Efficient TGF-beta induction of the Smad7 gene requires cooperation between AP-1, Sp1, and Smad proteins on the mouse Smad7 promoter.

Sma- and Mad-related protein 7 (Smad7) is an antagonist of transforming growth factor-beta (TGF-beta) signaling, which has been shown to be induced by TGF-beta itself and also by other stimuli. In an effort to understand the molecular mechanisms underlying the transcriptional regulation of the Smad7 gene by TGF-beta, we cloned and functionally characterized a mouse genomic DNA fragment encompassing the mouse Smad7 proximal promoter. This region was found to contain a CpG island and to be devoid of a classical TATA box.

Platelet-derived growth factor-mediated signaling through the Shb adaptor protein: effects on cytoskeletal organization.

The Src homology (SH) 2 domain adaptor protein Shb has previously been shown to interact with the platelet-derived growth factor (PDGF)-beta receptor. In this study we show an association between Shb and the PDGF-alpha receptor which is mediated by the SH2 domain of Shb and involves tyrosine residue 720 in the kinase insert domain of the receptor. To assess the role of Shb in PDGF-mediated signaling, we have overexpressed wild-type Shb or Shb carrying a mutation (R522K) which renders the SH2 domain inactive, in Patch mouse (PhB) fibroblasts expressing both PDGF receptors (PhB/Ralpha).

PDGF-C is a new protease-activated ligand for the PDGF alpha-receptor.

Platelet-derived growth factors (PDGFs) are important in many types of mesenchymal cell. Here we identify a new PDGF, PDGF-C, which binds to and activates the PDGF alpha-receptor. PDGF-C is activated by proteolysis and induces proliferation of fibroblasts when overexpressed in transgenic mice.

Smad7 mediates apoptosis induced by transforming growth factor beta in prostatic carcinoma cells.

Transforming growth factor beta (TGF-beta) is an important regulator of apoptosis in some cell types, but the underlying molecular mechanisms are largely unknown. TGF-beta signals through type I and type II receptors and downstream effector proteins, termed Smads. TGF-beta induces the phosphorylation of Smad2 and Smad3 (receptor-activated Smads) which associate with Smad4 and translocate to the nucleus, where they regulate gene transcription [1].

p110beta is up-regulated during differentiation of 3T3-L1 cells and contributes to the highly insulin-responsive glucose transport activity.

Activation of p85/p110 type phosphatidylinositol kinase is essential for aspects of insulin-induced glucose metabolism, including translocation of GLUT4 to the cell surface and glycogen synthesis. The enzyme exists as a heterodimer containing a regulatory subunit (e.g.

Predimerization of recombinant platelet-derived growth factor receptor extracellular domains increases antagonistic potency.

Platelet-derived growth factor (PDGF) is a dimeric growth factor acting through tyrosine kinase alpha- and beta-receptors. In both receptors, the extracellular parts are composed of five Ig-like domains. Functional mapping of the extracellular part of the receptors have shown that ligand-binding occurs to Ig-like domains 2 and 3 and that Ig-like domain 4 is involved in receptor-receptor interactions.

Signaling inputs converge on nuclear effectors in TGF-beta signaling.

Recent studies have consolidated the pivotal role of Smads as intracellular effectors of TGF-beta family members. Upon binding to their specific type I and type II serine/threonine kinase receptors, each family member activates a particular subset of Smad proteins. Activated, receptor-regulated Smads form hetero-oligomeric complexes with common-partner Smads that translocate into the nucleus, where they control the expression of target genes in a cell-type-specific manner.

Smad and AML proteins synergistically confer transforming growth factor beta1 responsiveness to human germ-line IgA genes.

Transcription of germ-line immunoglobulin heavy chain genes conditions them to participate in isotype switch recombination. Transforming growth factor-beta1 (TGF-beta1) stimulates promoter elements located upstream of the IgA1 and IgA2 switch regions, designated Ialpha1 and Ialpha2, and contributes to the development of IgA responses. We demonstrate that intracellular Smad proteins mediate activation of the Ialpha1 promoter by TGF-beta.

Platelet-derived growth factor (PDGF)-induced activation of signal transducer and activator of transcription (Stat) 5 is mediated by PDGF beta-receptor and is not dependent on c-src, fyn, jak1 or jak2 kinases.

Several growth factors activate signal transducers and activators of transcription (Stats) but the mechanism of Stat activation in receptor tyrosine kinase signalling has remained elusive. In the present study we have analysed the roles of different platelet-derived growth factor (PDGF)-induced tyrosine kinases in the activation of Stat5. Co-expression experiments in insect and mammalian cells demonstrated that both PDGF beta-receptor (PDGF beta-R) and Jak1, but not c-Src, induced the activation of Stat5.

The PI 3-kinase isoforms p110(alpha) and p110(beta) have differential roles in PDGF- and insulin-mediated signaling.

Phosphoinositide 3'-kinases constitute a family of lipid kinases implicated in signal transduction through tyrosine kinase receptors and heterotrimeric G protein-linked receptors. Phosphoinositide 3'-kinases that bind to the platelet-derived growth factor receptor are composed of two subunits: the p85 subunit acts as an adapter and couples the catalytic p110 subunit to the activated receptor. There are different isoforms of p85 as well as of p110, the individual roles of which have been elusive.

Characterization of the chronic myelomonocytic leukemia associated TEL-PDGF beta R fusion protein.

The t(5;12) translocation, associated with chronic myelomonocytic leukemia, generates a novel gene encoding a protein, TEL-PDGF beta R, composed of the 154 amino-terminal amino acids of the transcription factor TEL and the transmembrane and intracellular part of the PDGF beta-receptor (PDGF beta R). TEL also occurs as a tumor-associated fusion partner for the tyrosine kinases c-ABL, JAK2 and TRK-C. Previous studies have demonstrated growth promoting activity of TEL-PDGF beta R and also indicated that the TEL moiety activates the tyrosine kinase of the PDGF beta R through the formation of TEL-PDGF beta R oligomers.

Specificity, diversity, and regulation in TGF-beta superfamily signaling.

Transforming growth factor-beta (TGF-beta) superfamily members are multifunctional cell-cell signaling proteins that play pivotal roles in tissue homeostasis and development of multicellular animals. They mediate their pleiotropic effects from membrane to nucleus through distinct combinations of type I and type II serine/threonine kinase receptors and their downstream effectors, known as Smad proteins. Certain Smads, termed receptor-regulated Smads, become phosphorylated by activated type I receptors and form heteromeric complexes with a common-partner Smad4, which translocates into the nucleus to control gene transcription.

TGF-(beta) type I receptor/ALK-5 and Smad proteins mediate epithelial to mesenchymal transdifferentiation in NMuMG breast epithelial cells.

The capacities of different transforming growth factor-(beta) (TGF-(beta)) superfamily members to drive epithelial to mesenchymal transdifferentiation of the murine mammary epithelial cell line NMuMG were investigated. TGF-(beta)1, but not activin A or osteogenic protein-1 (OP-1)/bone morphogenetic protein-7 (BMP-7), was able to induce morphological transformation of NMuMG cells as shown by reorganisation of the actin cytoskeleton and relocalisation/downregulation of E-cadherin and (beta)-catenin, an effect that was abrogated by the more general serine/threonine kinase and protein kinase C inhibitor, staurosporine. TGF-(beta)1 bound to TGF-(beta) type I receptor (T(beta)R-I)/ALK-5 and T(beta)R-II, but not to activin type I receptor (ActR-I)/ALK-2.

Mechanism of action and in vivo role of platelet-derived growth factor.

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor.

Platelet-derived growth factor beta receptor regulates interstitial fluid homeostasis through phosphatidylinositol-3' kinase signaling.

Platelet-derived growth factor (PDGF) isoforms lead to mitogenic, survival, and chemotactic responses in a variety of mesenchymal cell types during development and in the adult. We have studied the importance of phosphatidylinositol-3' kinase (PI3K) signaling in these responses by mutating the PI3K-binding sites in the PDGF-beta receptor by gene targeting in embryonic stem cells. Homozygous mutant mice developed normally; however, cells derived from the mutants were less chemotactic and had largely lost their ability to contract collagen gels in response to PDGF.

The dermatofibrosarcoma protuberans-associated collagen type Ialpha1/platelet-derived growth factor (PDGF) B-chain fusion gene generates a transforming protein that is processed to functional PDGF-BB.

Dermatofibrosarcoma protuberans (DFSP) displays chromosomal rearrangements involving chromosome 17 and 22, which fuse the collagen type Ialpha1 (COLIA1) gene to the platelet-derived growth factor (PDGF) B-chain (PDGFB) gene. To characterize the functional and structural properties of the COLIA1/PDGFB fusion protein, we generated a stable NIH3T3 cell line that contained a tumor-derived chimeric gene resulting from a COIA1 intron 7-PDGFB intron 1 fusion. Expression of the fusion protein led to morphological transformation and increased growth rate of these cells.

Overactivation of phospholipase C-gamma1 renders platelet-derived growth factor beta-receptor-expressing cells independent of the phosphatidylinositol 3-kinase pathway for chemotaxis.

We have previously shown that porcine aortic endothelial cells expressing the Y934F platelet-derived growth factor (PDGF) beta-receptor mutant respond to PDGF-BB in a chemotaxis assay at about 100-fold lower concentration than do wild-type PDGF beta-receptor-expressing cells (Hansen, K., Johnell, M., Siegbahn, A.

Functional co-operation between the subunits in heterodimeric platelet-derived growth factor receptor complexes.

To determine the importance of the phosphorylation capacity of receptor kinase as well as the ability to serve as docking sites for SH2-domain-containing signal transduction molecules, we established pig aortic endothelial cell lines stably expressing kinase-active platelet-derived growth factor (PDGF) alpha-receptors together with kinase-inactive beta-receptors, and vice versa. After stimulation with PDGF-AB, heterodimeric receptor complexes were formed in which the kinase-inactive receptor was phosphorylated by the kinase-active receptor, although less efficiently than in heterodimers of wild-type receptors. The kinase-active receptor was only minimally phosphorylated.

Functional antagonism between activin and osteogenic protein-1 in human embryonal carcinoma cells.

Activin A and osteogenic protein-1 (OP-1) exerted antagonistic effects on each other's responses on the human Tera-2 embryonal carcinoma cell line. OP-1 dose dependently inhibited activin A-induced activation of p3TP-Lux transcriptional reporter, containing part of the human plasminogen activator inhibitor-1 (PAI-1) promoter, while activin A inhibited OP-1-mediated alkaline phosphatase induction. Approximately equimolar concentrations of both growth factors resulted in 50% inhibition of the respective biological responses.

SHP-2 binds to Tyr763 and Tyr1009 in the PDGF beta-receptor and mediates PDGF-induced activation of the Ras/MAP kinase pathway and chemotaxis.

Activation of the beta-receptor for platelet-derived growth factor (PDGF) by its ligand leads to autophosphorylation on a number of tyrosine residues. Here we show that Tyr763 in the kinase insert region is a novel autophosphorylation site, which after phosphorylation binds the protein tyrosine phosphatase SHP-2. SHP-2 has also previously been shown to bind to phosphorylated Tyr1009 in the PDGF beta-receptor.

Expression of Smad proteins in human colorectal cancer.

Escape from transforming growth factor-beta (TGF-beta)-induced inhibition of proliferation has been observed in many tumor cells and may contribute to loss of growth control. Smad proteins have been identified as major components in the intracellular signaling of TGF-beta family members. In this study, we examined the expression of receptor-activated, common-mediator and inhibitory Smads by immunohistochemistry in human colorectal cancers.

Eccrine sweat glands: expression of transforming growth factor-beta and bone morphogenetic protein type I receptors and their intracellular signalling Smad proteins.

The transforming growth factor-beta superfamily is thought to be involved in the regulation and control of growth and differentiation. These growth factors signal through transmembrane serine/threonine kinase receptors. The activation of type I receptor kinase phosphorylates a family of intracellular signalling proteins called Smads.

Increased smad expression and activation are associated with apoptosis in normal and malignant prostate after castration.

Transforming growth factor (TGF)-beta1 is induced in the prostate after castration and has been implicated in apoptosis of epithelial cells during involution. TGF-beta1-mediated receptor activation induces phosphorylation of Smad2 and Smad3, which form complexes with Smad4, that translocate to the nucleus to regulate transcription of target genes. Smad6 and Smad7 antagonize the action of signal-transducing Smads.

MEK is a negative regulator of Stat5b in PDGF-stimulated cells.

In this study we show that platelet-derived growth factor (PDGF)-induced DNA binding as well as transcriptional activation of Stat5b are markedly increased by inhibition of the MAP (mitogen-activated protein) kinase kinase MEK. In addition to the previously demonstrated tyrosine phosphorylation, we show that serine and threonine phosphorylation of Stat5b is increased in response to PDGF stimulation. However, inhibition of MEK had no effect on the phosphorylation level of Stat5b or on the nuclear translocation of Stat5b.