Biomedical subjects

U Engström

Publications and source records attributed to U Engström.

At least 19 recordsLinked to original sources

PubMed2001

Enhanced in vitro production of amyloid-like fibrils from mutant (S20G) islet amyloid polypeptide.

UNLABELLED: Islet amyloid polypeptide (IAPP, "amylin") is the amyloid-fibril-forming polypeptide in the islets of Langerhans associated with type 2 diabetes mellitus. A missense mutation in the IAPP gene associated with early-onset type 2 diabetes has been identified in the Japanese population. This mutation results in a glycine for serine substitution at position 20 of the mature IAPP molecule. Whether or not formation of islet amyloid with resulting destruction of islet tissue is the cause of this diabetes is yet not known. The present in vitro study was performed in order to investigate any influence of the amino acid substitution on the fibril formation capacity. Synthetic full-length wild type (IAPPwt) and mutant (IAPPS20G) as well as corresponding truncated peptides (position 18-29) were dissolved in dimethylsulfoxide (DMSO) or in 10% acetic acid at a concentration of 10 mg/mL and their fibril forming capacity was checked by Congo red staining, electron microscopy, a Congo red affinity assay and Thioflavine Tfluorometric assay. It was found that full-length and truncated IAPPS20G both formed more amyloid-like fibrils and did this faster compared to IAPPwt. The fibril morphology differed slightly between the preparations. CONCLUSION: The amino acid substitution (S20G) is situated close to the region of the IAPP molecule implicated in the IAPP fibrillogenesis. The significantly increased formation of amyloid-like fibrils by IAPPS20G is highly interesting and may be associated with an increased islet amyloid formation in vivo and of fundamental importance in the pathogenesis of this specific form of diabetes.

Amyloid↗

PubMed2000

Pro islet amyloid polypeptide (ProIAPP) immunoreactivity in the islets of Langerhans.

Islet amyloid is typically found in type 2 diabetes mellitus and is believed to participate in the beta cell deterioration. The islet amyloid fibril consists of the 37-amino-acid islet amyloid polypeptide (IAPP) but its pathogenesis is only partly understood. We developed several different rabbit antisera against the flanking peptides of the IAPP precursor (proIAPP) and the proIAPP processing sites in order to study the possible occurrence of unprocessed proIAPP or parts thereof in islet amyloid. We applied these antisera in an immunohistochemical study on, islet amyloid deposits present in a newly generated mouse strain that over-expresses human IAPP but is devoid of mouse IAPP. Male mice of this strain develop severe islet amyloidosis when given a high fat diet. Generally, the antisera showed no immunoreactivity with the amyloid. However, in scattered single beta cells, where amyloid could be seen intracellularly, immunoreactivity with one or more of the antisera co-localized with the amyloid. Although virtually all amyloid in human islets of Langerhans is found extracellularly, we propose that the initial amyloid formation occurs intracellularly, perhaps by not fully processed or folded (pro)IAPP. This amyloid, which may develop rapidly under certain circumstances, probably leads to cell death. If not degraded these amyloid spots may then act as nidus for further amyloid formation from fully processed IAPP, secreted from surrounding beta cells.

Amino Acid Sequence↗

PubMed1999

Medin: an integral fragment of aortic smooth muscle cell-produced lactadherin forms the most common human amyloid.

Aortic medial amyloid is a form of localized amyloid that occurs in virtually all individuals older than 60 years. The importance and impact of the amyloid deposits are unknown. In this study we have purified a 5.5-kDa aortic medial amyloid component, by size-exclusion chromatography and RP-HPLC, from three individuals, and we have shown by amino acid sequence analysis that the amyloid is derived from an integral proteolytic fragment of lactadherin. Lactadherin is a 364-aa glycoprotein, previously known to be expressed by mammary epithelial cells as a cell surface protein and secreted as part of the milk fat globule membrane. The multidomain protein has a C-terminal domain showing homology to blood coagulation factors V and VIII. We found that the main constituent of aortic medial amyloid is a 50-aa-long peptide, here called medin, that is positioned within the coagulation factor-like domain of lactadherin. Our result is supported by the specific labeling of aortic medial amyloid in light and electron microscopy with two rabbit antisera raised against two synthetic peptides corresponding to different parts of medin. By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. Furthermore, one of the synthetic peptides forms amyloid-like fibrils in vitro. Lactadherin was not previously known to be an amyloid precursor protein or to be expressed in aortic tissue. The structure of lactadherin may implicate an important regulatory function in the aorta.

Aged↗

PubMed1999

SHP-2 binds to Tyr763 and Tyr1009 in the PDGF beta-receptor and mediates PDGF-induced activation of the Ras/MAP kinase pathway and chemotaxis.

Activation of the beta-receptor for platelet-derived growth factor (PDGF) by its ligand leads to autophosphorylation on a number of tyrosine residues. Here we show that Tyr763 in the kinase insert region is a novel autophosphorylation site, which after phosphorylation binds the protein tyrosine phosphatase SHP-2. SHP-2 has also previously been shown to bind to phosphorylated Tyr1009 in the PDGF beta-receptor. Porcine aortic endothelial (PAE) cells transfected with a PDGF beta-receptor in which Tyr763 and Tyr1009 were mutated to phenylalanine residues failed to associate with SHP-2 after ligand stimulation. Moreover, PDGF-BB-induced Ras GTP-loading and Erk2 activation were severely compromised in the receptor mutant. Whereas the mitogenic response to PDGF-BB remained at the same level as in cells expressing wild-type PDGF beta-receptor, chemotaxis induced by PDGF-BB was significantly decreased in the case of the Y763F/Y1009F mutant cells, suggesting an important role for SHP-2 in chemotactic signaling.

Amino Acid Sequence↗

PubMed1998

Identification of vascular endothelial growth factor receptor-1 tyrosine phosphorylation sites and binding of SH2 domain-containing molecules.

Receptor tyrosine phosphorylation is crucial for signal transduction by creating high affinity binding sites for Src homology 2 domain-containing molecules. By expressing the intracellular domain of Flt-1/vascular endothelial growth factor receptor-1 in the baculosystem, we identified two major tyrosine phosphorylation sites at Tyr-1213 and Tyr-1242 and two minor tyrosine phosphorylation sites at Tyr-1327 and Tyr-1333 in this receptor. This pattern of phosphorylation of Flt-1 was also detected in vascular endothelial growth factor-stimulated cells expressing intact Flt-1. In vitro protein binding studies using synthetic peptides and immunoblotting showed that phospholipase C-gamma binds to both Y(p)1213 and Y(p)1333, whereas Grb2 and SH2-containing tyrosine protein phosphatase (SHP-2) bind to Y(p)1213, and Nck and Crk bind to Y(p)1333 in a phosphotyrosine-dependent manner. In addition, unidentified proteins with molecular masses around 74 and 27 kDa bound to Y(p)1213 and another of 75 kDa bound to Y(p)1333 in a phosphotyrosine-dependent manner. SHP-2, phospholipase C-gamma, and Grb2 could also be shown to bind to the intact Flt-1 intracellular domain. These results indicate that a spectrum of already known as well as novel phosphotyrosine-binding molecules are involved in signal transduction by Flt-1.

3T3 Cells↗

PubMed1998

The L45 loop in type I receptors for TGF-beta family members is a critical determinant in specifying Smad isoform activation.

Transforming growth factor-beta (TGF-beta) and bone morphogenetic proteins (BMPs) signal via distinct type I and type II receptors and Smad proteins. A nine amino acid sequence between kinase subdomains IV and V in type I receptors, termed the L45 loop, has been shown to be important in conferring signalling specificity. We examined the responses of a mutant TGF-beta type I receptor (TbetaR-I) and a mutant BMPR-IB, in which the L45 regions of these two receptors were exchanged. Swapping the four amino acid residues that are different in BMPR-IB for those in TbetaR-I, and vice versa, switched their type I receptor-restricted Smad activation and specificity in transcriptional responses. These studies identify the L45 loop regions in type I receptors as critical determinants in specifying Smad isoform activation.

Amino Acid Sequence↗

PubMed1998

Acceleration of amyloid protein A amyloidosis by amyloid-like synthetic fibrils.

Amyloid protein A (AA) amyloidosis is a consequence of some long-standing inflammatory conditions, and subsequently, an N-terminal fragment of the acute phase protein serum AA forms beta-sheet fibrils that are deposited in different tissues. It is unknown why only some individuals develop AA amyloidosis. In the mouse model, AA amyloidosis develops after approximately 25 days of inflammatory challenge. This lag phase can be shortened dramatically by administration of a small amount of amyloid extract containing an as yet undefined amyloid-enhancing factor. In the present study, we show that preformed amyloid-like fibrils made from short synthetic peptides corresponding to parts of several different amyloid fibril proteins exert amyloidogenic enhancing activity when given i.v. to mice at the induction of inflammation. We followed i.v. administered, radiolabeled, heterologous, synthetic fibrils to the lung and to the perifollicular area in the spleen and found that new AA-amyloid fibrils developed on these preformed fibrils. Our findings thus show that preformed, synthetic, amyloid-like fibrils have an in vivo nidus activity and that amyloid-enhancing activity may occur, at least in part, through this mechanism. Our findings also show that fibrils of a heterologous chemical nature exert amyloid-enhancing activity.

Amino Acid Sequence↗

PubMed1997

Phosphorylation of Ser465 and Ser467 in the C terminus of Smad2 mediates interaction with Smad4 and is required for transforming growth factor-beta signaling.

Members of the Smad family of intracellular signal transducers are essential for transforming growth factor-beta (TGF-beta) to exert its multifunctional effects. After activation of TGF-beta receptors, Smad2 and Smad3 become phosphorylated and form heteromeric complexes with Smad4. Thereafter, these activated Smad complexes translocate to the nucleus, where they may direct transcriptional responses. Here we report that TGF-beta mediates phosphorylation of Smad2 at two serine residues in the C terminus, i.e. Ser465 and Ser467, which are phosphorylated in an obligate order; phosphorylation of Ser465 requires that Ser467 be phosphorylated. Transfection of Smad2 with mutation of Ser465 and/or Ser467 to alanine residues into Mv1Lu cells resulted in dominant-negative inhibition of TGF-beta signaling. These Smad2 mutants were found to stably interact with an activated TGF-beta receptor complex, in contrast to wild-type Smad2, which interacts only transiently. Mutation of Ser465 and Ser467 in Smad2 abrogated complex formation of this mutant with Smad4 and blocked the nuclear accumulation not only of Smad2, but also of Smad4. Thus, heteromeric complex formation of Smad2 with Smad4 is required for nuclear translocation of Smad4. Moreover, peptides from the C terminus of Smad2 containing phosphorylated Ser465 and Ser467 were found to bind Smad4 in vitro, whereas the corresponding unphosphorylated peptides were less effective. Thus, phosphorylated Ser465 and Ser467 in Smad2 may provide a recognition site for interaction with Smad4, and phosphorylation of these sites is a key event in Smad2 activation.

Amino Acid Sequence↗

PubMed1997

Characterization of the interactions between PDZ domains of the protein-tyrosine phosphatase PTPL1 and the carboxyl-terminal tail of Fas.

The intracellular protein-tyrosine phosphatase PTPL1 has five PDZ domains and one of them, PDZ 2, has previously been shown to interact with the C-terminal tail of Fas, a member of the tumor necrosis factor receptor family. Using a peptide binding assay, we show that not only PDZ 2 but also PDZ 4 of PTPL1 interacts with high affinity with peptides derived from the C terminus of Fas. The five most C-terminal amino acid residues of Fas influence the affinity of the interaction. Whereas the glutamine and isoleucine residues in the 4th and 5th positions from the C terminus affect the interaction in a negative and positive manner, respectively, the three C-terminal amino acid residues (SLV) are necessary and sufficient for a high affinity interaction to occur. Both the carboxyl group and side chain of the valine residue at the C terminus of Fas are essential, and the leucine and serine residues in the 2nd and 3rd positions, respectively, from the C terminus are important for the interactions with PDZ 2 and PDZ 4 of PTPL1.

Amino Acid Sequence↗

PubMed1997

Altered immunoreactivity of islet amyloid polypeptide (IAPP) may reflect major modifications of the IAPP molecule in amyloidogenesis.

We have developed a mouse monoclonal antibody against rat/mouse islet amyloid polypeptide (IAPP). The antibody recognises an epitope in the N-terminal part of the molecule, which is conserved between different species. The antibody immunohistochemically labelled beta cells in normal islets of most different mammalian species including man and in one avian species. Previous immunohistochemical studies of human pancreatic tissue from individuals with non-insulin-dependent diabetes mellitus (NIDDM) have revealed a paradoxical and unexplained lack of IAPP immunoreactivity in beta cells close to amyloid in spite of the presence of IAPP mRNA. In contrast to these findings we show that the newly developed monoclonal IAPP antibody strongly labels such beta cells while islet amyloid deposits which are labelled by polyclonal antisera do not bind the monoclonal antibody. These findings with the polyclonal antisera and the monoclonal antibody indicate that IAPP undergoes one or several structural changes during the amyloidogenesis. Knowledge of these structural changes that may include abnormal folding or chemical modification of IAPP is probably important for the understanding of the amyloidogenesis and the pathogenesis of the islet lesion in NIDDM.

Amino Acid Sequence↗

PubMed1997

Prolactin-derived amyloid in the aging pituitary gland.

Small amyloid deposits occur commonly in different organs in association with aging. As in other amyloids, the fibrils in the age-associated forms are built up by specific proteins, unique to every histological type. The amyloid proteins that have been identified in localized amyloid of human endocrine organs have all been of polypeptide hormone nature, and these include calcitonin, islet amyloid polypeptide (amylin), and atrial natriuretic factor. In the present study, we add prolactin to the increasing group of known amyloid proteins and show that this hormone constitutes the amyloid fibrils of pituitary glands of aging individuals.

Aged↗

PubMed1996

Mutation of a Src phosphorylation site in the PDGF beta-receptor leads to increased PDGF-stimulated chemotaxis but decreased mitogenesis.

Ligand induced activation of the beta-receptor for platelet-derived growth factor (PDGF) leads to activation of Src family tyrosine kinases. We have explored the possibility that the receptor itself is a substrate for Src. We show that Tyr934 in the kinase domain of the PDGF receptor is phosphorylated by Src. Cell lines expressing a beta-receptor mutant, in which Tyr934 was replaced with a phenyalanine residue, showed reduced mitogenic signaling in response to PDGF-BB. In contrast, the mutant receptor mediated increased signals for chemotaxis and actin reorganization. Whereas the motility responses of cells expressing wild-type beta-receptors were attenuated by inhibition of phosphatidylinositol 3'-kinase, those of cells expressing the mutant receptor were only slightly influenced. In contrast, PDGF-BB-induced chemotaxis of the cells with the mutant receptor was attenuated by inhibition of protein kinase C, whereas the chemotaxis of cells expressing the wild-type beta-receptor was less affected. Moreover, the PDGF-BB-stimulated tyrosine phosphorylation of phospholipase C-gamma was increased in the mutant receptor cells compared with wild-type receptor cells. In conclusion, the characteristics of the Y934F mutant suggest that the phosphorylation of Tyr934 by Src negatively modulates a signal transduction pathway leading to motility responses which involves phospholipase C-gamma, and shifts the response to increased mitogenicity.

Actins↗

PubMed1996

Axial wall convergence of full veneer crown preparations. Documented for dental students and general practitioners.

The convergence angle in 478 full crown preparations was assessed. Of these preparations, 351 had been performed by general practitioners and 127 by dental students. Groups of preparations performed on incisors, premolars, and molars were compared, as were preparations performed by dentists and students. Two different convergence angles were measured for each tooth, buccolingually and mesiodistally. The results showed a mean angle of 21 degrees. The mean values for premolars and molars differed significantly. When a comparison was made of preparations performed by students, a significant difference was found between premolars and molars. The same comparison for general practitioners showed a significant difference both for incisors compared with molars and for premolars compared with molars. A wide range was found for the convergence of the axial walls, especially for the preparations performed by general practitioners.

Clinical Competence↗

PubMed1996

Hydrolysis of synthetic peptides by cruzipain, the major cysteine proteinase from Trypanosoma cruzi, provides evidence for self-processing and the possibility of more specific substrates for the enzyme.

Two synthetic peptides, peptide G, with the sequence KEEASSAVVGGPG, consisting of the last 10 amino acid residues of the catalytic domain, plus the first 3 at the C-terminal domain, of cruzipain, and peptide R, with the sequence KEEASSAVVRGPG, were hydrolyzed by the enzyme, as shown by reversed-phase HPLC. Peptide R was the best substrate, with a Vmax/K(m) ratio 6-fold higher as compared with peptide G, in good agreement with previous studies indicating that, in small peptides, cruzipain prefers R or K at P1. The optimal pH values for hydrolysis of peptides G and R were 6.8 and 8.0, respectively. A p-nitroanilide derivative containing the P1-P3 residues, Z-VVR-pNA, was an excellent substrate for cruzipain, with a K(m) value (33 microM at pH 9.0) lower than that for Bz-PFR-pNA (66 microM). These results open the possibility of synthesizing more specific substrates and inhibitors of cruzipain.

Amino Acid Sequence↗

PubMed1995

Demonstration of functionally different interactions between phospholipase C-gamma and the two types of platelet-derived growth factor receptors.

Phosphorylated tyrosine residues in receptor tyrosine kinases serve as binding sites for signal transduction molecules. We have identified two autophosphorylation sites, Tyr-988 and Tyr-1018, in the platelet-derived growth factor (PDGF) alpha-receptor carboxyl-terminal tail, which are involved in binding of phospholipase C-gamma (PLC-gamma). The capacities of the Y988F and Y1018F mutant PDGF alpha-receptors, expressed in porcine aortic endothelial cells, to bind PLC-gamma are 60 and 5% of that of the wild-type receptor, respectively. Phosphorylated but not unphosphorylated peptides containing Tyr-1018 are able to compete with the intact receptor for binding to immobilized PLC-gamma SH2 domains; a phosphorylated Tyr-988 peptide competes 10 times less efficiently. The complex between PLC-gamma and the PDGF alpha-receptor is more stable than that of PLC-gamma and the PDGF beta-receptor. However, PDGF stimulation results in a smaller fraction of tyrosine-phosphorylated PLC-gamma and a smaller accumulation of inositol trisphosphate in cells expressing the alpha-receptor as compared with cells expressing the beta-receptor. We conclude that phosphorylated Tyr-988 and Tyr-1018 in the PDGF alpha-receptor carboxyl-terminal tail bind PLC-gamma, but this association leads to only a relatively low level of tyrosine phosphorylation and activation of PLC-gamma.

Amino Acid Sequence↗

PubMed1995

Measurements of chromogranin A, chromogranin B (secretogranin I), chromogranin C (secretogranin II) and pancreastatin in plasma and urine from patients with carcinoid tumours and endocrine pancreatic tumours.

Chromogranins and/or secretogranins constitute a family of water-soluble acidic glycoproteins that are present in almost all endocrine, neuroendocrine and neuronal tissue. Antibodies against chromogranins have been widely used for immunohistochemical staining of endocrine tissue and tumours of neuroendocrine origin. Furthermore, measurements of circulating chromogranin A have been used as a reliable marker for neuroendocrine tumour growth. In this study, we describe the development of specific antibodies against chromogranin A, chromogranin B (secretogranin I), chromogranin C (secretogranin II) and pancreastatin. The antibodies were used for immunohistochemical staining of normal and neoplastic neuroendocrine tissue and development of reliable radioimmunoassays for chromogranin A, chromogranin B, chromogranin C and pancreastatin. In 44 patients with carcinoid tumours, 17 patients with sporadic endocrine pancreatic tumours and 11 patients with endocrine pancreatic tumours and the multiple endocrine neoplasia 1 syndrome, plasma measurements revealed elevated chromogranin A levels in 99%, elevated chromogranin B in 88%, elevated chromogranin C in 6% and elevated pancreastatin in 46% of the patients. Urinary measurements revealed elevated levels in 39%, 15%, 14% and 33% of the patients respectively. Gel permeation chromatography of plasma and urine showed that circulating chromogranin A, and immunoreactive fragments of chromogranin A, had a higher molecular weight distribution than the chromogranin A fragments excreted to the urine. Furthermore, it was noted that most of the patients excreting chromogranin A fragments to the urine had previously been treated with streptozotocin, a cytotoxic agent known to induce renal tubular dysfunction. The antibodies raised proved useful for immunohistochemical staining and visualised endocrine cells in pancreatic islets, adrenal medulla and the small intestine as well as in endocrine pancreatic tumours, pheochromocytoma and midgut carcinoid tumours. In conclusion, the antibodies raised were useful for both immunohistochemical staining of normal tissue and endocrine tumours as well as development of specific radioimmunoassays for plasma measurements of the different chromogranins. Furthermore, we show that plasma measurements of chromogranin A and B were superior to measurements of chromogranin C and pancreastatin and plasma measurements of the different chromogranins were more reliable as markers for tumour growth than the corresponding urine measurements.

Adult↗

PubMed1994

Fibrils from synthetic amyloid-related peptides enhance development of experimental AA-amyloidosis in mice.

Amyloid enhancing factor is an incompletely characterized activity of extracts from many amyloid-containing tissues and which greatly shortens the preamyloidotic phase during experimental induction of AA-amyloidosis. In this communication we show that amyloid-like fibrils made in vitro from synthetic peptides, corresponding to segments of amyloid fibril proteins, have amyloid enhancing factor-like activity. Thus, there is a possibility that amyloid enhancing factor activity depends on small fibrils serving as nucleation centers for fibril elongation.

Amino Acid Sequence↗

PubMed1994

Development of polyclonal antibodies and evaluation of a sensitive radioimmunoassay for detection and measurement of synaptophysin.

Polyclonal antibodies directed towards synaptophysin were raised against a synthesised peptide corresponding to amino acids 246 to 260 of the human synaptophysin sequence. The antibodies, when applied for immunocytochemical staining, showed a staining pattern identical to that of the commercially available monoclonal antibody SY-38. A radioimmunoassay for measurements of synaptophysin was developed using these antibodies and the peptide as standard and tracer. The radioimmunoassay was used for optimising the conditions for purification of synaptophysin from rat brain. No synaptophysin was detected in blood plasma in humans, not even during an embolisation treatment of tumour metastases in the liver, which induced tumour cell necrosis, in a patient with carcinoid tumours. By radioimmunoassay, synaptophysin was detected in cell homogenate from the PC-12 (160 ng/mg) and LCC-18 (40 ng/mg) cell lines and in the cell culture media. In the LCC-18 cell line the synaptophysin immunoreactivity was found in the plasma membrane, and the presence of synaptophysin was confirmed both by radioimmunoassay measurements and by the Northern blot technique. These data indicate that measurements of synaptophysin using this radioimmunoassay are reliable and that the assay can serve as a useful tool in further explorations of the biological effects of synaptophysin.

Animals↗