Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Filamin a”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1977

Filamin, a new high-molecular-weight protein found in smooth muscle and nonmuscle cells. Purification and properties of chicken gizzard filamin.

Filamin, a major high-molecular-weight protein of chicken gizzard smooth muscle, was purified to homogeneity by salt extraction, ammonium sulfate precipitation, agarose gel filtration, and diethylaminoethylcellulose ion-exchange chromatography. Purified filamin is an asymmetric oligomer consisting of two large subunits of identical size (2 X 250 000 daltons) as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, chemical cross-linking, sedimentation analysis (s10, wo = 10S) and Stokes'radius estimation (a = 120 A), It has no intersubunit disulfide but appears from oxidation studies to have adjacent thiols near the subunit interface. Filamin contains no amino sugars, methylated lysine, methylated histidine, or hydroxyproline, nor does it exhibit myosin-like ATPase activities. Its amino acid composition and physical properties differ from those of gizzard myosin, for which a pruification procedure is described. Filamin and the protein spectrin of erythrocyte membranes have strikingly similar physical properties, but they are chemically distinct.

Adenosine Triphosphatases↗
PubMed1976

Purification and properties of filamin, and actin binding protein from chicken gizzard.

Filamin, a protein recently identified in chicken gizzard (Wang, K., Ash, F., and Singer, S. J. (1975) Proc. Natl. Acad. Sci. U. S. A. 72, 4483-4486), has been purified free of other components and its molecular properties have been examined. Filamin has a sedimentation constant (S020,w) of 8.86 S and a partial specific volume of 0.734 ml/g. Sedimentation equilibrium experiments give a value of 498,000 for the molecular weight of native filamin. From these data a frictional ratio of 2.32 has been calculated. On sodium dodecyl sulfate gel electrophoresis, filamin migrates as a single protein band with an estimated molecular weight of 240,000. Filamin is a soluble protein and under a variety of conditions tested does not by itself form filaments or precipitate from solution. However, filamin binds to rabbit skeletal muscle F-actin, and the complex is readily sedimented by centrifugation to yield a gelatinous pellet containing actin and filamin. These results indicate that filamin is a dimeric protein with a moderate degree of asymmetry that binds to actin. The results also suggest that the distribution of filamin in cells is derived from its interaction with polymerized actin.

Actins↗
PubMed1978

Purification of mammalian filamin. Similarity to high molecular weight actin-binding protein in macrophages, platelets, fibroblasts, and other tissues.

We have purified the high molecular weight actin-binding protein, filamin from guinea pig vas deferens. We find this mammalian filamin is very similar to chicken gizzard filamin in subunit molecular weight, amnio acid composition, actin-binding properties, immunological cross-reactivity, and the ability to be phosphorylated by cyclic AMP-dependent protein kinase. Anti-filamin antibodies cross-react with a high molecular weight macrophage actin-binding protein, and with a high molecular weight protein in platelets and fibroblasts. Furthermore like filamin, these proteins are also phosphorylated and cyclic AMP stimulates their phosphorylation. Anti-filamin antibodies do not cross-react with the erythrocyte membrane protein spectrin or with high molecular weight proteins in brain extracts. We conclude that filamin from avian and mammalian smooth muscle are very similar proteins and furthermore that many, but not all, non-muscle cells contain a protein closely related to filamin.

Actins↗
PubMed1975

Filamin, a new high-molecular-weight protein found in smooth muscle and non-muscle cells.

A new high-molecular-weight protein, named filamin, was isolated from chicken gizzard. In chicken gizzard, filamin is present in an amount approximately 30-40% of that of myosin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of highly purified filamin revealed a single polypeptide of about 250,000 daltons. Rabbit antibody directed against purified chicken gizzard filamin did not crossreact with myosin purified from the same source. By the use of microcomplement fixation and indirect immunofluorescent staining with antibodies to chicken gizzard filamin, an antigenically similar or identical protein was found to be widely distributed both in other organs of the chicken and in cultured cells of other species, but not in chicken skeletal muscle. In cultured cells, filamin was found largely to be arranged as a filamentous array very similar to that found for myosin. These data imply that filamin is a widely occurring and chemically conserved component of filaments is smooth muscle and non-muscle cells.

Animals↗
PubMed1978

Cyclic AMP-dependent phosphorylation of filamin in mammalian smooth muscle.

Filamin is a high molecular weight actin-binding protein found in large quantities in smooth muscle and other non-muscle cells. We have studied the phosphorylation of filamin in a mammalian smooth muscle, the guinea pig vas deferens. Intact vas deferens incorporated [32P]orthophosphate into filamin. Incubation of particulate fractions of vas deferens with [gamma-32P]ATP resulted in 32P-labeling of filamin. Cyclic AMP stimulated this phosphorylation, whereas cyclic GMP and Ca2+ had no effect. Purified vas deferens filamin can be phosphorylated by purified cyclic AMP-dependent protein kinase. We have compared cyclic AMP and cyclic GMP effects on phosphorylation in smooth muscle. Cyclic GMP stimulated phosphorylation of two particulate proteins, G-I (Mr = 130,000) a protein previously described by Casnellie, J. E., and Greengard, P. (1974) Proc. Natl. Acad, Sci. U.S.A. 71, 1891-1895 and G-III (Mr = 240,000). Both proteins and the kinase responsible for their phosphorylation appear to be membrane-bound. Phosphorylation of both proteins is stimulated by cyclic GMP (Ka = 3 x 10(-8) M), cyclic AMP (Ka = 3 x 10(-7) M), and to a lesser degree by Ca2+. In contrast, filamin phosphorylation is due to a soluble kinase stimulated only by cyclic AMP (Ka = 3 x 10(-7) M) and not by cyclic GMP or Ca2+.

Actins↗
PubMed1977

Interaction of filamin with f-actin in solution.

Filamin is a major high-molecular-weight protein in smooth muscle which was recently identified and isolated [Wang, K., Ash, J. F. & Singer, S. J. (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 4483-4486]. In the present studies, we shown that highly purified chicken gizzard filamin and muscle F-actin react in solution to form aggregates containing both proteins. Occasionally, these aggregates coagulate and contract into a dense gel in the absence of MgATP or CaATP. Immunofluorescence and electron microscopic studies suggest that the F-actin filaments are collected into fiber bundles and a crosslinked fiber meshwork by the binding of filamin molecules. These studies suggest that the function of filamin intact cells may be to regulate the ultrastructural state of F-actin filaments in a variety of dynamic cellular processes.

Actins↗
PubMed1978

Tropomyosin inhibits the interaction of F-actin and filamin.

The value of flow birefringence of F-actin was greatly decreased by filamin due to precipitate formation. This precipitate could be dispersed into birefringent filaments by sonication. Tropomyosin inhibited precipitation of F-actin induced by filamin, and no decrease in birefringence occurred when filamin was added to tropomyosin-bound F-actin. Hence it appears that filamin acts on F-actin in non-muscle cells similarly to alpha-actinin.

Actins↗
PubMed1979

Interaction of alpha-actinin, filamin and tropomyosin with F-actin.

The abilities of alpha-actinin, filamin and tropomyosin to bind F-actin were examined by cosedimentation experiments. Results indicated that smooth muscle alpha-actinin and filamin can bind to actin filaments simultaneously with little evidence of competition. In contrast, tropomyosin exhibits marked competition with either filamin or alpha-actinin for sites on actin filaments.

Actinin↗
PubMed1978

Filamin-actin interaction. Dissociation of binding from gelation by Ca2+-activated proteolysis.

Chicken gizzard filamin has been digested with purified Ca2+-activated protease. The subunits of (Mr = 250,000) of the protein are cleaved asymmetrically into two fragments, heavy merofilamin, Mr = 240,000, and light merofilamin, Mr = 9,500. Digestion is complete at substrate to enzyme ratios of 100:1 and requires Ca2+ concentrations in excess of 0.3 mM. Heavy merofilamin binds to F-actin as evidenced by cosedimentation with F-actin, by direct observation under the electron microscope, and by its ability to inhibit actin activation of heavy meromyosin ATPase. Heavy merofilamin does not form a gel when mixed with actin, except at very low concentrations of KCl. Thus, actin binding and gelation are separable activities of filamin. We speculate that Ca2+-stimulated proteolysis may play a role in the regulation of actin-filamin interactions.

Actins↗
PubMed1978

Cyclic AMP-dependent phosphorylation of the actin-binding protein filamin.

Filamin is a high molecular weight protein that binds to actin filaments in cells. It is found in large amounts in several different cells and tissues, including smooth muscle, fibroblasts, platelets, and macrophages. It is immunologically related to the previously described macrophage high molecular weight actin-binding protein but clearly different from erythrocyte spectrin. Filamin is a phosphoprotein; it is phosphorylated in vivo in intact tissues and cells. It can be phosphorylated in vitro with endogenous kinases; cyclic AMP stimulates this phosohorylation. Furthermore, the purified protein can be phosphorylated by purified cyclic AMP-dependent protein kinase. In smooth muscle homogenates, the stimulation of filamin phosphorylation by cyclic AMP is specific. Cyclic GMP and Ca2+ do not increase its phosphorylation, although they do stimulate phosphorylation of other proteins.

Actins↗
PubMed1977

Intracellular distributions of mechanochemical proteins in cultured fibroblasts.

We have used methods that have allowed simultaneous fluorescent staining of intracellular actin together with either myosin, filamin, or tubulin in normal rat kidney fibroblasts in monolayer culture. In the main portions of the cell body, the actin, myosin, and filamin are all present in two structures: in one, the three proteins are present in the same fiber bundles (stress fibers); in the other, there is a diffuse distribution of the three proteins. On portions of the cell periphery however-in the basal regions of microspikes, in ruffles, and in regions of cell-cell contact-actin and filamin are present, but myosin is severely depleted or absent. Microtubules are present in the cell body in a distribution independent of the stress fibers and are mostly absent from the cell periphery. Microspikes and ruffles are highly dynamic structures on the cell surface, and regions of cell-cell contact generally result from the association of ruffles on the two contacting cells. Therefore, the presence of filamin and actin but not myosin in these specialized regions on the cell surface, together with the recent demonstration [Wang, K. & Singer, S. J. (1977) Proc. Natl. Acad. Sci. USA 74, 2021-2025)] that pure filamin interacts with individual F-actin filaments in solution to form fiber bundles and sheet-like structures, suggest that in vivo filamin-actin interactions play an important role in the control of actin filament structure, in cell motility, and in the stabilization of cell-cell contacts.

Cell Line↗
PubMed2026

Biallelic pathogenic variants in FLNB are associated with paediatric steroid-resistant nephrotic syndrome via podocyte cytoskeletal dysfunction.

BACKGROUND: Steroid-resistant nephrotic syndrome (SRNS) is a severe paediatric kidney disease and a leading cause of end-stage kidney disease in children, with a high genetic contribution. While over 80 monogenic causes of SRNS have been identified, a significant proportion of affected patients still lack a clear genetic diagnosis, indicating that additional causative genes remain to be discovered. METHODS: Through whole-exome sequencing of a paediatric SRNS cohort, we identified three probands carrying biallelic FLNB pathogenic variants. Sanger sequencing was performed for familial cosegregation verification and ACMG classification. Expression of Filamin B, Nephrin and Synaptopodin in renal tissues was assessed by immunohistochemistry/immunofluorescence. Wild-type and patient-derived variant FLNB plasmids were constructed and transfected into HEK293T cells and immortalised human podocytes (HPCs). The effects of these variants on protein expression, localisation and cytoskeletal organisation were assessed by western blotting and immunofluorescence. FLNB expression in HPCs was silenced using shRNA to evaluate the impact on podocyte marker proteins, cytoskeletal integrity and migratory capacity. A zebrafish flnb knockdown model was employed to validate its effects on renal development. RESULTS: All three probands presented with isolated SRNS without skeletal developmental abnormalities, and renal tissues showed significantly reduced Filamin B protein expression. In vitro, p.L117P and p.M1803L variants led to markedly reduced protein expression, while p.R470L and p.K2586R induced perinuclear aggregation of Filamin B accompanied by F-actin rearrangement. FLNB silencing led to downregulation of Nephrin and Synaptopodin, cytoskeletal disorganisation and impaired cell migration. Zebrafish flnb knockdown exhibited pericardial oedema, defective nephron development and abnormal podocyte foot processes. CONCLUSION: We report for the first time that biallelic FLNB pathogenic variants are associated with paediatric SRNS by disrupting Filamin B expression, cytoskeletal integrity and podocyte function, providing evidence that FLNB is a novel monogenic cause of SRNS.

Humans↗
PubMed1979

Identification of a high molecular weight actin-binding protein in skeletal muscle.

A large polypeptide having a molecular weight of 240,000 as determined by electrophoresis in the presence of sodium dodecyl sulfate has been identified in whole cell homogenates from chick skeletal muscle myoblasts and the rat myoblast L6 cell line. A similar polypeptide was identified in both thigh and breast chicken skeletal muscle, but the latter contained less of this protein per g of tissue. Antibodies made to gizzard filamin (an actin-binding protein having a molecular weight of 240,000) cross-reacted with the partially purified Mr = 240,000 protein from chicken skeletal muscle. With use of the indirect immunofluorescence technique, the filamin antibody localized in the Z-line region of chicken skeletal muscle myofibrils. These results indicate that skeletal muscle contains a filamin-like protein that may form an integral part of the myofibril structure.

Actins↗
PubMed2026

A novel FLNA p.Pro2469Ser variant is associated with impaired T and NK cell function and immune dysregulation.

FLNA encodes filamin A, a ubiquitously expressed actin-binding cytoskeletal protein that cross-links actin filaments and links them to membrane-associated signaling complexes. Although FLNA has been implicated in T-cell signaling and regulatory T-cell development in murine models, its role in human immune-cell function remains incompletely understood. Here, we investigated the immunological phenotype associated with a novel hemizygous FLNA variant identified in a pediatric patient presenting with recurrent infections and inflammatory manifestations. Whole-exome sequencing revealed a hemizygous c.7405C>T (p.Pro2469Ser) variant in FLNA, which was confirmed by Sanger sequencing. Its potential impact on immune-cell function and cytoskeletal organization was evaluated using confocal microscopy, flow cytometry, and molecular assays. Patient-derived T cells showed impaired activation and proliferation following CD3/CD28 and IL-2 stimulation, accompanied by reduced CD25 and CD69 upregulation. CD4+ T cells also exhibited reduced IFN-γ, TNF-α, and IL-2 production after stimulation. Despite elevated basal phospho-STAT5 levels, IL-2-induced STAT5 phosphorylation and TCR-associated signaling responses, including pZAP70, pLCK, and p38 MAPK activation, were attenuated. Confocal imaging together with image-based quantification demonstrated altered cortical cytoskeletal organization in patient T cells despite preserved FLNA expression. In parallel, NK cells showed impaired activation responses and reduced cytotoxic activity under the assay conditions used. Increased apoptosis was observed in CD4⁺, CD8⁺, and NK-cell populations. Inflammatory cytokines were elevated in plasma and colonic tissue, whereas colonic ZO-1 and FLNA expression were reduced. Collectively, these findings indicate that the FLNA p.Pro2469Ser variant is associated with altered immune-cell signaling, disturbed cortical cytoskeletal organization, and immune dysregulation. This study expands the phenotypic spectrum linked to FLNA variants and supports a role for filamin A in human immune-cell regulation.

Humans↗
PubMed1979

Isolation of a high molecular weight actin-binding protein from baby hamster kidney (BHK-21) cells.

A high molecular weight protein (HMWP) with properties similar to those of both actin-binding protein (ABP) and filamin has been isolated from cultured baby hamster kidney (BHK-21) cells. The protein was present in an actomyosin-depleted sucrose extract of the cells and was eluted, upon gel chromatography on Sepharose 4B, near the void volume. The subunit migration on sodium dodecyl sulfate/polyacrylamide gels and the amino acid composition of HMWP were similar to those of ABP and filamin. HMWP bound to and crosslinked F-actin from rabbit muscle, as shown by the formation of a gel that was sedimented with low-speed centrifugation. This interaction was insensitive to temperature and low concentrations of calcium ions, although it may depend on the presence of myosin. Observation of thin sections of the actin-HMWP gel revealed crosslinked complexes of laterally aggregated actin filaments. The axial period of the dense crosslinks was 34 nm. The HMWP may be involved in regulation of microfilament organization.

Actins↗