How filopodia respond to calcium in the absence of a calcium-binding structural protein: non-channel functions of TRP.

BACKGROUND: For many cell types, directional locomotion depends on their maintaining filopodia at the leading edge. Filopodia lack any Ca2+-binding structural protein but respond to store-operated Ca2+ entry (SOCE). METHODS: SOCE was induced by first replacing the medium with Ca2+-free salt solution with cyclopiazonic acid (CPA). This lowers Ca2+ in the ER and causes stromal interacting molecule (STIM) to be translocated to the cell surface. After this priming step, CPA was washed out, and Ca2+ influx restored by addition of extracellular Ca2+. Intracellular Ca2+ levels were measured by calcium orange fluorescence. Regulatory mechanisms were identified by pharmacological treatments. Proteins mediating SOCE were localized by immunofluorescence and analyzed after image processing. RESULTS: Depletion of the ER Ca2+ increased filopodia prevalence briefly, followed by a spontaneous decline that was blocked by inhibitors of endocytosis. Intracellular Ca2+ increased continuously for ~ 50 min. STIM and a transient receptor potential canonical (TRPC) protein were found in separate compartments, but an aquaporin unrelated to SOCE was present in both. STIM1- and TRPC1-bearing vesicles were trafficked on microtubules. During depletion, STIM1 migrated to the surface where it coincided with Orai in punctae, as expected. TRPC1 was partially colocalized with Vamp2, a rapidly releasable pool marker, and with phospholipases (PLCs). TRPC1 retreated to internal compartments during ER depletion. Replenishment of extracellular Ca2+ altered the STIM1 distribution, which came to resemble that of untreated cells. Vamp2 and TRPC1 underwent exocytosis and became homogeneously distributed on the cell surface. This was accompanied by an increased prevalence of filopodia, which was blocked by inhibitors of TRPC1/4/5 and endocytosis. CONCLUSIONS: Because the media were devoid of ligands that activate receptors during depletion and Ca2+ replenishment, we could attribute filopodia extension to SOCE. We propose that the Orai current stimulates exocytosis of TRPC-bearing vesicles, and that Ca2+ influx through TRPC inhibits PLC activity. This allows regeneration of the substrate, phosphatidylinositol 4,5 bisphosphate (PIP2), a platform for assembling proteins, e. g. Enabled and IRSp53. TRPC contact with PLC is required but is broken by TRPC dissemination. This explains how STIM1 regulates the cell's ability to orient itself in response to attractive or repulsive cues. Video Abstract.

Pattern analysis of microtubule-polymerizing and -depolymerizing agent combinations as cancer chemotherapies.

Subcellular distribution of mass can be analyzed by a technique that involves culturing cells on interferometers and digitizing their interference contours. Contour sampling resulted in 102 variables per cell, which were predictors of oncogenic transformation. Cell phenotypes can be deconstructed by use of latent factors, which represent the covariance of the real variables. The reversal of the cancer-type phenotype by a combination of microtubule-stabilizing and -depolymerizing agents was described previously. The implications of these results have been explored by clinicians who treated patients with the combination of docetaxel and vinorelbine (Navelbine). The current study was performed to determine the effects of different combinations on phenotype and in phases of the cell cycle other than mitosis. Combinations of paclitaxel with either colchicine, podophyllotoxin, nocodazole, or vinblastine caused phenotype reversal. Paclitaxel analogue, 7-deoxytaxol, by itself caused reversal. Factors #4, (filopodia), #5 (displacement and/or deep invaginations in the periphery), #8, and #12 took on values typical of normal cells, whereas the values of #7 (p21-activated kinase), and #13 (rounding up) shifted toward the cancer-type. All combinations altered microtubule arrangement at the cell edge. Delivery schedules and drug ratios used in clinical studies were subjected to analysis. Clinical response rates were better when the combination was not interspersed with a single agent (P=0.004). The results support the idea that efficacy depends upon simultaneous exposure to both agents, and suggest a novel mechanism for combination therapies. These therapies appear to restore in transformed cells some of the features of a contact-inhibited cell, and to impede progress through the cell cycle even when provided at nanomolar concentrations.

Membrane modulation in a methylotrophic bacterium Methylococcus capsulatus (Texas) as a function of growth substrate.

Methylococcus capsulatus (Texas), when grown on methane, undergoes with age a progressive degeneration of internal membrane structure with a simultaneous accumulation of intracellular inclusions. When M. capsulatus is grown on methanol, virtually no internal membranes are present but, instead, cells contain many intracellular droplets morphologically similar to inclusions in old methane-grown cells. Membranes are regenerated by the cells when a methanol-grown culture is transferred back to methane. The oxidative ability of methane- and methanol-grown cells was compared.

The organization and isolating function of insect rectal sheath cells: a freeze-fracture study.

In termites and roaches the well-defined rectal papillae each comprise a layer of columnar principal cells specialized for active transport and a layer of basal cells. The whole cell group is entirely surrounded by several series of flattened 'sheath cells' (formerly termed 'junctional cells') which abut onto the basal components of the papilla. The sheath cells secrete a specialized sclerified cuticle which forms the framework of the papilla. Their regularly pleated apical membrane is closely apposed to the cuticle and contains parallel and closely spaced rows of intramembranous particles. at this level, no subcuticular space is present and hence the space associated with the apical surface of the principal cells is defined as an isolated compartment. Typical septate junctions are present between the sheath and basal cells; however those linking adjacent sheath cells are structurally unusual: they extend to the basal surface rather than being restricted to the apical zone, are frequently interrupted and in replicas are represented by relatively short and irregularly oriented particle rows. Moreover, lateral sheath cell contacts display two further peculiarities: absence of an apical desmosomal ring and paucity of gap junctions. Structural observations suggest that the sheath cells isolate the principal cells from communication with the hemolymph, consequently enhancing their efficiency in water and ionic regulation. Comparable cells have been described in a number of insects, but the 'isolation' system presents varying degrees of complexity, for which an evolutionary scheme is proposed.

Actin-myosin interaction: the role of myosin in determining the actin pattern in self-assembled 'hybrid' contractile units.

Self-assembly of actin-myosin filamentous complexes was assayed by polymerizing rabbit G-ADP actin on formed filaments of lobster myosin. The resulting contractile units indicate a 12-member actin orbital rather than the six-member orbital obtained previously using rabbit myosin and actin. Furthermore, the pattern of actin distribution surrounding the myosin filament is similar to that of the lobster tonic muscle sarcomere rather than the trigonal actin position characteristic of vertebrate muscle. The results show that the pattern and mode of actin complexing is determined by the specific myosin and the arrangement of the cross-bridges on the organized filament.

Cell types in peripheral blood of the nurse shark: an approach to structure and function.

Ultrastructural and functional studies were carried out on nurse shark (Ginglymostoma cirratum) peripheral blood cells in order ot identify cells of definitive morphology and specific function. Along with erythrocytes and thrombocytes, four morphologically distinct leucocytes are recognized in peripheral blood: two types of granulocytes, the 'eosiniphil' and the 'granulocyte', and two mononuclear agranulocytic cells, one resembling mammalian macrophage and monocyte, the other resembling mammalian lymphocyte. Also present in peripheral circulation are blast-like cells and mitotic cells. In vitro phagocytosis was demonstrated by the monocyte-macrophage and the granulocyte while thrombocytes, eosinophils and lymphocytes showed no phagocytic activity in the system studied. It is stressed that care must be used in drawing functional analogies between blood cells of a mammal and an elasmobranch on the basis of morphological similarity alone.

Structural features associated with movement and 'catch' of sea-urchin spines.

Spine catch ligaments of a sea urchin Arbacia punctulata were extended under constant load. Ligaments from an undisturbed animal may show any extension rate from zero (catch state) to rapid extension to failure. Replacing the preparation bath with CA(2)- and Mg(2+)-free sea water reversibly abolishes the catch state. The fine structure of the outermuscle layer and inner ligament cone associated with the spine base is described. The unstriated paramyosin muscles bear thin flanges and form compact interlocking rows. Subsurface cisternae are associated with the plasma membrane. The muscles are innervated by glia-free axons ending in bulbous terminals containing lucent synaptic vesicles. The ligament comprises cylindrical bundles of collagen fibrils: one or more minute muscle fibers (paramyosin) lie parallel with and closely adjoining each bundle. The mean diameter of these muscles is 0.3 micrometers and they occupy 2-3% of the ligament's cross-sectional area. Axons containing electron-opaque secretory droplets accompany the muscles between the collagen bundles: the cell bodies of these neurones generally lie on the outer surface of the ligament. When an urchin points a spine, the ligament on the side of the contracting spine muscle shortens but does not buckle. A function of the intraligamental muscles is to effect this non-buckled shortening. The catch mechanism (which reside entirely within the ligament) may be due either to the intraligamental muscles and/or to a locked polymer mechanism in which matrix molecules between collagen fibrils are reversibly cross-linked by divalent cations.

Organization of native and in vitro-reassembled myosin filaments from lobster tonic muscle.

Tonic muscle of the crusher claw of the American lobster (Homarus americanus) was investigated with respect to sarcomeric organization and the capacity for self-assembly of extracted myosin for comparison with the same properties of rabbit muscle. Native myosin filaments in the lobster muscle are much longer than in rabbit skeletal fibers, and differ further in sarcomeric organization in showing an actin-to-myosin relationship in which two actin filaments are shared between adjacent myosins in a 12-membered orbital. The self-assembly of lobster myosin into filaments comparable in length and the fine structure to the natural filament was achieved in the presence of excess Mg2+, a condition not required for rabbit myosin self-assembly. Results of in situ and self-assembly studies indicate a difference in molecular organization between lobster and rabbit myosin filaments and of the inferred presence of regulatory factors in the formation of these ultrastructural elements. These studies represent the groundwork for an investigation of in vitro polymerization of actin in association with the synthetic lobster myosin filament.

Septate junctions in insects: comparison between intercellular and intramembranous structures.

Septate junctions have been studied in the hind-gut of Periplaneta americana, Incisitermes schwartzi and Thermobia domestica. The topographical disposition of intercellular septa revealed by lanthanum impregnation corresponds well with that of particle rows seen in freeze fracture preparations. However, there is no precise correspondence between the undulations of septa and the disposition of particles within a single row. The spacing of particles is variable and generally less than that of the undulation periodicity of septa. On the other hand, the disposition of septa, and of the rows of particles that correspond to them, appears to be variable: sometimes rectilinear and in close parallel, these may curve or form series of 'finger-print' loops. Moreover, the septa are evidently not deployed as continuous ribbons around the cell since intrruptions are freuqently observed. In addition to their mechanical role in intercellular cohesion, septate junctions apparently ensure a more or less complete closure of the intercellular space (i.e. provide a permeability barrier) and thus play a role comparable with that of tight junctions in epithelia of vertebrates.

Origin of ruffles: linkage to other protrusions, filopodia and lamellae.

Although growth factor-initiated cascades in cells are networked with mechanisms such as "inside-out signaling", it is not known how these pathways are integrated. Earlier studies reported that ruffling was enhanced and filopodia reduced in transformed cells. Since dissecting relationships among features was impossible if subjective recognition was relied upon, features in two epithelial cell lines were recognized by latent factor analysis. Factor-based classification revealed four protrusion classes, but none of them corresponded to ruffles. Loss of filopodia, defined by factor 4 (F4) values, accounted for the greatest change in features of oncogenically transformed cells. Factor 5 (F5, lamella) was unchanged during transformation of an airway epithelium cell line. The tumor promoter, phorbol 12-myristate 13-acetate (PMA), increased ruffling but decreased filopodia. F4 retained this relationship to ruffling in untreated cells and at multiple times after treatment. F5 values decreased but were positively correlated with measures of ruffling. Because factors are created as mutually orthogonal variables, this suggested that ruffles were not flagged in factor analysis because they originate from other features. Actin filament capping with sub-micromolar cytochalasin D (Cyto D) suppressed ruffling without affecting F4 or F5. Cyto D increased factor 7 (F7) values, thus showing specificity for this feature. However, cytochalasin treatment of PMA-treated cells that had developed stress fibers increased F4 and decreased F5. The results suggest that PMA changes the state of the cytoskeleton, causing protrusions to show novel responses to Cyto D compared to untreated cells. Results suggest that the factors identify physiologically distinct features.

Structural cross-bridges between microtubules and mitochondria in central axons of an insect (Periplaneta americana).

The distribution of microtubules and mitochondria in central axons of an insect (Periplaneta americana) is assessed by comparison between counts on micrographs and computed axon random 'models'. These studies show that the observed multiple association of microtubules with individual mitochondria is statistically highly significant. Electron micrographs of thin sections show that linkage is effected by physical cross-bridge, possibly comprising components from the microtubule and mitochondrion. Linear particle arrays are described on the outer mitochondrial membrane in freeze-fracture replicas, and tentatively related to the bridges seen in thin sections. The results are discussed in terms of proposed roles of microtubules in neurons and other cells.

Use of a spherical multiparameter transducer for flow cytometry.

Fused silicon dioxide, multiparameter flow transducers with 50 microns internal square cross section and approximately 60 microns length can simultaneously measure DC and RF impedance as well as fluorescence and multiple-angle light scattering. A spherical version of such a transducer was mounted in an EPICS CVA flow-cell housing and was installed on a research prototype equipped with an argon-ion laser. The signal that was produced by the spherical transducer with EPICS DNA-Check beads was 1.73 times greater than that produced with the standard cylindrical flow cell. Similarly, with EPICS Immuno-Brite beads, the average ratio was 1.96. The Coulter impedance and light-scattering measurements were similar to those produced with the conventional cylindrical outside flow cell, although the internal cross section of the sphere was square and that of the cylinder was circular. The theoretical arguments of Leif and Wells have been demonstrated to be correct. At present, monolithic, spherical fused-silica transducers are the optimal design for combined electrooptical, multiparameter flow cytometry analyzers.

Danazol therapy renders red cells resistant to osmotic lysis.

Danazol, an attenuated androgen, is useful in endometriosis, idiopathic thrombocytopenic purpura (ITP), and autoimmune hemolytic anemia (AIHA). However, its mechanism of action is unknown. We investigated the possibility that danazol affects cell membranes directly. Red cell osmotic fragility was studied in patients receiving danazol. A significant decrease in osmotic fragility was observed. Accompanying the change, peripheral blood smears showed many target cells and electron microscopy revealed extra folds in erythrocyte membranes. Twenty-two patients were studied prospectively before and after danazol. Osmotic fragility decreased significantly (P less than 0.001) in 1 month of therapy and progressed with further treatment. A rebound increase (P less than 0.01) was observed in 1 month after discontinuation of danazol among 16 patients. Incubation experiments showed that danazol-induced changes are not reversed with normal sera. Patient sera did not induce the changes in normal red cells. Danazol in vitro protected red cells from osmotic lysis at low concentrations but enhanced lysis at high concentrations. We suggest that danazol alters red cell membranes directly to increase their surface area, inducing target cell formation and increasing their resistance to osmotic lysis.

The treatment of idiopathic thrombocytopenia with vinblastine-loaded platelets.

We devised a method to enhance delivery of vinblastine to macrophages, the cells believed to be responsible for platelet destruction in idiopathic thrombocytopenic purpura. Our strategy was based on the ability of platelets to bind vinca alkaloids such as vinblastine. Platelets were incubated with an excess of vinblastine, concentrated and then, after excess alkaloid had been removed, given to 11 patients with idiopathic thrombocytopenia refractory to other treatment (including intravenous injections of vinca alkaloids). Platelet antibodies in the patients' plasma led to ingestion of the vinca-laden platelets by macrophages. There were six complete remissions, three partial remissions and two failures. Side effects in a few patients, reversible but annoying, were minimized as technics were refined. We conclude that in patients with idiopathic thrombocytopenia refractory to all other measures, including the use of vinca alkaloids, platelet-vinca complex may be effective.