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Richard M Robson

Publications and source records attributed to Richard M Robson.

5 recordsLinked to original sources
PubMed2006

Interactions of intermediate filament protein synemin with dystrophin and utrophin.

Synemin is a unique, very large intermediate filament (IF) protein present in all types of muscle cells, which forms heteropolymeric intermediate filaments (IFs) with the major IF proteins desmin and/or vimentin. We show herein that tissue-purified avian synemin directly interacts with both dystrophin and utrophin, and that specific expressed regions of both of the mammalian (human) synemin isoforms (alpha-synemin and beta-synemin) directly interact with specific expressed domains/regions of the dystrophin and utrophin molecules. Mammalian synemin is also shown to colocalize with dystrophin within muscle cell cultures. These results indicate that synemin is an important IF protein in muscle cells that helps fortify the linkage between the peripheral layer of cellular myofibrils and the costameric regions located along the sarcolemma and the sarcolemma region located within the neuromuscular and myotendinous junctions (NMJs and MTJs).

Animals↗
PubMed2005

Intermediate filament protein synemin is present in human reactive and malignant astrocytes and associates with ruffled membranes in astrocytoma cells.

Synemin, a very unique type VI intermediate filament (IF) protein, exhibits alternative splice variants termed alpha and beta. Unlike other IF proteins, synemin binds to actin-associated proteins, including alpha-actinin, vinculin, and alpha-dystrobrevin. Our previous work has demonstrated the presence of synemin in differentiating astrocytes. In this study, we have examined the presence of synemin in human astrocytes under pathological conditions, using rabbit antibodies raised against the C-terminal domain of human synemin produced in bacteria. Western blotting shows that astrocytic tumors contain greater amounts of alpha-synemin than do normal brain tissues. These tumors also contain beta-synemin, which is not detectable in normal brain. Immunohistochemistry demonstrates that, while synemin is present in normal adult brain only in vascular smooth muscle cells, it is newly synthesized by reactive and neoplastic astrocytes. Alpha- and beta-Synemins have also been detected by Western blotting and polymerase chain reaction in several human glioblastoma cell lines. In these cell lines, surprisingly, synemin is associated with ruffled membranes in addition to being distributed along the IF network. In ruffled membranes, synemin was found to co-localize with alpha-actinin. This unusual cellular localization for an IF protein is maintained after nocodazole-induced perinuclear coiling of the vimentin IF network. In addition, immunoprecipitation experiments demonstrate that synemin forms a complex with alpha-actinin in glioblastoma cells. Taken together with synemin localization within ruffled membranes, this finding suggests that synemin plays a role in motility of glioblastoma cells.

Actinin↗
PubMed2004

Characterization of an actin-binding site within the talin FERM domain.

Talin is a large cytoskeletal protein that couples integrins to F-actin. Three actin-binding sites (ABS1-3) have been reported: one in the N-terminal head, and two in the C-terminal rod domain. Although the C-terminal ABS3 has been partially characterized, the presence and properties of ABS1 within the talin head are less well defined. We show here that the talin head binds F-actin in vitro and in vivo at a specific site within the actin filament. Thus, purified talin head liberated from gizzard talin by calpain cleavage cosediments with F-actin in a low salt buffer at pH 6.4 (conditions that are optimal for binding intact talin), and using recombinant polypeptides, we have mapped ABS1 to the FERM domain within the talin head. Both the F2 and F3 FERM subdomains contribute to binding, and EGFP-tagged FERM subdomains colocalize with actin stress fibers when expressed in COS cells. High-resolution electron microscopy of actin filaments decorated with F2F3 localizes binding to a site that is distinct from that recognized by members of the calponin-homology superfamily. Finally, we show that the FERM domain can couple F-actin to PIPkin, and by inference to integrins, since they bind to the same pocket in the F3 subdomain. This suggests that the talin FERM domain functions as a linker between PIPkin or integrins and F-actin at sites of cell-matrix adhesions.

Actins↗
PubMed2002

Cytoskeletal derangements in hereditary myopathy with a desmin L345P mutation.

Patients with abnormal accumulations of desmin have been described in myopathies with or without cardiac involvement. Desmin deposits were sometimes associated with abnormal aggregates of other cytoskeletal proteins. In the present study we present how the cytoskeletal organisation of desmin, nestin, synemin, paranemin, plectin and alphaB-crystallin is altered in skeletal muscles from a patient with a L345P mutation in the desmin gene. In general, accumulations of desmin together with synemin, nestin, plectin and alphaB-crystallin were present between myofibrils and beneath the sarcolemma. However, as the biopsy samples were very myopathic, large variability in fibre size and fibre maturation was seen, thus the myofibrillar content and the cytoskeletal organisation varied considerably. In cultured satellite cells from the patient, desmin aggregates were not observed in initial passages, but occurred over time in culture in the form of perinuclear, peripheral or cytoplasmic deposits. Nestin colocalised to the abnormal desmin deposits to a larger extent than did vimentin. alphaB-Crystallin was only present in cells with a disrupted desmin network. Plectin was altered in a subset of cells with a disrupted desmin network, whereas synemin and paranemin were not detected. We conclude that the L345P desmin mutation has a profound influence on the cytoskeletal organisation both in vivo and in vitro, which reflects the pathogenesis of the desmin myopathy.

Cells, Cultured↗