Faculty Bibliography

Many biochemically diverse proteins can give rise to amyloid fibrils; however, they are all accompanied by P component and glucosaminoglycans. With antibodies specific to apolipoprotein E (apo E) we used immunohistochemical techniques to test for the presence of this protein in both cerebral and systemic amyloid. We found apo E immunoreactivity in all tested types of cerebral and systemic amyloid. In amyloid deposits apo E P, component and glucosaminoglycans may be acting as 'pathological molecular chaperones'. The latter we define as a group of unrelated proteins that induce beta-pleated conformation in amyloidogenic polypeptides

Amyloid beta (A beta), the major constituent of the fibrils composing senile plaques and vascular amyloid deposits in Alzheimer's disease (AD) and related disorders, is a 39-42-residue self-aggregating degradation peptide of a larger multidomain membrane glycoprotein designated amyloid precursor protein (APP). An array of biological functions has been assigned to different APP domains, including growth regulation, neurotoxicity, inhibitory activity of serine proteinases and promotion of cell-cell and cell-matrix interactions. A beta is generated through an as-yet-unknown catabolic pathway that by-passes or inhibits the cleavage of APP within the A beta sequence. We have identified a 16 kDa intermediate APP C-terminal fragment containing A beta in leptomeningeal vessels of aged normal individuals and AD patients by means of its immunoreactivity with a panel of four different anti-(APP C-terminal) antibodies, indicating a different pathway of APP processing. Previous studies have indicated that the APP C-terminal domain is the most likely to be involved in cell-matrix interactions. A 109-amino-acid construct C109 with a sequence analogous to the C-terminal of APP (positions 587-695 of APP695), similar in length and immunoreactivity to the 16 kDa fragment, was found to promote cell adhesion. By use of synthetic peptides, this activity was initially located to the extracellular 28 residues of A beta. Inhibition studies demonstrated that the sequence RHDS (amino acids 5-8 of A beta, corresponding to residues 601-604 of APP695 was responsible for the adhesion-promoting activity. The interaction is dependent on bivalent cations and can be blocked either by the tetrapeptides RHDS and RGDS or by an anti-(beta 1 integrin) antibody. Thus, through integrin-like surface receptors, APP or its derivative proteolytic fragments containing the sequence RHDS may modulate cell-cell or cell-matrix interactions

The 4-kilodalton (39 to 43 amino acids) amyloid beta protein (beta AP), which is deposited as amyloid in the brains of patients with Alzheimer's diseases, is derived from a large protein, the amyloid beta protein precursor (beta APP). Human mononuclear leukemic (K562) cells expressing a beta AP-bearing, carboxyl-terminal beta APP derivative released significant amounts of a soluble 4-kilodalton beta APP derivative essentially identical to the beta AP deposited in Alzheimer's disease. Human neuroblastoma (M17) cells transfected with constructs expressing full-length beta APP and M17 cells expressing only endogenous beta APP also released soluble 4-kilodalton beta AP, and a similar, if not identical, fragment was readily detected in cerebrospinal fluid from individuals with Alzheimer's disease and normal individuals. Thus cells normally produce and release soluble 4-kilodalton beta AP that is essentially identical to the 4-kilodalton beta AP deposited as insoluble amyloid fibrils in Alzheimer's disease

We present the immunohistochemical and biochemical identification of an amyloidoma localized to the cerebral white matter in a patient who shows no evidence of systemic or extracranial localized amyloid deposits. Immunohistologic and immunochemical studies, using antibodies against biochemically different amyloid fibrils and amyloid-associated proteins, showed reactivity with antibodies only to lambda light chain and serum amyloid P-component. Amino acid sequence analysis of the purified amyloid fibrils extracted from the brain tumor indicates that the amyloid protein is an unusual immunoglobulin lambda light chain, starting at residue five of the variable domain. These fibrils consist of lambda chain fragments of different lengths (10 to 30 kd) very likely arising by polymerization of the amyloid subunit or sequential proteolytic cleavage of the light chain, or both. After exposure to denaturing agents, the 10-kd subunit retains the characteristics of native amyloid fibrils by electron microscopy

BACKGROUND: The origin of the amyloid beta protein (A beta) that is the main constituent of amyloid fibrils occurring in the senile plaques and cerebrovasculature of individuals afflicted with Alzheimer's Disease, Down's Syndrome, Hereditary Cerebral Hemorrhage with Amyloidosis--Dutch Type, and Sporadic Cerebral Amyloid Angiopathy, is central to the pathogenesis of these disorders. Evidence exists to support a neuronal and/or a vascular origin. We have reported that platelets may serve as one possible source of the A beta sequence via an intact, membrane-associated Beta Protein Precursor (beta PP) which is encoded by a platelet transcript (BBRC 173:1292-1298, 1990). EXPERIMENTAL DESIGN: Immunoaffinity chromatography and western blotting of extracted cellular proteins, polymerase chain reaction amplification of beta PP mRNA, fluorescence activated flow cytometric analysis, and confocal scanning laser microscopy have been employed to characterize the presence and distribution of thrombocytic beta PP. RESULTS: Immunoblot analysis with antibodies specific for the carboxyl-terminal end of beta PP indicates that platelets and the Dami megakaryocyte cell line express membrane-associated species of intact beta PP ranging in molecular weight from 110 to 140 kilodaltons (kd), as well as carboxyl-terminal reactive forms ranging from 16 to 22 kd. Thrombin stimulation of platelets induces the release of five soluble beta PP species, which possess apparent isofocusing points in the range of 4.1-5.5. By contrast, extracts of peripheral blood mononuclear cells enriched by ficoll centrifugation, endothelial cells and a B cell line were not immunoreactive by western blot, even though beta PP transcripts could be amplified by polymerase chain reaction. The distribution of platelet beta PP was localized by flow cytometric analysis and scanning laser microscopy, using fluorescein-labeled antibodies. Study of the subcellular distribution of platelet beta PP indicates that these translation products are accumulated in discrete foci throughout the thrombocyte, possibly corresponding to secretory granules. CONCLUSIONS: The size of the carboxyl-terminal forms of beta PP indicate that the A beta sequence is present as a membrane associated constituent in unstimulated platelets, and may represent alternative pathways of beta PP processing. Cleavage or other abnormal processing of platelet-associated beta PP in Alzheimer's disease provides one mechanism whereby cerebral amyloid might derive from the circulation

Two synthetic peptides with sequences identical with those of fragments of the extracellular domain of the Alzheimer's-disease amyloid precursor protein (APP) were used to raise antibodies. SP28 comprises positions 597-624 of the APP695 isoform, whereas SP41 extends towards the N-terminus (amino acids 584-624) and contains the entire SP28 peptide. Using e.l.i.s.a. and inhibition experiments we identified the two beta-turn-containing segments 602-607 and 617-624 as the epitopes recognized by anti-SP41 and anti-SP28 respectively. Both antibodies immunolabelled amyloid lesions in brains from Alzheimer's-disease patients and patients with related disorders, whereas they were unreactive in control brains. However, when probed on immunoblots, anti-SP28 failed to detect full-length APP from baculovirus-infected Sf9 cells, and anti-SP41 reacted weakly compared with other anti-APP antisera. The data suggest that these antibodies are directed to conformational epitopes not existent in the native molecules but present after alternative APP processing

Urokinase (u-PA) proteolytically cleaves both human plasma (pFn) and cellular (cFn) dimeric fibronectin (M(r) 440,000) into four major polypeptides of approximately M(r) 210,000, 200,000, 25,000, and 6,000. Amino acid sequence analysis of the polypeptide fragments indicated that the enzymatic cleavage of Fn occurs at two sites: 1) between an arginine/alanine peptide bond located C-terminal to residue 259; this cleavage liberates the N-terminal M(r) 25,000 fragment and the M(r) 210,000 and M(r) 200,000 polypeptides derived from the A and B chains of Fn, respectively; and 2) between an arginine/threonine peptide bond located C-terminal to residue 2,299, thereby yielding an M(r) 6,000 dimeric fragment containing the C-terminal interchain disulfide bonds. Predigestion of Fn with u-PA increased the molecule's vulnerability to further attack by the enzymes plasmin and cathepsin D. These data provide further biochemical evidence for the proteolytic cleavage of fibronectin by plasminogen activators and substantiate that u-PA digestion of Fn may be an initial event in the local degradation of the extracellular matrix by malignant cells, possessing elevated levels of these enzymes

Gerstmann-Straussler-Scheinker disease (GSS) is a familial neurological disorder pathologically characterized by amyloid deposition in the cerebrum and cerebellum. In GSS, the amyloid is immunoreactive to antisera raised against the prion protein (PrP) 27-30, a proteinase K-resistant peptide of 27-30 kDa that is derived by limited proteolysis from an abnormal isoform of a neuronal sialoglycoprotein of 33-35 kDa designated PrPSc. Polyclonal antibodies raised against synthetic peptides homologous to residues 15-40 (P2), 90-102 (P1), and 220-232 (P3) of the amino acid sequence deduced from hamster PrP cDNA were used to investigate immunohistochemically the distribution of PrP and PrP fragments in the brains of two patients from the Indiana kindred of GSS. Two types of anti-PrP-immunoreactive deposits were found: (i) amyloid deposits, which were exclusively labeled by anti-P1 antiserum to residues 90-102 of PrP, and (ii) preamyloid deposits, which were labeled by all anti-PrP antisera but did not exhibit the tinctorial and optical properties of amyloid. The latter appeared as diffuse immunostaining of the neuropil that targeted to areas in which amyloid deposits were most abundant. They were partially resistant to proteinase K digestion and consisted ultrastructurally of amorphous, flaky, electron-dense material. These findings substantiate our previous observation that the major amyloid component in the GSS Indiana kindred is an internal fragment of PrP and indicate that full-length abnormal isoforms of PrP and/or large PrP fragments accumulate in brain regions most affected by amyloid deposition. These findings support the view that in the GSS Indiana kindred a stepwise degradation of PrP occurs in situ in the process of amyloid fibril formation

The partial amino acid sequences of the gamma chains of the bovine IgG2a(A1) and IgG2a(A2) allotypes were determined. Sequence differences were found in the CH1 domain, the hinge region, and the CH3 domain. The hinge regions displayed only 71.4% similarity and all of the differences were of a radical nature. The A2 hinge has isoleucine instead of serine at 229, histidine for asparagine at 235, proline for histidine at 238, and cysteine instead of proline in position 234; the latter has the potential for forming an additional interheavy chain disulphide bridge. The occurrence of such a bridge could explain the presence of a pepsin fragment consisting of the hinge region and the Fc. A corresponding fragment is not obtained with the A1 allotype. Both allotypes have a shortened hinge region and a truncated CH2 domain. This feature is characteristic of all reported sequences of IgG2 proteins but not IgG1 in cattle and the goat. This structural feature may be important in subclass-specific recognition by Fc gamma receptors in ruminants. A surprising discovery was the occurrence of five substitutions in the CH3 domain of the IgG2a(A2) in comparison with the A1, which are shared with the CH3 of IgG1. These permit the occurrence of isoallotypic determinants and can explain the difficulty encountered in preparing A2-specific antisera during which adsorption with IgG1 is a routine procedure. The primary sequence data we report confirm the presence of major structural differences between the A allotypes of cattle that was suggested by previous work. The sequence of the A1 allotype most closely agrees with the two IgG2 sequences deduced from their nucleotide sequences whereas the sequence differences in the hinge and C-terminal CH3 make IgG2a(A2) unique. The structural differences between allotypes could have major consequences for such biological activities as phagocytosis, transepithelial transport, lymphocyte and complement activation