of a heparan sulfate proteoglycan secreted from a nerve cell line (PC12) has an amino acid sequence and a size very similar to those of the amyloid beta protein precursor and that these molecules are antigenically related. This amyloid beta protein precursor-related protein is not found in the conditioned medium of a variant cell line (F3 PC12) that does not secrete heparan sulfate proteoglycan. The synaptic localization and metabolism of this class of proteoglycans are consistent with its potential involvement in central nervous system dysfunction.     

Nicotine is chemotactic for neutrophils and enhances neutrophil responsiveness to chemotactic peptides

Neutrophils contribute to chronic bronchitis and pulmonary emphysema associated with cigarette smoking. Nicotine was found to be chemotactic for human neutrophils but not monocytes, with a peak activity at approximately 31 micromolar. In lower concentrations (comparable to those in smokers' plasma), nicotine enhanced the response of neutrophils to two chemotactic peptides. In contrast to most other chemoattractants for neutrophils, however, nicotine did not affect degranulation or superoxide production. Nicotine thus may promote inflammation and consequent lung injury in smokers.     

The role of beta 2-microglobulin in peptide binding by class I molecules

Efficient transport of class I major histocompatibility complex molecules to the cell surface requires association of the class I heavy chain with endogenous peptide and the class I light chain, beta 2-microglobulin (beta 2M). A mutant cell line deficient in beta 2M transports low amounts of nonpeptide-associated heavy chains to the cell surface that can associate with exogenously provided beta 2M and synthetic peptide antigens. Normal beta 2M-sufficient cells grown in serum-free media devoid of beta 2M also require an exogenous source of beta 2M to efficiently bind synthetic peptide. Thus, class I molecules on normal cells do not spontaneously bind or exchange peptides.     

Endothelial cell gene expression of a neutrophil chemotactic factor by TNF-alpha, LPS, and IL-1 beta

Human endothelial cells produced a neutrophil chemotactic factor (NCF) upon stimulation with tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), or lipopolysaccharide (LPS). The expression of endothelial cell-derived NCF messenger RNA and biological activity was both time- and concentration-dependent. Maximal NCF mRNA expression occurred at 10 and at 2 nanograms per milliliter for TNF and IL-1 beta, respectively; mRNA expression was first observed 1 hour after stimulation and was maintained for at least 24 hours. In situ hybridization analysis showed that NCF mRNA peaked in treated cells by 24 hours, whereas unstimulated cells were negative. These studies demonstrated that endothelial cells may participate in neutrophil-mediated inflammation by synthesizing a chemotactic factor in response to specific monokines and LPS.     

The neutrophil-activating protein (NAP-1) is also chemotactic for T lymphocytes

T lymphocyte chemotactic factor (TCF) was purified to homogeneity from the conditioned media of phytohemagglutinin-stimulated human blood mononuclear leukocytes by a sequence of chromatography procedures. The amino-terminal amino acid sequence of the purified TCF showed identity with neutrophil-activating protein (NAP-1). Both TCF and recombinant NAP-1 (rNAP-1) were chemotactic for neutrophils and T lymphocytes in vitro supporting the identity of TCF with NAP-1. Injection of rNAP-1 into lymphatic drainage areas of lymph nodes in Fisher rats caused accelerated emigration of only lymphocytes in high endothelial venules. Intradermal injection of rNAP-1 caused dose-dependent accumulation of neutrophils and lymphocytes.     

Inhibition of platelet aggregation by monoclonal antibody reactive with beta 2-microglobulin chain of HLA complex

A mouse monoclonal antibody that reacts with beta 2-microglobulin, the light chain of class I major histocompatibility antigens, inhibited the second wave of human platelet aggregation induced by adenosine diphosphate and epinephrine and blocked aggregation and platelet protein phosphorylation induced by sodium arachidonate. Thrombin-induced platelet aggregation was inhibited at threshold concentrations but not at higher concentrations. The antibody also inhibited aggregation and secretion in response to thromboxane A2 or the stable endoperoxide analog, U46619. These results suggest that beta 2-microglobulin in the histocompatibility complex is intimately associated with transmission of the endoperoxide-thromboxane signal at the platelet membrane.     

Tertiary structure is a principal determinant to protein deamidation

The protein deamidation process involves the conversion of the amide side-chain moieties of asparagine and glutamine residues to carboxyl groups. This conversion is an unusual form of protein modification in that it requires catalysis by an intramolecular reaction where both the substrate (asparagine and glutamine side chains) and "catalytic site" (the peptide nitrogen of the succeeding residue) are constituents of several consecutive residues along the polypeptide chain. The stereochemical factors governing this process were studied with a data base derived from the neutron crystallographic structure of trypsin from which amide groups and oxygen can be unambiguously differentiated because of their different neutron scattering properties. The neutron structure allowed for the direct determination of those residues that were deamidated; 3 of 13 asparagine residues were found to be modified. These modified residues were clearly distinguished by a distinct local conformation and hydrogen-bonding structure in contrast to those observed for the other asparagine residues. No correlation was found between preference to deamidate and the chemical character of residues flanking the site, as had been proposed from previous peptide studies.     

CD2-associated protein haploinsufficiency is linked to glomerular disease susceptibility

Loss of CD2-associated protein (CD2AP), a component of the filtration complex in the kidney, causes death in mice at 6 weeks of age. Mice with CD2AP haploinsufficiency developed glomerular changes at 9 months of age and had increased susceptibility to glomerular injury by nephrotoxic antibodies or immune complexes. Electron microscopic analysis of podocytes revealed defects in the formation of multivesicular bodies, suggesting an impairment of the intracellular degradation pathway. Two human patients with focal segmental glomerulosclerosis had a mutation predicted to ablate expression of one CD2AP allele, implicating CD2AP as a determinant of human susceptibility to glomerular disease.     

SMEDWI-2 is a PIWI-like protein that regulates planarian stem cells

We have identified two genes, smedwi-1 and smedwi-2, expressed in the dividing adult stem cells (neoblasts) of the planarian Schmidtea mediterranea. Both genes encode proteins that belong to the Argonaute/PIWI protein family and that share highest homology with those proteins defined by Drosophila PIWI. RNA interference (RNAi) of smedwi-2 blocks regeneration, even though neoblasts are present, irradiation-sensitive, and capable of proliferating in response to wounding; smedwi-2(RNAi) neoblast progeny migrate to sites of cell turnover but, unlike normal cells, fail at replacing aged tissue. We suggest that SMEDWI-2 functions within dividing neoblasts to support the generation of cells that promote regeneration and homeostasis.     

The cholinergic neuronal differentiation factor from heart cells is identical to leukemia inhibitory factor

A protein secreted by cultured rat heart cells can direct the choice of neurotransmitter phenotype made by cultured rat sympathetic neurons. Structural analysis and biological assays demonstrated that this protein is identical to a protein that regulates the growth and differentiation of embryonic stem cells and myeloid cells, and that stimulates bone remodeling and acute-phase protein synthesis in hepatocytes. This protein has been termed D factor, DIA, DIF, DRF, HSFIII, and LIF. Thus, this cytokine, like IL-6 and TGF beta, regulates growth and differentiation in the embryo and in the adult in many tissues, now including the nervous system.     

The amyloid beta protein gene is not duplicated in brains from patients with Alzheimer's disease

Complementary DNAs (cDNAs) encoding portions of the amyloid beta protein were used to investigate possible amyloid gene duplication in sporadic Alzheimer's disease. A strategy employing two Eco RI restriction fragment length polymorphisms (RFLPs) detected by the amyloid cDNAs was used. RFLPs allow the detection of a 2:1 gene dosage in the DNA of any individual who is heterozygous for a particular RFLP. The amyloid gene regions homologous to the cDNAs used were not duplicated in the DNA from brains of individuals with sporadic Alzheimer's disease. Similar results were also obtained with a strategy employing a test for 3:2 gene dosage.     

Propolypeptide of von Willebrand factor circulates in blood and is identical to von Willebrand antigen II

The generally mild bleeding disorder of von Willebrand disease is associated with abnormalities of two distinct plasma proteins, the large multimeric von Willebrand factor (vWF), which mediates platelet adhesion, and von Willebrand antigen II (vW AgII), which is of unknown function. The two proteins were found to have a common biosynthetic origin in endothelial cells and megakaryocytes, which explains their simultaneous absence in the severe form of this hereditary disease. Shared amino acid sequences from a 100-kilodalton plasma glycoprotein and from vW AgII are identical to amino acid sequences predicted from a complementary DNA clone encoding the 5' end of vWF. In addition, these proteins have identical molecular weights and immunologic cross reactivities. Monoclonal antibodies prepared against both proteins recognize epitopes on the pro-vWF subunit and on a 100-kilodalton protein that are not present on the mature vWF subunit in endothelial cell lysates. In contrast, polyclonal antibodies against vWF recognize both pro-vWF and vWF subunits. Thus, the 100-kilodalton plasma glycoprotein and vW AgII are identical proteins and represent an extremely large propolypeptide that is first cleaved from pro-vWF during intracellular processing and then released into plasma.     

OSBP is a cholesterol-regulated scaffolding protein in control of ERK 1/2 activation

Oxysterol-binding protein (OSBP) is the founding member of a family of sterol-binding proteins implicated in vesicle transport, lipid metabolism, and signal transduction. Here, OSBP was found to function as a cholesterol-binding scaffolding protein coordinating the activity of two phosphatases to control the extracellular signal-regulated kinase (ERK) signaling pathway. Cytosolic OSBP formed a approximately 440-kilodalton oligomer with a member of the PTPPBS family of tyrosine phosphatases, the serine/threonine phosphatase PP2A, and cholesterol. This oligomer had dual specific phosphatase activity for phosphorylated ERK (pERK). When cell cholesterol was lowered, the oligomer disassembled and the level of pERK rose. The oligomer also disassembled when exposed to oxysterols. Increasing the amount of OSBP oligomer rendered cells resistant to the effects of cholesterol depletion and decreased the basal level of pERK. Thus, cholesterol functions through its interaction with OSBP outside of membranes to regulate the assembly of an oligomeric phosphatase that controls a key signaling pathway in the cell.     

HTLV-I trans-activator protein, tax, is a trans-repressor of the human beta-polymerase gene

Human T cell leukemia virus type I (HTLV-I) is the etiological agent for adult T cell leukemia (ATL). The HTLV-I trans-activator protein Tax can activate the expression of its own long terminal repeat (LTR) and many cellular and viral genes. Tax down-regulated the expression of human beta-polymerase (hu beta-pol), a cellular enzyme involved in host cell DNA repair. This finding suggests a possible correlation between HTLV-I infection and host chromosomal damage, which is often seen in ATL cells.     

Simian sarcoma virus--transformed cells secrete a mitogen identical to platelet-derived growth factor

Normal rat kidney (NRK) cells transformed by simian sarcoma virus (SSV) release into the culture medium a biologically active mitogen with properties identical to those of human platelet-derived growth factor (PDGF). Like PDGF, the growth factor derived from SSV-NRK cells was shown to be stable to heat and sensitive to reducing agents. It was capable of inhibiting binding of labeled PDGF to the receptor on human fibroblasts. It also stimulated the phosphorylation of the same membrane protein (185 kilodaltons) in isolated plasma membranes from human fibroblasts. Immunoprecipitation of metabolically labeled proteins released by SSV-NRK cells showed that a 34-kilodalton protein was specifically precipitated by antiserum to PDGF. Upon reduction, this protein had a molecular size of 17 kilodaltons. PDGF has been shown to consist of two 14- to 18-kilodalton proteins linked by disulfide bonds.