Studies on the cellular cytoskeleton have revealed that the signaling cascade triggered by palytoxin leads to actin filament system distortion.. The goal of the present minireview is to c
Trang 1Marine toxins and the cytoskeleton: a new view of
palytoxin toxicity
M Carmen Louzao, Isabel R Ares and Eva Cagide
Departamento de Farmacologia, Facultad de Veterinaria, Universidad de Santiago de Compostela, Lugo, Spain
Introduction
Palytoxin is a potent marine toxin that was first
isolated from a coelenterate tentatively identified as
Palythoasp This toxin was shown to be extremely
toxic to mammals, with a reported LD50value of just
0.45 lgÆkg)1 after intraperitoneal injection into mice
[1] In addition to being highly toxic, palytoxin has
large and complex structure (Fig 1), which was
deter-mined in the 1980s [2] This water-soluble molecule
consists of a long, partially unsaturated, aliphatic
backbone with spaced cyclic ethers and 64 chiral
centers Examination of the structure shows that there
is, in fact, a group of different palytoxins, whose molecular weights vary according to the species from which they are obtained Several biogenic origins of palytoxins have been proposed, as these toxins have been found not only in zooanthids but in sea anemo-nes, polychaete worms, crabs, and herbivorous fishes, probably due to an accumulation of the toxin by the food chain in the organisms living close to the zoan-thid colonies [3]
It has been reported that dinoflagellates of the genus Ostreopsis are the most probable origin of palytoxin [4,5] In fact, several toxins with palytoxin-like charac-teristics have been described and named according to
Keywords
actin filament; cytoskeleton; ostreocin-D;
Ostreopsis; ovatoxin-a; palytoxin
Correspondence
M C Louzao, Departamento de
Farmacologı´a, Facultad de Veterinaria,
Universidad de Santiago de Compostela,
Campus de Lugo, 27002 Lugo, Spain
Fax: +34 982 252 242
Tel: +34 982 252 242
E-mail: mcarmen.louzao@usc.es
(Received 7 July 2008, revised
12 September 2008, accepted
16 September 2008)
doi:10.1111/j.1742-4658.2008.06712.x
Palytoxin is a marine toxin first isolated from zoanthids (genus Palythoa), even though dinoflagellates of the genus Ostreopsis are the most probable origin of the toxin Ostreopsis has a wide distribution in tropical and sub-tropical areas, but recently these dinoflagellates have also started to appear
in the Mediterranean Sea Two of the most remarkable properties of paly-toxin are the large and complex structure (with different analogs, such as ostreocin-D or ovatoxin-a) and the extreme acute animal toxicity The
Na+⁄ K+-ATPase has been proposed as receptor for palytoxin The marine toxin is known to act on the Na+pump and elicit an increase in Na+ per-meability, which leads to depolarization and a secondary Ca2+ influx, interfering with some functions of cells Studies on the cellular cytoskeleton have revealed that the signaling cascade triggered by palytoxin leads to actin filament system distortion The activity of palytoxin on the actin cyto-skeleton is only partially associated with the cytosolic Ca2+changes; there-fore, this ion represents an important factor in altering this structure, but it
is not the only cause The goal of the present minireview is to compile the findings reported to date about: (a) how palytoxin and analogs are able to modify the actin cytoskeleton within different cellular models; and (b) what signaling mechanisms could be involved in the modulation of cytoskeletal dynamics by palytoxin
Abbreviations
F-actin, filamentous actin; G-actin, globular actin.
Trang 2the producing species [6] Among the nine different
Ostreopsis species existing, five of them have been
reported as producers of toxic substances [6], but just
four of them have been named: Ostreopsis siamensis
was reported to produce ostreocin-D (Fig 1), a potent
palytoxin analog with a LD50 value of 0.75 lgÆkg)1
when given intraperitoneally [4], Ostreopsis lenticularis
produces the neurotoxic ostreotoxins, Ostreopsis
mascarenensisproduces mascarenotoxins, and recently,
Ostreopsis ovatahas been identified as the producer of
ovatoxin-a [7]
Ostreopsis species are important components of
tropical and subtropical reef environments, but
recently these dinoflagellates also started to appear
in temperate waters, such as those from the
Mediter-ranean Sea, even producing toxic outbreaks [7,8]
Human toxicity due to palytoxin has been reported
as food poisoning (named clupeotoxism) and
respira-tory intoxications Palytoxin enters the food chain
and accumulates mainly in fishes such as sardines,
herrings and anchovies from tropical seas, causing neurological and gastrointestinal disturbances asso-ciated with clupeotoxism [1] Symptoms include a bitter and metallic taste followed by nausea, vomit-ing and diarrhea, with mild to acute lethargy Several hours later, burning sensations around the mouth and in the extremities, impairment of sensa-tion, muscle spasms and tremor myalgia, dyspnea and dysphonia occur, possibly leading to death due
to myocardial injury Recently, in Italy, exposure to marine aerosols has been reported that may also cause human illness, with fever being associated with serious respiratory distress, mild dyspnea, wheezes, and in some cases conjunctivitis [7,8] Italian coasts are not the only seawaters where Ostreopsis species have appear; they have been found in the waters around Spain and Greece as well, indicating that the expansion in the Mediterranean Sea of these species
in recent years is becoming a potential risk for human health in Europe
Fig 1 Palytoxin and ostreocin-D structures.
Trang 3Distortion of the Na+ pump
At the cellular level, a broad range of studies have
indicated that the Na+ pump or Na+⁄ K+-ATPase is
the higher-affinity cellular receptor for palytoxin [9,10]
This protein transports three Na+ out the cell in
exchange for two K+that are driven in by hydrolyzing
one molecule of ATP This generated electrochemical
gradient is essential in maintaining electrolyte
homeo-stasis The Na+⁄ K+-ATPase is also the specific target
for heart glycosides such as ouabain, which bind to
the pump and block it when the Na+-binding sites are
open to the extracellular side [10] Nevertheless,
paly-toxin seems to convert the pump into a nonspecific ion
channel, allowing Na+ and K+ fluxes [9,10] Despite
having a different interaction with the Na+⁄ K+
-ATPase, ouabain blocks palytoxin effects in several
systems, and palytoxin inhibits ouabain binding as well
It is known that changes in ion fluxes are the
imme-diate effects of palytoxin on the cells In particular,
increasing the Na+ permeability leads to
depolari-zation and a secondary Ca2+ influx [11,12] that may
lead to multiple events regulated by Ca2+-dependent
pathways The mechanisms by which this rise in
intra-cellular Ca2+ ([Ca2+]i) is produced have not been
completely elucidated Nevertheless, in excitable cells,
at least three mechanisms have been reported to be
involved in the intracellular Ca2+increase: (a)
voltage-dependent Ca2+channels activated by the initial
depo-larization of the membrane; (b) Na+–Ca2+ exchanger
in reverse mode, which drives Ca2+ into the cells
because of the intracellular Na+influx and membrane
depolarization; and (c) an as yet unidentified pathway
that is independent of changes in membrane potential
or changes in pH [9]
The actin cytoskeleton as a selective
target for palytoxins
Actin filaments or microfilaments are polymers of actin
that, together with a large number of actin-binding and
associated proteins, constitute the actin cytoskeleton
[13] For a long time, it was believed that the role of
this system was mainly structural, providing the
sup-port needed to maintain the shape and organization of
the cell and the scaffolding for the actions of catalytic
molecules such as motor proteins Nowadays, the actin
cytoskeleton is widely recognized as an enormously
dynamic structure that undergoes constant
reconstruc-tion and reorganizareconstruc-tion, which is possible because of its
ability to switch rapidly between a filamentous actin
(F-actin) polymeric form and a monomeric globular
actin (G-actin) form [14] This dynamism enables it to
quickly remodel its structure as a consequence of cellu-lar stimuli, and to participate in localized responses to external agents or regional events within a cell Many natural compounds that have been isolated from mar-ine sources exert their cytotoxicity by modulating cytoskeletal properties, in particular those concerning actin filaments [15–17] Although this phenomenon could seem surprising, it is not so surprising if one con-siders the pivotal role of this structure in many cellular functions In eukaryotic cells, the actin cytoskeleton is required for cell motility and surface remodeling; it is essential for several contractile activities, such as mus-cle contraction and the separation of daughter cells by the contractile ring during cytokinesis; it controls cell– cell and cell–substrate interactions, together with adhe-sion molecules; and it actively participates in signal transduction, cell volume regulation, secretion, and surface receptor modulation [18–23]
Although palytoxin has been investigated as a compound that is able to interfere with some of these cellular functions [24–27], its effects on the actin cyto-skeleton were not studied until few years ago The same is true of other palytoxin-like compounds, such
as ostreocin-D and ovatoxin-a, although in these cases almost no information is available concerning their biological activity The first investigations assaying palytoxin and ostreocin-D toxicities were performed in freshly isolated intestinal cells (rabbit enterocytes from the duodenum–jejunum), using fluorescent phalloidin
as an F-actin marker and laser-scanning cytometry and confocal microscopy as techniques for analysis [28] There were two reasons for starting this type of study with an intestinal model: (a) the great complexity
of the actin cytoskeleton in these cells; and (b) the severe gastrointestinal toxicity exerted by palytoxin
in vivo [29,30] Nanomolar concentrations (75 nm) of palytoxin or ostreocin-D, and 4 h of incubation, were enough to induce sharp F-actin disassembly and to almost halve the quantity of F-actin on intestinal cells Interestingly, a purified extract of O ovata that con-tained a putative palytoxin-like compound was tested under the same experimental system, and identical results were obtained [6] As previously described, the actin filament system seems to be closely linked to morphological cell characteristics, and therefore it could be reasonable to expect alterations in shape Nevertheless, they were not observed here Instead of this, enterocytes retained their typical columnar mor-phology after losing many of their microfilaments Similar cases using cultured cells have been reported in the literature [31], and other cytoskeletal components could also be participating in maintenance of the cytoarchitecture [32,33]
Trang 4The above assays were performed by incubating
tox-ins and intestinal cells in suspension After treatment,
they were attached to the substratum with
poly-l-lysine and later analyzed To ensure that floating
cells were sensitive to morphological modifications by
cytotoxic agents, latrunculin-A was tested with an
identical procedure to that used for palytoxin and
ostreocin-D [28] Latrunculin-A is a toxic compound
extracted from the Red Sea sponge Negombata
magni-fica that inhibits actin polymerization and induces
morphological changes in living cells [34,35]
Latruncu-lin-A-treated cells lost one-third of their total actin
content (reduction by 33 ± 6.7%) and underwent
rounding (Fig 2) This fact helps to confirm that
maintenance of cells in suspension was not responsible
for the absence of shape changes when palytoxins were
probed Another interesting feature observed in the
case of latrunculin-A was some brush border
disorga-nization in the apical region of intestinal cells that was
not found after palytoxin or ostreocin-D treatments
New findings have demonstrated again the palytoxin
activity on the cytoskeleton of intestinal cells This toxin induced dose- and time-dependent F-actin dis-ruption in cultured Caco-2 cells [36], a human carcino-genic line that undergoes spontaneous in vitro enterocytic differentiation [37] Interestingly, a correla-tion among partial F-actin breakdown after 1 h of palytoxin treatment (100 nm), morphological altera-tions and cell detachment from substratum was also found in that study In this respect, the outcome of ostreocin-D treatment of CaCo-2 cells remains unknown
The impact of palytoxin action on actin filament sys-tem is not restricted to epithelial cells In a recent report, Louzao et al [12] demonstrated that palytoxins were able also to interfere with the cytoskeleton of neuronal cells These assays were carried out on the human neuroblastoma cell line BE(2)-M17, an excit-able model previously utilized for exploring anticyto-skeletal effects and changes in ion fluxes in response to marine toxins [38–41] Here, palytoxin and ostreocin-D triggered a cascade of cytotoxic events, ranging from a
Fig 2 Left: histograms obtained with laser-scanning cytometry, displaying a reduction in the fluorescence associated with F-actin of freshly isolated rabbit intestinal cells incubated with palytoxin (upper) or latrunculin-A (lower) in comparison to control cells Previous to measure-ment, the cellular actin cytoskeleton was specifically stained with fluorescent phalloidin Right: transmission images recorded by confocal microscopy show the morphological differences between palytoxin (75 n M ) and latrunculin-A (10 l M ) treatments after 4 h of incubation Arrows indicate the alterations on microvilli induced in latrunculin-A-treated cells.
Trang 5rapid depolarization and cytosolic Ca2+ increase to
cytoarchitectural restructuring Time-dependent studies
using a 75 nm concentration of palytoxin and
ostreo-cin-D provided interesting insights into how these
toxins modify the cytoskeleton of neuroblastoma cells:
(a) the distortion of the actin cytoskeleton begins at
early stages, being detectable after 10 min of toxin
incubation; and (b) both microfilament reorganization
and morphological alterations are subsequent to the
start of F-actin disruption [12] In agreement with the
studies using the CaCo-2 cell line, palytoxin also elicited
loss of cellular adhesion and dose- and time-dependent
F-actin disassembly in neuroblastoma cells, leading to
its entire collapse in 24 h after toxin doses of 1 nm
Evidence from a number of systems suggests that
influx of Na+ and⁄ or Ca2+ is associated with many
palytoxin-induced responses, including muscle
contrac-tion, neurotransmitter release, and oncotic death
[25,42,43] A connection has also been found between
Ca2+ influx and palytoxin and ostreocin-D effects on
the actin cytoskeleton This phenomenon seems to
occur in different ways in the different cell types
inves-tigated Ares et al [28] found that in epithelial cells from the rabbit duodenum–jejunum, omission of extra-cellular Ca2+ (nominally Ca2+-free medium) halved the effect of palytoxins on F-actin disassembly Those data led to the idea that these toxins modified the actin filament system of intestinal cells not only by modulat-ing some signalmodulat-ing pathway activated by external
Ca2+, but also by acting on another, still unknown, element Results obtained with neuroblastoma cells indicated that palytoxin and ostreocin-D stimulated similar decreases in F-actin quantity, independently of extracellular Ca2+ entry This effect is not related to
Ca2+being released from internal stores, as palytoxin and ostreocin-D do not induce increases of Ca2+ in nominally Ca2+-free conditions [12] On the other hand, the presence or absence of extracellular Ca2+ was associated with a different F-actin organization in toxin-treated cells, which seems to suggest a new role for this cation in palytoxin action against the actin cytoskeleton (Fig 3) At present, in spite of the impor-tance of the unpolymerized actin pool for the mainte-nance of the F-actin system, the cellular response
Fig 3 Response induced by palytoxin and ostreocin-D on the actin cytoskeleton of neuroblastoma cells after 4 h of incubation under differ-ent extracellular Ca2+conditions Fluorescent phalloidin was utilized for labeling the cellular actin cytoskeleton before quantitative analysis with laser-scanning cytometry and imaging with confocal microscopy.
Trang 6triggered by palytoxin and ostreocin-D activity at this
level has not yet been reported Recent studies
per-formed by Ares et al have revealed that these marine
toxins also induce alterations in G-actin of
neuroblas-toma cells (I R Ares, E Cagide, M C Louzao,
B Espin˜a, M R Vieytes, T Yasumoto and L M
Botana, unpublished results)
Conclusions and perspectives
This minireview compiles the latest findings on how
palytoxin and ostreocin-D are able to act on the actin
filament system within cells A signaling pathway
involv-ing Ca2+influx is partially related to that activity
How-ever, as Ca2+ influx is not responsible for some of the
effects elicited by palytoxins on the cellular actin
cyto-skeleton, more factors must be involved Assuming that
the Na+pump is the target of palytoxin, one interesting
option would be that Na+⁄ K+-ATPase per se activates
some mechanism connected to the actin cytoskeleton
after its interaction with palytoxin (or ostreocin-D, if
they share the same target) This possibility arise from
several recent studies, where has been suggested that in
addition to pumping ions, Na+⁄ K+-ATPase also acts
as a signal transducer [44,45] In this respect, studies
carried out with ouabain, a natural blocker of the Na+
pump and an inhibitor of palytoxin action, have
pro-vided interesting findings Through the partial inhibition
of Na+⁄ K+-ATPase, and regardless of changes in
intra-cellular ion concentrations, ouabain-induced signaling
pathways have been recently found in several cellular
models [44–47] It has been proposed that the
ouabain-bound Na+⁄ K+-ATPase is capable of recruiting and
activating protein tyrosine kinases through specific
protein–protein interactions [45] On the other hand, it
should be not forgotten that the Na+pump could
inter-act with cytoskeletal components Specific cytoskeletal
proteins thought to interact with Na+⁄ K+-ATPase,
either directly or indirectly, include spectrin, actin and
ankyrin [48,49], and even regulation of Na+ pump
activity might depend on its linkage to the actin filament
system [50,51] In any case, the study of the possible
existence of some Na+⁄ K+-ATPase-mediated signaling
mechanism involved in the modulation of actin
cytoskel-etal dynamics by palytoxins opens a new line to follow
in the future in this field of investigation
References
1 Onuma Y, Satake M, Ukena T, Roux J, Chanteau S,
Rasolofonirina N, Ratsimaloto M, Naoki H &
Yasum-oto T (1999) Identification of putative palytoxin as the
cause of clupeotoxism Toxicon 37, 55–65
2 Moore RE & Bartolini G (1981) Structure of palytoxin
J Am Chem Soc 103, 2491–2494
3 Mebs D (1998) Occurrence and sequestration of toxins
in food chains Toxicon 36, 1519–1522
4 Usami M, Satake M, Ishida S, Inoue A, Kan Y & Yasumoto T (1995) Palytoxin analogs from the dino-flagellate Ostreopsis siamensis J Am Chem Soc 117, 5389–5390
5 Taniyama S, Arakawa O, Terada M, Nishio S, Takatani T, Mahmud Y & Noguchi T (2003) Ostreopsis sp., a possible origin of palytoxin (PTX) in parrotfish Scarus ovifrons Toxicon 42, 29–33
6 Vale C & Ares IR (2007) Biochemistry of palytoxins and ostreocins In Phycotoxins Chemistry and Biochem-istry (Botana LM, ed.), pp 95–118 Blackwell Publish-ing, Ames, IA
7 Ciminiello P, Dell’Aversano C, Fattorusso E, Forino
M, Tartaglione L, Grillo C & Melchiorre N (2008) Putative palytoxin and its new analogue, ovatoxin-a, in Ostreopsis ovatacollected along the Ligurian coasts dur-ing the 2006 toxic outbreak J Am Soc Mass Spectrom
19, 111–120
8 Gallitelli M, Ungaro N, Addante LM, Procacci V, Silver NG & Sabba` C (2005) Respiratory illness as a reaction to tropical algal blooms occurring in a temper-ate climtemper-ate JAMA 293, 2599–2600
9 Scheiner-Bobis G (1998) Ion-transporting ATPases as ion channels Naunyn Schmiedebergs Arch Pharmacol
357, 477–482
10 Hilgemann DW (2003) From a pump to a pore: how palytoxin opens the gates Proc Natl Acad Sci USA 100, 386–388
11 Louzao MC, Vieytes MR, Yasumoto T, Yotsu-Ya-mashita M & Botana LM (2006) Changes in membrane potential: an early signal triggered by neurologically active phycotoxins Chem Res Toxicol 19, 788–793
12 Louzao MC, Ares IR, Vieytes MR, Valverde I, Vieites
JM, Yasumoto T & Botana LM (2007) The cytoskele-ton, a structure that is susceptible to the toxic mecha-nism activated by palytoxins in human excitable cells FEBS J 274, 1991–2004
13 dos Remedios CG, Chhabra D, Kekic M, Dedova IV, Tsubakihara M, Berry DA & Nosworthy NJ (2003) Actin binding proteins: regulation of cytoskeletal micro-filaments Physiol Rev 83, 433–473
14 Pollard TD, Blanchoin L & Mullins RD (2000) Molecu-lar mechanisms controlling actin filament dynamics in nonmuscle cells Annu Rev Biophys Biomol Struct 29, 545–576
15 Fiorentini C, Matarrese P, Fattorossi A & Donelli G (1996) Okadaic acid induces changes in the organization
of F-actin in intestinal cells Toxicon 34, 937–945
16 Twiner MJ, Hess P, Dechraoui MY, McMahon T, Samons MS, Satake M, Yasumoto T, Ramsdell JS & Doucette GJ (2005) Cytotoxic and cytoskeletal effects
Trang 7of azaspiracid-1 on mammalian cell lines Toxicon 45,
891–900
17 Allingham JS, Klenchin VA & Rayment I (2006)
Actin-targeting natural products: structures, properties and
mechanisms of action Cell Mol Life Sci 63, 2119–2134
18 Calderwood DA, Shattil SJ & Ginsberg MH (2000)
Integrins and actin filaments: reciprocal regulation of cell
adhesion and signaling J Biol Chem 275, 22607–22610
19 Papakonstanti EA, Vardaki EA & Stournaras C (2000)
Actin cytoskeleton: a signaling sensor in cell volume
regulation Cell Physiol Biochem 10, 257–264
20 Pollard TD & Borisy GG (2003) Cellular motility
dri-ven by assembly and disassembly of actin filaments
Cell 112, 453–465
21 Biron D, Alvarez-Lacalle E, Tlusty T & Moses E (2005)
Molecular model of the contractile ring Phys Rev Lett
95, 98–102
22 Gerthoffer WT (2005) Actin cytoskeletal dynamics in
smooth muscle contraction Can J Physiol Pharmacol
83, 851–856
23 Posern G & Treisman R (2006) Actin’ together: serum
response factor, its cofactors and the link to signal
transduction Trends Cell Biol 16, 588–596
24 Ishida Y, Satake N, Habon J, Kitano H & Shibata S
(1985) Inhibitory effect of ouabain on the
palytoxin-induced contraction of human umbilical artery
J Pharmacol Exp Ther 232, 557–560
25 Nakanishi A, Yoshizumi M, Morita K, Murakumo Y,
Houchi H & Oka M (1991) Palytoxin: a potent
stimula-tor of catecholamine release from cultured bovine
adre-nal chromaffin cells Neurosci Lett 121, 163–165
26 Contreras RG, Flores-Maldonado C, Lazaro A,
Shosh-ani L, Flores-Benitez D, Larre I & Cereijido M (2004)
Ouabain binding to Na+,K+-ATPase relaxes cell
attachment and sends a specific signal (NACos) to the
nucleus J Membr Biol 198, 147–158
27 Oku N, Sata NU, Matsunaga S, Uchida H & Fusetani
N (2004) Identification of palytoxin as a principle which
causes morphological changes in rat 3Y1 cells in the
zoanthid Palythoa aff margaritae Toxicon 43, 21–25
28 Ares IR, Louzao MC, Vieytes MR, Yasumoto T &
Botana LM (2005) Actin cytoskeleton of rabbit
intesti-nal cells is a target for potent marine phycotoxins
J Exp Biol 208, 4345–4354
29 Drenckhahn D & Dermietzel R (1988) Organization of
the actin filament cytoskeleton in the intestinal brush
border: a quantitative and qualitative immunoelectron
microscope study J Cell Biol 107, 1037–1048
30 Ito E, Ohkusu M & Yasumoto T (1996) Intestinal
injuries caused by experimental palytoxicosis in mice
Toxicon 34, 643–652
31 Patel K, Harding P, Haney LB & Glass WF (2003)
Regulation of the mesangial cell myofibroblast
phenotype by actin polymerization J Cell Physiol 195,
435–445
32 Domnina LV, Rovensky JA, Vasiliev JM & Gelfand
IM (1985) Effect of microtubule-destroying drugs on the spreading and shape of cultured epithelial cells
J Cell Sci 74, 267–282
33 Goldman RD, Khuon S, Chou YH, Opal P & Steinert
PM (1996) The function of intermediate filaments in cell shape and cytoskeletal integrity J Cell Biol 134, 971– 983
34 Coue´ M, Brenner SL, Spector I & Korn E (1987) Inhi-bition of actin polymerization by latrunculin A FEBS Lett 213, 316–318
35 Cai S, Liu X, Glasser A, Volberg T, Filla M, Geiger B, Polansky JR & Kaufman PL (2000) Effect of latruncu-lin-A on morphology and actin-associated adhesions of cultured human trabecular meshwork cells Mol Vis 6, 132–143
36 Valverde I, Lago J, Vieites JM & Cabado AG (2008)
In vitro approaches to evaluate palytoxin-induced toxic-ity and cell death in intestinal cells J Appl Toxicol 28, 294–302
37 Chantret I, Barbat A, Dussaulx E, Brattain MG & Zweibaum A (1988) Epithelial polarity, villin expres-sion, and enterocytic differentiation of cultured human colon carcinoma cells: a survey of twenty cell lines Cancer Res 48, 1936–1942
38 Louzao MC, Cagide E, Vieytes MR, Sasaki M, Fuwa
H, Yasumoto T & Botana LM (2006) The sodium channel of human excitable cells is a target for
gambier-ol Cell Physiol Biochem 17, 257–268
39 Ares IR, Louzao MC, Espina B, Vieytes MR, Miles
CO, Yasumoto T & Botana LM (2007) Lactone ring of pectenotoxins: a key factor for their activity on cyto-skeletal dynamics Cell Physiol Biochem 19, 283–292
40 Cagide E, Louzao MC, Ares IR, Vieytes MR, Yotsu-Yamashita M, Paquette LA, Yasumoto T & Botana
LM (2007) Effects of a synthetic analog of polycaverno-side A on human neuroblastoma cells Cell Physiol Biochem 19, 185–194
41 Vilarino N, Ares IR, Cagide E, Louzao MC, Vieytes
MR, Yasumoto T & Botana LM (2008) Induction of actin cytoskeleton rearrangement by methyl okadaate – comparison with okadaic acid FEBS J 275, 926–934
42 Karaki H, Nagase H, Ohizumi Y, Satake N & Shibata
S (1988) Palytoxin-induced contraction and release of endogenous noradrenaline in rat tail artery Br J Phar-macol 95, 183–188
43 Schilling WP, Snyder D, Sinkins WG & Estacion M (2006) Palytoxin-induced cell death cascade in bovine aortic endothelial cells Am J Physiol Cell Physiol 291, C657–C667
44 Liu J, Tian J, Haas M, Shapiro JI, Askari A & Xie Z (2000) Ouabain interaction with cardiac Na+⁄ K+-ATPase initiates signal cascades independent of changes
in intracellular Na+ and Ca2+ concentrations J Biol Chem 275, 27838–27844
Trang 845 Xie Z & Askari A (2002) Na(+)⁄ K(+)-ATPase as a
signal transducer Eur J Biochem 269, 2434–2439
46 Aizman O, Uhlen P, Lal M, Brismar H & Aperia A
(2001) Ouabain, a steroid hormone that signals with
slow calcium oscillations Proc Natl Acad Sci USA 98,
13420–13424
47 Aydemir-Koksoy A, Abramowitz J & Allen JC (2001)
Ouabain-induced signaling and vascular smooth muscle
cell proliferation J Biol Chem 276, 46605–46611
48 Koob R, Kraemer D, Trippe G, Aebi U & Drenckhahn
D (1990) Association of kidney and parotid
Na+,K(+)-ATPase microsomes with actin and analogs
of spectrin and ankyrin Eur J Cell Biol 53, 93–100
49 Devarajan P, Scaramuzzino DA & Morrow JS (1994) Ankyrin binds to two distinct cytoplasmic domains of Na,K-ATPase alpha subunit Proc Natl Acad Sci USA
91, 2965–2969
50 Cantiello HF (1997) Changes in actin filament organiza-tion regulate Na+,K(+)-ATPase activity Role of actin phosphorylation Ann NY Acad Sci 834, 559–561
51 Gomes P & Soares-da-Silva P (2002) Dopamine-induced inhibition of Na+-K+-ATPase activity requires integ-rity of actin cytoskeleton in opossum kidney cells Acta Physiol Scand 175, 93–101