Role of Protein Transamidation in Serotonin-Induced
Proliferation and Migration of Pulmonary Artery
Smooth Muscle Cells
Yinglin Liu1, Lin Wei2, Debra L. Laskin1, and Barry L. Fanburg2
1Rutgers University, Piscataway, New Jersey; and2Tufts Medical Center, Pulmonary Critical Care and Sleep Division, Tupper Research Institute,
Pulmonary hypertension is characterized by elevated pulmonary
artery pressure and pulmonary artery smooth muscle cell (SMC)
proliferation and migration. Clinical and experimental evidence
suggests that serotonin (5-HT) is important in these responses. We
previously demonstrated the participation of the 5-HT transporter
and intracellular 5-HT (5-HTi) in the pulmonary vascular SMC-
the intracellular actions of 5-HT is unknown. We speculated that
5-HTi activates SMC growth by post-translational transamidation of
proteinsvia transglutaminase (TGase) activity, a processreferred to
as serotonylation. To test this hypothesis, serotonylation of pulmo-
nary artery SMC proteins, and their role in 5-HT–induced prolifera-
time-dependent increase in serotonylation of multiple proteins
in both bovine and rat pulmonary artery SMCs. Inhibition of
TGase with dansylcadaverin blocked this activity, as well as SMC-
proliferative and migratory responses to 5-HT. Serotonylation of
proteins also was blocked by 5-HT transporter inhibitors, and was
enhanced by inhibition of monoamine oxidase, an enzyme known
to degrade 5-HTi, indicating that 5-HTi levels regulate serotonyla-
sequencing revealed that a major protein serotonylated by
TGase was fibronectin (FN). 5-HT–stimulated SMC serotonylation
and proliferation were blocked by FN small interfering (si) RNA.
These findings, together with previous observations that FN
expression in the lung strongly correlates with the progression of
pulmonary hypertension in both experimental animals and
humans, suggest an important role of FN serotonylation in the
pathogenesis of this disease.
Keywords: serotonin; transglutaminase; fibronectin; protein serotony-
lation; smooth muscle cell growth
Serotonin (also known as 5-hydroxytryptamine [5-HT]) is one
of the most potent naturally occurring pulmonary vasoconstric-
tors (1). Clinical, experimental, and human genetic data support
a relationship between 5-HT, pulmonary artery remodeling, and
pulmonary hypertension. Our laboratories and others have
demonstrated the importance of both the 5-HT transporter
(5-HTT) and 5-HT receptors in pulmonary vascular smooth
muscle cell (SMC)–proliferative and migratory responses to
5-HT (2–7). We also have shown that 5-HT transport via the
5-HTT triggers activation of platelet-derived growth factor
receptor–b and mitogen-activated protein kinase, which partic-
ipate in proliferation of pulmonary artery SMCs (2, 8). Further-
more, inhibition of intracellular monoamine oxidase (MAO),
which degrades 5-HT, markedly enhances 5-HT–induced pro-
liferation of SMCs (9–11). These data indicate that intracellular
5-HT (5-HTi) is an important signal for SMC proliferation;
however, the mechanism underlying this activity is unknown.
Transglutaminases (TGases), which are abundant in blood
and vascular SMCs (12, 13), catalyze post-translational modifi-
cations of proteins in a calcium-dependent manner (14, 15).
This involves the formation of a covalent bond between the
g-carboxamide group of peptide-bound glutamine residues and
either the amino groups of a primary amine substrate of TGases
(16) or the e-amine group of peptide-bound lysine residues (17).
Modification of TGase substrate proteins by transamidation has
been shown to be important in cell survival, apoptosis, and
cytoskeleton organization (18, 19). The primary amine, 5-HT, is
a TGase substrate. TGase-catalyzed transamidation of proteins
with 5-HT is referred to as serotonylation. Serotonylation of
platelet procoagulant proteins, including fibrinogens and throm-
bospondin, facilitates platelet activation and blood clot forma-
tion (20, 21). Recent studies have shown that serotonylation of
RhoA and smooth muscle b-actin plays an important role in
aortic vascular contractility (22, 23). This 5-HT covalent de-
rivative modification reaction is illustrated in Figure 1.
We speculated that serotonylation of TGase substrate pro-
teins modulates their functions in pulmonary artery SMCs, and
this was investigated in the present studies. 5-HT was found to
initiate serotonylation of several different proteins in bovine
and rat pulmonary artery SMCs, including fibronectin (FN).
Moreover, inhibition of TGase activity reduced both 5-HT–
induced protein serotonylation and proliferation and migration
of SMCs. These data suggest that serotonylation of proteins in
SMCs is important in 5-HT–induced functional responses.
Serotonylation of FN may be particularly relevant, as it has
been reported that both 5-HTT expression and FN accumula-
tion in the lung are directly correlated with the progression of
pulmonary hypertension (24–26).
MATERIALS AND METHODS
Cell Culture and Functional Evaluation
SMCs from bovine and rat pulmonary artery were isolated as pre-
viously described (3, 27). Cells were cultured in Dulbecco’s modified
Eagle’s medium containing 10% FBS, 1% penicillin, and 0.5% strepto-
mycin. Cells from passages 3–9 were used. SMC proliferation was
Serotonylation of pulmonary artery smooth muscle cell
proteins may be important in the development of pulmo-
nary hypertension. More knowledge about this process is
needed and is provided in this article.
(Received in original form February 25, 2010 and in final form May 25, 2010)
This work was supported by National Institute of Health grants HL085260-01
(B.L.F), GM034310, ES004738, CA132624, AR055073, and ES005022 (D.L.L),
and by American Heart Association grant 0725961-H (Y.L.).
Correspondence and requests for reprints should be addressed to Barry
Fanburg, M.D., Tufts Medical Center, Pulmonary, Critical Care and Sleep
Division, 800 Washington Street, #257, Boston, MA 02111. E-mail: BFanburg@
Am J Respir Cell Mol Biol
Originally Published in Press as DOI: 10.1165/rcmb.2010-0078OC on June 17, 2010
Internet address: www.atsjournals.org
Vol 44. pp 548–555, 2011
assessed by incorporation of [3H]-thymidine as previously described (28).
Cell migration was analyzed in a wound healing assay (8).
Preparation of Whole-Cell Lysates
SMCs were rinsed with ice-cold PBS and then scraped into 200 ml lysis
buffer. After 30 minutes at 48C, lysates were centrifuged at 20,800 3 g
for 8 minutes, and supernatants containing cell proteins were collected.
Measurement of Protein Serotonylation
Cells were washed with serum free Dulbecco’s modified Eagle’s
medium and incubated with 1 mmol/L 5-HT for 1–60 minutes. Cells
were then lysed with RIPA buffer, and 100 mg protein was separated by
4–12% SDS-PAGE gradient gel (Invitrogen, Carlsbad, CA) electro-
phoresis. Serotonylated proteins were detected by Western blotting
with anti-5-HT–BSA conjugate antibody (1:2,000) (Sigma, St. Louis,
Measurement of FN Serotonylation
Serononylated FN was quantified by immunoprecipitation with anti-
bovine FN antibody (Santa Cruz Biologicals, Santa Cruz, CA),
followed by immunoblotting with anti–5-HT–BSA conjugate antibody
(1:2,000). The membrane was stripped and reblotted with anti-FN
antibody for normalization.
Transfection of SMCs with FN Small Interfering RNA
Transfection of FN siRNA was performed using Lipofectamine 2,000
from Invitrogen, according to the manufacturer’s instructions. Briefly,
bovine SMCs were transfected with FN siRNA and control siRNA at
final concentrations of 20 or 50 nmol/L. After 48-hour incubation, the
cells were treated with 5-HT. Cell proliferation was measured 24 hours
later. To confirm the efficiency of FN siRNA transfection, cells were
plated in 35-mm plates and transfected with control and FN siRNA for
48 hours. FN expression in cell lysates was assessed by Western blotting
analysis with anti-FN antibody.
Tandem Mass Spectrometric Peptide Sequencing
Slices or spots excised from gels were digested with modified trypsin
(Promega, Madison, WI). In-gel tryptic digest samples were analyzed
by liquid chromatography (LC)–tandem mass spectrometry (MS/MS)
at the University of Medicine and Dentistry of New Jersey/Rutgers
University Core Facility. Nanospray LC-MS/MS of tryptic digests were
conducted using an LTQ linear ion trap mass spectrometer (Thermo
Electron, San Jose, CA). A total of 18 Peak list files for MS/MS spectra
were generated by Bioworks software (ThermoFinnigan, San Jose,
CA) and compared with a bovine database (ENSEMBL 28.35a.1
NCBI35, May 2005) using a local implementation of X! Tandem
software. Identified proteins of interest were confirmed manually.
Means (6SE) were calculated, and statistically significant differences
between groups were determined by one-way ANOVA followed by
Turkey’s post hoc comparisons. An effect was considered significant at
a P value less than 0.05.
5-HT Induces Transglutamidation of Proteins in Bovine
Pulmonary Artery SMC Extracts
In initial experiments, we analyzed the effects of 5-HT on
protein serotonylation in SMC extracts. As shown in Figure 2A,
incubation of SMC protein extract with 5-HT at 1,000 mmol/L
significantly induced protein binding of 5-HT antibody. Multi-
ple 5-HT binding proteins were noted in the range of 120–
240 kD. Lower molecular weight bands in the 50- to 70-kD
range were also observed; however, these were unaffected by
5-HT. Prominent protein binding in the 220- 240-kD range was
blocked by the TGase inhibitor, dansylcadaverin (DSC), which
binds to the enzyme active site of TGase and inactivates the
transmidation activity (29–31). Figure 2B shows that the for-
mation of the 220- to 240-kD TGase-modified protein was
significantly reduced in the presence of the calcium chelator,
EGTA, demonstrating that it is Ca21dependent. Preincubation
of anti–5-HT–BSA anti-serum with 10 mmol/L 5-HT competi-
tively blocked 5-HT binding to the 220- to 240-kD protein, while
minimally affecting the lower molecular weight bands, demon-
strating the specificity of binding of the antibody (Figure 2C).
5-HT Stimulates Protein Serotonylation in Intact Primary
Pulmonary Artery SMCs
We next analyzed the effects of 5-HT on serotonylation of
cellular proteins in intact bovine and rat pulmonary artery
SMCs. Binding of 5-HT to the 220–240 kD protein in bovine
SMCs was dose and time dependent, reaching a maximal level
at 40 minutes and 10–100 mmol/L (Figures 3A and 3B). Similar
results were observed in rat SMCs (Figure 3C). Of note, in rat
cells, nonspecific 5-HT binding in the 50–70 kD range was not
Various cell types, including SMCs, actively transport 5-HT
into cells via a 5-HTT (9, 10, 32). We speculated that, once
accumulated in the cells, 5-HTi is metabolized via MAO into 5-
hydroxyindoleacetic acid, or incorporated into TGase substrate
proteins by TGase-mediated transglutamidation. To test this
hypothesis, SMCs were pretreated for 30 minutes with the 5-
HTT inhibitors, imipramine and fluoxetine, the MAO inhibitor,
phenelzine, or the TGase inhibitor, DSC. Figure 4A shows that
imipramine and fluoxetine caused a dose-dependent inhibition
of 5-HT–induced protein serotonylation of the 220–240 kD
band(s). In contrast, inhibition of MAO with phenelzine
enhanced protein serotonylation (Figure 4B). As observed in
cell extracts, the TGase inhibitor, DSC, blocked protein sero-
tonylation induced by 5-HT in intact cells (Figure 4C).
Identification of Major Target Proteins Modified by
Serotonylation by MS/MS
Liquid chromatography-mass spectrometry analysis revealed
four proteins, including nonmuscle myosin heavy chain IIB
(227 kD), FN (257 kD), plakin (195 kD), and filamin B (278 kD),
as the major serotonylated proteins in the 220–240 kD band(s) in
5-HT–treated cell lysate (data not shown). Immunoprecipitation
and Western blot analysis confirmed that FN was one major
protein serotonylated by 5-HT (Figure 5A).
As FN is an important extracellular matrix (ECM) protein,
we next assessed whether 5-HT treatment resulted in FN
accumulation in the medium. A major band in the 220-kD
position and lower and higher molecular weight bands were
detected in conditioned medium from 5-HT–treated cells, in-
dicating possible degraded fragments and crosslinked products
of FN with other extracellular proteins (Figure 5B).
lated modification of proteins by transglutami-
Schematic illustration of serotony-
Liu, Wei, Laskin, et al.: Serotonylation of Proteins in Pulmonary Artery Smooth Muscle Cells549
Role of Serotonylation in 5-HT–Induced SMC Proliferation
and Migration Responses
To evaluate the role of protein serotonylation in SMC function,
we analyzed the effects of the TGase inhibitor, DSC, on 5-HT–
induced proliferation and migration of bovine SMCs. DSC
pretreatment (200 mmol/L) caused an inhibition of SMC pro-
liferation, as measured by thymidine incorporation (Figure 6A).
Similarly, DSC pretreatment prevented 5-HT–initiated SMC
migration, as demonstrated by wound healing and Boyden
chamber assays (Figures 6B and 6C).
Silencing Cellular FN Inhibits SMC-Proliferative Response to 5-HT
To test the role of FN in SMC proliferation induced by 5-HT,
bovine SMCs were transfected with specific FN siRNA. We
induced protein serotonylation
in bovine pulmonary artery
smooth muscle cell (SMC)
protein extract. SMCs were
washed with Hanks’ balanced
salt solution, harvested, soni-
cated at 48C for 10 seconds,
and then centrifuged
5 minutes at 10,000 3 g.
Supernatants containing cell
extracts then were analyzed
for protein serotonylation. (A)
Proteins in Tris-buffered saline
buffer were incubated with 0–
1,000 mmol/L 5-HT at 378C for
60 minutes in the presence or
absence of the TGase inhibi-
200 mmol/L). Reactions were
terminated by the addition of
5 mmol/L EGTA on ice. Pro-
teins were concentrated and
desalted with micro-filter col-
umns (Pierce, Rockford, IL) by
(Sigma) for protein serotonyla-
tion. (B) Protein serotonylation
was induced by 1 mmol/L 5-HT
in SMC protein extract for
60 minutes and assessed by
Western blotting. (C) Anti–5-
HT–BSA anti-serum was prein-
cubated with 10 mmol/L 5-HT
for 2 hours to neutralize 5-HT–
binding activity. Proteins from
control (2) and 5-HT–treated
cell lysates (1) were immuno-
blotted with 0.5 mg/ml 5-HT
anti-serum control or neutral-
ized 5-HT anti-serum. Protein
molecular weight marker is
shown to the left in all figures.
Bar graphs represent means
(6SD) (n 5 3). *Significant
difference from the untreated
controls at (P , 0.05);#signif-
icant difference from 5-HT–
treated cells (P , 0.05).
550 AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGYVOL 442011
found that transfection of FN siRNA, but not control siRNA,
reduced FN expression to less than 5% of basal level after
72-hour incubation (Figure 7A). FN siRNA also completely
blocked SMC proliferation in response to 5-HT (Figure 7B).
The process of protein serotonylation was previously demon-
strated in platelets, where it was shown that transamidation of
surface procoagulant proteins, including fibrinogen and throm-
bospondin, facilitates activation and blood clot formation (20,
21). Serotonylation of proteins also has been reported to
modulate insulin secretion in pancreatic b cells (33). Moreover,
Guilluy and colleagues (34) found that transamidation of RhoA
by 5-HT led to its activation and depletion in aortic SMCs.
Recent studies have demonstrated that serotonylation of con-
tractile and cytoskeleton proteins, including 42-kD smooth
muscle actin, is important in isometric contraction of 5-HT–
biotin–treated aortic smooth muscle (22).
Cellular internalization of 5-HT through the 5-HTT leads to
SMC signaling and proliferation (11, 35). The present studies
demonstrate that protein serotonylation participates in the
proliferative and migratory response of SMCs to 5-HT. Thus,
we found that 5-HT induces serotonylation of several 220- to
approximately 240-kD proteins; moreover, TGase inhibition
blocks this effect. We also detected approximately 65-kD
serotonylated proteins in bovine, but not in rat, SMCs. Antibody
neutralization studies demonstrated that the 220- to 240-kD pro-
tein(s), but not the approximately 65-kD one(s), specifically
bound the 5-HT antibody. It is likely that bovine SMCs express
some endogenous BSA precursor protein (69 kD), which reacts
with anti–5-HT–BSA antibody (36). Our findings that seroto-
nylation is blocked by 5-HTT inhibitors support a role of 5-HTi
in this process. 5-HT, at a concentration of 1 mmol/L, was used
in these studies because our previous results showed that this
concentration of 5-HT is actively transported by the 5-HTT,
whereas higher concentrations enter the cell by diffusion (9, 10).
We also found that serotonylation of proteins is increased in
the presence of a MAO inhibitor, which prevents degradation
of internalized 5-HT. These data indicate that serotonylation
of proteins is regulated by the activity of the 5-HTT, MAO,
and TGases. Whereas 5-HTT mediates uptake of 5-HT into
the cells, both MAO and TGase control 5-HTi metabolism of
The importance of protein serotonylation in the pulmonary
artery SMC-proliferative and migratory responses to 5-HT were
also investigated. Our findings, that inhibition of TGase blocked
these responses, support the concept that this enzymatic process
is key to the biologic activity of 5-HT in SMCs.
MS/MS peptide sequencing revealed that the major proteins
modified by serotonylation include nonmuscle myosin heavy
chain IIB (229 kD), plakin (195 kD), FN (257 kD), and filamin
B (278 kD). FN is known to participate in SMC proliferation
(34, 41). Immunoprecipitation techniques confirmed that FN
was specifically serotonylated by 5-HT. The finding that FN
siRNA blocked the proliferative effects of 5-HT on SMCs
provides additional support for a role of this protein in SMC
function. However, at the present time, it is not clear whether
other serotonylated proteins also participate in these mitogenic
effects. We demonstrated that serotonylated FN (Figure 5B)
(DMEM) and then incubated with 5-HT. (A) Cells were incubated for 5–60 minutes with 5-HT (1 mmol/L). (B) Cells were incubated with 5-HT (1–
(1,000 mmol/L) for 60 minutes. (C) Rat cells were incubated with 5-HT (0–10 mmol/L) for 60 minutes. After incubation, cell extracts were obtained,
electrophoresed, and subjected to immunoblotting, as noted in MATERIALS AND METHODS. Bar graphs represent means (6SD) (n 5 3). *Significant
difference from the untreated controls (P , 0.05).
5-HT–mediated protein serotonylation in SMCs. Bovine SMCs were washed with serum-free Dulbecco’s modified Eagle’s medium
Liu, Wei, Laskin, et al.: Serotonylation of Proteins in Pulmonary Artery Smooth Muscle Cells 551
and other proteins (data not shown) are present in cell culture
medium when SMCs are incubated with 5-HT. We therefore
suspected that serotonylated FNs may be released into medium
upon cellular interaction with 5-HT. This could be analogous to
the process by which it gains access to intercellular matrix and
interacts with a5b1-, aIIbb3-, a4b1-, and a4b7-integrins, leading
to differentiation, proliferation, migration, and apoptosis (37–
41). The intact FN molecule has four glutamine residue sites
sensitive to tissue TGases. The glutamine residues at positions 3
and 4 of the FN amino terminus have been identified as the
transglutamination sites for plasma and tissue TGase (42).
In the hypertensive pulmonary vessel wall, vascular SMCs
acquire a proliferative, synthetic phenotype, and migrate into
the subendothelium (43–45). It has been reported that increased
expression of FN not only contributes to the migration of
vascular SMCs, but also induces the transformation of these
Figure 4. Modulation of protein serotonylation in SMCs in culture by 5-HT transporter (5-HTT), monoamine oxidase (MAO), and TGase. Bovine
SMCs were washed with serum-free DMEM and then pretreated with (A) 5-HTT inhibitor, imipramine or fluoxetine (1,10 mmol/L) (B) MAO inhibitor,
phenelzine (50 mmol/L), or (C) TGase inhibitor, DSC (200 mmol/L) for 30 minutes. Protein serotonylation was then induced by 5-HT (1 mmol/L) for
30 minutes. Cells lysates underwent electrophoresis, and serotonylation was analyzed by Western blotting with anti–5-HT–BSA conjugate antibody.
Bar graphs represent means (6SD) for n 5 3. *Significant difference from the untreated controls (P , 0.05);#significant difference from 5-HT–
treated cells (P , 0.05).
in SMCs. Bovine SMCs were washed with serum-free
DMEM and incubated with 5-HT (1 mmol/L) for 1 hour.
(A) 5-HT–induced FN serotonylation was assessed by
immunoprecipitation (IP) of FN in whole-cell lysates,
followed by electrophoresis and immunoblotting (IB) with
anti–5-HT–BSA conjugate antibody. Total FN was mea-
sured with anti-FN antibody on the stripped membrane
(lower panel). (B) Release of FN into the medium. Medium
(4 ml) from control (2) and 5-HT–incubated (1) SMCs
was concentrated and desalted. FN in the concentrated
medium (50 ml) was assessed by Western blotting with
anti-FN antibody. Lower panel shows FN in the cell lysate.
5-HT–induced fibronectin (FN) serotonylation
552AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGY VOL 442011
cells into a proliferative phenotype (38, 46). Furthermore, FN
deposition in lung is highly correlated with the severity of
pulmonary hypertension in rodents with chronic hypoxia and in
patients with pulmonary hypertensive (24, 25). Recent studies
demonstrate that interactions between aIIbb3-integrin and 5-
HTT regulate 5-HT transport and platelet aggregation in mice
and humans, indicating cross-talk between 5-HTT signaling and
FN/integrin signaling (47).
Our studies provide evidence of crosslinking of cellular FN
and FN fragments in culture medium from 5-HT–treated SMCs.
FN crosslinking with other ECM components is a critical step in
ECM assembly, and numerous reports have demonstrated that
some FN fragments resulting from enzymatic degradation are
migration responses. Growth-arrested bovine SMCs were pretreated
with TGase inhibitor, DSC (200 mmol/L) for 30 minutes. (A) To test the
proliferation response, cells were stimulated with 5-HT (1 mmol/L) for
24 hours. Cell proliferation was analyzed by measuring [3H]-thymidine
incorporation (n 5 6). (B) Migration was assessed by a wound healing
test. Wounding was performed by scraping through the cell monolayer
with a sterile 1-ml pipette tip immediately after the addition of 5-HT
(10 mmol/L). At 20 hours after 5-HT treatment, cell migration images
were taken at four wound sites along the wounding scratch by Nikon
phase-contrast microscopy at 100-fold. Triplicate results were obtained
in three separate experiments, and a representative experiment is
shown. The scale bar shown on the photomicrographs 5 0.2 mm.
(C) Cell migration was further accessed by Boyden chamber assay.
Migrated cells on the bottom of the Transwell filter were stained with
crystal violet 20 hours after 5-HT treatment. *Significant difference from
control (P , 0.05);#significant difference from 5-HT alone (P , 0.05).
Role of TGase in 5-HT–induced SMC proliferation and
Figure 7. Silencing of cellular FN inhibits SMC-proliferative response to
5-HT. (A) Effects of FN siRNA on its protein expression and serotony-
lation. Bovine SMCs in 60-mm plates were transfected with FN siRNA
and control siRNA using lipofectamine 2,000 for 48 hours. Cells were
then treated with 5-HT (1 mmol/L) for 40 minutes. FN serotonylation
was evaluated by its immunoprecipitation. FN expression was analyzed
in total cell lysates by Western blot and normalized with expression of
tubulin on the stripped membrane. (B) Inhibition of 5-HT–induced
SMC proliferation by FN siRNA. SMCs transfected with FN siRNA and
control siRNA were growth arrested in serum-free medium for 72 hours
before treatment with 5-HT (1 mmol/L). Cell proliferation was moni-
tored by [3H]-thymidine incorporation for 24 hours. Data presented are
means (6SD) (n 5 3). *Significant difference from control (P , 0.05);
#significant difference from control siRNA 50 nM 1 5-HT (P , 0.05).
Liu, Wei, Laskin, et al.: Serotonylation of Proteins in Pulmonary Artery Smooth Muscle Cells553
potent inducers of cell migration (48, 49). Conformational
change of the FN molecule may expose certain hidden gluta-
mine residues important in the formation of covalent bonds
between FN and the e-amino group of a lysine residue in fibrin.
Serotonylated modification of FN may cause a conformational
change in the FN that subsequently triggers FN crosslinking
with ECM proteins, leading to SMC growth.
In summary, the present studies demonstrate that tissue
TGases use 5-HTi to modify substrate proteins (in particular,
FN) post-translationally, and that this is important in regulating
5-HT–induced proliferation and migration of pulmonary artery
SMCs. Furthermore, this action may play an important role in
the development of pulmonary hypertension.
Author Disclosure: Y.L. received a sponsored grant from the American Heart
Association for $10,001–$50,000; B.L.F. received a sponsored grant from the
National Institute of Health for more than $100,001; neither of the other authors
has a financial relationship with a commercial entity that has an interest in the
subject of this manuscript.
Acknowledgments: The authors thank Dr. H. Zheng and other members of the
Biological Mass Spectrometry Facility of University of Medicine and Dentistry of
New Jersey/Robert Wood Johnson Medical Center for tandem mass spectromet-
ric peptide sequencing analysis.
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Liu, Wei, Laskin, et al.: Serotonylation of Proteins in Pulmonary Artery Smooth Muscle Cells555