Genomic organization and biosynthesis of secreted and cytoplasmic forms of gelsolin

Lewy bodies are immunoreactive with antibodies raised to gelsolin related amyloid-Finnish type

Lewy bodies (LB) are intraneuronal, cytoplasmic inclusion bodies. They are invariably present in Parkinson's and diffuse LB diseases. Their composition by direct biochemical methods is unknown, although LBs are immunoreactive with a number of antibodies, including anti-ubiquitin and anti-neurofilament antibodies. Familial amyloidosis, Finnish type (FAF), is an autosomal-dominant form of systemic amyloidosis. The authors have isolated and partially sequenced the amyloid. The protein has significant sequence identity with gelsolin, an actin-modulating protein. Rabbit polyclonal antibodies raised to the FAF amyloid not only immunostain the amyloid but also LBs in the cortex and substantia nigra of Parkinson's and diffuse LB disease brains. Immunoreactivity is absorbed by the purified amyloid but is unaffected by ubiquitin. This provides a link between the LB and one of the human amyloidoses, FAF.

Enhanced motility in NIH 3T3 fibroblasts that overexpress gelsolin

Increasing the content of the actin-binding protein gelsolin in cultured mouse fibroblasts by up to 125 percent by gene transfection proportionally enhanced the rate at which the cells migrated through porous filters toward a gradient of serum and closed a wound made on a confluent monolayer of cells in a tissue culture dish. These results provide direct evidence that gelsolin, which promotes both actin assembly and disassembly in vitro, is an important element in fibroblast locomotion and demonstrate that the manipulation of intracellular machinery can increase cell motility.

Mutation in gelsolin gene in Finnish hereditary amyloidosis

Familial amyloidosis, Finnish type (FAF), is an autosomal dominant form of familial amyloid polyneuropathy. The novel amyloid fibril protein found in these patients is a degradation fragment of gelsolin, an actin-binding protein. We found a mutation (adenine for guanine) at nucleotide 654 of the gelsolin gene in genomic DNA isolated from five FAF patients. This site is polymorphic since the normal allele was also present in all the patients tested. This mutation was not found in two unaffected family members and 11 normal controls. The A for G transition causes an amino acid substitution (asparagine for aspartic acid) that was found at position 15 of the amyloid protein. The mutation and consequent amino acid substitution may lead to the development of FAF.

Isolation and characterization of cardiac amyloid in familial amyloid polyneuropathy type IV (Finnish): relation of the amyloid protein to variant gelsolin

Amyloid subunit protein was isolated from familial amyloid polyneuropathy type IV (Finnish type) cardiac tissue and purified to homogeneity. N-terminal amino acid sequence analysis shows that the amyloid protein is a fragment of the inner region of human gelsolin. When compared with the predicted sequence of human plasma gelsolin, the amyloid protein contains an asparagine-for-aspartic acid substitution at position 15 corresponding to residue 187 of the secreted protein. Antibodies raised against the amyloidogenic region of gelsolin specifically stained the amyloid deposited in tissues in familial amyloidosis type IV. The results show that the subunit amyloid protein in familial amyloid polyneuropathy type IV represents a unique type of amyloid derived from a variant (Asn-187) gelsolin molecule by limited proteolysis.

The action of brevin, an F-actin severing protein, on the mechanical properties and ATPase activity of skinned smooth muscle

Brevin is a protein which regulates the actin gel-sol transformation: it severs F-actin filaments into shorter ones. This action is Ca-dependent and is prevented by tropomyosin. We tested the effect of brevin on isometric contractions of skinned smooth muscle (taenia coli) and noted a dramatic loss of tension that possibly reflects some F-actin fragmentation. This effect is tentatively attributed to a partial loss of tropomyosin in the skinning procedure. We also studied the effect of brevin on unloaded shortenings of skinned preparations: thin bundles and enzymatically dissociated cells. We observed a marked increase of the velocity of shortening in the presence of brevin. This effect cannot be attributed to an increased ATPase activity as the latter is slightly reduced in the presence of brevin. We interpret this result as reflecting a decrease in internal resistance to movement, possibly by solation of an actin-filamin domain.

Expression of scinderin, an actin filament-severing protein, in different tissues

Scinderin is a calcium-dependent actin filament-severing protein recently discovered in the chromaffin cells of adrenal medulla. In view of the wide tissue distribution of gelsolin, another actin filament-severing protein, experiments were performed to determine the tissue expression of scinderin. Extracts prepared from different bovine tissues were tested by actin-DNase I Sepharose 4B-binding procedure and immunoprecipitation followed by immunoblotting with scinderin and gelsolin antibodies. Among the tissues tested, scinderin was found to be present in the adrenal medulla, brain, anterior and posterior pituitaries, kidney, salivary gland and testis. Scinderin was not found in liver, plasma, skeletal and heart muscles. Gelsolin was expressed in all of the above tissues. The results suggest that scinderin seems to be restricted to tissues with high secretory activity.

Comparative two-dimensional gel analysis and microsequencing identifies gelsolin as one of the most prominent downregulated markers of transformed human fibroblast and epithelial cells

A systematic comparison of the protein synthesis patterns of cultured normal and transformed human fibroblasts and epithelial cells, using two-dimensional gel protein analysis combined with computerized imaging and data acquisition, identified a 90-kD protein (SSP 5714) as one of the most striking downregulated markers typical of the transformed state. Using the information stored in the comprehensive human cellular protein database, we found this protein strongly expressed in several fetal tissues and one of them, epidermis, served as a source for preparative two-dimensional gel electrophoresis. Partial amino acid sequences were generated from peptides obtained by in situ digestion of the electroblotted protein. These sequences identified the marker protein as gelsolin, a finding that was confirmed by two-dimensional immunoblotting of human MRC-5 fibroblast proteins using specific antibodies and by coelectrophoresis with purified human gelsolin. These results suggest that an important regulatory protein of the microfilament system may play a role in defining the phenotype of transformed human fibroblast and epithelial cells in culture.

Amyloid in familial amyloidosis, Finnish type, is antigenically and structurally related to gelsolin

Immunohistochemical studies of six patients with familial amyloidosis, Finnish type, showed that their amyloid deposits did not react with polyclonal antibodies against the amyloid proteins of other, established forms of systemic or cerebral amyloidosis. However, strong immunoreactivity was observed with rabbit antiserum raised against a low molecular weight purified amyloid subunit isolated from one of the patients. This immunoreactivity was abolished by absorption with the low molecular weight amyloid fraction. The amino terminal sequence of the amyloid protein subunit was homologous to gelsolin, an actin-modulating protein, and the amyloid deposits in tissues reacted with a monoclonal antibody against gelsolin. These studies show that the amyloid protein in familial amyloidosis, Finnish type, is not related to previously identified forms of amyloid, including prealbumin (transthyretin) variants, but represents a novel amyloidogenic protein related to gelsolin, a plasma and cytoplasmic protein.

Amyloid protein in familial amyloidosis (Finnish type) is homologous to gelsolin, an actin-binding protein

Familial amyloidosis, Finnish type, is clinically characterized by cranial neuropathy and lattice corneal dystrophy. It is an autosomal dominant form of systemic amyloidosis with small deposits of congophilic material occurring in most tissues, particularly in association with blood vessel walls and basement membranes. Amyloid fibrils were extracted from the kidney of patient VUO, and rabbit antiserum raised against the 12 kDa purified amyloid subunit displayed strong immunohistochemical reactivity with the amyloid deposits. The amino terminal sequence of this 12 kDa amyloid protein (ATEVPVSWESFNNGD) showed homology with gelsolin (or actin depolymerizing factor), a 93 kDa plasma protein. The amyloid peptide is a degradation product, starting at position 173, of the gelsolin molecule.

Identification of the functional profilin gene, its localization to chromosome subband 17p13.3, and demonstration of its deletion in some patients with Miller-Dieker syndrome

Profilin is a conserved actin-monomer-binding protein which is found in all eukaryotes, including yeast. Although amino acid sequence analysis and RNase protection analysis suggest a single profilin isoform in mammalian cells, Southern blot analysis of human and somatic cell hybrid DNA indicates several loci in the human genome which hybridize with the profilin cDNA. We therefore isolated human genomic clones to analyze these genetic loci in detail. Only one of the cloned loci has typical features of a functional gene, including upstream transcriptional elements and typical exon-intron structure. Four other isolated loci are all diverged, intronless pseudogenes and are likely to be nonfunctional. The functional gene was localized to human chromosome band 17p13 by analysis of somatic cell hybrids and by in situ chromosomal localization. The Miller-Dieker syndrome (MDS), a rare congenital disorder manifested by characteristic facial abnormalities and lissencephaly (smooth brain), is associated with microdeletions of the distal 17p region. RFLP analysis of a patient with MDS, and analysis of somatic cell hybrids containing partially deleted chromosomes 17 from patients with MDS, using the profilin gene probe, indicate that profilin is localized to chromosome subband 17p13.3. These results also indicate that profilin is the first identified cloned gene which is part of the genetic material deleted in some patients with MDS but that other patients have smaller deletions not affecting the profilin locus. Thus, single allelic deletion of the profilin locus may contribute to the clinical phenotype of the MDS in some patients but does not play a major role in the essential phenotype.

Finnish hereditary amyloidosis. Amino acid sequence homology between the amyloid fibril protein and human plasma gelsoline

Amyloid fibrils were isolated from the kidney of a patient with Finnish hereditary amyloidosis. After solubilization of the fibrils in guanidine-HCl, fractionation by gel filtration, and purification by reverse-phase high-performance liquid chromatography, a homogeneous amyloid protein with an apparent Mr of 9000 was obtained. The protein was subjected to enzymatic digestion by trypsin and endoproteinase Lys-C. The amino acid sequences were determined for 6 of the released peptides and they were all found to be identical to the reported, deduced primary structure of human plasma gelsoline in the region of amino acids 235-269. The results show that the amyloid fibril protein in Finnish hereditary amyloidosis represents a new type of amyloid protein that shows amino acid sequence homology with gelsoline, an actin-modulating protein.

Human gene for torsion dystonia located on chromosome 9q32-q34

Torsion dystonia is a movement disorder of unknown etiology characterized by loss of control of voluntary movements appearing as sustained muscle contractions and/or abnormal postures. Dystonic movements can be caused by lesions in the basal ganglia, drugs, or gene defects. Several hereditary forms have been described, most of which have autosomal dominant transmission with variable expressivity. In the Ashkenazi Jewish population the defective gene frequency is about 1/10,000. Here, linkage analysis using polymorphic DNA and protein markers has been used to locate a gene responsible for susceptibility to dystonia in a large, non-Jewish kinship. Affected members of this family have a clinical syndrome similar to that found in the Jewish population. This dystonia gene (ITD1) shows tight linkage with the gene encoding gelsolin, an actin binding protein, and appears by multipoint linkage analysis to lie in the q32-q34 region of chromosome 9 between ABO and D9S26, a region that also contains the locus for dopamine-beta-hydroxylase.

Identification of critical functional and regulatory domains in gelsolin

Gelsolin can sever actin filaments, nucleate actin filament assembly, and cap the fast-growing end of actin filaments. These functions are activated by Ca2+ and inhibited by polyphosphoinositides (PPI). We report here studies designed to delineate critical domains within gelsolin by deletional mutagenesis, using COS cells to secrete truncated plasma gelsolin after DNA transfection. Deletion of 11% of gelsolin from the COOH terminus resulted in a major loss of its ability to promote the nucleation step in actin filament assembly, suggesting that a COOH-terminal domain is important in this function. In contrast, derivatives with deletion of 79% of the gelsolin sequence exhibited normal PPI-regulated actin filament-severing activity. Combined with previous results using proteolytic fragments, we deduce that an 11-amino acid sequence in the COOH terminus of the smallest severing gelsolin derivative identified here mediates PPI-regulated binding of gelsolin to the sides of actin filaments before severing. Deletion of only 3% of gelsolin at the COOH terminus, including a dicarboxylic acid sequence similar to that found on the NH2 terminus of actin, resulted in a loss of Ca2+-requirement for filament severing and monomer binding. Since these residues in actin have been implicated as potential binding sites for gelsolin, our results raise the possibility that the analogous sequence at the COOH terminus of gelsolin may act as a Ca2+-regulated pseudosubstrate. However, derivatives with deletion of 69-79% of the COOH-terminal residues of gelsolin exhibited normal Ca2+ regulation of severing activity, establishing the intrinsic Ca2+ regulation of the NH2-terminal region. One or both mechanisms of Ca2+ regulation may occur in members of the gelsolin family of actin-severing proteins.

Smooth muscle gelsolin and a Ca2+-sensitive contractile cell model

Smooth muscle gelsolin, termed smooth muscle 90-kDa protein in our previous paper (Kanno et al. FEBS Lett. 1985; 184:202-206), was purified from bovine aorta. Antibody prepared against smooth muscle gelsolin was used to detect the presence of gelsolin in human lung fibroblast MRC-5 cells permeabilized with Triton X-100 (MRC-5 cell models). These cells contracted in the presence of MgATP and Ca2+ in doses over 1 microM. Immunofluorescence microscopy using phalloidin and antigelsolin antibody showed that gelsolin was distributed along the stress fibers, except for a marginal bundle of cells, when MRC-5 cells were growth-arrested in serum-depleted medium. Making use of immunoblotting and indirect immunofluorescence techniques, we demonstrated that gelsolin is not retained in the MRC-5 cell models. We used purified smooth muscle gelsolin as a specific agent to sever the actin filaments. Preincubation of MRC-5 cell models with gelsolin led to a destruction of stress fibers, in a dose- and Ca2+ -dependent manner. The contractility was also lost, in the same manner described above, thereby indicating that a continuous distribution of actin filaments within the stress fibers is required for cell contraction. Treatment of MRC-5 cells with the Ca2+ ionophore A23187 induced an extracellular Ca2+ -dependent contraction but not a massive destruction of stress fibers, thereby indicating that most of the endogenous gelsolin was inactive under these conditions. Our interpretation of these results is that increases in cytoplasmic Ca2+ concentrations are sufficient for the contraction but may be too transient to activate endogenous gelsolin and thereby disrupt the stress fibers. Indeed, the inhibition of contraction of the MRC-5 cell, as induced by smooth muscle gelsolin, required preincubation in the presence of Ca2+, before the addition of MgATP. These results suggest that destruction of the stress fibers by endogenous gelsolin, which leads to inhibition of cell contraction, may occur if the cytoplasmic Ca2+ is maintained at high concentrations for a few minutes.

Nucleotide sequence of pig plasma gelsolin. Comparison of protein sequence with human gelsolin and other actin-severing proteins shows strong homologies and evidence for large internal repeats

Pig plasma gelsolin (Mr = 81595; 739 residues) contains 704 identical residues out of a maximum 730 when compared to the cytoplasmic form of human gelsolin. The cDNA sequence also codes for a peptide of 33 residues N-terminal to the nine-residue plasma extension sequence previously reported: these 33 residues are highly homologous to the human signal peptide and plasma extension. Comparison of the gelsolin sequences with chicken brush border villin, severin from Dictyostelium discoideum and fragmin from Physarum polycephalum shows a strong evolutionary relationship between all these proteins. There are six large repeating segments in gelsolin and villin, and three similar segments in severin and fragmin. Although these multiple repeats cannot be related to any known function of these actin-severing proteins, this superfamily of proteins appears to have evolved from an ancestral sequence of 120 to 130 amino acid residues.

Proteins regulating actin assembly in oogenesis and early embryogenesis of Xenopus laevis: gelsolin is the major cytoplasmic actin-binding protein

Oocytes, notably those of amphibia, accumulate large pools of nonfilamentous ("soluble") actin, both in the cytoplasm and in the nucleoplasm, which coexist with extensive actin filament arrays in the cytoplasmic cortex. Because the regulation of oogenically accumulated actin is important in various processes of oogenesis, egg formation, fertilization and early embryogenesis, we have purified and characterized the major actin-binding proteins present in oocytes of Xenopus laevis. Here we report that the major actin-binding component in the ooplasm, but not in the nucleus, is a polypeptide of Mr approximately 93,000 on SDS-PAGE that reduces actin polymerization in vitro in a Ca2+-dependent manner but promotes nucleation events, and also reduces the viscosity of actin polymers, indicative of severing activity. We have raised antibodies against the purified oocyte protein and show that it is different from villin, is also prominent in unfertilized eggs and early embryos and is very similar to a corresponding protein present in various tissues and in cultured cells, and appears to be spread over the cytoplasm. Using these antibodies we have isolated a cDNA clone from a lambda gt11 expression library of ovarian poly(A)+-RNA. Determination of the amino acid sequence derived from the nucleotide sequence, together with the directly determined sequence of the amino terminus of the native protein, has shown that this clone encodes the carboxy-terminal half of gelsolin. We conclude that gelsolin is the major actin-modulating protein in oogenesis and early embryogenesis of amphibia, and probably also of other species, that probably also plays an important role in the various Ca2+-dependent gelation and contractility processes characteristic of these development stages.

Identification of a polyphosphoinositide-modulated domain in gelsolin which binds to the sides of actin filaments

Gelsolin is a Ca2+- and polyphosphoinositide-modulated actin-binding protein which severs actin filaments, nucleates actin assembly, and caps the "barbed" end of actin filaments. Proteolytic cleavage analysis of human plasma gelsolin has shown that the NH2-terminal half of the molecule severs actin filaments almost as effectively as native gelsolin in a Ca2+-insensitive but polyphosphoinositide-inhibited manner. Further proteolysis of the NH2-terminal half generates two unique fragments (CT14N and CT28N), which have minimal severing activity. Under physiological salt conditions, CT14N binds monomeric actin coupled to Sepharose but CT28N does not. In this paper, we show that CT28N binds stoichiometrically and with high affinity to actin subunits in filaments, suggesting that it preferentially recognizes the conformation of polymerized actin. Analysis of the binding data shows that actin filaments have one class of CT28N binding sites with Kd = 2.0 X 10(-7) M, which saturates at a CT28N/actin subunit ratio of 0.8. Binding of CT28N to actin filaments is inhibited by phosphatidylinositol 4,5-bisphosphate micelles. In contrast, neither CT14N nor another actin-binding domain located in the COOH-terminal half of gelsolin form stable stoichiometric complexes with actin along the filaments, and their binding to actin monomers is not inhibited by PIP2. Based on these observations, we propose that CT28N is the polyphosphoinositide-regulated actin-binding domain which allows gelsolin to bind to actin subunits within a filament before serving.