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At least 109 records · Page 6Linked to original sources
PubMed2003

Inhibition of cell survival signal protein kinase B/Akt by curcumin in human prostate cancer cells.

Although curcumin has been shown to inhibit prostate tumor growth in animal models, its mechanism of action is not clear. To better understand the anti-cancer effects of curcumin, we investigated the effects of curcumin on cell survival factor Akt in human prostate cancer cell lines, LNCaP, PC-3, and DU-145. Our results demonstrated differential activation of Akt. Akt was constitutively activated in LNCaP and PC-3 cells. Curcumin inhibited completely Akt activation in both LNCaP and PC-3 cells. The presence of 10% serum decreased the inhibitory effect of curcumin in PC-3 cells whereas complete inhibition was observed in 0.5% serum. Very little or no activation of Akt was observed in serum starved DU-145 cells (0.5% serum). The presence of 10% serum activated Akt in DU-145 cells and was not inhibited by curcumin. Results suggest that one of the mechanisms of curcumin inhibition of prostate cancer may be via inhibition of Akt. To our knowledge this is the first report on the curcumin inhibition of Akt activation in LNCaP and PC-3 but not in DU-145 cells.

Antineoplastic Agents↗
PubMed2004

Platelet-derived growth factor-BB phosphorylates heat shock protein 27 in cardiac myocytes.

It is recognized that heat shock protein 27 (HSP27) is highly expressed in heart. In the present study, we investigated whether platelet-derived growth factor (PDGF) phosphorylates HSP27 in mouse myocytes, and the mechanism underlying the HSP27 phosphorylation. Administration of PDGF-BB induced the phosphorylation of HSP27 at Ser-15 and -85 in mouse cardiac muscle in vivo. In primary cultured myocytes, PDGF-BB time dependently phosphorylated HSP27 at Ser-15 and -85. PDGF-BB stimulated the phosphorylation of p44/p42 mitogen-activated protein (MAP) kinase, p38 MAP kinase, and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) among the MAP kinase superfamily. SB203580, a specific inhibitor of p38 MAP kinase, reduced the PDGF-BB-stimulated phosphorylation of HSP27 at both Ser-15 and -85, and phosphorylation of p38 MAP kinase. However, PD98059, a specific inhibitor of MEK, or SP600125, a specific inhibitor of SAPK/JNK, failed to affect the HSP27 phosphorylation. These results strongly suggest that PDGF-BB phosphorylates HSP27 at Ser-15 and -85 via p38 MAP kinase in cardiac myocytes.

Animals↗
PubMed2004

Angiopoietin 1, PDGF-B, and TGF-beta gene regulation in endothelial cell and smooth muscle cell interaction.

The vascular wall is mainly composed of endothelial cells (ECs) and smooth muscle cells (SMCs). The crosstalking between these two cell types is critical in the vascular maturation process. Genetic studies suggest that the Tie2/angiopoietin 1 (Ang1) pathway regulates vascular remodeling. However, the molecular mechanism is unclear. PDGF is a potent chemoattractant for SMCs, and TGF-beta regulates SMC differentiation. Here, we examined gene regulation. PDGF-B stimulation upregulated Ang1 expression in SMCs through the PI3K and PKC pathways. PDGF-B stimulation also produced an acute induction of TGF-beta expression in SMCs through the MAPK/ERK pathway. Interestingly, TGF-beta negatively regulated Ang1 expression induced by the PDGF-B stimulation in SMCs. Reciprocally, we observed that stimulation of ECs with either Ang1 or TGF-beta slightly downregulated PDGF expression. A combination of both TGF-beta with Ang1 produced much stronger downregulation of PDGF. Our data showed complex gene regulations that include both positive and negative regulations between ECs and SMCs to maintain vascular homeostasis.

Angiopoietin-1↗
PubMed2004

Differential regulation of platelet-derived growth factor stimulated migration and proliferation in osteoblastic cells.

Osteoblastic migration and proliferation in response to growth factors are essential for skeletal development, bone remodeling, and fracture repair, as well as pathologic processes, such as metastasis. We studied migration in response to platelet-derived growth factor (PDGF, 10 ng/ml) in a wounding model. PDGF stimulated a twofold increase in migration of osteoblastic MC3T3-E1 cells and murine calvarial osteoblasts over 24-48 h. PDGF also stimulated a tenfold increase in 3H-thymidine (3H-TdR) incorporation in MC3T3-E1 cells. Migration and DNA replication, as measured by BrdU incorporation, could be stimulated in the same cell. Blocking DNA replication with aphidicolin did not reduce the distance migrated. To examine the role of mitogen-activated protein (MAP) kinases in migration and proliferation, we used specific inhibitors of p38 MAP kinase, extracellular signal regulated kinase (ERK), and c-Jun N-terminal kinase (JNK). For these signaling studies, proliferation was measured by carboxyfluorescein diacetate succinimidyl ester (CFSE) using flow cytometry. Inhibition of the p38 MAP kinase pathway by SB203580 and SB202190 blocked PDGF-stimulated migration but had no effect on proliferation. Inhibition of the ERK pathway by PD98059 and U0126 inhibited proliferation but did not inhibit migration. Inhibition of JNK activity by SP600125 inhibited both migration and proliferation. Hence, the stimulation of migration and proliferation by PDGF occurred by both overlapping and independent pathways. The JNK pathway was involved in both migration and proliferation, whereas the p38 pathway was predominantly involved in migration and the ERK pathway predominantly involved in proliferation.

Animals↗
PubMed2004

Effects of low density lipoprotein receptor-related protein-1 on the expression of platelet-derived growth factor beta-receptor in vitro.

The low density lipoprotein receptor related protein-1 (LRP-1) is a cargo transport receptor that undergoes constitutive endocytosis and recycling. Platelet-derived growth factor-BB (PDGF-BB) binds to LRP-1 and may bridge LRP-1 to PDGF receptors. Bridging of LRP-1 to other receptors by bifunctional ligands may represent a general mechanism whereby LRP-1 facilitates internalization of membrane proteins. The goal of this study was to determine whether LRP-1 regulates cell-surface levels of PDGF beta-receptor or PDGF beta-receptor degradation following treatment with PDGF-BB. Unexpectedly, in both murine embryonic fibroblasts (MEFs) and HT 1080 fibrosarcoma cells, LRP-1 expression was associated with increased levels of PDGF beta-receptor. In MEFs, the mechanism involved increased PDGF beta-receptor transcription and/or RNA stabilization. LRP-1 expression was not associated with increased levels of PDGF beta-receptor in Chinese hamster ovary (CHO) cells, suggesting that cell context is important. The kinetics of PDGF beta-receptor phosphorylation, in response to PDGF-BB, and the extent of degradation of PDGF beta-receptor were equivalent in LRP-1-expressing and -deficient MEFs. We conclude that PDGF beta-receptor expression and cell surface levels may be regulated by LRP-1; however, this activity is cell type-specific. LRP-1 does not directly regulate PDGF beta-receptor phosphorylation or degradation in PDGF-BB-treated cells.

Animals↗
PubMed2005

Role of c-Jun N-terminal kinase in the PDGF-induced proliferation and migration of human adipose tissue-derived mesenchymal stem cells.

Platelet-derived growth factor (PDGF) is a critical regulator of proliferation and migration for mesenchymal type cells. In this study, we examined the role of mitogen-activated protein (MAP) kinases in the PDGF-BB-induced proliferation and migration of human adipose tissue-derived mesenchymal stem cells (hATSCs). The PDGF-induced proliferation was prevented by a pretreatment with the c-Jun N-terminal kinase (JNK) inhibitor, SP600125. However, it was not prevented by a pretreatment with a p38 MAP kinase inhibitor, SB202190, and a specific inhibitor of the upstream kinase of extracellular signal-regulated kinase (ERK1/2), U0126. Treatment with PDGF induced the activation of JNK and ERK in hATSCs, and pretreatment with SP600125 specifically inhibited the PDGF-induced activation of JNK. Treatment with PDGF induced the cell cycle transition from the G0/G1 phase to the S phase, the elevated expression of cyclin D1, and the phosphorylation of Rb, which were prevented by a pretreatment with SP600125. In addition, the PDGF-induced migration of hATSCs was completely blocked by a pretreatment with SP600125, but not with U0126 and SB202190. These results suggest that JNK protein kinase plays a key role in the PDGF-induced proliferation and migration of mesenchymal stem cells.

Adipose Tissue↗
PubMed2005

PDGF-BB induces vascular smooth muscle cell expression of high molecular weight FGF-2, which accumulates in the nucleus.

Basic fibroblast growth factor (FGF-2) and platelet-derived growth factor (PDGF) are implicated in vascular remodeling secondary to injury. Both growth factors control vascular endothelial and smooth muscle cell proliferation, migration, and survival through overlapping intracellular signaling pathways. In vascular smooth muscle cells PDGF-BB induces FGF-2 expression. However, the effect of PDGF on the different forms of FGF-2 has not been elucidated. Here, we report that treatment of vascular aortic smooth muscle cells with PDGF-BB rapidly induces expression of 20.5 and 21 kDa, high molecular weight (HMW) FGF-2 that accumulates in the nucleus and nucleolus. Conversely, PDGF treatment has little or no effect on 18 kDa, low-molecular weight FGF-2 expression. PDGF-BB-induced upregulation of HMW FGF-2 expression is controlled by sustained activation of extracellular signal-regulated kinase (ERK)-1/2 and is abolished by actinomycin D. These data describe a novel interaction between PDGF-BB and FGF-2, and indicate that the nuclear forms of FGF-2 may mediate the effect of PDGF activity on vascular smooth muscle cells.

Animals↗
PubMed2005

Nicotinic and PDGF-receptor function are essential for nicotine-stimulated mitogenesis in human vascular smooth muscle cells.

Cigarette smoking is implicated in the formation of occlusive vascular diseases. Nicotine's role in this process is incompletely understood. Nicotine's effect on human aortic vascular smooth muscle cells (HaVSMC) and the role of the nicotinic receptor (nAChR), platelet-derived growth factor (PDGF), and the PDGF-receptor (PDGF-R) in this response were studied. Nicotine's mitogenic effect was characterized by three methods: thymidine incorporation, a viability/proliferation assay based on metabolic conversion of tetrazolium salt to formazan dye and cell counting. Nicotine administration (10(-6) M) stimulated cell cycle entry marked by increased DNA synthesis, PCNA and cyclin D1 production, and increased cell division. Nicotinic receptor blockade with d-tubocurarine, a nicotinic AchR blocker, decreased nicotine-induced DNA synthesis, and cell division (0.33 +/- 0.04, 0.77 +/- 0.31-fold decrease, respectively). Nicotine increased cellular PDGF-BB transcript levels and protein release (ELISA: 1.6 +/- 0.5-fold increase) but not PDGF-AA or PDGF-AB release. Nicotine increased PDGFbeta-receptor protein content. PDGF inactivation with anti-PDGF antibody abolished nicotine-induced DNA synthesis (1.9 +/- 0.08-fold decrease). PDGF-R blockade with the PDGF-R antagonist tyrphostin AG 1295 decreased nicotine-induced DNA synthesis and cell division (0.25 +/- 0.01, 0.44 +/- 0.2-fold decrease, respectively). PDGF-R blockade reversed nicotine-stimulated increases in PDGF release, PDGF-BB transcripts, and PDGF-receptor levels (0.68 +/- 0.34; 0.46 +/- 0.01; 0.28 +/- 0.01-fold decrease, respectively). In conclusion, nicotine-mediated activation of nAChRs increases PDGF-BB transcription and protein production as well as PDGF beta-receptor levels. PDGF-BB/PDGF-R interaction is vital in nicotine's mitogenic actions on human aortic smooth muscle cells.

Adult↗
PubMed2005

The low-density lipoprotein receptor-related protein-1 associates transiently with lipid rafts.

The low-density lipoprotein receptor-related protein-1 (LRP-1) is a multifunctional receptor that undergoes constitutive endocytosis and recycling. To identify LRP-1 in lipid rafts, we biotin-labeled cells using a membrane-impermeable reagent and prepared Triton X-100 fractions. Raft-associated proteins were identified in streptavidin affinity-precipitates of the Triton X-100-insoluble fraction. PDGF beta-receptor was identified exclusively in lipid rafts, whereas transferrin receptor was excluded. LRP-1 distributed partially into rafts in murine embryonic fibroblasts (MEFs) and HT 1080 cells, but not in smooth muscle cells and CHO cells. LRP-1 partitioning into rafts was not altered by ligands, including alpha2-macroglobulin, platelet-derived growth factor-BB, and receptor-associated protein (RAP). To examine LRP-1 trafficking between membrane microdomains, we developed a novel method based on biotinylation and detergent fractionation. Association of LRP-1 with rafts was transient; by 15 min, nearly all of the LRP-1 that was initially raft-associated exited this compartment. LRP-1 in the Triton X-100-soluble fraction, which excludes lipid rafts, demonstrated complex kinetics, with phases reflecting import from rafts, endocytosis, and recycling. Potassium depletion blocked LRP-1 endocytosis but did not inhibit trafficking of LRP-1 from rafts into detergent-soluble microdomains. Our data support a model in which LRP-1 transiently associates with rafts but does not form a stable pool. Fluid movement of LRP-1 between microdomains may facilitate its function in promoting the endocytosis of other plasma membrane proteins, such as the urokinase receptor, which localizes in lipid rafts.

Animals↗
PubMed2006

Phosphatidylinositol 3-kinase/Akt auto-regulates PDGF-BB-stimulated interleukin-6 synthesis in osteoblasts.

It has been reported that platelet-derived growth factor (PDGF)-BB stimulates the synthesis of interleukin (IL)-6 in osteoblasts. In the present study, we investigated whether the phosphatidylinositol 3-kinase (PI3K)/Akt is involved in the PDGF-BB-induced IL-6 synthesis in osteoblast-like MC3T3-E1 cells. PDGF-BB markedly induced the phosphorylation of Akt and GSK-3beta. Akt inhibitor, 1L-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate, significantly amplified the synthesis of IL-6 by PDGF-BB. The PDGF-BB-induced GSK-3beta phosphorylation was suppressed by the Akt inhibitor. The IL-6 synthesis stimulated by PDGF-BB was markedly enhanced by LY294002 and wortmannin, inhibitors of PI3K. Wortmannin and LY294002 suppressed the PDGF-BB-induced phosphorylation of Akt and GSK-3beta. Taken together, these results strongly suggest that PI3K/Akt negatively regulates the PDGF-BB-stimulated IL-6 synthesis in osteoblasts.

3T3 Cells↗
PubMed2002

p38 MAP kinase mediates platelet-derived growth factor-stimulated migration of hepatic myofibroblasts.

Although the migration of hepatic myofibroblasts (HMFs) contributes to the development of fibrosis, the signals regulating migration of these cells are poorly understood. In this study, we tested the hypothesis that HMF migration is stimulated by platelet-derived growth factor-BB (PDGF-BB) through p38 mitogen-activated protein (MAP) kinase and extracellular signal-regulated kinase (ERK) signaling pathways. This hypothesis was addressed by directly visualizing the migration of cultured human HMFs into a wound. PDGF-BB stimulated membrane ruffling, migration, and proliferation. PDGF-BB also induced activation of p38 MAP kinase, its downstream effector, heat shock protein (HSP) 27, ERK 1 and ERK 2, and p125 focal adhesion kinase (FAK). Selective antagonism of p38 MAP kinase blocked PDGF-BB-stimulated HSP 27 phosphorylation, membrane ruffling, and migration, but did not alter PDGF-BB-induced proliferation. Selective antagonism of ERK kinase inhibited PDGF-BB-induced ERK phosphorylation and proliferation, but did not affect PDGF-BB-stimulated migration. Concentrations of PDGF-BB that stimulated migration and proliferation did not influence myosin-dependent contractility. Neither selective inhibition of p38 MAP kinase nor ERKs altered PDGF-BB-induced activation of FAK. In conclusion, these results provide novel evidence indicating that (1) HMF migration is stimulated by PDGF-BB through the regulation of membrane ruffling by a p38 MAP kinase signaling pathway, (2) whereas p38 MAP kinase mediates PDGF-BB-stimulated migration, but not proliferation, ERKs mediate PDGF-induced proliferation, but not migration, and (3) increases in myosin-dependent contractility are not required for PDGF-BB-stimulated migration.

Becaplermin↗
PubMed1992

Regulation of vascular smooth muscle cell integrin expression by transforming growth factor beta1 and by platelet-derived growth factor-BB.

We have examined the ability of transforming growth factor-beta 1 (TGF-beta 1) and platelet-derived growth factor-BB (PDGF-BB) to regulate the expression of various integrins in cultured rabbit vascular smooth muscle cells (SMC). We found that expression of the alpha v beta 3 integrin complex was induced by both growth factors, although TGF-beta 1 appeared to be the more potent inducer. mRNA level of the beta 3 integrin subunit was undetectable in quiescent cells and enhanced by both growth factors, while the alpha v integrin subunit mRNA level did not change with growth factor addition. Therefore, appearance of the alpha v beta 3 integrin protein complex after growth factor stimulation was due to increased expression of the beta 3 integrin subunit mRNA. The TGF-beta 1 induced increase in beta 3 integrin mRNA was delayed, but did not require prior protein synthesis, since cycloheximide was unable to block the increase in beta 3 mRNA level. By contrast, PDGF-BB induced a more rapid increase in beta 3 integrin mRNA level that peaked by 6 h after growth factor addition and no detectable beta 3 integrin mRNA remained after 24 h. Interestingly, the PDGF-BB induced elevation of beta 3 integrin, although more rapid, was completely inhibited by cycloheximide. Expression of the alpha 5 integrin subunit in response to growth factors was very similar to beta 3. However, in contrast to beta 3 and alpha 5, neither TGF-beta 1 nor PDGF-BB were able to alter the expression of the beta 1 integrin subunit in vascular SMC. However, in TGF-beta 1 treated cells, there was a large increase in expression of a 190 kDa polypeptide that was associated with the beta 1 integrin subunit. This 190 kDa polypeptide was not detected in PDGF treated SMC or in TGF-beta 1 treated fibroblasts. The alpha 1 integrin subunit has a MW of approximately 190 kDa and is capable of complexing with beta 1. Analysis of the alpha 1 integrin subunit mRNA level indicated that it was indeed induced by TGF-beta 1, but not by PDGF-BB, suggesting that the 190 kDa polypeptide may be the alpha 1 integrin subunit. These results indicate that TGF-beta 1 and PDGF-BB are potent but distinct activators of integrin expression in vascular SMC.

Animals↗
PubMed1993

Transforming growth factor-beta, basic fibroblast growth factor, and platelet-derived growth factor-BB interact to affect proliferation of clonally derived porcine satellite cells.

Transforming growth factor beta-1 (TGF-beta) stimulated porcine satellite cell proliferation in basal serum-free medium by 25%, but inhibited growth in serum-containing medium by 58%. The effect of TGF-beta on cell proliferation in serum-free medium was examined in combination with the following human recombinant growth factors: platelet-derived growth factor-BB (PDGF), basic fibroblast growth factor (FGF), insulin-like growth factor I (IGF-I), and epidermal growth factor (EGF). TGF-beta inhibited PDGF-stimulated proliferation, enhanced FGF-stimulated proliferation, and had no effect on proliferation stimulated by IGF-I. The response of satellite cells to EGF and TGF-beta in serum-free medium was not different than TGF-beta alone. TGF-beta depressed proliferation stimulated by the following combinations of two growth factors: PDGF and IGF-I, PDGF and EGF, PDGF and FGF, and IGF-I and EGF. In combination with IGF-I and FGF, TGF-beta did not affect proliferation. TGF-beta inhibited proliferation stimulated by the combination of PDGF, EGF, and IGF-I, but had no effect on proliferation stimulated by combinations of three growth factors that included FGF. FGF stimulated proliferation in Minimum Essential Medium containing 10% porcine serum (MEM-10% PS) by 13% above control. When the combination of TGF-beta and FGF was added to MEM-10% PS, a 78% increase in proliferation was observed. Polyclonal antihuman PDGF-AB (this form neutralizes PDGF-AA, AB, and BB) reduced proliferation in MEM-10% PS by 44%. The combination of TGF-beta and anti-PDGF-AB reduced proliferation by 59%, indicating the effects were not additive. These data indicate that: (1) FGF and TGF-beta interact to increase proliferation of clonally derived porcine satellite cells, and (2) the inhibitory effect of TGF-beta on proliferation of clonally derived porcine satellite cells can be primarily attributed to a reduction in the mitogenic effects of PDGF.

Animals↗
PubMed1993

Fibroblast growth factor, epidermal growth factor, insulin-like growth factors, and platelet-derived growth factor-BB stimulate proliferation of clonally derived porcine myogenic satellite cells.

Clonally derived cultures of porcine skeletal muscle satellite cells were developed. The mitogenic effects of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), insulin-like growth factors (IGF-I and -II), and platelet-derived growth factors (PDGF-AA and -BB) were examined. Individually, bFGF, IGFs, and PDGF-BB stimulated proliferation of porcine satellite cells grown in basal serum-free medium or Minimum Essential Medium containing 2% fetal bovine serum (MEM-2% FBS). EGF stimulated proliferation in MEM-2% FBS, but neither EGF nor PDGF-AA were mitogenic when added to serum-free medium. The interactions among bFGF, EGF, IGF-I, and PDGF-BB were examined in serum-free medium, using growth factor concentrations shown in dose-response experiments to induce maximal proliferative responses (10 ng/ml bFGF, EGF and PDGF-BB, and 50 ng/ml IGF-I). The combination of bFGF and IGF-I dramatically increased proliferation, and IGF-I also synergized with EGF to increase proliferation. EGF, IGF-I, and bFGF interacted with PDGF-BB to stimulate proliferation. With the exception of EGF and bFGF, combinations of two growth factors typically resulted in greater than additive responses. Simultaneous exposure of satellite cells to bFGF, PDGF-BB, EGF, and IGF-I produced a fivefold increase in DNA compared to cells grown in basal serum-free medium. Elimination of EGF did not reduce the mitogenic response, yet removal of IGF-I, bFGF, or PDGF-BB reduced proliferation by approximately 40, 20, and 10%, respectively. These mitogens are likely physiological regulators of porcine satellite cell activity.

Animals↗
PubMed1994

Age related induction of platelet-derived growth factor A-chain mRNA in normal human fibroblasts.

We have previously found that stimulation of normal neonatal fibroblasts with PDGF or EGF leads to a transient induction of PDGF A-chain mRNA and the synthesis of PDGF-AA proteins. This finding may imply the existence of an autocrine feedback mechanism to amplify the mitogenic signal under certain conditions. We have now studied the PDGF-BB mediated PDGF A-chain induction in a set of fibroblasts from young and old donors to clarify if the levels of induction are correlated to the donor age and the replicative capacity of the cells. The PDGF A-chain induction was found to be reduced in cells from old donors compared with cells from embryonic and neonatal donors. The different cell strains were also characterized further with respect to PDGF receptor expression and PDGF binding properties. PDGF beta-receptors were found to be enhanced in old donor cell strains, whereas the PDGF alpha-receptors showed more variability in expression between the strains. The PDGF A-chain mRNA induction was also decreased or absent in late passage human fibroblasts (senescent cells) when compared with early passage cells. These data suggest that the PDGF A-chain mRNA induction is regulated by an age related mechanism in human fibroblasts.

Aged↗
PubMed1994

NIH 3T3 cells transfected with a yeast H(+)-ATPase have altered sensitivity to insulin, insulin growth factor-I, and platelet-derived growth factor-AA.

The role of intracellular pH (pHin) in the regulation of cell growth in both normal and transformed cells is a topic of considerable controversy. In an effort to study this relationship NIH 3T3 cells were stably transfected with the gene for the yeast H(+)-ATPase, constitutively elevating their pHin. The resulting cell line, RN1a, has a transformed phenotype: The cells are serum independent for growth, clone in soft agar, and form tumors in nude mice. In the present study, we further characterize this system in order to understand how transfection with this proton pump leads to serum-independent growth, using defined media to investigate the effects of specific growth factors on the transfected and parental NIH 3T3 cells. While both cell lines show similar growth increases in response to platelet-derived growth factor (PDGF)-BB and epidermal growth factor (EGF), they respond differently to insulin, insulin-like growth factor-I (IGF-I) and PDGF-AA. RN1a cells exhibit increased growth at nanomolar concentrations of insulin but the parental cells had only a relatively minor response to insulin at 10 microM. Both cell lines showed some response to IGF-I in the nanomolar range but the response of RN1a cells was much larger. Differences in insulin and IGF-I receptor number alone could not explain these results. The two cell lines also respond differently to PDGF-AA. RN1a cells are relatively insensitive to stimulation by PDGF-AA and express fewer PDGF alpha receptors as shown by Northern blots and receptor-binding studies. We propose a unifying hypothesis in which the H(+)-ATPase activates a downstream element in the PDGF-AA signal transduction pathway that complements insulin and IGF-I signals, while leading to downregulation of the PDGF alpha receptor.

3T3 Cells↗
PubMed1994

Separation of mouse crushed muscle extract into distinct mitogenic activities by heparin affinity chromatography.

Extracts from gently crushed adult mouse skeletal muscles (CMEs) contain potent myoblast mitogens, and may be used as a model system to investigate myotrophic factors released by adult muscles following injury. CME was separated into four peaks of mitogenic activity by heparin affinity chromatography. The fraction of CME that did not bind to heparin contained transferrin (Tf). Three peaks of mitogenic activity were eluted from the heparin-agarose columns at NaCl concentrations of 0.4 M, 0.9 M, and 2.0 M. A 46 kDa protein that shared antigenicity with the BB isoform of platelet-derived growth factor (PDGF-BB) was present in the 0.4 M NaCl eluant. Mitogenic activity in the 2.0 M NaCl peak eluted identically to purified basic fibroblast growth factor (bFGF), did not act additively to saturating amounts of purified bFGF, and was neutralized by anti-bFGF antibodies. The 0.9 M NaCl eluant acted additively to the combination of three known growth factors for myoblasts, bFGF, insulin-like growth factor 1, and epidermal growth factor, to stimulate C2 myoblast proliferation, suggesting this fraction contains a mitogenic activity which does not utilize (and hence compete for) receptors for the known mitogens for myoblasts. Additionally, the 0.9 M NaCl eluant did not stimulate proliferation of fibroblast-like cells derived from muscle tissue. The unbound, 0.4 M NaCl, 0.9 M NaCl, and 2.0 M NaCl eluants from the heparin-agarose column acted additively to one another to stimulate myoblast proliferation. Our data suggest that Tf, PDGF-BB-like molecules, bFGF-like activity, and an uncharacterized heparin-binding myoblast mitogen could be released after muscle injury and act to stimulate satellite cell proliferation.

Animals↗
PubMed1994

Differential activation by platelet-derived growth factor-BB of mitogen activated protein kinases in starved or nonstarved AKR-2B fibroblasts.

More than 90% of serum-deprived (starved) AKR-2B mouse fibroblasts are stimulated to divided by the addition of platelet-derived growth factor (PDGF)-BB. In density-arrested (nonstarved) cells, PDGF-BB affords protection from cell death without stimulation of cell division. In both cultivation conditions the cells express similar amounts of PDGF beta-receptors and the receptor kinase activity was identical as judged by its autophosphorylation capacity. Three signaling pathways were studied in detail: 1) Phospholipase C-gamma (PLC-gamma) and [Ca2+]i increase, 2) activation of the phosphatidylinositol-3 kinase (PI-3 kinase), and 3) activation of mitogen activated kinases I and II (MAP kinases I and II). There was no difference in starved or nonstarved cells regarding PLC-gamma activation, increase of [Ca2+]i, and stimulation of PI-3 kinase activity. But most remarkably the activation of MAP-I was largely suppressed in nonstarved cells. The implications of these signaling pathways in cell protection or cell division are discussed.

Animals↗