| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Tufts-New England Medical Center, Pulmonary, Critical Care and Sleep Division, Tupper Research Institute, Boston, Massachusetts, USA
1Correspondence: Pulmonary, Critical Care and Sleep Division, Tufts-New England Medical Center, 750 Washington St., #257, Boston, MA 02111, USA. E-mail: bfanburg{at}tufts-nemc.org
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Key Words: serotonin • pulmonary hypertension
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
, 2)
. This action requires both 5-HT uptake through a 5-HT active transport process via the 5-HT transporter (5-HTT) and binding of 5-HT to one or multiple 5-HT receptors (5-HTRs) (3
4
5)
. Cell receptors containing intrinsic tyrosine kinases (RTKs), such as platelet-derived growth factor receptor (PDGFR), are also present on the cell surface. It was originally thought that GPCRs and RTKs along with their downstream effectors were distinct and linear signaling pathways. However, more recent studies have shown that many agonists of GPCRs, including angiotensin II, endothelin-1, and thrombin, can activate RTKs in the absence of exogenously added growth factors (6
7
8)
. The process is referred to as transactivation of RTKs by GPCRs through autophosphorylation of the RTKs via intrinsic tyrosine kinase activity.
Some information is available regarding 5-HT in relation to this process. It has been reported that Ap Trk1, a Trk-like RTK, mediates ERK activation by 5-HT in sensory neurons (9)
. In a study with a stably transfected mouse fibroblast cell line, Nebigil et al. showed that 5-HT causes autoactivation of PDGFRß (10)
. Gooz et al. more recently reported that the 5-HT 2A receptor induces ERK phosphorylation and cellular proliferation of renal mesangial cells through Adam-17 tumor necrosis factor-converting enzyme activation (11)
. No previous study has examined transactivation of PDGFR by 5-HT in smooth muscle cells. This is important because 5-HT has been associated with pulmonary hypertension in humans (12
13
14
15
16)
, and patients with pulmonary artery hypertension have enhanced activation of PDGFRß in their lungs (17)
. Furthermore, activation of PRGFR has been demonstrated in lungs of experimental animal models of pulmonary hypertension (17
, 18)
. In the present study we show for the first time that PDGFRß of SMCs in culture is autophosphorylated by 5-HT and that both phosphorylation and 5-HT-induced SMC proliferation and migration are blocked by tyrosine kinase inhibition. Furthermore, activation of PDGFRß by 5-HT is dependent on the 5-HTT, but not 5-HT, receptors and the formation of reactive oxygen species. This is the first identification of the association of the 5-HTT with transactivation of PDGFRß.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Cell culture
SMCs from bovine pulmonary artery were isolated by a modification of the method of Ross, as described (3)
, and cultured in RPMI 1640 medium containing 10% FBS, 1% penicillin, and 0.5% streptomycin. Cells from passages 3 to 12 were used.
Incorporation of [3H]thymidine
SMCs seeded in 96-well plates were growth-arrested for 72 h in medium containing 0.1% FBS. Cells were incubated with and without 1 µmol/L 5-HT in the same medium for 20 h, then labeled with [methyl-3H]thymidine (20 µCi/ml) for 4 h. Where noted, inhibitors were added 30 min before the 5-HT. DMSO (0.1%) was added to the vehicle control group. After labeling, experiments were terminated by aspiration of medium and the cells were harvested onto 96-well microplate filter paper using a Tomtic harvester. Radioactivity was counted in a Trilux liquid scintillation and luminescence counter (Perkin Elmer Life Science, Boston, MA, USA).
Boyden chamber assay
Migration assays were performed using a standard modified Boyden chamber assay, which determines cellular migration through a porous membrane as described previously (2)
. Briefly, confluent PASMCs were starved with serum-free RPMI medium for 24 h, then trypsinized and washed in serum-free RPMI before plating onto a Transwell plate (12 mm Transwell with 12.0 µm pore polycarbonate membrane insert; Corning Incorporated Costar, Corning, NY, USA) at 2.5 x 104 cells/insert. Cells were then treated with 10 µM 5-HT with or without 30 min pretreatment with inhibitors. After 18
20 h of incubation, the media were removed and cells were fixed with 0.75 ml 100% methanol for 15 min, then stained in 0.75 ml 1.88% Crystal Violet (in 20% methanol) for 1 h. The dye was then rinsed in cold water and the top surface of the Transwell membrane was wiped with a cotton swab to remove cells remaining on the upper side of the membrane. Cells that had traversed the membrane were counted in bright-field microscopy at 160-fold magnification to calculate the average number of cells in five individual fields. Each experiment was performed at least three times, with a minimum of n = 4.
Wound healing assay
Cell migration was assessed in a wound healing assay as described by Lampugnani (19)
. Confluent PASMCs were starved with serum-free RPMI medium for 24 h, then preincubated with 10 µmol/L AG1296 or 1 µmol/L imatinib for 30 min before treatment with 10 µmol/L 5-HT. Wounds were made by scraping through the cell monolayer with a sterile 1 ml pipette tip. After overnight incubation at 37°C, cells were fixed with 4% formaldehyde, and phase contrast images at three sites along the wounding scratch were examined and photographed by Nikon phase contrast microscopy at 100-fold magnification.
Preparation of whole cell lysates
Treated SMCs were rinsed with ice-cold PBS, then incubated for 15 min at 4°C in RIPA lysis buffer. Lysates were centrifuged at 14,000 g for 10 min to collect supernatants.
Retrovirus infection
Human wild-type (WT) PDGFRß and kinase-inactive type PDGFRß K634R in a p-LXSN retroviral expression vector, gifts from Professor Vijaya Ramesh (Massachusetts General Hospital, Boston, MA, USA), were packaged in 293T cells using Lipofectamine 2000 (20)
. After 48 h culture of cells, virus-containing medium was obtained from the 293T cells and used to infect SMCs. For infections, SMCs in cell culture dishes were digested with trypsin plus EDTA solution, then 4 x 105 cells were suspended in 1 ml retrovirus-containing medium and plated in 60 mm dishes in the presence of 8 µg/ml polybrene. After 16 h, the infected cells were cultured in RPMI medium containing 10% FBS for a further 24 h before experimentation.
Immunoprecipitation assay
Immunoprecipitation experiments were performed by binding 5 µg of PDGFRß polyclonal antibody with 0.5 mg of whole cell lysate. Samples were rocked at 4°C overnight. Protein A Sepharose beads were then added and rocked at 4°C for 2 h. The precipitated immune complexes were washed with RIPA buffer three times and the reaction was terminated by the addition of 5 x Laemmli sample buffer. Samples were denatured at 95°C for 10 min and resolved by SDS-PAGE electrophoresis. Phophorylation of PDGFRß was analyzed by immunoblotting of immunoprecipitated PDGFRß product with p-tyrosine antibody (1:1000). Coimmunoprecipitation of the 5-HTT with PDGFRß was measured by immunoblotting of the immunoprecipated PDGFRß product with 5-HTT antibody (1:1000).
Western blot analysis
Site-specific phosphorylation of PDGFRß and total PDGFRß expression were analyzed using phospho-PDGFRß Tyr751 rabbit polyclonal antibody and PDGFRß polyclonal antibody, respectively. The immunoreactive band was bonded with horseradish peroxidase-conjugated secondary antibody and subsequently visualized using an ECLTM chemiluminescent Western blot detection kit (Pierce, Rockford, IL, USA). Quantification of bands was done by gel densitometry with UN-SCAN-IT gel automatic digitizing system software from Silk Scientific Inc (Orem, UT, USA) and protein phosphorylation was normalized for total protein band densitometry.
Modified tyrosine phosphatase assay
The oxidized protein tyrosine phosphatases (PTPases) were measured by alkylation utilizing a modified PTP assay (21)
. Eighty percent confluent SMCs were deprived of serum for 24 h and subsequently stimulated with 1 µmol/L 5-HT for 10 min. The cells were rinsed and lysed with 0.5 ml of degassed lysis buffer [25 mmol/L sodium acetate, pH 5.5, 1% Nonidet P-40, 150 mmol/L NaCl, 10% glycerol, leupeptin (10 µg/ml), and aprotinin (10 µg/ml)] containing 10 mmol/L iodoacetic acid. Cell lysates were collected in a brown centrifuge tube that was placed on a mixer and shaken for 30 min for the alkylation of the active site Cys in the PTPase. After 30 min at room temperature in the dark, the labeling reaction was quenched by adding 0.1 ml of 200 mmol/L cold iodoacetic acid in 0.8 mol/L Tris-HCl (pH 7.5), followed by the addition of 0.05 ml of 1 mol/L DTT to recover the oxidized Cys to active Cys of PTPase. The reaction mixtures were then centrifuged at 10,000 g for 20 min. The PTPase activity was measured in a 96-well plate coated with poly(Glu4-pTyr) peptides according to the manufacturer's protocol (Universal Tyrosine Phosphatase Assay Kit, Takara Bio, Japan). The oxidization levels of PTPases were recorded by measuring the relative fold increase of liberated phosphate.
Infusion of 5-HT in mice
Groups of 12-wk-old mice (C57/B16, Charles River, Wilmington, MA, USA) were anesthetized with intraperitoneal ketamine (100 mg/kg) and xylazine (10 mg/kg). Miniosmotic infusion pumps (Alzet, Palo Alto, CA, USA, Model 2001) containing 200 µl saline or 20 mmol/L 5-HT-HCl (Sigma) were implanted subcutaneously between the scapulae. 5-HT was administered continuously with an infusion rate of 0.97 µl/h for 48 and 96 h. Animals were maintained in room air and sacrificed at 48 and 96 h for recovery of lungs. Lungs were frozen and later homogenized in lysis buffer (50 mmol/L Tris pH7.5, 1% Triton, 150 mmol/L NaCl, 5 mmol/L MgCl2, 10% glycerol, 10 µg/ml aprotinin, 10 µg/ml leupeptin, 25 mmol/L sodium orthovanadate, and 10 µmol/L PMSF). The protein contents of lysates were measured and adjusted to the same concentration in each sample with lysis buffer. The lysates were denatured at 95°C for 10 min and resolved by SDS-PAGE electrophoresis. Phophorylation of PDGFRß was analyzed by immunoblotting with p-PDGFRß (Tyr751) antibody (1:1000). The membrane was stripped and reblotted with anti-PDGFRß and anti-actin antibodies for normalization.
Statistical analysis
Means ± SD were calculated and statistically significant differences between groups were determined by 1-way ANOVA, followed by Tukey's post hoc comparisons. An effect was considered significant when P < 0.05.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
, 1 µmol/L 5-HT induced PDGFRß tyrosine phosphorylation, with peak activation at 15 min; the level of PDGFRß protein remained unchanged. 5-HT-activated PDGFRß phosphorylation was blocked completely by the PDGFR tyrosine kinase inhibitor, imatinib, at 1 µmol/L (Fig. 2
A). Similarly, PDGF-activated PDGFRß was blocked by imatinib. AG1296, another PDGFR tyrosine kinase inhibitor, also blocked PDGFRß activation by 5-HT (Fig. 2B
). SMCs overexpressing the kinase mutant PDGFRß (K634R) showed diminution of PDGFRß phosphorylation by both 5-HT and PDGF-BB (Fig. 2C
), while overexpression of wild-type PDGFRß exhibited stimulation of PDGFRß tyrosine phosphorylation above that of noninfected SMCs. These results show that 5-HT, like PDGF, transactivates PDGFRß in pulmonary artery smooth muscle cells.
|
|
PDGFRß is transactivated by 5-HT through the 5-HTT
To determine whether a specific 5-HT receptor subtype was responsible for the PDGFRß transactivation by 5-HT, cells were pretreated with 5-HT 1B/1D receptor antagonist GR55562 or 5-HT2 receptor antagonist ketanserin before stimulation by 5-HT. As shown in Fig. 3
A, neither GR55562 nor ketanserin blocked the 5-HT-induced PDGFRß phosphorylation. This finding implies that 5-HT transactivates PDGFRß independently of 5-HT1B/1D and 2 receptors. Our previous studies have demonstrated that 5-HT-activated mitogenic signaling requires both 5-HT uptake through a 5-HT active transport process via the 5-HTT and binding of 5-HT to one or multiple 5-HT receptors (5-HTRs) (3
4
5)
. We therefore investigated the influence of 5-HTT on PDGFRß transactivation using a variety of 5-HT uptake inhibitors. Pretreatment with 5-HTT inhibitors imipramine (10 µmol/L), fluoxetine (10 µmol/L), or paroxetine (10 µmol/L) all significantly inhibited 5-HT-induced PDGFRß tyrosine phosphorylation (Fig. 3B
). 5-HT active transport is associated with the Na+/K+ APTase pump (22)
. Therefore, we accessed the influence of inhibition of Na+/K+-ATPase activity on 5-HT-activated PDGFRß phosphorylation. Inhibition of Na+/K+-ATPase by ouabain also blocked the transactivation of PDGFRß (Fig. 4
).
|
|
We further examined whether 5-HTT interacts with the PDGFRß. Coimmunoprecipitation experiments showed that, upon 5-HT stimulation, 5-HTT is recruited to PDGFRß with a kinetic profile similar to that of 5-HT-induced PDGFRß tyrosine phosphorylation (Fig. 5
A). Of note, inhibition of 5-HTT activity by fluoxetine markedly reduced the association between 5-HTT and PDGFRß (Fig. 5B
).
|
Generation of reactive oxygen species (ROS) is necessary for PDGFRß transactivation by 5-HT
We previously reported that 5-HT acting through the 5-HTT stimulates NADPH oxidase to generate ROS in bovine PASMCs (23
, 24)
. To determine the influence of ROS generation on PDGFRß transactivation, we assessed the phosphorylation of PDGFRß induced by 5-HT after pretreatment of SMCs with the ROS scavenger N-acetylcysteine (NAC) and the NADPH oxidase inhibitor, diphenyliodonium (DPI). As shown in Fig. 6
A, NAC and DPI significantly reduced 5-HT-induced phosphorylation of PDGFRß. We further investigated the action of exogenous H2O2 on phosphorylation of PDGFRß. As shown in Fig. 6B
, 1 mmol/L H2O2 produced a 6-fold increase in the phosphorylation of PDGFRß. ROS have been reported to transiently oxidize the catalytic cysteine of tyrosine phosphatases (PTPases) to inhibit their activity and thereby enhance protein phosphorylation (25)
. We further examined the effect of 5-HT on oxidized inactivation of PTPase in our SMCs. As shown in Fig. 6C
, stimulation of oxidation of PTPase occurred after 10 min of 5-HT treatment. Taken together, these results indicate that 5-HT-stimulated production of ROS serves as an intermediate in the transactivation of PDGFRß by 5-HT, and the effect could occur through inhibition of PTPase activity by its oxidation.
|
5-HT-induced transactivation of PDGFRß participates in SMC proliferation and migration induced by 5-HT
The PDGFR kinase inhibitor imatinib, at a concentration that completely inhibits PDGFRß phosphorylation (1 µM), blocked 5-HT-induced thymidine incorporation in our SMCs (Fig. 7
A). Similar data were obtained when the SMCs were pretreated with another PDGFR kinase inhibitor, AG1296 (Fig. 7B
). We also tested the influence of PDGFR kinase inhibitors on cell migration induced by 5-HT. We have used two approaches to study the migration of SMCs, one a qualitative wound healing assay and the other a quantitative Boyden chamber assay. As shown in Fig. 7C
, stimulation of cells with 10 µmol/L 5-HT for 20 h caused enhanced cell migration by both the wound healing image and the Boyden chamber assay. Pretreatment of cells with 1 µmol/L imatinib completely blocked the 5-HT-stimulated cell migration. These data support the participation of 5-HT-transactivated PDGFRß in SMC proliferation and migration induced by 5-HT.
|
In vivo activation of PDGFRß in lungs of mice infused with 5-HT
We next examined whether 5-HT is able to activate PDGFRß in vivo in lungs of mice infused with 5-HT. For these experiments we administered 5-HT by miniosmotic infusion pumps installed subcutaneously in mice. In experimental animals, 19.7 nmol/h of 5-HT·HCl was delivered for 2 and 4 days. PDGFRß expression and phosphorylation were examined by Western blot analysis in the homogenates of lung tissue. As shown in Fig. 8
, lungs of animals infused with 5-HT for both 48 and 96 h exhibited twice the level of PDGFRß phosphorylation obtained from saline-infused control animals, as measured by site-specific phosphorylation of PDGFRß. The short-term 5-HT treatment did not change PDGFRß protein expression. The data show that a PDGFRß signal can be induced by 5-HT in animal lungs in vivo and is consistent with previous reports of activation of PDGFRß in experimentally induced pulmonary hypertension in rodents and in pulmonary artery hypertension in humans (17)
.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
, 5-HTT actively transports 5-HT molecules across the membrane with conformational changes. We previously demonstrated that 5-HTT is actively accompanied by the formation of ROS via NADPH oxidase (23
, 24
, 27
, 28)
. The 5-HTT and 5-HTRs have been cloned (1)
as separate molecules. The reason for the redundancy of these 5-HT-related molecules on the cell surface is not known, but we previously suggested that they may have combinatorial actions in cell signaling (4
, 5)
. The 5-HTT has never been assessed for its possible function as a GPCR; like PDGFRs, however, it binds 5-HT.
Our studies clearly demonstrate the ability of the 5-HTT to transactivate PDGFRß. First, we found that the transactivation is blocked by three recognized inhibitors of 5-HTT, but not by inhibition of 5-HT 1B and 2 receptors. Furthermore, tyrosine kinase-catalyzed autoactivation of PDGFRß by 5-HT is blocked by ouabain, a known inhibitor of Na+/K+ATPase that participates in the active transport of 5-HT by the 5-HTT (22
, 29)
. Second, immunoprecipitation experiments demonstrated that the PDGFRß binds the 5-HTT and inhibition of 5-HTT activity inhibits the binding. Unlike the phosphorylation of 5-HTT occurring with sequestration of the 5-HTT (30)
, where protein kinase C (PKC) -mediated phosphorylation of 5-HTT at serine and threonine residues occurs, there was no evidence of phosphorylation of the 5-HTT at tyrosine residues in the interaction occurring in our experiments (data not shown). This implies that PDGFRß kinase does not modify the 5-HTT protein within the complex, but the interaction between PDGFRß and 5-HTT may require an active conformation change of 5-HTT since inhibition of 5-HTT activation with fluoxetine reduces the binding. The precise nature of the binding of the 5-HTT to the PDGFRß needs further study.
Specific mechanisms involved in the transactivation of RTKs by GPCRs in general have been avidly explored. Several possible mechanisms have been proposed (31
32
33)
. One mechanism involves the GPCR-triggered recruitment of RTKs in a complex with cytoplasmic tyrosine kinases (for example, Src and Pyk), with subsequent activation of the RTK (32)
. Choudhury et al. reported that c-Src couples PI 3 kinase/Akt and MAPK signaling to PDGF-induced DNA signaling in mesangial cells (33)
. From studies with embryonic fibroblasts from peroxiredoxin-deficient mice, Choi et al. concluded that endogenous cellular H2O2 mediates PDGFRß phosphorylation and that this is regulated by peroxiredoxin II (25)
. Chen et al. showed that H2O2 generated from mitochondrial function participates in transactivation of epidermal growth factor (34)
.
We have found that inhibition of NADPH oxidase with DPI or the use of an antioxidant (NAC) blocks the transactivation of PDGFRß by 5-HT. Similarly, exposure of SMCs to H2O2 stimulates the phosphorylation of PDGFRß. From these studies we conclude that active transport of 5-HT intracellularly activates PDGFRß through concurrent formation of ROS. These findings are consistent with our previous studies showing generation of ROS through activation of the 5-HTT in these cells (23
, 24)
. It has also been reported that oxidant stress itself stimulates active transport of 5-HT by platelets, further linking the 5-HTT to ROS generation (35)
.
Our data show that 5-HT stimulates oxidation of protein tyrosine phosphatase (PTPase). PTPases, which negatively control RTK activity, are very sensitive to oxidation and are transiently inactivated by oxidation with hydrogen peroxide. In turn, RTK signaling is activated (36)
. Thus, formation of ROS by the cells through NADPH oxidase activation may inhibit tyrosine phosphatase as a mechanistic explanation of enhanced tyrosine autophosphorylation of PDGFRß. A similar mechanism was proposed by Rhee et al. for various other activated tyrosine phosphorylations that occur by oxidation of intermediates generated in cell signaling (25)
.
Imatinib and AG 1296 are known inhibitors of PDGFR kinase that participates in autophosphorylation and activation of PDGFR (37)
. In the present study, these inhibitors blocked activation of PDGFRß by 5-HT in the SMCs. They also blocked 5-HT-induced stimulation of SMC proliferation and migration. Since imatinib also blocks other tyrosine kinases such as those of c-KIT and c-Abl (38)
, it is possible that the effects of imatinib on SMC proliferation and migration may not be related specifically to their effects on PDGFR tyrosine kinase. Thus, we also approached this problem using cells infected with the PDGFRß mutant, K 634R, to further explore the action of 5-HT on SMC proliferation. However, we were unable to block stimulation of SMC proliferation of cells infected with this mutant (unpublished data) despite its inhibition of PDGFRß phosphorylation by 70%. There are several explanations for this observation of the PDGFRß mutant's failure to block SMC proliferation. It is known that a large percent of receptor sites must be blocked to inhibit PDGF-induced cellular proliferation, and it is possible that the PDGFR
isoform also participates in the signaling. We assume we were unable to block sufficient receptor sites and did not influence the receptor portion of the PDGFR with the use of the infected PDGFRß mutant. Imatinib and AG 1296, on the other hand, produced a total block of the PDGFR phosphorylation that resulted in inhibition of 5-HT-induced SMC proliferation and migration.
Finally, our demonstration of activation of PDGFRß in mouse lung in vivo with 5-HT infusions complements our in vitro signaling studies. Here we found that PDGFRß phosphorylation was enhanced within 48–96 h infusion of 5-HT. This is important as it has been shown that PDGFRß activation participates in monocrotaline- and hypoxia-induced pulmonary hypertension in rodents, which is blocked by the administration of imatinib (17)
. Similarly, PDGFRß activation occurs in pulmonary hypertension induced in calves by ligation of the ductus arteriosus (18)
. PDGFRß has also been found to be activated in pulmonary hypertension in humans (17)
. Other studies have supported the induction of pulmonary hypertension in mice with administration of 5-HT under specific conditions (39)
. Thus, to the extent that 5-HT participates in pulmonary hypertension in both clinical and experimental conditions, transactivation of PDGFRß by the 5-HTT may be an important component of the hypertensive process.
|
ACKNOWLEDGMENTS |
|---|
Received for publication January 3, 2007. Accepted for publication April 5, 2007.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  H. Lei, G. Velez, P. Hovland, T. Hirose, D. Gilbertson, and A. Kazlauskas Growth Factors Outside the PDGF Family Drive Experimental PVR Invest. Ophthalmol. Vis. Sci., July 1, 2009; 50(7): 3394 - 3403. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y. Liu, W. Ren, R. Warburton, D. Toksoz, and B. L. Fanburg Serotonin induces Rho/ROCK-dependent activation of Smads 1/5/8 in pulmonary artery smooth muscle cells FASEB J, July 1, 2009; 23(7): 2299 - 2306. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Lei and A. Kazlauskas Growth Factors Outside of the Platelet-derived Growth Factor (PDGF) Family Employ Reactive Oxygen Species/Src Family Kinases to Activate PDGF Receptor {alpha} and Thereby Promote Proliferation and Survival of Cells J. Biol. Chem., March 6, 2009; 284(10): 6329 - 6336. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y. Liu and B. L. Fanburg Phospholipase D signaling in serotonin-induced mitogenesis of pulmonary artery smooth muscle cells Am J Physiol Lung Cell Mol Physiol, September 1, 2008; 295(3): L471 - L478. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. L. Zaiman, M. Podowski, S. Medicherla, K. Gordy, F. Xu, L. Zhen, L. A. Shimoda, E. Neptune, L. Higgins, A. Murphy, et al. Role of the TGF-{beta}/Alk5 Signaling Pathway in Monocrotaline-induced Pulmonary Hypertension Am. J. Respir. Crit. Care Med., April 15, 2008; 177(8): 896 - 905. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
