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Departments of Pharmacology and Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10032
Submitted 4 November 2002 ; accepted in final form 13 March 2003
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONREFERENCES |
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development
Caveolin-1 is the ubiquitous isoform detected in tissues as full-length
caveolin-1
and an 
3 kDa smaller caveolin-1
isoform
[generated through an alternative transcription initiation site at an internal
methionine at position 32 (5)].
Caveolin-1 self-assembles to form high-molecular-mass homooligomers that
directly bind glycosphingolipids and cholesterol and (through protein-protein
and protein-lipid interactions) drive caveolae biogenesis. Caveolin-3 is the
structurally related muscle-specific caveolin gene family member whose role in
striated muscle cells is largely analogous to that of caveolin-1 in nonmuscle
cells. Caveolin-1 or -3 expression in cells that lack caveolin/caveolae is
sufficient to sculpt vesicles with morphological features of caveolae; both
caveolin-1 and caveolin-3 act as molecular scaffolds, to sequester and
regulate signaling by certain lipid-modified signaling proteins [G
subunits, Ras and Src
(26)].
Caveolin-2 is a structurally related caveolin family member with a tissue distribution that largely overlaps with caveolin-1 (25). However, the functional properties of caveolin-2 are quite distinct from those of caveolin-1 or caveolin-3. Caveolin-2 is detected as a mixture of monomers and dimers that are retained in the Golgi complex or lipid droplets in cells that lack caveolin-1 or -3; caveolin-2 alone does not assemble into high-molecular-mass oligomers or drive caveolae formation (13). However, in most native cells that coexpress caveolin-1 and -2, caveolin-2 is recovered in stable Triton-insoluble heterooligomeric complexes along with caveolin-1 (24). Caveolin-2 might be expected to interact in a fashion analogous to caveolin-3 and influence caveolae biogenesis in striated muscle cells, including cardiomyocytes. However, there is as yet no consensus in the literature as to whether cardiomyocytes express caveolin-2. Although several laboratories detected caveolin-2 mRNA or protein in cardiac preparations (7, 12, 17), some investigators argue that endothelial cells and fibroblasts (rather than cardiomyocytes) are the source of caveolin-2 in intact heart preparations (7, 17). Indeed, Yarbrough et al. (30) recently identified caveolin-3, but not caveolin-1 or caveolin-2, by immunoblot analysis with isoform-selective antibodies and low-density vesicles purified from isolated adult rat cardiomyocytes.
Flotillin-1 and flotillin-2/epidermal surface antigen (ESA) comprise
another family of 45-kDa caveolae-associated proteins. Although not
structural homologs of caveolin, flotillins act as functional homologs to
drive caveolae-like vesicle formation when expressed alone in insect cells; in
cells that coexpress flotillins and caveolins, flotillin-1 and flotillin-2
form stable complexes that are coimmunoprecipitated (along with caveolin-2) by
the caveolin-1 antibody (29).
Although flotillin-1 (which is abundant in striated muscle tissues) and
flotillin-2 (which is relatively ubiquitous) are both detected in extracts
from mouse myocardium and neonatal rat cardiomyocyte cultures
(19,
29), a role for flotillins in
the formation and/or structural organization of caveolae-like vesicles in
muscle cells has never been considered.
Recent studies in cell culture and genetically engineered mouse models suggest that tight regulation of caveolin-3 expression (and caveolae biogenesis) is critical for normal muscle physiology (4). Accordingly, this study examines caveolin/flotillin isoform expression in cardiomyocytes. The goals were to determine whether caveolin-3 expression is developmentally regulated, whether cardiomyocytes coexpress caveolin-2 and caveolin-3 and whether caveolin-3-caveolin-2 interactions might contribute to caveola biogenesis in cardiomyocytes.
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METHODS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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Cardiomyocytes were isolated from the hearts of 2-day-old Wistar rats by a trypsin dispersion procedure according to a protocol that incorporates a differential attachment procedure to enrich for cardiomyocytes followed by irradiation (19). Cells were plated at a density of 0.5 x 106 cells/ml (high density; to generate a confluent monolayer) or 0.25 x 106 cells/ml (low density; to yield cultures with reduced cell-cell contacts) on protamine sulfate-coated culture dishes and cultured in MEM (GIBCO-BRL) with 10% fetal calf serum, 5 x 10-6 M hypoxanthine, and 12 mM NaHCO3. For some experiments, cultures highly enriched in cardiac fibroblasts were obtained from cells adherent to culture dishes during the preplating step (19). Adult rat ventricular myocytes were disaggregated according to methods described previously and used within 1–6 h of isolation (10).
Caveolin-rich membranes were prepared according to a detergent-free
purification scheme described previously
(19). Briefly, cells from five
100-mm-diameter dishes were scraped into 0.5 M sodium carbonate (pH 11.0; 0.5
ml/dish) and combined for each preparation. The extract was sequentially
disrupted by homogenization with a Dounce homogenizer, a Polytron tissue
grinder, and a tip sonicator. The homogenate was adjusted to 40% sucrose by
adding an equal volume of 80% sucrose prepared in MES-buffered saline [25 mM
MES (pH 6.5) and 0.15 M NaCl], placed on the bottom of an ultracentrifuge
tube, overlaid with a 5–35% discontinuous sucrose gradient, and
centrifuged at 38,000 rpm for 16–18 h in a SW40 rotor (Beckman). After
centrifugation, aliquots of fractions were dissolved in sample buffer
containing SDS and 2-mercaptoethanol and heated before electrophoresis in
SDS-PAGE gels optimized for resolution of low-molecular-weight proteins to
detect the distinct molecular forms of caveolin-2 (with a 3-cm-long 10% spacer
gel above a 6-cm 16.5% polyacrylamide separating gel). Samples were then
transferred to nitrocellulose and immunoblotted with anti-caveolin-1 (MAb
2234), anti-caveolin-2 (MAb 65), anti-caveolin-3 (MAb 26), anti-flotillin, or
anti-ESA purchased from BD Transduction Laboratories. Evidence that
anti-caveolin-2 (MAb 65) recognizes caveolin-2, but does not cross-react with
either caveolin-1 or caveolin-3, has been previously published
(24). The
anti-1-adrenergic receptor antibodies were from Santa Cruz
Biotechnology. In Figs. 1 and
3, immunoblot analysis of
different proteins was with different nitrocellulose membranes; membranes were
probed for caveolin-2, stripped, and reprobed for caveolin-3 in Figs.
2 and
4. Immunodetection was with
chemiluminescence.
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For immunoprecipitation, cardiomyocytes from one 100-mm-diameter dish were rinsed with ice-cold PBS and harvested by the addition of 0.7 ml of extraction buffer [10 mM Tris-Cl (pH 8), 150 mM NaCl, 50 µg/ml aprotinin, 0.1 mM leupeptin, 50 µg/ml benzamidine, 2 mM phenylmethylsulfonyl fluoride, 50 µM pepstatin A, 0.1 mM sodium vanadate, 50 mM NaF, 1% Triton X-100, and 60 mM octyl glucoside]. Scraped cells were sonicated and centrifuged at 4°C for 15 min at maximal speed in a microcentrifuge. The supernatant was incubated with anti-caveolin-2 or anti-caveolin-3 antibodies for 1 h at 4°C followed by the addition of 70 µl of protein A/G Plus-agarose beads (Santa Cruz Biotechnology) and overnight incubation at 4°C. The beads were washed three times with washing buffer [10 mM Tris-Cl (pH 8), 150 mM NaCl, 2 mM phenylmethylsulfonyl fluoride, and 1% Triton X-100], and bound proteins were eluted with SDS-PAGE sample buffer and subjected to immunoblot analysis as described above.
For immunofluorescence studies, cardiomyocytes isolated from neonatal
ventricles were plated on fibronectin-coated glass coverslips; the adherent
cardiac fibroblasts obtained during the preplating step were cultured for 3
days, resuspended, and plated on fibronectin-coated glass coverslips in
parallel. Cells were fixed with 3% paraformaldehyde in PBS at room temperature
for 30 min and permeabilized with 0.1% Triton X-100 in PBS containing 0.2% BSA
for 10 min. Nonspecific binding sites were blocked by incubating coverslips
for 30 min in PBS containing 0.2% BSA, 0.1% Triton X-100, and 10% normal goat
serum. Cells were then incubated overnight at 4°C with mouse monoclonal
anti-caveolin-1 (MAb 2234, 1:50), anti-caveolin-2 (MAb 65, 1:20), or
anti-caveolin-3 (MAb 26, 1:1,000) alone or with polyclonal
anti--actinin (1:50; Santa Cruz) raised in the rabbit (to minimize
cross-reactivity with distinctly tagged secondary antibodies for
double-labeling experiments). Primary antibodies were diluted in PBS with 0.1%
Triton X-100 and 0.2% BSA. Cells were washed three times (10 min each) with
PBS, and primary antibodies were visualized by incubation with appropriate
secondary antibodies conjugated to Alexa dyes (Molecular Probes, Eugene, OR);
Alexa Fluor 594 goat anti-rabbit IgG (1:1,000) was used to visualize
-actinin, and Alexa 488 Fluor goat anti-mouse IgG (1:1,000) was used to
visualize caveolin isoforms. Slides were mounted with 20 mg/ml propyl gallate
in 90% glycerol and images were captured with a cooled charge-coupled device
camera (Princeton Instruments, Trenton, NJ) mounted on a Nikon TE 200
microscope (40x neofluor/1.3 NA objective) and processed with Metamorph
imaging software.
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RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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To resolve previous uncertainties regarding the source of caveolins
identified in cardiac tissues, caveolin/flotillin expression also was examined
in cardiomyocytes isolated from intact ventricles.
Figure 1B shows that
caveolin-2, caveolin-3, flotillin-1, and flotillin-2/ESA immunoreactivity were
abundant in extracts from cultured neonatal and isolated adult ventricular
myocytes. Caveolin-2 was detected predominantly as the full-length isoform in
ventricular tissue but as multiple distinct bands, with mobilities
corresponding to full-length caveolin-2, caveolin-2 (believed to
be generated by alternative translation initiation from a single RNA species,
analogous to the mechanism described for caveolin-1), and caveolin-2
[an isoform with an as yet unknown structure
(11)] in neonatal rat
cardiomyocyte cultures. Caveolin-2 also was detected as full-length
caveolin-2 and the smaller caveolin-2 isoforms in adult rat
cardiomyocytes. Remarkably, the abundance of caveolin-2 and caveolin-3 was
relatively similar in neonatal cardiac cultures and in isolated adult
cardiomyocytes. The substantially higher levels of caveolin-2 and caveolin-3
in neonatal cardiomyocyte cultures than in postnatal day 2
ventricular tissue suggests that caveolin-2 and caveolin-3 are induced in
parallel during cardiomyocyte culture. Indeed,
Fig. 2 shows that caveolin-2
and caveolin-3 expression increase markedly between day 1 and day
4 of culture; flotillin-1 expression is relatively more constant in
comparison. Previous studies established that caveolin-1 expression is
markedly influenced by cell density in NIH 3T3 cells [in which caveolins play
an important role to regulate growth and tumor formation
(6)]. However, caveolin-2 and
caveolin-3 levels differ little in cardiomyocyte cultures grown at low or high
density for 4 days; although Fig.
2 shows a modest reduction in caveolin-2 and caveolin-3 expression
at day 6 in the high-density cultures relative to the low-density
cultures, this difference was not consistently observed in other experiments.
Of note, a caveolin-2 isoform whose mobility corresponds to that of
caveolin-2 was particularly prominent in cardiomyocytes that failed to
adhere to substrate during the first 24 h of culture; this form of caveolin-2
is detected only at much lower levels in adherent neonatal cardiomyocyte
cultures.
Changes in the level of expression of certain cardiomyocyte gene products
have been attributed to a postnatal surge in thyroid hormone secretion
(8). Because the
-adrenergic receptor-G-adenylyl cyclase complex targets to
caveolae in cardiomyocytes [and caveolin-3 regulates the catalytic activity of
cardiac adenylyl cyclase isoforms
(3,
14,
28)], we examined whether
thyroid hormone regulates caveolin/flotillin expression.
Figure 3 shows that thyroid
hormone does not alter caveolin or flotillin isoform expression in
cardiomyocyte cultures (under conditions in which the predicted thyroid
hormone-dependent change in 1-adrenergic receptor expression
is prominent). These results indicate that the developmental regulation of
caveolin isoform expression is not mediated by thyroid hormone. These results
also argue that structural changes in the abundance of caveolae on the cell
surface are unlikely to contribute to thyroid hormone-dependent changes in
sympathetic tone in cardiomyocytes.
Cardiomyocytes (which express caveolin-3 but not caveolin-1) provide a convenient assay system to determine whether caveolin-2 forms complexes with caveolin-3 and contributes to caveolae biogenesis. In nonmuscle cells, caveolin-2 assembles into high-molecular-mass heterooligomers that are recovered in light vesicular fractions only when coexpressed with caveolin-1; caveolin-2 is excluded from light vesicles in cells that lack caveolin-1 (15). In light of previous reports that caveolin-2 does not coassemble into high-molecular-mass heterooligomers with caveolin-3 [under conditions in which caveolin-1-caveolin-2 interactions are prominent (24)], we expected to recover caveolin-2 in the heavy fractions of bottom-loaded sucrose gradients (separate from caveolin-3). However, with an established biochemical fractionation scheme that uses homogenization in sodium carbonate followed by equilibrium centrifugation to separate caveolin-3-enriched membranes from other cell membranes and cytosolic proteins, we recovered caveolin-2 (including the more rapidly migrating isoforms) in low-density vesicles along with caveolin-3 (Fig. 4A). However, it should be noted that both caveolin-2 and caveolin-3 proteins were readily detectable in fivefold greater amounts of protein pooled from the heavy sucrose gradient fractions (fractions 8–13, Fig. 4A, right). Of note, caveolin-1 was not detected in the low-density vesicle fraction prepared from cardiomyocyte cultures, although it is abundant in a similar vesicle fraction prepared from fibroblasts used as positive controls (Fig. 4B). These results argue that the cardiomyocytes themselves (rather than a low level of caveolin-2-enriched contaminating fibroblasts) must be the source of caveolin-2 detected in these experiments.
Immunocytochemistry was used as an additional strategy to exclude the
possibility that a contaminating nonmuscle cell is the source of caveolin-2
immunoreactivity in cardiomyocyte cultures.
Figure 5B shows that
cardiac fibroblasts display strong and similar immunostaining patterns for
caveolin-1 and caveolin-2; both are detected as punctate stains throughout the
cell and along the cell surface [very similar to the immunostaining patterns
previously described in 3T3-L1 fibroblasts
(24)]. Caveolin-3
immunoreactivity is not detected in cardiac fibroblasts. In contrast, caveolin
isoform expression in cardiomyocytes was quite different
(Fig. 5A).
Immunocytochemistry was performed on cardiomyocyte cultures grown on glass
coverslips coated with fibronectin to promote cell attachment. Because
fibronectin is considerably more conducive to cell attachment than protamine
sulfate (the surface used to promote cell attachment to the plastic culture
dishes used for biochemical assays), we performed double-labeling
immunofluorescence with a polyclonal anti--actinin IgG to discriminate
cardiomyocytes from any caveolin-2-expressing cardiac fibroblasts that might
contaminate the cultures. In fact, although most cells in these cultures were
identified by their highly organized -actinin sarcomeric banding
pattern as cardiomyocytes, isolated cells with -actinin-decorated
stress fibers (a staining pattern characteristic of cardiac fibroblasts) were
detected. Foci with cardiomyocytes adjacent to a cardiac fibroblast were
chosen for illustration (to facilitate comparisons of caveolin expression and
subcellular localization in cardiomyocytes and cardiac fibroblasts).
Figure 5A shows that
the fibroblasts (with -actinin-decorated stress fibers) stain for
caveolin-1 (but not caveolin-3), whereas cardiomyocytes (with organized
sarcomeric banding patterns) stain for caveolin-3 (but not caveolin-1).
Caveolin-3 is detected in cardiomyocytes as scattered puncta throughout the
cytoplasm and at the cell surface (with surface staining for caveolin-3
particularly prominent at sites of cell-cell contact, where caveolae are
described to morphologically concentrate). In contrast, the anti-caveolin-2
antibody stained both cell types with similar intensity but with different
patterns. Caveolin-2 is detected as a punctate stain throughout the cytosol
and along the cell surface in fibroblasts but as a diffuse cytosolic (and an
occasional more intense juxtanuclear) stain in cardiomyocytes. Differences
between the caveolin-2 staining pattern in cardiac fibroblasts and
cardiomyocytes (and between the caveolin-2 and caveolin-3 staining patterns in
cardiomyocytes) were unexpected. However, this result is somewhat reminiscent
of results recently reported for skeletal muscle, in which caveolin-3 is
detected exclusively at the cell surface and caveolin-1 stains the cytoplasm
(12).
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Although the immunocytochemical studies identify differences in the subcellular distributions of caveolin-2 and caveolin-3, the biochemical studies suggest that at least some fraction of caveolin-2 might associate and coassemble in heterooligomeric complexes with caveolin-3 in cardiomyocytes (because caveolin-2 targets with caveolin-3 to low-density membranes). To determine whether caveolin-3 interacts in vivo with caveolin-2, cardiomyocytes were solubilized in octyl glucoside (a detergent thought to release caveolin proteins from membranes by displacing endogenous lipids such as glycosphingolipids and cholesterol from membranes). Extracts were subjected to immunoprecipitation with an antibody that selectively recognizes caveolin-3 (and does not cross-react with other caveolae-associated proteins); anti-caveolin-3 immunoprecipitates were subject to Western blot analysis with antibodies that recognize caveolin-2. Figure 6 shows that immunoprecipitation with anti-caveolin-3 effectively clears caveolin-3 immunoreactivity from the cell lysate and leads to the coimmunoprecipitation of caveolin-2 protein. However, not all of the caveolin-2 protein is cleared from the lysates under these conditions, suggesting either that the caveolin-3-caveolin-2 interaction is not sufficiently stable to withstand the immunoprecipitation protocol or that caveolin-2 exists as distinct caveolin-3-interacting and free pools in cardiomyocytes. We also performed the converse experiment; although we were not able to identify conditions to effectively immunoprecipitate all caveolin-2 protein with the anti-caveolin-2 IgG (data not shown), we found that immunoprecipitation of caveolin-2 results in the coprecipitation of caveolin-3. Controls demonstrating that caveolin-3 does not coimmunoprecipitate with an irrelevant mouse IgG1 antibody have been published (19).
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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as well as
smaller isoforms. Although these more rapidly migrating caveolin-2 species
were tentatively identified as caveolin-2 and caveolin-2 (on the
basis of their mobilities), it is reasonable to also consider the possible
presence of a novel caveolin-2 splice variant (lacking the COOH-terminal 49
amino acids) recently amplified from the mouse heart and other tissues
(9), although not yet
identified by Northern or Western blot analysis in native tissues. This
caveolin-2 splice variant migrates in SDS-PAGE just slightly faster than
caveolin-2; it localizes to intracellular reticular membranes (rather
than surface membranes) when expressed in heterologous expression systems,
similar to a pool of caveolin-2 protein in cardiomyocytes. A rapidly migrating
form of caveolin-2 that comigrates with caveolin-2 (but could represent
a proteolytic product of the full-length caveolin-2) accumulates in
cardiomyocytes that fail to adhere to substrate during the first 24 h of
culture. This caveolin-2 species deserves further study in view of recent
evidence that caveolin-2 is a target for regulatory phosphorylation during
integrin ligation as well as maturation of the caveolin complex
(23).
The identification of caveolin-2 in cardiomyocytes in this study is at odds
with conclusions promulgated by two other laboratories whose studies were
performed in genetic models of caveolin isoform overexpression and/or gene
deletion in mice or cardiomyocytes isolated from the adult rat ventricle
(17,
30). Differences in the
results obtained in this and previous studies cannot be ascribed to
species-dependent differences in caveolin-2 expression, because we detected
relatively similar levels of caveolin-2 expression in neonatal rat and
neonatal mouse cardiomyocyte cultures (data not shown). The detection of
caveolin-2 protein in cardiomyocyte cultures also cannot be ascribed to
anti-caveolin-2 antibody cross-reactivity with other caveolin isoforms, given
the markedly different mobilities of the bands recognized by anti-caveolin-2
vs. other anti-caveolin antibodies [and the previous rigorous characterization
of this anti-caveolin-2 antibody's specificity–it does not cross-react
with either caveolin-1 or caveolin-3
(24,
27)]. Age-dependent
differences in caveolin-2 expression also are ruled out by the observation
that caveolin-2 is detected in both neonatal and adult rat cardiomyocytes
(albeit at different levels). Finally, although we could identify an
occasional cardiac fibroblast in the cardiomyocyte cultures grown on
fibronectin-coated glass coverslips (and exploited this for the
immunocytochemistry experiments), the presence of caveolin-2 immunoreactivity
in the cardiomyocyte cultures used for biochemical fractionation cannot be
ascribed to the presence of a caveolin-1/caveolin-2-enriched contaminating
cell type in light of 1) the absence of any detectable caveolin-1
immunoreactivity in biochemical studies on extracts from cardiomyocyte
cultures (including in substantial amounts of protein derived from the
caveolin-3-enriched vesicle fraction) and 2) the very distinct
repertoire of signals we have reported
(21,
22) for Gq
and the protease-activated receptor-1 (PAR-1, the prototypical thrombin
receptor) in cardiomyocyte and cardiac fibroblast cultures. The signaling
properties of Gq and PAR-1 in cardiomyocytes, which are quite distinct
from their actions in cardiac fibroblasts, could only be detected in cultures
of pure cardiomyocytes (which do not contain significant levels of cardiac
fibroblast contamination). Rather, this study suggests that the divergent
results between this and previous studies might be reconciled by two factors.
First, it is possible that a relatively diffuse caveolin-2 staining pattern in
cardiomyocytes might be obscured (or dismissed as nonspecific) in the context
of the more intense membrane staining for caveolin-2 in endothelial cells and
other nonmuscle cell elements in immunohistochemical studies of tissue
sections. Alternatively, the failure to detect caveolin-2 in some previous
studies might be the result of technical factors such as the amount and/or
purity of the samples used for immunoblot analysis.
Changes in caveolin-1 or caveolin-3 expression impact substantially on caveolae biogenesis, but the factors that regulate caveolin isoform expression during development and in disease states remain largely unknown. Engelman et al. (2) reported that caveolin-3 mRNA and protein are first detected in mouse embryos at day 15; although caveolin-1 and caveolin-2 mRNAs are detected at a somewhat earlier stage (day 7), these proteins also are not detected until day 15, identifying caveolins as late markers of differentiation during embryogenesis. Other studies indicate that caveolin-1 expression is downregulated in rapidly growing cells (or in cells transformed by an oncogene), whereas caveolin-1 expression is dramatically upregulated as cells reach confluence or differentiate (6). Caveolin-3 behaves in a similar fashion, in that it is not detected in precursor myoblasts but becomes abundant in differentiated myotubes (24, 27). Results of these studies establish that caveolin-3 and caveolin-2 expression increase with age (through a mechanism distinct from the regulatory effects of thyroid hormone) and during culture of ventricular cardiomyocytes. The results support the notion that caveolin expression is induced during cardiomyocyte differentiation.
Mechanisms that regulate caveolin-2 protein expression have remained even more elusive. The observation that caveolin-2 expression remains constant during oncogenic transformation of NIH 3T3 cells [in which caveolin-1 levels are dramatically downregulated (25)] has been taken as evidence that caveolin-2 mRNA expression is regulated independently of other caveolin isoforms. However, other studies demonstrate that caveolin-2 protein levels are dramatically upregulated (without a change in steady-state mRNA levels) after expression of recombinant caveolin-1 in K562 cells that lack endogenous caveolin-1 (15). Conversely, caveolin-2 protein is reduced in caveolin-1-null and caveolin-1/-3 double-knockout mice (16). These studies have been taken as evidence that caveolin-2 protein is stabilized when in heteroligomeric complexes with caveolin-1. The parallel increase in caveolin-3 and -2 expression during cardiac development could suggest a similar regulatory interaction between caveolin-3 and caveolin-2 in cardiomyocytes.
In summary, these studies identify caveolin-2 expression and caveolin-2 interactions with caveolin-3 in cardiomyocytes. The identification of caveolin-2 in a broad range of cardiomyocyte preparations suggests that the previous inclination to dismiss caveolin-2 as irrelevant to the biology of cardiomyocytes may have been premature. Rather, these studies suggest that caveolin-2 might participate with caveolin-3 in the biogenesis of caveolae (and the spatial organization of biochemical and ionic events at specialized surface membranes) in cardiomyocytes. However, the distinct immunocytochemical staining patterns for caveolin-2 and caveolin-3 in cardiomyocytes also suggest that caveolin-2 may have additional heretofore unrecognized functions in cardiomyocytes.
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ACKNOWLEDGMENTS |
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This work was supported by National Heart, Lung, and Blood Institute Grant HL-28958 and by a Servier Strategic Alliance grant.
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FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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  D. Volonte, C. F. McTiernan, M. Drab, M. Kasper, and F. Galbiati Caveolin-1 and caveolin-3 form heterooligomeric complexes in atrial cardiac myocytes that are required for doxorubicin-induced apoptosis Am J Physiol Heart Circ Physiol, January 1, 2008; 294(1): H392 - H401. [Abstract] [Full Text] [PDF]
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R. S Ostrom Caveolins muscle their way into the regulation of cell differentiation, development, and function. Focus on "Muscle-specific interaction of caveolin isoforms: differential complex formation between caveolins in fibroblastic vs. muscle cells." Am J Physiol Cell Physiol, March 1, 2005; 288(3): C507 - C509. [Full Text] [PDF]
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F. Capozza, A. W. Cohen, M. W.-C. Cheung, F. Sotgia, W. Schubert, M. Battista, H. Lee, P. G. Frank, and M. P. Lisanti Muscle-specific interaction of caveolin isoforms: differential complex formation between caveolins in fibroblastic vs. muscle cells Am J Physiol Cell Physiol, March 1, 2005; 288(3): C677 - C691. [Abstract] [Full Text] [PDF]
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 A. W. Cohen, R. Hnasko, W. Schubert, and M. P. Lisanti Role of Caveolae and Caveolins in Health and Disease Physiol Rev, October 1, 2004; 84(4): 1341 - 1379. [Abstract] [Full Text] [PDF]
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 R. Cagliani, N. Bresolin, A. Prelle, A. Gallanti, F. Fortunato, M. Sironi, P. Ciscato, G. Fagiolari, S. Bonato, S. Galbiati, et al. A CAV3 microdeletion differentially affects skeletal muscle and myocardium Neurology, December 9, 2003; 61(11): 1513 - 1519. [Abstract] [Full Text] [PDF]
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 A. W. Cohen, T. P. Combs, P. E. Scherer, and M. P. Lisanti Role of caveolin and caveolae in insulin signaling and diabetes Am J Physiol Endocrinol Metab, December 1, 2003; 285(6): E1151 - E1160. [Abstract] [Full Text] [PDF]
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