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PubMed2006

The activity status of cofilin is directly related to invasion, intravasation, and metastasis of mammary tumors.

Understanding the mechanisms controlling cancer cell invasion and metastasis constitutes a fundamental step in setting new strategies for diagnosis, prognosis, and therapy of metastatic cancers. LIM kinase1 (LIMK1) is a member of a novel class of serine-threonine protein kinases. Cofilin, a LIMK1 substrate, is essential for the regulation of actin polymerization and depolymerization during cell migration. Previous studies have made opposite conclusions as to the role of LIMK1 in tumor cell motility and metastasis, claiming either an increase or decrease in cell motility and metastasis as a result of LIMK1 over expression (Zebda, N., O. Bernard, M. Bailly, S. Welti, D.S. Lawrence, and J.S. Condeelis. 2000. J. Cell Biol. 151:1119-1128; Davila, M., A.R. Frost, W.E. Grizzle, and R. Chakrabarti. 2003. J. Biol. Chem. 278:36868-36875; Yoshioka, K., V. Foletta, O. Bernard, and K. Itoh. 2003. Proc. Natl. Acad. Sci. USA. 100:7247-7252; Nishita, M., C. Tomizawa, M. Yamamoto, Y. Horita, K. Ohashi, and K. Mizuno. 2005. J. Cell Biol. 171:349-359). We resolve this paradox by showing that the effects of LIMK1 expression on migration, intravasation, and metastasis of cancer cells can be most simply explained by its regulation of the output of the cofilin pathway. LIMK1-mediated decreases or increases in the activity of the cofilin pathway are shown to cause proportional decreases or increases in motility, intravasation, and metastasis of tumor cells.

Animals↗
PubMed1984

Identification and characterization of osteoclast-like cells and their progenitors in cultures of feline marrow mononuclear cells.

The predominant cell responsible for bone resorption, the multinucleated osteoclast, has been difficult to study because of inaccessibility. When feline marrow-derived mononuclear cells are established in long-term culture, multinucleated cells form within 48 h, reaching maximum numbers at 16 d. We have observed that these cultured cells have many of the features of osteoclasts. Morphologically, they are multinucleated, contain large numbers of branched mitochondria, have a peripheral cytoplasm lacking organelles (a clear zone), and have extensive cell-surface processes. In addition to these ultrastructural features, the cells contain a tartrate-resistant acid phosphatase, the activity of which is increased by parathyroid hormone (PTH) and inhibited by calcitonin. PTH, prostaglandin E2, and 1,25(OH)2 vitamin D3 increased multinucleated cell formation, while calcitonin inhibited the stimulatory effects of PTH. Time-lapse cinemicrographic and autoradiographic studies indicated that the multinucleated cells formed by fusion of the mononuclear progenitors. The multinucleated cells were phagocytic and stained with nonspecific esterase, consistent with their being derived from immature monocytes. Further, cell populations enriched for multinucleated cells release 45Ca from devitalized bone. Density-gradient centrifugation on Percoll was used to enrich and characterize the mononuclear progenitors of these multinucleated cells. The progenitor cells were found predominantly in Percoll density layers of 1.065 to 1.08 g/ml and were enriched up to 30-fold as compared to unfractionated cells. The bone marrow mononuclear cells that formed the multinucleated cells were initially nonadherent to plastic, stained heavily with nonspecific esterase, and appeared to be immature monocytes histologically. These data indicate that the multinucleated osteoclast-like cells in our cultures are derived from nonadherent monocytic progenitor cells that are responsive to osteotropic hormones. The ability to grow and characterize these cells in vitro should facilitate studies to elucidate the role these cells play in normal and pathologic states of bone resorption.

Acid Phosphatase↗
PubMed2000

Dynamic positioning of mitotic spindles in yeast: role of microtubule motors and cortical determinants.

In the budding yeast Saccharomyces cerevisiae, movement of the mitotic spindle to a predetermined cleavage plane at the bud neck is essential for partitioning chromosomes into the mother and daughter cells. Astral microtubule dynamics are critical to the mechanism that ensures nuclear migration to the bud neck. The nucleus moves in the opposite direction of astral microtubule growth in the mother cell, apparently being "pushed" by microtubule contacts at the cortex. In contrast, microtubules growing toward the neck and within the bud promote nuclear movement in the same direction of microtubule growth, thus "pulling" the nucleus toward the bud neck. Failure of "pulling" is evident in cells lacking Bud6p, Bni1p, Kar9p, or the kinesin homolog, Kip3p. As a consequence, there is a loss of asymmetry in spindle pole body segregation into the bud. The cytoplasmic motor protein, dynein, is not required for nuclear movement to the neck; rather, it has been postulated to contribute to spindle elongation through the neck. In the absence of KAR9, dynein-dependent spindle oscillations are evident before anaphase onset, as are postanaphase dynein-dependent pulling forces that exceed the velocity of wild-type spindle elongation threefold. In addition, dynein-mediated forces on astral microtubules are sufficient to segregate a 2N chromosome set through the neck in the absence of spindle elongation, but cytoplasmic kinesins are not. These observations support a model in which spindle polarity determinants (BUD6, BNI1, KAR9) and cytoplasmic kinesin (KIP3) provide directional cues for spindle orientation to the bud while restraining the spindle to the neck. Cytoplasmic dynein is attenuated by these spindle polarity determinants and kinesin until anaphase onset, when dynein directs spindle elongation to distal points in the mother and bud.

Anaphase↗
PubMed2001

RhoA inactivation by p190RhoGAP regulates cell spreading and migration by promoting membrane protrusion and polarity.

The binding of extracellular matrix proteins to integrins triggers rearrangements in the actin cytoskeleton by regulating the Rho family of small GTPases. The signaling events that mediate changes in the activity of Rho proteins in response to the extracellular matrix remain largely unknown. We have demonstrated in previous studies that integrin signaling transiently suppresses RhoA activity through stimulation of p190RhoGAP. Here, we investigated the biological significance of adhesion-dependent RhoA inactivation by manipulating p190RhoGAP signaling in Rat1 fibroblasts. The inhibition of RhoA activity that is induced transiently by adhesion was antagonized by expression of dominant negative p190RhoGAP. This resulted in impaired cell spreading on a fibronectin substrate, reduced cell protrusion, and premature assembly of stress fibers. Conversely, overexpression of p190RhoGAP augmented cell spreading. Dominant negative p190RhoGAP elevated RhoA activity in cells on fibronectin and inhibited migration, whereas overexpression of the wild-type GAP decreased RhoA activity, promoted the formation of membrane protrusions, and enhanced motility. Cells expressing dominant negative p190RhoGAP, but not control cells or cells overexpressing the wild-type GAP, were unable to establish polarity in the direction of migration. Taken together, these data demonstrate that integrin-triggered RhoA inhibition by p190RhoGAP enhances spreading and migration by regulating cell protrusion and polarity.

Actins↗
PubMed2002

Structural determinants of Ras-Raf interaction analyzed in live cells.

The minimum structure of the Raf-1 serine/threonine kinase that recognizes active Ras was used to create a green fluorescent fusion protein (GFP) for monitoring Ras activation in live cells. In spite of its ability to bind activated Ras in vitro, the Ras binding domain (RBD) of Raf-1 (Raf-1[51-131]GFP) failed to detect Ras in Ras-transformed NIH 3T3 fibroblasts and required the addition of the cysteine-rich domain (CRD) (Raf-1[51-220]GFP) to show clear localization to plasma membrane ruffles. In normal NIH 3T3 cells, (Raf-1[51-220]GFP) showed minimal membrane localization that was enhanced after stimulation with platelet-derived growth factor or phorbol-12-myristate-13-acetate. Mutations within either the RBD (R89L) or CRD (C168S) disrupted the membrane localization of (Raf-1[51-220]GFP), suggesting that both domains contribute to the recruitment of the fusion protein to Ras at the plasma membrane. The abilities of the various constructs to localize to the plasma membrane closely correlated with their inhibitory effects on mitogen-activated protein kinase kinase1 and mitogen-activated protein kinase activation. Membrane localization of full-length Raf-1-GFP was less prominent than that of (Raf-1[51-220]GFP) in spite of its strong binding to RasV12 and potent activation of mitogen-activated protein kinase. These finding indicate that both RBD and CRD are necessary to recruit Raf-1 to active Ras at the plasma membrane, and that these domains are not fully exposed in the Raf-1 molecule. Visualization of activated Ras in live cells will help to better understand the dynamics of Ras activation under various physiological and pathological conditions.

3T3 Cells↗
PubMed2003

A dynamin-cortactin-Arp2/3 complex mediates actin reorganization in growth factor-stimulated cells.

The mechanisms by which mammalian cells remodel the actin cytoskeleton in response to motogenic stimuli are complex and a topic of intense study. Dynamin 2 (Dyn2) is a large GTPase that interacts directly with several actin binding proteins, including cortactin. In this study, we demonstrate that Dyn2 and cortactin function to mediate dynamic remodeling of the actin cytoskeleton in response to stimulation with the motogenic growth factor platelet-derived growth factor. On stimulation, Dyn2 and cortactin coassemble into large, circular structures on the dorsal cell surface. These "waves" promote an active reorganization of actin filaments in the anterior cytoplasm and function to disassemble actin stress fibers. Importantly, inhibition of Dyn2 and cortactin function potently blocked the formation of waves and subsequent actin reorganization. These findings demonstrate that cortactin and Dyn2 function together in a supramolecular complex that assembles in response to growth factor stimulation and mediates the remodeling of actin to facilitate lamellipodial protrusion at the leading edge of migrating cells.

Actin-Related Protein 3↗
PubMed2003

Actin filament turnover regulated by cross-linking accounts for the size, shape, location, and number of actin bundles in Drosophila bristles.

Drosophila bristle cells are shaped during growth by longitudinal bundles of cross-linked actin filaments attached to the plasma membrane. We used confocal and electron microscopy to examine actin bundle structure and found that during bristle elongation, snarls of uncross-linked actin filaments and small internal bundles also form in the shaft cytoplasm only to disappear within 4 min. Thus, formation and later removal of actin filaments are prominent features of growing bristles. These transient snarls and internal bundles can be stabilized by culturing elongating bristles with jasplakinolide, a membrane-permeant inhibitor of actin filament depolymerization, resulting in enormous numbers of internal bundles and uncross-linked filaments. Examination of bundle disassembly in mutant bristles shows that plasma membrane association and cross-bridging adjacent actin filaments together inhibits depolymerization. Thus, highly cross-bridged and membrane-bound actin filaments turn over slowly and persist, whereas poorly cross-linked filaments turnover more rapidly. We argue that the selection of stable bundles relative to poorly cross-bridged filaments can account for the size, shape, number, and location of the longitudinal actin bundles in bristles. As a result, filament turnover plays an important role in regulating cytoskeleton assembly and consequently cell shape.

Actin Cytoskeleton↗
PubMed2003

Induction of apoptosis in starfish eggs requires spontaneous inactivation of MAPK (extracellular signal-regulated kinase) followed by activation of p38MAPK.

Mitogen-activated protein kinase (MAPK) (extracellular signal-regulated kinase) prevents DNA replication and parthenogenesis in maturing oocytes. After the meiotic cell cycle in starfish eggs, MAPK activity is maintained until fertilization. When eggs are fertilized, inactivation of MAPK occurs, allowing development to proceed. Without fertilization, highly synchronous apoptosis of starfish eggs starts 10 h after germinal vesicle breakdown, which varies according to season and individual animals. For induction of the apoptosis, MAPK should be activated for a definite period, called the MAPK-dependent period, during which eggs develop competence to die, although the exact duration of the period was unclear. In this study, we show that the duration of the MAPK-dependent period was approximately 8 h. Membrane blebbing occurred approximately 2 h after the MAPK-dependent period. Surprisingly, when MAPK was inhibited by U0126 after the MAPK-dependent period, activation of caspase-3 occurred earlier than in the control eggs. Thus, inactivation of MAPK is a prerequisite for apoptosis. Also, even in the absence of the inhibitor, MAPK was inactivated spontaneously when eggs began to bleb, indicating that inactivation of MAPK after the MAPK-dependent period acts upstream of caspase-3. Inactivation of MAPK also resulted in the activation of p38MAPK, which may contribute to apoptotic body formation.

Animals↗
PubMed2005

Proteolysis of cortactin by calpain regulates membrane protrusion during cell migration.

Calpain 2 regulates membrane protrusion during cell migration. However, relevant substrates that mediate the effects of calpain on protrusion have not been identified. One potential candidate substrate is the actin binding protein cortactin. Cortactin is a Src substrate that drives actin polymerization by activating the Arp2/3 complex and also stabilizes the cortical actin network. We now provide evidence that proteolysis of cortactin by calpain 2 regulates membrane protrusion dynamics during cell migration. We show that cortactin is a calpain 2 substrate in fibroblasts and that the preferred cleavage site occurs in a region between the actin binding repeats and the alpha-helical domain. We have generated a mutant cortactin that is resistant to calpain proteolysis but retains other biochemical properties of cortactin. Expression of the calpain-resistant cortactin, but not wild-type cortactin, impairs cell migration and increases transient membrane protrusion, suggesting that calpain proteolysis of cortactin limits membrane protrusions and regulates migration in fibroblasts. Furthermore, the enhanced protrusion observed with the calpain-resistant cortactin requires both the Arp2/3 binding site and the Src homology 3 domain of cortactin. Together, these findings suggest a novel role for calpain-mediated proteolysis of cortactin in regulating membrane protrusion dynamics during cell migration.

Actins↗
PubMed2006

Conditional dominant mutations in the Caenorhabditis elegans gene act-2 identify cytoplasmic and muscle roles for a redundant actin isoform.

Animal genomes each encode multiple highly conserved actin isoforms that polymerize to form the microfilament cytoskeleton. Previous studies of vertebrates and invertebrates have shown that many actin isoforms are restricted to either nonmuscle (cytoplasmic) functions, or to myofibril force generation in muscle cells. We have identified two temperature-sensitive and semidominant embryonic-lethal Caenorhabditis elegans mutants, each with a single mis-sense mutation in act-2, one of five C. elegans genes that encode actin isoforms. These mutations alter conserved and adjacent amino acids predicted to form part of the ATP binding pocket of actin. At the restrictive temperature, both mutations resulted in aberrant distributions of cortical microfilaments associated with abnormal and striking membrane ingressions and protrusions. In contrast to the defects caused by these dominant mis-sense mutations, an act-2 deletion did not result in early embryonic cell division defects, suggesting that additional and redundant actin isoforms are involved. Accordingly, we found that two additional actin isoforms, act-1 and act-3, were required redundantly with act-2 for cytoplasmic function in early embryonic cells. The act-1 and -3 genes also have been implicated previously in muscle function. We found that an ACT-2::GFP reporter was expressed cytoplasmically in embryonic cells and also was incorporated into contractile filaments in adult muscle cells. Furthermore, one of the dominant act-2 mutations resulted in uncoordinated adult movement. We conclude that redundant C. elegans actin isoforms function in both muscle and nonmuscle contractile processes.

Actin Cytoskeleton↗
PubMed2006

Lack of adenomatous polyposis coli protein correlates with a decrease in cell migration and overall changes in microtubule stability.

Most sporadic colorectal tumors carry truncation mutations in the adenomatous polyposis coli (APC) gene. The APC protein is involved in many processes that govern gut tissue. In addition to its involvement in the regulation of beta-catenin, APC is a cytoskeletal regulator with direct and indirect effects on microtubules. Cancer-related truncation mutations lack direct and indirect binding sites for microtubules in APC, suggesting that loss of this function contributes to defects in APC-mutant cells. In this study, we show that loss of APC results in disappearance of cellular protrusions and decreased cell migration. These changes are accompanied by a decrease in overall microtubule stability and also by a decrease in posttranslationally modified microtubules in the cell periphery particularly the migrating edge. Consistent with the ability of APC to affect cell shape, the overexpression of APC in cells can induce cellular protrusions. These data demonstrate that cell migration and microtubule stability are linked to APC status, thereby revealing a weakness in APC-deficient cells with potential therapeutic implications.

Acetylation↗
PubMed2002

Glandular hairs of Sigesbeckia jorullensis Kunth (Asteraceae): morphology, histochemistry and composition of essential oil.

Long-stalked glandular hairs of outer and inner involucral bracts of Sigesbeckia jorullensis, which are important for epizoic fruit propagation, were investigated using light and scanning electron microscopy. The essential oil secreted by the hairs was analysed by chromatographic methods including gas chromatography/mass spectrometry and with a laser microprobe mass analyser. The glandular hairs consisted of a large multicellular stalk and a multicellular secreting head. The apical layer of glandular head cells was characterized by leucoplasts and calcium oxalate crystals. Below the apical cells there were up to six layers of cells containing many chloroplasts around the nucleus and surrounded by vacuoles filled with flavonoids and tannins. The essential oil originating in the head cells was secreted into the subcuticular space and may be liberated by rupture of the cuticle. It was mainly composed of sesqui- and diterpenes, with the sesquiterpene hydrocarbon germacrene-D as the main component. Monoterpenes, n-alkanes and their derivatives as well as flavonoid aglycones were also detected. The stickiness of the essential oil is probably associated with the high content of oxygenated sesqui- and diterpenes. In addition to long-stalked trichomes, small biseriate trichomes occurred, secreting small quantities of essential oil into a subcuticular space.

Asteraceae↗
PubMed2002

Secretory trichomes, a substitutive floral nectar source in Lundia A. DC. (Bignoniaceae), a genus lacking a functional disc.

This is the first report of corolla-borne secretory trichomes that substitute in role for a non-functional disc in a species of the neotropical genus Lundia A. DC. (Bignoniaceae). The floral biology and flowering phenology of Lundia cordata were investigated at two remnants of tropical rainforest in northeastern Brazil. This species is a typically omithophilous liana, with reddish, tubular, scentless flowers. The flowers are resupinate, protandrous and last for 2 d. There is a vestigial non-functional perigynous disc and nectar is secreted by glandular trichomes distributed along the internal surface of the corolla. The nectar is stored at the base of the corolla tube, thus showing secondary nectar presentation. The nectariferous trichomes are multi-cellular, uniseriate, with a basal foot cell rooting in the epidermis, one neck cell, and a glandular head with 13 cells on average. Three species of hummingbirds (Amazilia fimbriata, Eupetomena macroura and Phaethornis pretrei) serve as pollinators. Phaethornis ruber, Xylocopa bees, wasps and diurnal moths are considered nectar thieves.

Animals↗
PubMed2002

UV-B is required for normal development of oil glands in Ocimum basilicum L. (sweet basil).

Plants of Ocimum basilicum L. grown under glass were exposed to short treatments with supplementary UV-B. The effect of UV-B on volatile essential oil content was analysed and compared with morphological effects on the peltate and capitate glandular trichomes. In the absence of UV-B, both peltate and capitate glands were incompletely developed in both mature and developing leaves, the oil sacs being wrinkled and only partially filled. UV-B was found to have two main effects on the glandular trichomes. During the first 4 d of treatment, both peltate and capitate glands filled and their morphology reflected their 'normal' mature development as reported in the literature. During the following days there was a large increase in the number of broken oil sacs among the peltate glands as the mature glands broke open, releasing volatiles. Neither the number of glands nor the qualitative or quantitative composition of the volatiles was affected by UV-B. There seems to be a requirement for UV-B for the filling of the glandular trichomes of basil.

Cell Surface Extensions↗
PubMed2002

Pseudopollen and food-hair diversity in Polystachya Hook. (Orchidaceae).

Labellar food-hairs in Polystachya Hook. exhibit considerable morphological diversity. The commonest type of trichome is uniseriate, two to four-celled, with a clavate or subclavate terminal cell. This type occurs amongst representatives of most sections examined. Other trichomes are bristle-like with tapering or fusiform terminal cells, whereas representatives of section Polystachya have uniseriate, moniliform trichomes that fragment with the formation of rounded or elliptical component cells. Most contain protein and, while some contain starch, lipid is invariably absent. The presence of particular types of labellar trichomes does not coincide with variations in vegetative morphology. Thus, current taxonomic treatment of the genus indicates that trichome types, with perhaps the sole exception of moniliform, pseudopollen-forming hairs found in section Polystachya only, have limited taxonomic value. However, the remarkable similarity between pseudopollen-forming hairs of Polystachya and those of the Neotropical genus Maxillaria in terms of morphology, cellular dimensions and food content indicates that pseudopollen may have arisen several times and evolved in response to similar pollinator pressures.

Cell Surface Extensions↗
PubMed2003

Morphology of floral papillae in Maxillaria Ruiz & Pav. (Orchidaceae).

BACKGROUND AND AIMS: The labellar papillae and trichomes of Maxillaria Ruiz & Pav. show great diversity. Although papillae also occur upon other parts of the flower (e.g. column and anther cap), these have not yet been studied. Labellar trichomes of Maxillaria are useful in taxonomy, but hitherto the taxonomic value of floral papillae has not been assessed. The aim of this paper is to describe the range of floral papillae found in Maxillaria and to determine whether papillae are useful as taxonomic characters. METHODS: Light microscopy, histochemistry, low-vacuum scanning and transmission electron microscopy. KEY RESULTS: A total of 75 taxa were studied. Conical papillae with rounded or pointed tips were the most common. The column and anther cap usually bear conical, obpyriform or villiform papillae, whereas those around the stigmatic surface and at the base of the anther are often larger and swollen. Labellar papillae show greater diversity, and may be conical, obpyriform, villiform, fusiform or clavate. Papillae may also occur on multiseriate trichomes that perhaps function as pseudostamens. Labellar papillae contain protein but most lack lipid. The occurrence of starch, however, is more variable. Many papillae contain pigment or act as osmophores, thereby attracting insects. Rewards such as nectar or a protein-rich, wax-like, lipoidal substance may be secreted by papillae onto the labellar surface. Some papillae may have a protective role in preventing desiccation. Species of diverse vegetative morphology may have identical floral papillae, whereas others of similar vegetative morphology may not. CONCLUSIONS: Generally, floral papillae in Maxillaria have little taxonomic value. Nevertheless, the absence of papillae from members of the M. cucullata alliance, the occurrence of clavate papillae with distended apices in the M. rufescens alliance and the presence of papillose trichomes in some species may yet prove to be useful.

Amino Acids, Aromatic↗
PubMed2003

Pollinarium morphology and floral rewards in Brazilian Maxillariinae (Orchidaceae).

BACKGROUND AND AIMS: There is strong support for the monophyly of the orchid subtribe Maxillariinae s.l., yet generic boundaries within it are unsatisfactory and need re-evaluation. In an effort to assemble sets of morphological characters to distinguish major clades within this subtribe, the pollinarium morphology and floral rewards of representative Brazilian species of this subtribe were studied. METHODS: The study was based on fresh material from 60 species and seven genera obtained from cultivated specimens. Variation of pollinarium structure and floral rewards was assessed using a stereomicroscope and by SEM analysis. KEY RESULTS: Four morphological types of pollinaria are described. Type 1 appears to be the most widespread and is characterized by a well-developed tegula. Type 2 lacks a stipe and the pollinia are attached directly to the viscidium. Type 3 also lacks a stipe, and the viscidium is rigid and dark. In Type 4, the stipe consists of the whole median rostelar portion and, so far, is known only from Maxillaria uncata. Nectar, trichomes, wax-like and resin-like secretions are described as flower rewards for different groups of species within the genus Maxillaria. Data on the biomechanics and pollination biology are also discussed and illustrated. In Maxillariinae flowers with arcuate viscidia, the pollinaria are deposited on the scuttellum of their Hymenopteran pollinators. In contrast, some flowers with rounded to rectangular, pad-like viscidia fix their pollinaria on the face of their pollinators. CONCLUSIONS: Pollinarium morphology and floral features related to pollination in Brazilian Maxillariinae are more diverse than previously suggested. It is hoped that the data presented herein, together with other data sources such as vegetative traits and molecular tools, will be helpful in redefining and diagnosing clades within the subtribe Maxillariinae.

Animals↗